/*
  ==============================================================================

   This file is part of the JUCE framework.
   Copyright (c) Raw Material Software Limited

   JUCE is an open source framework subject to commercial or open source
   licensing.

   By downloading, installing, or using the JUCE framework, or combining the
   JUCE framework with any other source code, object code, content or any other
   copyrightable work, you agree to the terms of the JUCE End User Licence
   Agreement, and all incorporated terms including the JUCE Privacy Policy and
   the JUCE Website Terms of Service, as applicable, which will bind you. If you
   do not agree to the terms of these agreements, we will not license the JUCE
   framework to you, and you must discontinue the installation or download
   process and cease use of the JUCE framework.

   JUCE End User Licence Agreement: https://juce.com/legal/juce-8-licence/
   JUCE Privacy Policy: https://juce.com/juce-privacy-policy
   JUCE Website Terms of Service: https://juce.com/juce-website-terms-of-service/

   Or:

   You may also use this code under the terms of the AGPLv3:
   https://www.gnu.org/licenses/agpl-3.0.en.html

   THE JUCE FRAMEWORK IS PROVIDED "AS IS" WITHOUT ANY WARRANTY, AND ALL
   WARRANTIES, WHETHER EXPRESSED OR IMPLIED, INCLUDING WARRANTY OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, ARE DISCLAIMED.

  ==============================================================================
*/

namespace juce
{

//==============================================================================
class WebKitSymbols final : public DeletedAtShutdown
{
public:
    //==============================================================================
    bool isWebKitAvailable() const noexcept  { return webKitIsAvailable; }

    //==============================================================================
    JUCE_GENERATE_FUNCTION_WITH_DEFAULT (webkit_settings_new, juce_webkit_settings_new,
                                         (), WebKitSettings*)

    JUCE_GENERATE_FUNCTION_WITH_DEFAULT (webkit_settings_set_hardware_acceleration_policy, juce_webkit_settings_set_hardware_acceleration_policy,
                                         (WebKitSettings*, int), void)

    JUCE_GENERATE_FUNCTION_WITH_DEFAULT (webkit_settings_set_user_agent, juce_webkit_settings_set_user_agent,
                                         (WebKitSettings*, const gchar*), void)

    JUCE_GENERATE_FUNCTION_WITH_DEFAULT (webkit_web_view_new_with_settings, juce_webkit_web_view_new_with_settings,
                                         (WebKitSettings*), GtkWidget*)

    JUCE_GENERATE_FUNCTION_WITH_DEFAULT (webkit_web_view_load_uri, juce_webkit_web_view_load_uri,
                                         (WebKitWebView*, const gchar*), void)

    JUCE_GENERATE_FUNCTION_WITH_DEFAULT (webkit_policy_decision_use, juce_webkit_policy_decision_use,
                                         (WebKitPolicyDecision*), void)

    JUCE_GENERATE_FUNCTION_WITH_DEFAULT (webkit_policy_decision_ignore, juce_webkit_policy_decision_ignore,
                                         (WebKitPolicyDecision*), void)

    JUCE_GENERATE_FUNCTION_WITH_DEFAULT (webkit_web_view_go_back, juce_webkit_web_view_go_back,
                                         (WebKitWebView*), void)

    JUCE_GENERATE_FUNCTION_WITH_DEFAULT (webkit_web_view_go_forward, juce_webkit_web_view_go_forward,
                                         (WebKitWebView*), void)

    JUCE_GENERATE_FUNCTION_WITH_DEFAULT (webkit_web_view_reload, juce_webkit_web_view_reload,
                                         (WebKitWebView*), void)

    JUCE_GENERATE_FUNCTION_WITH_DEFAULT (webkit_web_view_stop_loading, juce_webkit_web_view_stop_loading,
                                         (WebKitWebView*), void)

    JUCE_GENERATE_FUNCTION_WITH_DEFAULT (webkit_uri_request_get_uri, juce_webkit_uri_request_get_uri,
                                         (WebKitURIRequest*), const gchar*)

    JUCE_GENERATE_FUNCTION_WITH_DEFAULT (webkit_navigation_action_get_request, juce_webkit_navigation_action_get_request,
                                         (WebKitNavigationAction*), WebKitURIRequest*)

