webview.h

/*
 * MIT License
 *
 * Copyright (c) 2017 Serge Zaitsev
 * Copyright (c) 2022 Steffen André Langnes
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */
#ifndef WEBVIEW_H
#define WEBVIEW_H
 
#ifndef WEBVIEW_API
#define WEBVIEW_API extern
#endif
 
#ifndef WEBVIEW_VERSION_MAJOR
// The current library major version.
#define WEBVIEW_VERSION_MAJOR 0
#endif
 
#ifndef WEBVIEW_VERSION_MINOR
// The current library minor version.
#define WEBVIEW_VERSION_MINOR 10
#endif
 
#ifndef WEBVIEW_VERSION_PATCH
// The current library patch version.
#define WEBVIEW_VERSION_PATCH 0
#endif
 
#ifndef WEBVIEW_VERSION_PRE_RELEASE
// SemVer 2.0.0 pre-release labels prefixed with "-".
#define WEBVIEW_VERSION_PRE_RELEASE ""
#endif
 
#ifndef WEBVIEW_VERSION_BUILD_METADATA
// SemVer 2.0.0 build metadata prefixed with "+".
#define WEBVIEW_VERSION_BUILD_METADATA ""
#endif
 
// Utility macro for stringifying a macro argument.
#define WEBVIEW_STRINGIFY(x) #x
 
// Utility macro for stringifying the result of a macro argument expansion.
#define WEBVIEW_EXPAND_AND_STRINGIFY(x) WEBVIEW_STRINGIFY(x)
 
// SemVer 2.0.0 version number in MAJOR.MINOR.PATCH format.
#define WEBVIEW_VERSION_NUMBER                                                                \
  WEBVIEW_EXPAND_AND_STRINGIFY(WEBVIEW_VERSION_MAJOR)                                       \
  "." WEBVIEW_EXPAND_AND_STRINGIFY(WEBVIEW_VERSION_MINOR) "." WEBVIEW_EXPAND_AND_STRINGIFY( \
      WEBVIEW_VERSION_PATCH)
 
// Holds the elements of a MAJOR.MINOR.PATCH version number.
typedef struct
{
  // Major version.
  unsigned int major;
  // Minor version.
  unsigned int minor;
  // Patch version.
  unsigned int patch;
} webview_version_t;
typedef struct {…};
 
// Holds the library's version information.
typedef struct
{
  // The elements of the version number.
  webview_version_t version;
  // SemVer 2.0.0 version number in MAJOR.MINOR.PATCH format.
  char version_number[32];
  // SemVer 2.0.0 pre-release labels prefixed with "-" if specified, otherwise
  // an empty string.
  char pre_release[48];
  // SemVer 2.0.0 build metadata prefixed with "+", otherwise an empty string.
  char build_metadata[48];
} webview_version_info_t;
typedef struct {…};
 
#ifdef __cplusplus
extern "C"
{
#endif
 
  typedef void* webview_t;
 
  // Creates a new webview instance. If debug is non-zero - developer tools will
  // be enabled (if the platform supports them). Window parameter can be a
  // pointer to the native window handle. If it's non-null - then child WebView
  // is embedded into the given parent window. Otherwise a new window is created.
  // Depending on the platform, a GtkWindow, NSWindow or HWND pointer can be
  // passed here. Returns null on failure. Creation can fail for various reasons
  // such as when required runtime dependencies are missing or when window creation
  // fails.
  WEBVIEW_API webview_t webview_create(int debug, void* window);
 
  // Destroys a webview and closes the native window.
  WEBVIEW_API void webview_destroy(webview_t w);
 
  // Runs the main loop until it's terminated. After this function exits - you
  // must destroy the webview.
  WEBVIEW_API void webview_run(webview_t w);
 
  // Stops the main loop. It is safe to call this function from another other
  // background thread.
  WEBVIEW_API void webview_terminate(webview_t w);
 
  // Posts a function to be executed on the main thread. You normally do not need
  // to call this function, unless you want to tweak the native window.
  WEBVIEW_API void webview_dispatch(webview_t w, void (*fn)(webview_t w, void* arg), void* arg);
 
  // Returns a native window handle pointer. When using GTK backend the pointer
  // is GtkWindow pointer, when using Cocoa backend the pointer is NSWindow
  // pointer, when using Win32 backend the pointer is HWND pointer.
  WEBVIEW_API void* webview_get_window(webview_t w);
 
  // Updates the title of the native window. Must be called from the UI thread.
  WEBVIEW_API void webview_set_title(webview_t w, const char* title);
 
// Window size hints
#define WEBVIEW_HINT_NONE 0  // Width and height are default size
#define WEBVIEW_HINT_MIN 1   // Width and height are minimum bounds
#define WEBVIEW_HINT_MAX 2   // Width and height are maximum bounds
#define WEBVIEW_HINT_FIXED 3 // Window size can not be changed by a user
  // Updates native window size. See WEBVIEW_HINT constants.
  WEBVIEW_API void webview_set_size(webview_t w, int width, int height, int hints);
 
  // Navigates webview to the given URL. URL may be a properly encoded data URI.
  // Examples:
  // webview_navigate(w, "https://github.com/webview/webview");
  // webview_navigate(w, "data:text/html,%3Ch1%3EHello%3C%2Fh1%3E");
  // webview_navigate(w, "data:text/html;base64,PGgxPkhlbGxvPC9oMT4=");
  WEBVIEW_API void webview_navigate(webview_t w, const char* url);
 
  // Set webview HTML directly.
  // Example: webview_set_html(w, "<h1>Hello</h1>");
  WEBVIEW_API void webview_set_html(webview_t w, const char* html);
 
  // Injects JavaScript code at the initialization of the new page. Every time
  // the webview will open a the new page - this initialization code will be
  // executed. It is guaranteed that code is executed before window.onload.
  WEBVIEW_API void webview_init(webview_t w, const char* js);
 
  // Evaluates arbitrary JavaScript code. Evaluation happens asynchronously, also
  // the result of the expression is ignored. Use RPC bindings if you want to
  // receive notifications about the results of the evaluation.
  WEBVIEW_API void webview_eval(webview_t w, const char* js);
 
  // Binds a native C callback so that it will appear under the given name as a
  // global JavaScript function. Internally it uses webview_init(). Callback
  // receives a request string and a user-provided argument pointer. Request
  // string is a JSON array of all the arguments passed to the JavaScript
  // function.
  WEBVIEW_API void webview_bind(webview_t w, const char* name,
                                void (*fn)(const char* seq, const char* req, void* arg),
                                void* arg);
 
  // Removes a native C callback that was previously set by webview_bind.
  WEBVIEW_API void webview_unbind(webview_t w, const char* name);
 
  // Allows to return a value from the native binding. Original request pointer
  // must be provided to help internal RPC engine match requests with responses.
  // If status is zero - result is expected to be a valid JSON result value.
  // If status is not zero - result is an error JSON object.
  WEBVIEW_API void webview_return(webview_t w, const char* seq, int status, const char* result);
 
  // Get the library's version information.
  // @since 0.10
  WEBVIEW_API const webview_version_info_t* webview_version();
 
#ifdef __cplusplus
}
 
#ifndef WEBVIEW_HEADER
 
#if !defined(WEBVIEW_GTK) && !defined(WEBVIEW_COCOA) && !defined(WEBVIEW_EDGE)
#if defined(__APPLE__)
#define WEBVIEW_COCOA
#elif defined(__unix__)
#define WEBVIEW_GTK
#elif defined(_WIN32)
#define WEBVIEW_EDGE
#else
#error "please, specify webview backend"
#endif
#endif
 
#ifndef WEBVIEW_DEPRECATED
#if __cplusplus >= 201402L
#define WEBVIEW_DEPRECATED(reason) [[deprecated(reason)]]
#elif defined(_MSC_VER)
#define WEBVIEW_DEPRECATED(reason) __declspec(deprecated(reason))
#else
#define WEBVIEW_DEPRECATED(reason) __attribute__((deprecated(reason)))
#endif
#endif
 
#ifndef WEBVIEW_DEPRECATED_PRIVATE
#define WEBVIEW_DEPRECATED_PRIVATE WEBVIEW_DEPRECATED("Private API should not be used")
#endif
 
#include <array>
#include <atomic>
#include <functional>
#include <future>
#include <map>
#include <string>
#include <utility>
#include <vector>
#include <locale>
#include <codecvt>
#include <cstring>
 
namespace webview
{
 
  using dispatch_fn_t = std::function<void()>;
 
  namespace detail
  {
 
    // The library's version information.
    constexpr const webview_version_info_t library_version_info{
      { WEBVIEW_VERSION_MAJOR, WEBVIEW_VERSION_MINOR, WEBVIEW_VERSION_PATCH },
      WEBVIEW_VERSION_NUMBER,
      WEBVIEW_VERSION_PRE_RELEASE,
      WEBVIEW_VERSION_BUILD_METADATA
    };
 
    inline int json_parse_c(const char* s, size_t sz, const char* key, size_t keysz,
                            const char** value, size_t* valuesz)
    {
      enum
      {
        JSON_STATE_VALUE,
        JSON_STATE_LITERAL,
        JSON_STATE_STRING,
        JSON_STATE_ESCAPE,
        JSON_STATE_UTF8
      } state = JSON_STATE_VALUE;
      const char* k = nullptr;
      int index = 1;
      int depth = 0;
      int utf8_bytes = 0;
 
      *value = nullptr;
      *valuesz = 0;
 
      if (key == nullptr)
      {
        index = static_cast<decltype(index)>(keysz);
        if (index < 0)
        {
          return -1;
        }
        keysz = 0;
      }
 
      for (; sz > 0; s++, sz--)
      {
        enum
        {
          JSON_ACTION_NONE,
          JSON_ACTION_START,
          JSON_ACTION_END,
          JSON_ACTION_START_STRUCT,
          JSON_ACTION_END_STRUCT
        } action = JSON_ACTION_NONE;
        auto c = static_cast<unsigned char>(*s);
        switch (state)
        {
          case JSON_STATE_VALUE:
            if (c == ' ' || c == '\t' || c == '\n' || c == '\r' || c == ',' || c == ':')
            {
              continue;
            }
            else if (c == '"')
            {
              action = JSON_ACTION_START;
              state = JSON_STATE_STRING;
            }
            else if (c == '{' || c == '[')
            {
              action = JSON_ACTION_START_STRUCT;
            }
            else if (c == '}' || c == ']')
            {
              action = JSON_ACTION_END_STRUCT;
            }
            else if (c == 't' || c == 'f' || c == 'n' || c == '-' ||
                     (c >= '0' && c <= '9'))
            {
              action = JSON_ACTION_START;
              state = JSON_STATE_LITERAL;
            }
            else
            {
              return -1;
            }
            break;
          case JSON_STATE_LITERAL:
            if (c == ' ' || c == '\t' || c == '\n' || c == '\r' || c == ',' ||
                c == ']' || c == '}' || c == ':')
            {
              state = JSON_STATE_VALUE;
              s--;
              sz++;
              action = JSON_ACTION_END;
            }
            else if (c < 32 || c > 126)
            {
              return -1;
            } // fallthrough
          case JSON_STATE_STRING:
            if (c < 32 || (c > 126 && c < 192))
            {
              return -1;
            }
            else if (c == '"')
            {
              action = JSON_ACTION_END;
              state = JSON_STATE_VALUE;
            }
            else if (c == '\\')
            {
              state = JSON_STATE_ESCAPE;
            }
            else if (c >= 192 && c < 224)
            {
              utf8_bytes = 1;
              state = JSON_STATE_UTF8;
            }
            else if (c >= 224 && c < 240)
            {
              utf8_bytes = 2;
              state = JSON_STATE_UTF8;
            }
            else if (c >= 240 && c < 247)
            {
              utf8_bytes = 3;
              state = JSON_STATE_UTF8;
            }
            else if (c >= 128 && c < 192)
            {
              return -1;
            }
            break;
          case JSON_STATE_ESCAPE:
            if (c == '"' || c == '\\' || c == '/' || c == 'b' || c == 'f' || c == 'n' ||
                c == 'r' || c == 't' || c == 'u')
            {
              state = JSON_STATE_STRING;
            }
            else
            {
              return -1;
            }
            break;
          case JSON_STATE_UTF8:
            if (c < 128 || c > 191)
            {
              return -1;
            }
            utf8_bytes--;
            if (utf8_bytes == 0)
            {
              state = JSON_STATE_STRING;
            }
            break;
          default:
            return -1;
        }
 
        if (action == JSON_ACTION_END_STRUCT)
        {
          depth--;
        }
 
        if (depth == 1)
        {
          if (action == JSON_ACTION_START || action == JSON_ACTION_START_STRUCT)
          {
            if (index == 0)
            {
              *value = s;
            }
            else if (keysz > 0 && index == 1)
            {
              k = s;
            }
            else
            {
              index--;
            }
          }
          else if (action == JSON_ACTION_END || action == JSON_ACTION_END_STRUCT)
          {
            if (*value != nullptr && index == 0)
            {
              *valuesz = (size_t)(s + 1 - *value);
              return 0;
            }
            else if (keysz > 0 && k != nullptr)
            {
              if (keysz == (size_t)(s - k - 1) && memcmp(key, k + 1, keysz) == 0)
              {
                index = 0;
              }
              else
              {
                index = 2;
              }
              k = nullptr;
            }
          }
        }
 
        if (action == JSON_ACTION_START_STRUCT)
        {
          depth++;
        }
      }
      return -1;
    }
 
    inline std::string json_escape(const std::string& s)
    {
      // TODO: implement
      return '"' + s + '"';
    }
 
    inline int json_unescape(const char* s, size_t n, char* out)
    {
      int r = 0;
      if (*s++ != '"')
      {
        return -1;
      }
      while (n > 2)
      {
        char c = *s;
        if (c == '\\')
        {
          s++;
          n--;
          switch (*s)
          {
            case 'b':
              c = '\b';
              break;
            case 'f':
              c = '\f';
              break;
            case 'n':
              c = '\n';
              break;
            case 'r':
              c = '\r';
              break;
            case 't':
              c = '\t';
              break;
            case '\\':
              c = '\\';
              break;
            case '/':
              c = '/';
              break;
            case '\"':
              c = '\"';
              break;
            default: // TODO: support unicode decoding
              return -1;
          }
        }
        if (out != nullptr)
        {
          *out++ = c;
        }
        s++;
        n--;
        r++;
      }
      if (*s != '"')
      {
        return -1;
      }
      if (out != nullptr)
      {
        *out = '\0';
      }
      return r;
    }
 
    inline std::string json_parse(const std::string& s, const std::string& key, const int index)
    {
      const char* value = nullptr;
      size_t value_sz = 0;
      if (key.empty())
      {
        json_parse_c(s.c_str(), s.length(), nullptr, index, &value, &value_sz);
      }
      else
      {
        json_parse_c(s.c_str(), s.length(), key.c_str(), key.length(), &value, &value_sz);
      }
      if (value != nullptr)
      {
        if (value[0] != '"')
        {
          return { value, value_sz };
        }
        int n = json_unescape(value, value_sz, nullptr);
        if (n > 0)
        {
          char* decoded = new char[1ull + n];
          json_unescape(value, value_sz, decoded);
          std::string result(decoded, n);
          delete[] decoded;
          return result;
        }
      }
      return "";
    }
 
  } // namespace detail
 
  WEBVIEW_DEPRECATED_PRIVATE
  inline int json_parse_c(const char* s, size_t sz, const char* key, size_t keysz,
                          const char** value, size_t* valuesz)
  {
    return detail::json_parse_c(s, sz, key, keysz, value, valuesz);
  }
 
  WEBVIEW_DEPRECATED_PRIVATE
  inline std::string json_escape(const std::string& s)
  {
    return detail::json_escape(s);
  }
 
  WEBVIEW_DEPRECATED_PRIVATE
  inline int json_unescape(const char* s, size_t n, char* out)
  {
    return detail::json_unescape(s, n, out);
  }
 
  WEBVIEW_DEPRECATED_PRIVATE
  inline std::string json_parse(const std::string& s, const std::string& key, const int index)
  {
    return detail::json_parse(s, key, index);
  }
 
} // namespace webview
 
#if defined(WEBVIEW_GTK)
//
// ====================================================================
//
// This implementation uses webkit2gtk backend. It requires gtk+3.0 and
// webkit2gtk-4.0 libraries. Proper compiler flags can be retrieved via:
//
//   pkg-config --cflags --libs gtk+-3.0 webkit2gtk-4.0
//
// ====================================================================
//
#include <JavaScriptCore/JavaScript.h>
#include <gtk/gtk.h>
#include <webkit2/webkit2.h>
 
namespace webview
{
  namespace detail
  {
 
    class gtk_webkit_engine
    {
      public:
      gtk_webkit_engine(bool debug, void* window) : m_window(static_cast<GtkWidget*>(window))
      {
        if (gtk_init_check(nullptr, nullptr) == FALSE)
        {
          return;
        }
        m_window = static_cast<GtkWidget*>(window);
        if (m_window == nullptr)
        {
          m_window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
        }
        g_signal_connect(G_OBJECT(m_window), "destroy",
                         G_CALLBACK(+[](GtkWidget*, gpointer arg)
                                    { static_cast<gtk_webkit_engine*>(arg)->terminate(); }),
                         this);
        // Initialize webview widget
        m_webview = webkit_web_view_new();
        WebKitUserContentManager* manager =
            webkit_web_view_get_user_content_manager(WEBKIT_WEB_VIEW(m_webview));
        g_signal_connect(manager, "script-message-received::external",
                         G_CALLBACK(+[](WebKitUserContentManager*,
                                        WebKitJavascriptResult* r, gpointer arg)
                                    {
                                      auto* w = static_cast<gtk_webkit_engine*>(arg);
                                      char* s = get_string_from_js_result(r);
                                      w->on_message(s);
                                      g_free(s);
                                    }),
                         this);
        webkit_user_content_manager_register_script_message_handler(manager, "external");
        init("window.external={invoke:function(s){window.webkit.messageHandlers."
             "external.postMessage(s);}}");
 
        gtk_container_add(GTK_CONTAINER(m_window), GTK_WIDGET(m_webview));
        gtk_widget_grab_focus(GTK_WIDGET(m_webview));
 
        WebKitSettings* settings = webkit_web_view_get_settings(WEBKIT_WEB_VIEW(m_webview));
        webkit_settings_set_javascript_can_access_clipboard(settings, true);
        if (debug)
        {
          webkit_settings_set_enable_write_console_messages_to_stdout(settings, true);
          webkit_settings_set_enable_developer_extras(settings, true);
        }
 
        gtk_widget_show_all(m_window);
      }
      virtual ~gtk_webkit_engine() = default;
      void* window()
      {
        return (void*)m_window;
      }
      void run()
      {
        gtk_main();
      }
      void terminate()
      {
        gtk_main_quit();
      }
      void dispatch(std::function<void()> f)
      {
        g_idle_add_full(G_PRIORITY_HIGH_IDLE, (GSourceFunc)([](void* f) -> int {
                          (*static_cast<dispatch_fn_t*>(f))();
                          return G_SOURCE_REMOVE;
                        }),
                        new std::function<void()>(f),
                        [](void* f) { delete static_cast<dispatch_fn_t*>(f); });
      }
 
      void set_title(const std::string& title)
      {
        gtk_window_set_title(GTK_WINDOW(m_window), title.c_str());
      }
 
      void set_size(int width, int height, int hints)
      {
        gtk_window_set_resizable(GTK_WINDOW(m_window), hints != WEBVIEW_HINT_FIXED);
        if (hints == WEBVIEW_HINT_NONE)
        {
          gtk_window_resize(GTK_WINDOW(m_window), width, height);
        }
        else if (hints == WEBVIEW_HINT_FIXED)
        {
          gtk_widget_set_size_request(m_window, width, height);
        }
        else
        {
          GdkGeometry g;
          g.min_width = g.max_width = width;
          g.min_height = g.max_height = height;
          GdkWindowHints h =
              (hints == WEBVIEW_HINT_MIN ? GDK_HINT_MIN_SIZE : GDK_HINT_MAX_SIZE);
          // This defines either MIN_SIZE, or MAX_SIZE, but not both:
          gtk_window_set_geometry_hints(GTK_WINDOW(m_window), nullptr, &g, h);
        }
      }
 
      void navigate(const std::string& url)
      {
        webkit_web_view_load_uri(WEBKIT_WEB_VIEW(m_webview), url.c_str());
      }
 
      void add_navigate_listener(std::function<void(const std::string&, void*)> callback,
                                 void* arg)
      {
        g_signal_connect(WEBKIT_WEB_VIEW(m_webview), "load-changed",
                         G_CALLBACK(on_load_changed), this);
        navigateCallbackArg = arg;
        navigateCallback = std::move(callback);
      }
 
      void add_scheme_handler(const std::string& scheme,
                              std::function<void(const std::string&, void*)> callback,
                              void* arg)
      {
        auto view = WEBKIT_WEB_VIEW(m_webview);
        auto context = webkit_web_view_get_context(view);
 
        scheme_handlers.insert({ scheme, { .arg = arg, .fkt = callback } });
        webkit_web_context_register_uri_scheme(context, scheme.c_str(), scheme_handler,
                                               static_cast<gpointer>(this), nullptr);
      }
 
      void set_html(const std::string& html)
      {
        webkit_web_view_load_html(WEBKIT_WEB_VIEW(m_webview), html.c_str(), nullptr);
      }
 
      void init(const std::string& js)
      {
        WebKitUserContentManager* manager =
            webkit_web_view_get_user_content_manager(WEBKIT_WEB_VIEW(m_webview));
        webkit_user_content_manager_add_script(
            manager, webkit_user_script_new(
                         js.c_str(), WEBKIT_USER_CONTENT_INJECT_TOP_FRAME,
                         WEBKIT_USER_SCRIPT_INJECT_AT_DOCUMENT_START, nullptr, nullptr));
      }
 
      void eval(const std::string& js)
      {
        webkit_web_view_run_javascript(WEBKIT_WEB_VIEW(m_webview), js.c_str(), nullptr,
                                       nullptr, nullptr);
      }
 
      private:
      virtual void on_message(const std::string& msg) = 0;
 
      struct handler_t
      {
        void* arg;
        std::function<void(const std::string&, void*)> fkt;
      };
 
      std::map<std::string, handler_t> scheme_handlers;
 
      void scheme_handler_call(const std::string& scheme, const std::string& url)
      {
        auto handler = scheme_handlers.find(scheme);
        if (handler != scheme_handlers.end())
        {
          const auto& arg = handler->second;
          arg.fkt(url, arg.arg);
        }
      }
 
      static void scheme_handler(WebKitURISchemeRequest* request, gpointer user_data)
      {
        auto _this = static_cast<gtk_webkit_engine*>(user_data);
 
        auto scheme = webkit_uri_scheme_request_get_scheme(request);
        auto uri = webkit_uri_scheme_request_get_uri(request);
        _this->scheme_handler_call(scheme, uri);
      }
 
      static char* get_string_from_js_result(WebKitJavascriptResult* r)
      {
        char* s = nullptr;
#if WEBKIT_MAJOR_VERSION >= 2 && WEBKIT_MINOR_VERSION >= 22
        JSCValue* value = webkit_javascript_result_get_js_value(r);
        s = jsc_value_to_string(value);
#else
        JSGlobalContextRef ctx = webkit_javascript_result_get_global_context(r);
        JSValueRef value = webkit_javascript_result_get_value(r);
        JSStringRef js = JSValueToStringCopy(ctx, value, nullptr);
        size_t n = JSStringGetMaximumUTF8CStringSize(js);
        s = g_new(char, n);
        JSStringGetUTF8CString(js, s, n);
        JSStringRelease(js);
#endif
        return s;
      }
 