    JUCE_GENERATE_FUNCTION_WITH_DEFAULT (webkit_navigation_policy_decision_get_frame_name, juce_webkit_navigation_policy_decision_get_frame_name,
                                         (WebKitNavigationPolicyDecision*), const gchar*)

    JUCE_GENERATE_FUNCTION_WITH_DEFAULT (webkit_navigation_policy_decision_get_navigation_action, juce_webkit_navigation_policy_decision_get_navigation_action,
                                         (WebKitNavigationPolicyDecision*), WebKitNavigationAction*)

    JUCE_GENERATE_FUNCTION_WITH_DEFAULT (webkit_web_view_get_uri, juce_webkit_web_view_get_uri,
                                         (WebKitWebView*), const gchar*)

    //==============================================================================
    JUCE_GENERATE_FUNCTION_WITH_DEFAULT (gtk_init, juce_gtk_init,
                                         (int*, char***), void)

    JUCE_GENERATE_FUNCTION_WITH_DEFAULT (gtk_plug_new, juce_gtk_plug_new,
                                         (::Window), GtkWidget*)

    JUCE_GENERATE_FUNCTION_WITH_DEFAULT (gtk_scrolled_window_new, juce_gtk_scrolled_window_new,
                                         (GtkAdjustment*, GtkAdjustment*), GtkWidget*)

    JUCE_GENERATE_FUNCTION_WITH_DEFAULT (gtk_container_add, juce_gtk_container_add,
                                         (GtkContainer*, GtkWidget*), void)

    JUCE_GENERATE_FUNCTION_WITH_DEFAULT (gtk_widget_show_all, juce_gtk_widget_show_all,
                                         (GtkWidget*), void)

    JUCE_GENERATE_FUNCTION_WITH_DEFAULT (gtk_plug_get_id, juce_gtk_plug_get_id,
                                         (GtkPlug*), ::Window)

    JUCE_GENERATE_FUNCTION_WITH_DEFAULT (gtk_main, juce_gtk_main,
                                         (), void)

    JUCE_GENERATE_FUNCTION_WITH_DEFAULT (gtk_main_quit, juce_gtk_main_quit,
                                         (), void)

    JUCE_GENERATE_FUNCTION_WITH_DEFAULT (g_unix_fd_add, juce_g_unix_fd_add,
                                         (gint, GIOCondition, GUnixFDSourceFunc, gpointer), guint)

    JUCE_GENERATE_FUNCTION_WITH_DEFAULT (g_object_ref, juce_g_object_ref,
                                         (gpointer), gpointer)

    JUCE_GENERATE_FUNCTION_WITH_DEFAULT (g_object_unref, juce_g_object_unref,
                                         (gpointer), void)

    JUCE_GENERATE_FUNCTION_WITH_DEFAULT (g_signal_connect_data, juce_g_signal_connect_data,
                                         (gpointer, const gchar*, GCallback, gpointer, GClosureNotify, GConnectFlags), gulong)

    //==============================================================================
    JUCE_GENERATE_FUNCTION_WITH_DEFAULT (gdk_set_allowed_backends, juce_gdk_set_allowed_backends,
                                         (const char*), void)

    //==============================================================================
    JUCE_DECLARE_SINGLETON_SINGLETHREADED_MINIMAL (WebKitSymbols)

private:
    WebKitSymbols() = default;

    ~WebKitSymbols()
    {
        clearSingletonInstance();
    }

    template <typename FuncPtr>
    struct SymbolBinding
    {
        FuncPtr& func;
        const char* name;
    };

    template <typename FuncPtr>
    SymbolBinding<FuncPtr> makeSymbolBinding (FuncPtr& func, const char* name)
    {
        return { func, name };
    }

    template <typename FuncPtr>
    bool loadSymbols (DynamicLibrary& lib, SymbolBinding<FuncPtr> binding)
    {
        if (auto* func = lib.getFunction (binding.name))
        {
            binding.func = reinterpret_cast<FuncPtr> (func);
            return true;
        }

        return false;
    }

    template <typename FuncPtr, typename... Args>
    bool loadSymbols (DynamicLibrary& lib, SymbolBinding<FuncPtr> binding, Args... args)
    {
        return loadSymbols (lib, binding) && loadSymbols (lib, args...);
    }