      GtkWidget* m_window;
      GtkWidget* m_webview;
 
      void* navigateCallbackArg = nullptr;
      std::function<void(const std::string&, void*)> navigateCallback = nullptr;
 
      static void on_load_changed(WebKitWebView* web_view, WebKitLoadEvent load_event,
                                  gpointer arg)
      {
        if (load_event == WEBKIT_LOAD_FINISHED)
        {
          auto inst = static_cast<gtk_webkit_engine*>(arg);
          inst->navigateCallback(webkit_web_view_get_uri(web_view),
                                 inst->navigateCallbackArg);
        }
      }
    };
 
  } // namespace detail
 
  using browser_engine = detail::gtk_webkit_engine;
 
} // namespace webview
 
#elif defined(WEBVIEW_COCOA)
 
//
// ====================================================================
//
// This implementation uses Cocoa WKWebView backend on macOS. It is
// written using ObjC runtime and uses WKWebView class as a browser runtime.
// You should pass "-framework Webkit" flag to the compiler.
//
// ====================================================================
//
 
#include <CoreGraphics/CoreGraphics.h>
#include <objc/NSObjCRuntime.h>
#include <objc/objc-runtime.h>
 
namespace webview
{
  namespace detail
  {
    namespace objc
    {
 
      // A convenient template function for unconditionally casting the specified
      // C-like function into a function that can be called with the given return
      // type and arguments. Caller takes full responsibility for ensuring that
      // the function call is valid. It is assumed that the function will not
      // throw exceptions.
      template <typename Result, typename Callable, typename... Args>
      Result invoke(Callable callable, Args... args) noexcept
      {
        return reinterpret_cast<Result (*)(Args...)>(callable)(args...);
      }
 
      // Calls objc_msgSend.
      template <typename Result, typename... Args> Result msg_send(Args... args) noexcept
      {
        return invoke<Result>(objc_msgSend, args...);
      }
 
    } // namespace objc
 
    enum NSBackingStoreType : NSUInteger
    {
      NSBackingStoreBuffered = 2
    };
 
    enum NSWindowStyleMask : NSUInteger
    {
      NSWindowStyleMaskTitled = 1,
      NSWindowStyleMaskClosable = 2,
      NSWindowStyleMaskMiniaturizable = 4,
      NSWindowStyleMaskResizable = 8
    };
 
    enum NSApplicationActivationPolicy : NSInteger
    {
      NSApplicationActivationPolicyRegular = 0
    };
 
    enum WKUserScriptInjectionTime : NSInteger
    {
      WKUserScriptInjectionTimeAtDocumentStart = 0
    };
 
    enum NSModalResponse : NSInteger
    {
      NSModalResponseOK = 1
    };
 
    // Convenient conversion of string literals.
    inline id operator"" _cls(const char* s, std::size_t)
    {
      return (id)objc_getClass(s);
    }
    inline SEL operator"" _sel(const char* s, std::size_t)
    {
      return sel_registerName(s);
    }
    inline id operator"" _str(const char* s, std::size_t)
    {
      return objc::msg_send<id>("NSString"_cls, "stringWithUTF8String:"_sel, s);
    }
 
    class cocoa_wkwebview_engine
    {
      public:
      cocoa_wkwebview_engine(bool debug, void* window)
          : m_debug{ debug }, m_parent_window{ window }
      {
        auto app = get_shared_application();
        auto delegate = create_app_delegate();
        objc_setAssociatedObject(delegate, "webview", (id)this, OBJC_ASSOCIATION_ASSIGN);
        objc::msg_send<void>(app, "setDelegate:"_sel, delegate);
 
        // See comments related to application lifecycle in create_app_delegate().
        if (window)
        {
          on_application_did_finish_launching(delegate, app);
        }
        else
        {
          // Start the main run loop so that the app delegate gets the
          // NSApplicationDidFinishLaunchingNotification notification after the run
          // loop has started in order to perform further initialization.
          // We need to return from this constructor so this run loop is only
          // temporary.
          objc::msg_send<void>(app, "run"_sel);
        }
      }
      virtual ~cocoa_wkwebview_engine() = default;
      void* window()
      {
        return (void*)m_window;
      }
      void terminate()
      {
        auto app = get_shared_application();
        objc::msg_send<void>(app, "terminate:"_sel, nullptr);
      }
      void run()
      {
        auto app = get_shared_application();
        objc::msg_send<void>(app, "run"_sel);
      }
      void dispatch(std::function<void()> f)
      {
        dispatch_async_f(dispatch_get_main_queue(), new dispatch_fn_t(f),
                         (dispatch_function_t)([](void* arg) {
                           auto f = static_cast<dispatch_fn_t*>(arg);
                           (*f)();
                           delete f;
                         }));
      }
      void set_title(const std::string& title)
      {
        objc::msg_send<void>(
            m_window, "setTitle:"_sel,
            objc::msg_send<id>("NSString"_cls, "stringWithUTF8String:"_sel, title.c_str()));
      }
      void set_size(int width, int height, int hints)
      {
        auto style = static_cast<NSWindowStyleMask>(NSWindowStyleMaskTitled |
                                                    NSWindowStyleMaskClosable |
                                                    NSWindowStyleMaskMiniaturizable);
        if (hints != WEBVIEW_HINT_FIXED)
        {
          style = static_cast<NSWindowStyleMask>(style | NSWindowStyleMaskResizable);
        }
        objc::msg_send<void>(m_window, "setStyleMask:"_sel, style);
 
        if (hints == WEBVIEW_HINT_MIN)
        {
          objc::msg_send<void>(m_window, "setContentMinSize:"_sel,
                               CGSizeMake(width, height));
        }
        else if (hints == WEBVIEW_HINT_MAX)
        {
          objc::msg_send<void>(m_window, "setContentMaxSize:"_sel,
                               CGSizeMake(width, height));
        }
        else
        {
          objc::msg_send<void>(m_window, "setFrame:display:animate:"_sel,
                               CGRectMake(0, 0, width, height), YES, NO);
        }
        objc::msg_send<void>(m_window, "center"_sel);
      }
      void navigate(const std::string& url)
      {
        auto nsurl = objc::msg_send<id>(
            "NSURL"_cls, "URLWithString:"_sel,
            objc::msg_send<id>("NSString"_cls, "stringWithUTF8String:"_sel, url.c_str()));
 
        objc::msg_send<void>(
            m_webview, "loadRequest:"_sel,
            objc::msg_send<id>("NSURLRequest"_cls, "requestWithURL:"_sel, nsurl));
      }
 
      void add_navigate_listener(std::function<void(const std::string&, void*)> callback,
                                 void* arg)
      {
        m_navigateCallback = callback;
        m_navigateCallbackArg = arg;
      }
 
      void add_scheme_handler(const std::string& scheme,
                              std::function<void(const std::string&, void*)> callback,
                              void* arg)
      {
        // TODO: Implement
      }
 
      void set_html(const std::string& html)
      {
        objc::msg_send<void>(
            m_webview, "loadHTMLString:baseURL:"_sel,
            objc::msg_send<id>("NSString"_cls, "stringWithUTF8String:"_sel, html.c_str()),
            nullptr);
      }
      void init(const std::string& js)
      {
        // Equivalent Obj-C:
        // [m_manager addUserScript:[[WKUserScript alloc] initWithSource:[NSString
        // stringWithUTF8String:js.c_str()]
        // injectionTime:WKUserScriptInjectionTimeAtDocumentStart forMainFrameOnly:YES]]
        objc::msg_send<void>(
            m_manager, "addUserScript:"_sel,
            objc::msg_send<id>(
                objc::msg_send<id>("WKUserScript"_cls, "alloc"_sel),
                "initWithSource:injectionTime:forMainFrameOnly:"_sel,
                objc::msg_send<id>("NSString"_cls, "stringWithUTF8String:"_sel, js.c_str()),
                WKUserScriptInjectionTimeAtDocumentStart, YES));
      }
      void eval(const std::string& js)
      {
        objc::msg_send<void>(
            m_webview, "evaluateJavaScript:completionHandler:"_sel,
            objc::msg_send<id>("NSString"_cls, "stringWithUTF8String:"_sel, js.c_str()),
            nullptr);
      }
 
      private:
      virtual void on_message(const std::string& msg) = 0;
      id create_app_delegate()
      {
        // Note: Avoid registering the class name "AppDelegate" as it is the
        // default name in projects created with Xcode, and using the same name
        // causes objc_registerClassPair to crash.
        auto cls =
            objc_allocateClassPair((Class) "NSResponder"_cls, "WebviewAppDelegate", 0);
        class_addProtocol(cls, objc_getProtocol("NSTouchBarProvider"));
        class_addMethod(cls, "applicationShouldTerminateAfterLastWindowClosed:"_sel,
                        (IMP)(+[](id, SEL, id) -> BOOL { return 1; }), "c@:@");
        // If the library was not initialized with an existing window then the user
        // is likely managing the application lifecycle and we would not get the
        // "applicationDidFinishLaunching:" message and therefore do not need to
        // add this method.
        if (!m_parent_window)
        {
          class_addMethod(cls, "applicationDidFinishLaunching:"_sel,
                          (IMP)(+[](id self, SEL, id notification)
                                {
                                  auto app =
                                      objc::msg_send<id>(notification, "object"_sel);
                                  auto w = get_associated_webview(self);
                                  w->on_application_did_finish_launching(self, app);
                                }),
                          "v@:@");
        }
        objc_registerClassPair(cls);
        return objc::msg_send<id>((id)cls, "new"_sel);
      }
      id create_script_message_handler()
      {
        auto cls = objc_allocateClassPair((Class) "NSResponder"_cls,
                                          "WebkitScriptMessageHandler", 0);
        class_addProtocol(cls, objc_getProtocol("WKScriptMessageHandler"));
        class_addMethod(
            cls, "userContentController:didReceiveScriptMessage:"_sel,
            (IMP)(+[](id self, SEL, id, id msg)
                  {
                    auto w = get_associated_webview(self);
                    w->on_message(objc::msg_send<const char*>(
                        objc::msg_send<id>(msg, "body"_sel), "UTF8String"_sel));
                  }),
            "v@:@@");
        objc_registerClassPair(cls);
        auto instance = objc::msg_send<id>((id)cls, "new"_sel);
        objc_setAssociatedObject(instance, "webview", (id)this, OBJC_ASSOCIATION_ASSIGN);
        return instance;
      }
      static id create_webkit_ui_delegate()
      {
        auto cls = objc_allocateClassPair((Class) "NSObject"_cls, "WebkitUIDelegate", 0);
        class_addProtocol(cls, objc_getProtocol("WKUIDelegate"));
        class_addMethod(
            cls,
            "webView:runOpenPanelWithParameters:initiatedByFrame:completionHandler:"_sel,
            (IMP)(+[](id, SEL, id, id parameters, id, id completion_handler)
                  {
                    auto allows_multiple_selection =
                        objc::msg_send<BOOL>(parameters, "allowsMultipleSelection"_sel);
                    auto allows_directories =
                        objc::msg_send<BOOL>(parameters, "allowsDirectories"_sel);
 
                    // Show a panel for selecting files.
                    auto panel = objc::msg_send<id>("NSOpenPanel"_cls, "openPanel"_sel);
                    objc::msg_send<void>(panel, "setCanChooseFiles:"_sel, YES);
                    objc::msg_send<void>(panel, "setCanChooseDirectories:"_sel,
                                         allows_directories);
                    objc::msg_send<void>(panel, "setAllowsMultipleSelection:"_sel,
                                         allows_multiple_selection);
                    auto modal_response =
                        objc::msg_send<NSModalResponse>(panel, "runModal"_sel);
 
                    // Get the URLs for the selected files. If the modal was canceled
                    // then we pass null to the completion handler to signify
                    // cancellation.
                    id urls = modal_response == NSModalResponseOK
                                  ? objc::msg_send<id>(panel, "URLs"_sel)
                                  : nullptr;
 
                    // Invoke the completion handler block.
                    auto sig = objc::msg_send<id>("NSMethodSignature"_cls,
                                                  "signatureWithObjCTypes:"_sel, "v@?@");
                    auto invocation = objc::msg_send<id>(
                        "NSInvocation"_cls, "invocationWithMethodSignature:"_sel, sig);
                    objc::msg_send<void>(invocation, "setTarget:"_sel,
                                         completion_handler);
                    objc::msg_send<void>(invocation, "setArgument:atIndex:"_sel, &urls,
                                         1);
                    objc::msg_send<void>(invocation, "invoke"_sel);
                  }),
            "v@:@@@@");
        objc_registerClassPair(cls);
        return objc::msg_send<id>((id)cls, "new"_sel);
      }
      id create_webkit_navigation_delegate()
      {
        auto cls =
            objc_allocateClassPair((Class) "NSObject"_cls, "WebkitNavigationDelegate", 0);
        class_addProtocol(cls, objc_getProtocol("WKNavigationDelegate"));
        class_addMethod(cls, "webView:didFinishNavigation:"_sel,
                        (IMP)(+[](id delegate, SEL sel, id webview, id navigation)
                              {
                                auto w = get_associated_webview(delegate);
                                auto url = objc::msg_send<id>(webview, "URL"_sel);
                                auto nstr = objc::msg_send<id>(url, "absoluteString"_sel);
                                auto str = objc::msg_send<char*>(nstr, "UTF8String"_sel);
                                w->m_navigateCallback(str, w->m_navigateCallbackArg);
                              }),
                        "v@:@");
        objc_registerClassPair(cls);
        auto instance = objc::msg_send<id>((id)cls, "new"_sel);
        objc_setAssociatedObject(instance, "webview", (id)this, OBJC_ASSOCIATION_ASSIGN);
        return instance;
      }
      static id get_shared_application()
      {
        return objc::msg_send<id>("NSApplication"_cls, "sharedApplication"_sel);
      }
      static cocoa_wkwebview_engine* get_associated_webview(id object)
      {
        auto w = (cocoa_wkwebview_engine*)objc_getAssociatedObject(object, "webview");
        assert(w);
        return w;
      }
      static id get_main_bundle() noexcept
      {
        return objc::msg_send<id>("NSBundle"_cls, "mainBundle"_sel);
      }
      static bool is_app_bundled() noexcept
      {
        auto bundle = get_main_bundle();
        if (!bundle)
        {
          return false;
        }
        auto bundle_path = objc::msg_send<id>(bundle, "bundlePath"_sel);
        auto bundled = objc::msg_send<BOOL>(bundle_path, "hasSuffix:"_sel, ".app"_str);
        return !!bundled;
      }
      void on_application_did_finish_launching(id /*delegate*/, id app)
      {
        // See comments related to application lifecycle in create_app_delegate().
        if (!m_parent_window)
        {
          // Stop the main run loop so that we can return
          // from the constructor.
          objc::msg_send<void>(app, "stop:"_sel, nullptr);
        }
 
        // Activate the app if it is not bundled.
        // Bundled apps launched from Finder are activated automatically but
        // otherwise not. Activating the app even when it has been launched from
        // Finder does not seem to be harmful but calling this function is rarely
        // needed as proper activation is normally taken care of for us.
        // Bundled apps have a default activation policy of
        // NSApplicationActivationPolicyRegular while non-bundled apps have a
        // default activation policy of NSApplicationActivationPolicyProhibited.
        if (!is_app_bundled())
        {
          // "setActivationPolicy:" must be invoked before
          // "activateIgnoringOtherApps:" for activation to work.
          objc::msg_send<void>(app, "setActivationPolicy:"_sel,
                               NSApplicationActivationPolicyRegular);
          // Activate the app regardless of other active apps.
          // This can be obtrusive so we only do it when necessary.
          objc::msg_send<void>(app, "activateIgnoringOtherApps:"_sel, YES);
        }
 
        // Main window
        if (!m_parent_window)
        {
          m_window = objc::msg_send<id>("NSWindow"_cls, "alloc"_sel);
          auto style = NSWindowStyleMaskTitled;
          m_window = objc::msg_send<id>(
              m_window, "initWithContentRect:styleMask:backing:defer:"_sel,
              CGRectMake(0, 0, 0, 0), style, NSBackingStoreBuffered, NO);
        }
        else
        {
          m_window = (id)m_parent_window;
        }
 
        // Webview
        auto config = objc::msg_send<id>("WKWebViewConfiguration"_cls, "new"_sel);
        m_manager = objc::msg_send<id>(config, "userContentController"_sel);
        m_webview = objc::msg_send<id>("WKWebView"_cls, "alloc"_sel);
 
        if (m_debug)
        {
          // Equivalent Obj-C:
          // [[config preferences] setValue:@YES forKey:@"developerExtrasEnabled"];
          objc::msg_send<id>(
              objc::msg_send<id>(config, "preferences"_sel), "setValue:forKey:"_sel,
              objc::msg_send<id>("NSNumber"_cls, "numberWithBool:"_sel, YES),
              "developerExtrasEnabled"_str);
        }
 
        // Equivalent Obj-C:
        // [[config preferences] setValue:@YES forKey:@"fullScreenEnabled"];
        objc::msg_send<id>(objc::msg_send<id>(config, "preferences"_sel),
                           "setValue:forKey:"_sel,
                           objc::msg_send<id>("NSNumber"_cls, "numberWithBool:"_sel, YES),
                           "fullScreenEnabled"_str);
 
        // Equivalent Obj-C:
        // [[config preferences] setValue:@YES forKey:@"javaScriptCanAccessClipboard"];
        objc::msg_send<id>(objc::msg_send<id>(config, "preferences"_sel),
                           "setValue:forKey:"_sel,
                           objc::msg_send<id>("NSNumber"_cls, "numberWithBool:"_sel, YES),
                           "javaScriptCanAccessClipboard"_str);
 
        // Equivalent Obj-C:
        // [[config preferences] setValue:@YES forKey:@"DOMPasteAllowed"];
        objc::msg_send<id>(objc::msg_send<id>(config, "preferences"_sel),
                           "setValue:forKey:"_sel,
                           objc::msg_send<id>("NSNumber"_cls, "numberWithBool:"_sel, YES),
                           "DOMPasteAllowed"_str);
 
        auto ui_delegate = create_webkit_ui_delegate();
        objc::msg_send<void>(m_webview, "initWithFrame:configuration:"_sel,
                             CGRectMake(0, 0, 0, 0), config);
        objc::msg_send<void>(m_webview, "setUIDelegate:"_sel, ui_delegate);
 
        auto navigation_delegate = create_webkit_navigation_delegate();
        objc::msg_send<void>(m_webview, "setNavigationDelegate:"_sel, navigation_delegate);
        auto script_message_handler = create_script_message_handler();
        objc::msg_send<void>(m_manager, "addScriptMessageHandler:name:"_sel,
                             script_message_handler, "external"_str);
 
        init(R""(
      window.external = {
        invoke: function(s) {
          window.webkit.messageHandlers.external.postMessage(s);
        },
      };
      )"");
        objc::msg_send<void>(m_window, "setContentView:"_sel, m_webview);
        objc::msg_send<void>(m_window, "makeKeyAndOrderFront:"_sel, nullptr);
      }
      bool m_debug;
      void* m_parent_window;
      id m_window;
      id m_webview;
      id m_manager;
      void* m_navigateCallbackArg = nullptr;
      std::function<void(const std::string&, void*)> m_navigateCallback = 0;
    };
 
  } // namespace detail
 
  using browser_engine = detail::cocoa_wkwebview_engine;
 
} // namespace webview
 
#elif defined(WEBVIEW_EDGE)
 
//
// ====================================================================
//
// This implementation uses Win32 API to create a native window. It
// uses Edge/Chromium webview2 backend as a browser engine.
//
// ====================================================================
//
 
#define WIN32_LEAN_AND_MEAN
#include <shlobj.h>
#include <shlwapi.h>
#include <stdlib.h>
#include <windows.h>
 
#include "WebView2.h"
 
#ifdef _MSC_VER
#pragma comment(lib, "advapi32.lib")
#pragma comment(lib, "ole32.lib")
#pragma comment(lib, "shell32.lib")
#pragma comment(lib, "shlwapi.lib")
#pragma comment(lib, "user32.lib")
#pragma comment(lib, "version.lib")
#endif
 
namespace webview
{
  namespace detail
  {
 
    using msg_cb_t = std::function<void(const std::string)>;
 
    // Converts a narrow (UTF-8-encoded) string into a wide (UTF-16-encoded) string.
    inline std::wstring widen_string(const std::string& input)
    {
      if (input.empty())
      {
        return std::wstring();
      }
      UINT cp = CP_UTF8;
      DWORD flags = MB_ERR_INVALID_CHARS;
      auto input_c = input.c_str();
      auto input_length = static_cast<int>(input.size());
      auto required_length =
          MultiByteToWideChar(cp, flags, input_c, input_length, nullptr, 0);
      if (required_length > 0)
      {
        std::wstring output(static_cast<std::size_t>(required_length), L'\0');
        if (MultiByteToWideChar(cp, flags, input_c, input_length, &output[0],
                                required_length) > 0)
        {
          return output;
        }
      }
      // Failed to convert string from UTF-8 to UTF-16
      return std::wstring();
    }
 
    // Converts a wide (UTF-16-encoded) string into a narrow (UTF-8-encoded) string.
    inline std::string narrow_string(const std::wstring& input)
    {
      if (input.empty())
      {
        return std::string();
      }
      UINT cp = CP_UTF8;
      DWORD flags = WC_ERR_INVALID_CHARS;
      auto input_c = input.c_str();
      auto input_length = static_cast<int>(input.size());
      auto required_length =
          WideCharToMultiByte(cp, flags, input_c, input_length, nullptr, 0, nullptr, nullptr);
      if (required_length > 0)
      {
        std::string output(static_cast<std::size_t>(required_length), '\0');
        if (WideCharToMultiByte(cp, flags, input_c, input_length, &output[0],
                                required_length, nullptr, nullptr) > 0)
        {
          return output;
        }
      }
      // Failed to convert string from UTF-16 to UTF-8
      return std::string();
    }
 
    // Parses a version string with 1-4 integral components, e.g. "1.2.3.4".
    // Missing or invalid components default to 0, and excess components are ignored.
    template <typename T>
    std::array<unsigned int, 4> parse_version(const std::basic_string<T>& version) noexcept
    {
      auto parse_component = [](auto sb, auto se) -> unsigned int
      {
        try
        {
          auto n = std::stol(std::basic_string<T>(sb, se));
          return n < 0 ? 0 : n;
        }
        catch (std::exception&)
        {
          return 0;
        }
      };
      auto end = version.end();
      auto sb = version.begin(); // subrange begin
      auto se = sb;              // subrange end
      unsigned int ci = 0;       // component index
      std::array<unsigned int, 4> components{};
      while (sb != end && se != end && ci < components.size())
      {
        if (*se == static_cast<T>('.'))
        {
          components[ci++] = parse_component(sb, se);
          sb = ++se;
          continue;
        }
        ++se;
      }
      if (sb < se && ci < components.size())
      {
        components[ci] = parse_component(sb, se);
      }
      return components;
    }
 
    template <typename T, std::size_t Length>
    auto parse_version(const T (&version)[Length]) noexcept
    {
      return parse_version(std::basic_string<T>(version, Length));
    }
 
    std::wstring get_file_version_string(const std::wstring& file_path) noexcept
    {
      DWORD dummy_handle; // Unused
      DWORD info_buffer_length = GetFileVersionInfoSizeW(file_path.c_str(), &dummy_handle);
      if (info_buffer_length == 0)
      {
        return std::wstring();
      }
      std::vector<char> info_buffer;
      info_buffer.reserve(info_buffer_length);
      if (!GetFileVersionInfoW(file_path.c_str(), 0, info_buffer_length, info_buffer.data()))
      {
        return std::wstring();
      }
      auto sub_block = L"\\StringFileInfo\\040904B0\\ProductVersion";
      LPWSTR version = nullptr;
      unsigned int version_length = 0;
      if (!VerQueryValueW(info_buffer.data(), sub_block, reinterpret_cast<LPVOID*>(&version),
                          &version_length))
      {
        return std::wstring();
      }
      if (!version || version_length == 0)
      {
        return std::wstring();
      }
      return std::wstring(version, version_length);
    }
 
    // A wrapper around COM library initialization. Calls CoInitializeEx in the
    // constructor and CoUninitialize in the destructor.
    class com_init_wrapper
    {
      public:
      com_init_wrapper(DWORD dwCoInit)
      {
        // We can safely continue as long as COM was either successfully
        // initialized or already initialized.
        // RPC_E_CHANGED_MODE means that CoInitializeEx was already called with
        // a different concurrency model.
        switch (CoInitializeEx(nullptr, dwCoInit))
        {
          case S_OK:
          case S_FALSE:
            m_initialized = true;
            break;
        }
      }
 
      ~com_init_wrapper()
      {
        if (m_initialized)
        {
          CoUninitialize();
          m_initialized = false;
        }
      }
 
      com_init_wrapper(const com_init_wrapper& other) = delete;
      com_init_wrapper& operator=(const com_init_wrapper& other) = delete;
      com_init_wrapper(com_init_wrapper&& other) = delete;
      com_init_wrapper& operator=(com_init_wrapper&& other) = delete;
 
      bool is_initialized() const
      {
        return m_initialized;
      }
 
      private:
      bool m_initialized = false;
    };
 
    // Holds a symbol name and associated type for code clarity.
    template <typename T> class library_symbol
    {
      public:
      using type = T;
 
      constexpr explicit library_symbol(const char* name) : m_name(name)
      {
      }
      constexpr const char* get_name() const
      {
        return m_name;
      }
 
      private:
      const char* m_name;
    };
 
    // Loads a native shared library and allows one to get addresses for those
    // symbols.
    class native_library
    {
      public:
      explicit native_library(const wchar_t* name) : m_handle(LoadLibraryW(name))
      {
      }
 
      ~native_library()
      {
        if (m_handle)
        {
          FreeLibrary(m_handle);
          m_handle = nullptr;
        }
      }
 
      native_library(const native_library& other) = delete;
      native_library& operator=(const native_library& other) = delete;
      native_library(native_library&& other) = default;
      native_library& operator=(native_library&& other) = default;
 
      // Returns true if the library is currently loaded; otherwise false.
      operator bool() const
      {
        return is_loaded();
      }
 
      // Get the address for the specified symbol or nullptr if not found.
      template <typename Symbol> typename Symbol::type get(const Symbol& symbol) const
      {
        if (is_loaded())
        {
          return reinterpret_cast<typename Symbol::type>(
              GetProcAddress(m_handle, symbol.get_name()));
        }
        return nullptr;
      }
 
      // Returns true if the library is currently loaded; otherwise false.
      bool is_loaded() const
      {
        return !!m_handle;
      }
 
      void detach()
      {
        m_handle = nullptr;
      }
 
      private:
      HMODULE m_handle = nullptr;
    };
 
    struct user32_symbols
    {
      using DPI_AWARENESS_CONTEXT = HANDLE;
      using SetProcessDpiAwarenessContext_t = BOOL(WINAPI*)(DPI_AWARENESS_CONTEXT);
      using SetProcessDPIAware_t = BOOL(WINAPI*)();
 
      static constexpr auto SetProcessDpiAwarenessContext =
          library_symbol<SetProcessDpiAwarenessContext_t>("SetProcessDpiAwarenessContext");
      static constexpr auto SetProcessDPIAware =
          library_symbol<SetProcessDPIAware_t>("SetProcessDPIAware");
    };
 
    struct shcore_symbols
    {
      typedef enum
      {
        PROCESS_PER_MONITOR_DPI_AWARE = 2
      } PROCESS_DPI_AWARENESS;
      using SetProcessDpiAwareness_t = HRESULT(WINAPI*)(PROCESS_DPI_AWARENESS);
 
      static constexpr auto SetProcessDpiAwareness =
          library_symbol<SetProcessDpiAwareness_t>("SetProcessDpiAwareness");
    };
 
    class reg_key
    {
      public:
      explicit reg_key(HKEY root_key, const wchar_t* sub_key, DWORD options,
                       REGSAM sam_desired)
      {
        HKEY handle;
        auto status = RegOpenKeyExW(root_key, sub_key, options, sam_desired, &handle);
        if (status == ERROR_SUCCESS)
        {
          m_handle = handle;
        }
      }
 
      explicit reg_key(HKEY root_key, const std::wstring& sub_key, DWORD options,
                       REGSAM sam_desired)
          : reg_key(root_key, sub_key.c_str(), options, sam_desired)
      {
      }
 
      virtual ~reg_key()
      {
        if (m_handle)
        {
          RegCloseKey(m_handle);
          m_handle = nullptr;
        }
      }
 
      reg_key(const reg_key& other) = delete;
      reg_key& operator=(const reg_key& other) = delete;
      reg_key(reg_key&& other) = delete;
      reg_key& operator=(reg_key&& other) = delete;
 
      bool is_open() const
      {
        return !!m_handle;
      }
      bool get_handle() const
      {
        return m_handle;
      }
 
      std::wstring query_string(const wchar_t* name) const
      {
        DWORD buf_length = 0;
        // Get the size of the data in bytes.
        auto status =
            RegQueryValueExW(m_handle, name, nullptr, nullptr, nullptr, &buf_length);
        if (status != ERROR_SUCCESS && status != ERROR_MORE_DATA)
        {
          return std::wstring();
        }
        // Read the data.
        std::wstring result(buf_length / sizeof(wchar_t), 0);
        auto buf = reinterpret_cast<LPBYTE>(&result[0]);
        status = RegQueryValueExW(m_handle, name, nullptr, nullptr, buf, &buf_length);
        if (status != ERROR_SUCCESS)
        {
          return std::wstring();
        }
        // Remove trailing null-characters.
        for (std::size_t length = result.size(); length > 0; --length)
        {
          if (result[length - 1] != 0)
          {
            result.resize(length);
            break;
          }
        }
        return result;
      }
 
      private:
      HKEY m_handle = nullptr;
    };
 
    inline bool enable_dpi_awareness()
    {
      auto user32 = native_library(L"user32.dll");
      if (auto fn = user32.get(user32_symbols::SetProcessDpiAwarenessContext))
      {
        if (fn(DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE))
        {
          return true;
        }
        return GetLastError() == ERROR_ACCESS_DENIED;
      }
      if (auto shcore = native_library(L"shcore.dll"))
      {
        if (auto fn = shcore.get(shcore_symbols::SetProcessDpiAwareness))
        {
          auto result = fn(shcore_symbols::PROCESS_PER_MONITOR_DPI_AWARE);
          return result == S_OK || result == E_ACCESSDENIED;
        }
      }
      if (auto fn = user32.get(user32_symbols::SetProcessDPIAware))
      {
        return !!fn();
      }
      return true;
    }
 
// Enable built-in WebView2Loader implementation by default.
#ifndef WEBVIEW_MSWEBVIEW2_BUILTIN_IMPL
#define WEBVIEW_MSWEBVIEW2_BUILTIN_IMPL 1
#endif
 
// Link WebView2Loader.dll explicitly by default only if the built-in
// implementation is enabled.
#ifndef WEBVIEW_MSWEBVIEW2_EXPLICIT_LINK
#define WEBVIEW_MSWEBVIEW2_EXPLICIT_LINK WEBVIEW_MSWEBVIEW2_BUILTIN_IMPL
#endif
 
// Explicit linking of WebView2Loader.dll should be used along with
// the built-in implementation.
#if WEBVIEW_MSWEBVIEW2_BUILTIN_IMPL == 1 && WEBVIEW_MSWEBVIEW2_EXPLICIT_LINK != 1
#undef WEBVIEW_MSWEBVIEW2_EXPLICIT_LINK
#error Please set WEBVIEW_MSWEBVIEW2_EXPLICIT_LINK=1.
#endif
 
#if WEBVIEW_MSWEBVIEW2_BUILTIN_IMPL == 1
    // Gets the last component of a Windows native file path.
    // For example, if the path is "C:\a\b" then the result is "b".
    template <typename T>
    std::basic_string<T> get_last_native_path_component(const std::basic_string<T>& path)
    {
      if (auto pos = path.find_last_of(static_cast<T>('\\'));
          pos != std::basic_string<T>::npos)
      {
        return path.substr(pos + 1);
      }
      return std::basic_string<T>();
    }
#endif /* WEBVIEW_MSWEBVIEW2_BUILTIN_IMPL */
 
    template <typename T> struct cast_info_t
    {
      using type = T;
      IID iid;
    };
 
    namespace mswebview2
    {
      static constexpr IID IID_ICoreWebView2CreateCoreWebView2ControllerCompletedHandler{
        0x6C4819F3, 0xC9B7, 0x4260, 0x81, 0x27, 0xC9, 0xF5, 0xBD, 0xE7, 0xF6, 0x8C
      };
      static constexpr IID IID_ICoreWebView2CreateCoreWebView2EnvironmentCompletedHandler{
        0x4E8A3389, 0xC9D8, 0x4BD2, 0xB6, 0xB5, 0x12, 0x4F, 0xEE, 0x6C, 0xC1, 0x4D
      };
      static constexpr IID IID_ICoreWebView2PermissionRequestedEventHandler{
        0x15E1C6A3, 0xC72A, 0x4DF3, 0x91, 0xD7, 0xD0, 0x97, 0xFB, 0xEC, 0x6B, 0xFD
      };
      static constexpr IID IID_ICoreWebView2WebMessageReceivedEventHandler{
        0x57213F19, 0x00E6, 0x49FA, 0x8E, 0x07, 0x89, 0x8E, 0xA0, 0x1E, 0xCB, 0xD2
      };
 
#if WEBVIEW_MSWEBVIEW2_BUILTIN_IMPL == 1
      enum class webview2_runtime_type
      {
        installed = 0,
        embedded = 1
      };
 
      namespace webview2_symbols
      {
        using CreateWebViewEnvironmentWithOptionsInternal_t = HRESULT(STDMETHODCALLTYPE*)(
            bool, webview2_runtime_type, PCWSTR, IUnknown*,
            ICoreWebView2CreateCoreWebView2EnvironmentCompletedHandler*);
        using DllCanUnloadNow_t = HRESULT(STDMETHODCALLTYPE*)();
 
        static constexpr auto CreateWebViewEnvironmentWithOptionsInternal =
            library_symbol<CreateWebViewEnvironmentWithOptionsInternal_t>(
                "CreateWebViewEnvironmentWithOptionsInternal");
        static constexpr auto DllCanUnloadNow =
            library_symbol<DllCanUnloadNow_t>("DllCanUnloadNow");
      } // namespace webview2_symbols
#endif /* WEBVIEW_MSWEBVIEW2_BUILTIN_IMPL */
 
#if WEBVIEW_MSWEBVIEW2_EXPLICIT_LINK == 1
      namespace webview2_symbols
      {
        using CreateCoreWebView2EnvironmentWithOptions_t = HRESULT(STDMETHODCALLTYPE*)(
            PCWSTR, PCWSTR, ICoreWebView2EnvironmentOptions*,
            ICoreWebView2CreateCoreWebView2EnvironmentCompletedHandler*);
        using GetAvailableCoreWebView2BrowserVersionString_t =
            HRESULT(STDMETHODCALLTYPE*)(PCWSTR, LPWSTR*);
 
        static constexpr auto CreateCoreWebView2EnvironmentWithOptions =
            library_symbol<CreateCoreWebView2EnvironmentWithOptions_t>(
                "CreateCoreWebView2EnvironmentWithOptions");
        static constexpr auto GetAvailableCoreWebView2BrowserVersionString =
            library_symbol<GetAvailableCoreWebView2BrowserVersionString_t>(
                "GetAvailableCoreWebView2BrowserVersionString");
      } // namespace webview2_symbols
#endif /* WEBVIEW_MSWEBVIEW2_EXPLICIT_LINK */
 
      class loader
      {
        public:
        HRESULT create_environment_with_options(
            PCWSTR browser_dir, PCWSTR user_data_dir,
            ICoreWebView2EnvironmentOptions* env_options,
            ICoreWebView2CreateCoreWebView2EnvironmentCompletedHandler* created_handler)
            const
        {
#if WEBVIEW_MSWEBVIEW2_EXPLICIT_LINK == 1
          if (m_lib.is_loaded())
          {
            if (auto fn = m_lib.get(
                    webview2_symbols::CreateCoreWebView2EnvironmentWithOptions))
            {
              return fn(browser_dir, user_data_dir, env_options, created_handler);
            }
          }
#if WEBVIEW_MSWEBVIEW2_BUILTIN_IMPL == 1
          return create_environment_with_options_impl(browser_dir, user_data_dir,
                                                      env_options, created_handler);
#else
          return S_FALSE;
#endif
#else
          return ::CreateCoreWebView2EnvironmentWithOptions(browser_dir, user_data_dir,
                                                            env_options, created_handler);
#endif /* WEBVIEW_MSWEBVIEW2_EXPLICIT_LINK */
        }
 
        HRESULT
        get_available_browser_version_string(PCWSTR browser_dir, LPWSTR* version) const
        {
#if WEBVIEW_MSWEBVIEW2_EXPLICIT_LINK == 1
          if (m_lib.is_loaded())
          {
            if (auto fn = m_lib.get(
                    webview2_symbols::GetAvailableCoreWebView2BrowserVersionString))
            {
              return fn(browser_dir, version);
            }
          }
#if WEBVIEW_MSWEBVIEW2_BUILTIN_IMPL == 1
          return get_available_browser_version_string_impl(browser_dir, version);
#else
          return S_FALSE;
#endif
#else
          return ::GetAvailableCoreWebView2BrowserVersionString(browser_dir, version);
#endif /* WEBVIEW_MSWEBVIEW2_EXPLICIT_LINK */
        }
 
        private:
#if WEBVIEW_MSWEBVIEW2_BUILTIN_IMPL == 1
        struct client_info_t
        {
          bool found = false;
          std::wstring dll_path;
          std::wstring version;
          webview2_runtime_type runtime_type;
        };
 
        HRESULT create_environment_with_options_impl(
            PCWSTR browser_dir, PCWSTR user_data_dir,
            ICoreWebView2EnvironmentOptions* env_options,
            ICoreWebView2CreateCoreWebView2EnvironmentCompletedHandler* created_handler)
            const
        {
          auto found_client = find_available_client(browser_dir);
          if (!found_client.found)
          {
            return -1;
          }
          auto client_dll = native_library(found_client.dll_path.c_str());
          if (auto fn = client_dll.get(
                  webview2_symbols::CreateWebViewEnvironmentWithOptionsInternal))
          {
            return fn(true, found_client.runtime_type, user_data_dir, env_options,
                      created_handler);
          }
          if (auto fn = client_dll.get(webview2_symbols::DllCanUnloadNow))
          {
            if (!fn())
            {
              client_dll.detach();
            }
          }
          return ERROR_SUCCESS;
        }
 
        HRESULT
        get_available_browser_version_string_impl(PCWSTR browser_dir, LPWSTR* version) const
        {
          if (!version)
          {
            return -1;
          }
          auto found_client = find_available_client(browser_dir);
          if (!found_client.found)
          {
            return -1;
          }
          auto info_length_bytes =
              found_client.version.size() * sizeof(found_client.version[0]);
          auto info = static_cast<LPWSTR>(CoTaskMemAlloc(info_length_bytes));
          if (!info)
          {
            return -1;
          }
          CopyMemory(info, found_client.version.c_str(), info_length_bytes);
          *version = info;
          return 0;
        }
 
        client_info_t find_available_client(PCWSTR browser_dir) const
        {
          if (browser_dir)
          {
            return find_embedded_client(api_version, browser_dir);
          }
          auto found_client =
              find_installed_client(api_version, true, default_release_channel_guid);
          if (!found_client.found)
          {
            found_client =
                find_installed_client(api_version, false, default_release_channel_guid);
          }
          return found_client;
        }
 
        std::wstring make_client_dll_path(const std::wstring& dir) const
        {
          auto dll_path = dir;
          if (!dll_path.empty())
          {
            auto last_char = dir[dir.size() - 1];
            if (last_char != L'\\' && last_char != L'/')
            {
              dll_path += L'\\';
            }
          }
          dll_path += L"EBWebView\\";
#if defined(_M_X64) || defined(__x86_64__)
          dll_path += L"x64";
#elif defined(_M_IX86) || defined(__i386__)
          dll_path += L"x86";
#elif defined(_M_ARM64) || defined(__aarch64__)
          dll_path += L"arm64";
#else
#error WebView2 integration for this platform is not yet supported.
#endif
          dll_path += L"\\EmbeddedBrowserWebView.dll";
          return dll_path;
        }
 
        client_info_t find_installed_client(unsigned int min_api_version, bool system,
                                            const std::wstring& release_channel) const
        {
          std::wstring sub_key = client_state_reg_sub_key;
          sub_key += release_channel;
          auto root_key = system ? HKEY_LOCAL_MACHINE : HKEY_CURRENT_USER;
          reg_key key(root_key, sub_key, 0, KEY_READ | KEY_WOW64_32KEY);
          if (!key.is_open())
          {
            return {};
          }
          auto ebwebview_value = key.query_string(L"EBWebView");
 
          auto client_version_string = get_last_native_path_component(ebwebview_value);
          auto client_version = parse_version(client_version_string);
          if (client_version[2] < min_api_version)
          {
            // Our API version is greater than the runtime API version.
            return {};
          }
 
          auto client_dll_path = make_client_dll_path(ebwebview_value);
          return { true, client_dll_path, client_version_string,
                 webview2_runtime_type::installed };
        }
 
        client_info_t find_embedded_client(unsigned int min_api_version,
                                           const std::wstring& dir) const
        {
          auto client_dll_path = make_client_dll_path(dir);
 
          auto client_version_string = get_file_version_string(client_dll_path);
          auto client_version = parse_version(client_version_string);
          if (client_version[2] < min_api_version)
          {
            // Our API version is greater than the runtime API version.
            return {};
          }
 
          return { true, client_dll_path, client_version_string,
                 webview2_runtime_type::embedded };
        }
 
        // The minimum WebView2 API version we need regardless of the SDK release
        // actually used. The number comes from the SDK release version,
        // e.g. 1.0.1150.38. To be safe the SDK should have a number that is greater
        // than or equal to this number. The Edge browser webview client must
        // have a number greater than or equal to this number.
        static constexpr unsigned int api_version = 1150;
 
        static constexpr auto client_state_reg_sub_key =
            L"SOFTWARE\\Microsoft\\EdgeUpdate\\ClientState\\";
 
        // GUID for the stable release channel.
        static constexpr auto stable_release_guid =
            L"{F3017226-FE2A-4295-8BDF-00C3A9A7E4C5}";
 
        static constexpr auto default_release_channel_guid = stable_release_guid;
#endif /* WEBVIEW_MSWEBVIEW2_BUILTIN_IMPL */
 
#if WEBVIEW_MSWEBVIEW2_EXPLICIT_LINK == 1
        native_library m_lib{ L"WebView2Loader.dll" };
#endif
      };
 
      namespace cast_info
      {
        static constexpr auto controller_completed =
            cast_info_t<ICoreWebView2CreateCoreWebView2ControllerCompletedHandler>{
              IID_ICoreWebView2CreateCoreWebView2ControllerCompletedHandler
            };
 
        static constexpr auto environment_completed =
            cast_info_t<ICoreWebView2CreateCoreWebView2EnvironmentCompletedHandler>{
              IID_ICoreWebView2CreateCoreWebView2EnvironmentCompletedHandler
            };
 
        static constexpr auto message_received =
            cast_info_t<ICoreWebView2WebMessageReceivedEventHandler>{
              IID_ICoreWebView2WebMessageReceivedEventHandler
            };
 
        static constexpr auto permission_requested =
            cast_info_t<ICoreWebView2PermissionRequestedEventHandler>{
              IID_ICoreWebView2PermissionRequestedEventHandler
            };
      } // namespace cast_info
    }     // namespace mswebview2
 
    class webview2_com_handler
        : public ICoreWebView2CreateCoreWebView2EnvironmentCompletedHandler,
          public ICoreWebView2CreateCoreWebView2ControllerCompletedHandler,
          public ICoreWebView2WebMessageReceivedEventHandler,
          public ICoreWebView2PermissionRequestedEventHandler,
          public ICoreWebView2NavigationCompletedEventHandler
    {
      using webview2_com_handler_cb_t =
          std::function<void(ICoreWebView2Controller*, ICoreWebView2* webview)>;
 
      public:
      webview2_com_handler(HWND hwnd, msg_cb_t msgCb, webview2_com_handler_cb_t cb)
          : m_window(hwnd), m_msgCb(msgCb), m_cb(cb)
      {
      }
 
      virtual ~webview2_com_handler() = default;
      webview2_com_handler(const webview2_com_handler& other) = delete;
      webview2_com_handler& operator=(const webview2_com_handler& other) = delete;
      webview2_com_handler(webview2_com_handler&& other) = delete;
      webview2_com_handler& operator=(webview2_com_handler&& other) = delete;
 
      ULONG STDMETHODCALLTYPE AddRef()
      {
        return ++m_ref_count;
      }
      ULONG STDMETHODCALLTYPE Release()
      {
        if (m_ref_count > 1)
        {
          return --m_ref_count;
        }
        delete this;
        return 0;
      }
      HRESULT STDMETHODCALLTYPE QueryInterface(REFIID riid, LPVOID* ppv)
      {
        using namespace mswebview2::cast_info;
 
        if (!ppv)
        {
          return E_POINTER;
        }
 
        // All of the COM interfaces we implement should be added here regardless
        // of whether they are required.
        // This is just to be on the safe side in case the WebView2 Runtime ever
        // requests a pointer to an interface we implement.
        // The WebView2 Runtime must at the very least be able to get a pointer to
        // ICoreWebView2CreateCoreWebView2EnvironmentCompletedHandler when we use
        // our custom WebView2 loader implementation, and observations have shown
        // that it is the only interface requested in this case. None have been
        // observed to be requested when using the official WebView2 loader.
 
        if (cast_if_equal_iid(riid, controller_completed, ppv) ||
            cast_if_equal_iid(riid, environment_completed, ppv) ||
            cast_if_equal_iid(riid, message_received, ppv) ||
            cast_if_equal_iid(riid, permission_requested, ppv))
        {
          return S_OK;
        }
 
        return E_NOINTERFACE;
      }
      HRESULT STDMETHODCALLTYPE Invoke(HRESULT res, ICoreWebView2Environment* env)
      {
        if (SUCCEEDED(res))
        {
          res = env->CreateCoreWebView2Controller(m_window, this);
          if (SUCCEEDED(res))
          {
            return S_OK;
          }
        }
        try_create_environment();
        return S_OK;
      }
      HRESULT STDMETHODCALLTYPE Invoke(HRESULT res, ICoreWebView2Controller* controller)
      {
        if (FAILED(res))
        {
          // See try_create_environment() regarding
          // HRESULT_FROM_WIN32(ERROR_INVALID_STATE).
          // The result is E_ABORT if the parent window has been destroyed already.
          switch (res)
          {
            case HRESULT_FROM_WIN32(ERROR_INVALID_STATE):
            case E_ABORT:
              return S_OK;
          }
          try_create_environment();
          return S_OK;
        }
 
        ICoreWebView2* webview;
        ::EventRegistrationToken token;
        controller->get_CoreWebView2(&webview);
        webview->add_WebMessageReceived(this, &token);
        webview->add_PermissionRequested(this, &token);
        webview->add_NavigationCompleted(this, &token);
 
        m_cb(controller, webview);
        return S_OK;
      }
      HRESULT STDMETHODCALLTYPE Invoke(ICoreWebView2* sender,
                                       ICoreWebView2WebMessageReceivedEventArgs* args)
      {
        LPWSTR message;
        args->TryGetWebMessageAsString(&message);
        m_msgCb(narrow_string(message));
        sender->PostWebMessageAsString(message);
 
        CoTaskMemFree(message);
        return S_OK;
      }
      HRESULT STDMETHODCALLTYPE Invoke(ICoreWebView2* sender,
                                       ICoreWebView2PermissionRequestedEventArgs* args)
      {
        COREWEBVIEW2_PERMISSION_KIND kind;
        args->get_PermissionKind(&kind);
        if (kind == COREWEBVIEW2_PERMISSION_KIND_CLIPBOARD_READ)
        {
          args->put_State(COREWEBVIEW2_PERMISSION_STATE_ALLOW);
        }
        return S_OK;
      }
      HRESULT STDMETHODCALLTYPE Invoke(ICoreWebView2* sender,
                                       ICoreWebView2NavigationCompletedEventArgs* args)
      {
        PWSTR uri = nullptr;
        auto hr = sender->get_Source(&uri);
        if (SUCCEEDED(hr))
        {
          auto curi = std::wstring_convert<std::codecvt_utf8<wchar_t> >().to_bytes(uri);
          if (navigateCallback)
            navigateCallback(curi, navigateCallbackArg);
        }
        CoTaskMemFree(uri);
        return hr;
      }
 
      // Checks whether the specified IID equals the IID of the specified type and
      // if so casts the "this" pointer to T and returns it. Returns nullptr on
      // mismatching IIDs.
      // If ppv is specified then the pointer will also be assigned to *ppv.
      template <typename T>
      T* cast_if_equal_iid(REFIID riid, const cast_info_t<T>& info,
                           LPVOID* ppv = nullptr) noexcept
      {
        T* ptr = nullptr;
        if (IsEqualIID(riid, info.iid))
        {
          ptr = static_cast<T*>(this);
          ptr->AddRef();
        }
        if (ppv)
        {
          *ppv = ptr;
        }
        return ptr;
      }
 
      // Set the function that will perform the initiating logic for creating
      // the WebView2 environment.
      void set_attempt_handler(std::function<HRESULT()> attempt_handler) noexcept
      {
        m_attempt_handler = attempt_handler;
      }
 
      // Retry creating a WebView2 environment.
      // The initiating logic for creating the environment is defined by the
      // caller of set_attempt_handler().
      void try_create_environment() noexcept
      {
        // WebView creation fails with HRESULT_FROM_WIN32(ERROR_INVALID_STATE) if
        // a running instance using the same user data folder exists, and the
        // Environment objects have different EnvironmentOptions.
        // Source:
        // https://docs.microsoft.com/en-us/microsoft-edge/webview2/reference/win32/icorewebview2environment?view=webview2-1.0.1150.38
        if (m_attempts < m_max_attempts)
        {
          ++m_attempts;
          auto res = m_attempt_handler();
          if (SUCCEEDED(res))
          {
            return;
          }
          // Not entirely sure if this error code only applies to
          // CreateCoreWebView2Controller so we check here as well.
          if (res == HRESULT_FROM_WIN32(ERROR_INVALID_STATE))
          {
            return;
          }
          try_create_environment();
          return;
        }
        // Give up.
        m_cb(nullptr, nullptr);
      }
 
      void STDMETHODCALLTYPE add_navigate_listener(
          std::function<void(const std::string&, void*)> callback, void* arg)
      {
        navigateCallback = std::move(callback);
        navigateCallbackArg = arg;
      }
 
      private:
      HWND m_window;
      msg_cb_t m_msgCb;
      webview2_com_handler_cb_t m_cb;
      std::atomic<ULONG> m_ref_count{ 1 };
      std::function<HRESULT()> m_attempt_handler;
      unsigned int m_max_attempts = 5;
      unsigned int m_attempts = 0;
      void* navigateCallbackArg = nullptr;
      std::function<void(const std::string&, void*)> navigateCallback = 0;
    };
 
    class win32_edge_engine
    {
      public:
      win32_edge_engine(bool debug, void* window)
      {
        if (!is_webview2_available())
        {
          return;
        }
        if (!m_com_init.is_initialized())
        {
          return;
        }
        enable_dpi_awareness();
        if (window == nullptr)
        {
          HINSTANCE hInstance = GetModuleHandle(nullptr);
          HICON icon = (HICON)LoadImage(hInstance, IDI_APPLICATION, IMAGE_ICON,
                                        GetSystemMetrics(SM_CXICON),
                                        GetSystemMetrics(SM_CYICON), LR_DEFAULTCOLOR);
 
          WNDCLASSEXW wc;
          ZeroMemory(&wc, sizeof(WNDCLASSEX));
          wc.cbSize = sizeof(WNDCLASSEX);
          wc.hInstance = hInstance;
          wc.lpszClassName = L"webview";
          wc.hIcon = icon;
          wc.lpfnWndProc =
              (WNDPROC)(+[](HWND hwnd, UINT msg, WPARAM wp, LPARAM lp) -> LRESULT
                        {
                          auto w =
                              (win32_edge_engine*)GetWindowLongPtr(hwnd, GWLP_USERDATA);
                          switch (msg)
                          {
                            case WM_SIZE:
                              w->resize(hwnd);
                              break;
                            case WM_CLOSE:
                              DestroyWindow(hwnd);
                              break;
                            case WM_DESTROY:
                              w->terminate();
                              break;
                            case WM_GETMINMAXINFO:
                            {
                              auto lpmmi = (LPMINMAXINFO)lp;
                              if (w == nullptr)
                              {
                                return 0;
                              }
                              if (w->m_maxsz.x > 0 && w->m_maxsz.y > 0)
                              {
                                lpmmi->ptMaxSize = w->m_maxsz;
                                lpmmi->ptMaxTrackSize = w->m_maxsz;
                              }
                              if (w->m_minsz.x > 0 && w->m_minsz.y > 0)
                              {
                                lpmmi->ptMinTrackSize = w->m_minsz;
                              }
                            }
                            break;
                            default:
                              return DefWindowProcW(hwnd, msg, wp, lp);
                          }
                          return 0;
                        });
          RegisterClassExW(&wc);
          m_window = CreateWindowW(L"webview", L"", WS_OVERLAPPEDWINDOW, CW_USEDEFAULT,
                                   CW_USEDEFAULT, 640, 480, nullptr, nullptr, hInstance,
                                   nullptr);
          if (m_window == nullptr)
          {
            return;
          }
          SetWindowLongPtr(m_window, GWLP_USERDATA, (LONG_PTR)this);
        }
        else
        {
          m_window = *(static_cast<HWND*>(window));
        }
 
        ShowWindow(m_window, SW_SHOW);
        UpdateWindow(m_window);
        SetFocus(m_window);
 
        auto cb = std::bind(&win32_edge_engine::on_message, this, std::placeholders::_1);
 
        embed(m_window, debug, cb);
        resize(m_window);
        m_controller->MoveFocus(COREWEBVIEW2_MOVE_FOCUS_REASON_PROGRAMMATIC);
      }
 
      virtual ~win32_edge_engine()
      {
        if (m_com_handler)
        {
          m_com_handler->Release();
          m_com_handler = nullptr;
        }
        if (m_webview)
        {
          m_webview->Release();
          m_webview = nullptr;
        }
        if (m_controller)
        {
          m_controller->Release();
          m_controller = nullptr;
        }
      }
 
      win32_edge_engine(const win32_edge_engine& other) = delete;
      win32_edge_engine& operator=(const win32_edge_engine& other) = delete;
      win32_edge_engine(win32_edge_engine&& other) = delete;
      win32_edge_engine& operator=(win32_edge_engine&& other) = delete;
 
      void run()
      {
        MSG msg;
        BOOL res;
        while ((res = GetMessage(&msg, nullptr, 0, 0)) != -1)
        {
          if (msg.hwnd)
          {
            TranslateMessage(&msg);
            DispatchMessage(&msg);
            continue;
          }
          if (msg.message == WM_APP)
          {
            auto f = (dispatch_fn_t*)(msg.lParam);
            (*f)();
            delete f;
          }
          else if (msg.message == WM_QUIT)
          {
            return;
          }
        }
      }
      void* window()
      {
        return (void*)m_window;
      }
      void terminate()
      {
        PostQuitMessage(0);
      }
      void dispatch(dispatch_fn_t f)
      {
        PostThreadMessage(m_main_thread, WM_APP, 0, (LPARAM) new dispatch_fn_t(f));
      }
 
      void set_title(const std::string& title)
      {
        SetWindowTextW(m_window, widen_string(title).c_str());
      }
 
      void set_size(int width, int height, int hints)
      {
        auto style = GetWindowLong(m_window, GWL_STYLE);
        if (hints == WEBVIEW_HINT_FIXED)
        {
          style &= ~(WS_THICKFRAME | WS_MAXIMIZEBOX);
        }
        else
        {
          style |= (WS_THICKFRAME | WS_MAXIMIZEBOX);
        }
        SetWindowLong(m_window, GWL_STYLE, style);
 
        if (hints == WEBVIEW_HINT_MAX)
        {
          m_maxsz.x = width;
          m_maxsz.y = height;
        }
        else if (hints == WEBVIEW_HINT_MIN)
        {
          m_minsz.x = width;
          m_minsz.y = height;
        }
        else
        {
          RECT r;
          r.left = r.top = 0;
          r.right = width;
          r.bottom = height;
          AdjustWindowRect(&r, WS_OVERLAPPEDWINDOW, 0);
          SetWindowPos(m_window, nullptr, r.left, r.top, r.right - r.left,
                       r.bottom - r.top,
                       SWP_NOZORDER | SWP_NOACTIVATE | SWP_NOMOVE | SWP_FRAMECHANGED);
          resize(m_window);
        }
      }
 
      void navigate(const std::string& url)
      {
        auto wurl = widen_string(url);
        m_webview->Navigate(wurl.c_str());
      }
 
      void init(const std::string& js)
      {
        auto wjs = widen_string(js);
        m_webview->AddScriptToExecuteOnDocumentCreated(wjs.c_str(), nullptr);
      }
 
      void eval(const std::string& js)
      {
        auto wjs = widen_string(js);
        m_webview->ExecuteScript(wjs.c_str(), nullptr);
      }
 
      void add_navigate_listener(std::function<void(const std::string&, void*)> callback,
                                 void* arg)
      {
        m_com_handler->add_navigate_listener(callback, arg);
      }
 
      void add_scheme_handler(const std::string& scheme,
                              std::function<void(const std::string&, void*)> callback,
                              void* arg)
      {
        // TODO: Implement
      }
 
      void set_html(const std::string& html)
      {
        m_webview->NavigateToString(widen_string(html).c_str());
      }
 
      private:
      bool embed(HWND wnd, bool debug, msg_cb_t cb)
      {
        std::atomic_flag flag = ATOMIC_FLAG_INIT;
        flag.test_and_set();
 
        wchar_t currentExePath[MAX_PATH];
        GetModuleFileNameW(nullptr, currentExePath, MAX_PATH);
        wchar_t* currentExeName = PathFindFileNameW(currentExePath);
 
        wchar_t dataPath[MAX_PATH];
        if (!SUCCEEDED(SHGetFolderPathW(nullptr, CSIDL_APPDATA, nullptr, 0, dataPath)))
        {
          return false;
        }
        wchar_t userDataFolder[MAX_PATH];
        PathCombineW(userDataFolder, dataPath, currentExeName);
 
        m_com_handler = new webview2_com_handler(
            wnd, cb,
            [&](ICoreWebView2Controller* controller, ICoreWebView2* webview)
            {
              if (!controller || !webview)
              {
                flag.clear();
                return;
              }
              controller->AddRef();
              webview->AddRef();
              m_controller = controller;
              m_webview = webview;
              flag.clear();
            });
 
        m_com_handler->set_attempt_handler(
            [&]
            {
              return m_webview2_loader.create_environment_with_options(
                  nullptr, userDataFolder, nullptr, m_com_handler);
            });
        m_com_handler->try_create_environment();
 
        MSG msg = {};
        while (flag.test_and_set() && GetMessage(&msg, nullptr, 0, 0))
        {
          TranslateMessage(&msg);
          DispatchMessage(&msg);
        }
        if (!m_controller || !m_webview)
        {
          return false;
        }
        ICoreWebView2Settings* settings = nullptr;
        auto res = m_webview->get_Settings(&settings);
        if (res != S_OK)
        {
          return false;
        }
        res = settings->put_AreDevToolsEnabled(debug ? TRUE : FALSE);
        if (res != S_OK)
        {
          return false;
        }
        init("window.external={invoke:s=>window.chrome.webview.postMessage(s)}");
        return true;
      }
 
      void resize(HWND wnd)
      {
        if (m_controller == nullptr)
        {
          return;
        }
        RECT bounds;
        GetClientRect(wnd, &bounds);
        m_controller->put_Bounds(bounds);
      }
 
      bool is_webview2_available() const noexcept
      {
        LPWSTR version_info = nullptr;
        auto res =
            m_webview2_loader.get_available_browser_version_string(nullptr, &version_info);
        // The result will be equal to HRESULT_FROM_WIN32(ERROR_FILE_NOT_FOUND)
        // if the WebView2 runtime is not installed.
        auto ok = SUCCEEDED(res) && version_info;
        if (version_info)
        {
          CoTaskMemFree(version_info);
        }
        return ok;
      }
 
      virtual void on_message(const std::string& msg) = 0;
 
      // The app is expected to call CoInitializeEx before
      // CreateCoreWebView2EnvironmentWithOptions.
      // Source:
      // https://docs.microsoft.com/en-us/microsoft-edge/webview2/reference/win32/webview2-idl#createcorewebview2environmentwithoptions
      com_init_wrapper m_com_init{ COINIT_APARTMENTTHREADED };
      HWND m_window = nullptr;
      POINT m_minsz = POINT{ 0, 0 };
      POINT m_maxsz = POINT{ 0, 0 };
      DWORD m_main_thread = GetCurrentThreadId();
      ICoreWebView2* m_webview = nullptr;
      ICoreWebView2Controller* m_controller = nullptr;
      webview2_com_handler* m_com_handler = nullptr;
      mswebview2::loader m_webview2_loader;
    };
 
  } // namespace detail
 
  using browser_engine = detail::win32_edge_engine;
 
} // namespace webview
 
#endif /* WEBVIEW_GTK, WEBVIEW_COCOA, WEBVIEW_EDGE */
 
namespace webview
{
 
  class webview : public browser_engine
  {
    public:
    webview(bool debug = false, void* wnd = nullptr) : browser_engine(debug, wnd)
    {
    }
 
    void navigate(const std::string& url)
    {
      if (url.empty())
      {
        browser_engine::navigate("about:blank");
        return;
      }
      browser_engine::navigate(url);
    }
 
    using binding_t = std::function<void(std::string, std::string, void*)>;
    class binding_ctx_t
    {
      public:
      binding_ctx_t(binding_t callback, void* arg) : callback(callback), arg(arg)
      {
      }
      // This function is called upon execution of the bound JS function
      binding_t callback;
      // This user-supplied argument is passed to the callback
      void* arg;
    };
 
    using sync_binding_t = std::function<std::string(std::string)>;
 
    // Synchronous bind
    void bind(const std::string& name, sync_binding_t fn)
    {
      auto wrapper = [this, fn](const std::string& seq, const std::string& req, void* /*arg*/)
      { resolve(seq, 0, fn(req)); };
      bind(name, wrapper, nullptr);
    }
 
    // Asynchronous bind
    void bind(const std::string& name, binding_t fn, void* arg)
    {
      if (bindings.count(name) > 0)
      {
        return;
      }
      bindings.emplace(name, binding_ctx_t(fn, arg));
      auto js = "(function() { var name = '" + name + "';" + R""(
      var RPC = window._rpc = (window._rpc || {nextSeq: 1});
      window[name] = function() {
        var seq = RPC.nextSeq++;
        var promise = new Promise(function(resolve, reject) {
          RPC[seq] = {
            resolve: resolve,
            reject: reject,
          };
        });
        window.external.invoke(JSON.stringify({
          id: seq,
          method: name,
          params: Array.prototype.slice.call(arguments),
        }));
        return promise;
      }
    })())"";
      init(js);
      eval(js);
    }
 
    void unbind(const std::string& name)
    {
      auto found = bindings.find(name);
      if (found != bindings.end())
      {
        auto js = "delete window['" + name + "'];";
        init(js);
        eval(js);
        bindings.erase(found);
      }
    }
 
    void resolve(const std::string& seq, int status, const std::string& result)
    {
      dispatch(
          [seq, status, result, this]()
          {
            if (status == 0)
            {
              eval("window._rpc[" + seq + "].resolve(" + result +
                   "); delete window._rpc[" + seq + "]");
            }
            else
            {
              eval("window._rpc[" + seq + "].reject(" + result +
                   "); delete window._rpc[" + seq + "]");
            }
          });
    }
 
    private:
    void on_message(const std::string& msg) override
    {
      auto seq = detail::json_parse(msg, "id", 0);
      auto name = detail::json_parse(msg, "method", 0);
      auto args = detail::json_parse(msg, "params", 0);
      auto found = bindings.find(name);
      if (found == bindings.end())
      {
        return;
      }
      const auto& context = found->second;
      context.callback(seq, args, context.arg);
    }
 
    std::map<std::string, binding_ctx_t> bindings;
  };
} // namespace webview
 
WEBVIEW_API webview_t webview_create(int debug, void* wnd)
{
  auto w = new webview::webview(debug, wnd);
  if (!w->window())
  {
    delete w;
    return nullptr;
  }
  return w;
}
 
WEBVIEW_API void webview_destroy(webview_t w)
{
  delete static_cast<webview::webview*>(w);
}
 
WEBVIEW_API void webview_run(webview_t w)
{
  static_cast<webview::webview*>(w)->run();
}
 
WEBVIEW_API void webview_terminate(webview_t w)
{
  static_cast<webview::webview*>(w)->terminate();
}
 
WEBVIEW_API void webview_dispatch(webview_t w, void (*fn)(webview_t, void*), void* arg)
{
  static_cast<webview::webview*>(w)->dispatch([=]() { fn(w, arg); });
}
 
WEBVIEW_API void* webview_get_window(webview_t w)
{
  return static_cast<webview::webview*>(w)->window();
}
 
WEBVIEW_API void webview_set_title(webview_t w, const char* title)
{
  static_cast<webview::webview*>(w)->set_title(title);
}
 
WEBVIEW_API void webview_set_size(webview_t w, int width, int height, int hints)
{
  static_cast<webview::webview*>(w)->set_size(width, height, hints);
}
 
WEBVIEW_API void webview_navigate(webview_t w, const char* url)
{
  static_cast<webview::webview*>(w)->navigate(url);
}
 
WEBVIEW_API void webview_set_html(webview_t w, const char* html)
{
  static_cast<webview::webview*>(w)->set_html(html);
}
 
WEBVIEW_API void webview_init(webview_t w, const char* js)
{
  static_cast<webview::webview*>(w)->init(js);
}
 
WEBVIEW_API void webview_eval(webview_t w, const char* js)
{
  static_cast<webview::webview*>(w)->eval(js);
}
 
WEBVIEW_API void webview_bind(webview_t w, const char* name,
                              void (*fn)(const char* seq, const char* req, void* arg), void* arg)
{
  static_cast<webview::webview*>(w)->bind(
      name,
      [=](const std::string& seq, const std::string& req, void* arg)
      { fn(seq.c_str(), req.c_str(), arg); },
      arg);
}
 
WEBVIEW_API void webview_unbind(webview_t w, const char* name)
{
  static_cast<webview::webview*>(w)->unbind(name);
}
 
WEBVIEW_API void webview_return(webview_t w, const char* seq, int status, const char* result)
{
  static_cast<webview::webview*>(w)->resolve(seq, status, result);
}
 
WEBVIEW_API const webview_version_info_t* webview_version()
{
  return &webview::detail::library_version_info;
}
 
#endif /* WEBVIEW_HEADER */
#endif /* __cplusplus */
#endif /* WEBVIEW_H */