    //==============================================================================
    bool loadWebkitSymbols()
    {
        return loadSymbols (webkitLib,
                            makeSymbolBinding (juce_webkit_settings_new,                                     "webkit_settings_new"),
                            makeSymbolBinding (juce_webkit_settings_set_hardware_acceleration_policy,        "webkit_settings_set_hardware_acceleration_policy"),
                            makeSymbolBinding (juce_webkit_settings_set_user_agent,                          "webkit_settings_set_user_agent"),
                            makeSymbolBinding (juce_webkit_web_view_new_with_settings,                       "webkit_web_view_new_with_settings"),
                            makeSymbolBinding (juce_webkit_policy_decision_use,                              "webkit_policy_decision_use"),
                            makeSymbolBinding (juce_webkit_policy_decision_ignore,                           "webkit_policy_decision_ignore"),
                            makeSymbolBinding (juce_webkit_web_view_go_back,                                 "webkit_web_view_go_back"),
                            makeSymbolBinding (juce_webkit_web_view_go_forward,                              "webkit_web_view_go_forward"),
                            makeSymbolBinding (juce_webkit_web_view_reload,                                  "webkit_web_view_reload"),
                            makeSymbolBinding (juce_webkit_web_view_stop_loading,                            "webkit_web_view_stop_loading"),
                            makeSymbolBinding (juce_webkit_uri_request_get_uri,                              "webkit_uri_request_get_uri"),
                            makeSymbolBinding (juce_webkit_web_view_load_uri,                                "webkit_web_view_load_uri"),
                            makeSymbolBinding (juce_webkit_navigation_action_get_request,                    "webkit_navigation_action_get_request"),
                            makeSymbolBinding (juce_webkit_navigation_policy_decision_get_frame_name,        "webkit_navigation_policy_decision_get_frame_name"),
                            makeSymbolBinding (juce_webkit_navigation_policy_decision_get_navigation_action, "webkit_navigation_policy_decision_get_navigation_action"),
                            makeSymbolBinding (juce_webkit_web_view_get_uri,                                 "webkit_web_view_get_uri"));
    }

    bool loadGtkSymbols()
    {
        return loadSymbols (gtkLib,
                            makeSymbolBinding (juce_gtk_init,                 "gtk_init"),
                            makeSymbolBinding (juce_gtk_plug_new,             "gtk_plug_new"),
                            makeSymbolBinding (juce_gtk_scrolled_window_new,  "gtk_scrolled_window_new"),
                            makeSymbolBinding (juce_gtk_container_add,        "gtk_container_add"),
                            makeSymbolBinding (juce_gtk_widget_show_all,      "gtk_widget_show_all"),
                            makeSymbolBinding (juce_gtk_plug_get_id,          "gtk_plug_get_id"),
                            makeSymbolBinding (juce_gtk_main,                 "gtk_main"),
                            makeSymbolBinding (juce_gtk_main_quit,            "gtk_main_quit"),
                            makeSymbolBinding (juce_g_unix_fd_add,            "g_unix_fd_add"),
                            makeSymbolBinding (juce_g_object_ref,             "g_object_ref"),
                            makeSymbolBinding (juce_g_object_unref,           "g_object_unref"),
                            makeSymbolBinding (juce_g_signal_connect_data,    "g_signal_connect_data"),
                            makeSymbolBinding (juce_gdk_set_allowed_backends, "gdk_set_allowed_backends"));
    }

    //==============================================================================
    DynamicLibrary gtkLib { "libgtk-3.so" }, webkitLib { "libwebkit2gtk-4.0.so" };
    const bool webKitIsAvailable = loadWebkitSymbols() && loadGtkSymbols();

    JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (WebKitSymbols)
};

JUCE_IMPLEMENT_SINGLETON (WebKitSymbols)

//==============================================================================
extern "C" int juce_gtkWebkitMain (int argc, const char* const* argv);

class CommandReceiver
{
public:
    struct Responder
    {
        virtual ~Responder() {}

        virtual void handleCommand (const String& cmd, const var& param) = 0;
        virtual void receiverHadError() = 0;
    };

    CommandReceiver (Responder* responderToUse, int inputChannelToUse)
        : responder (responderToUse), inChannel (inputChannelToUse)
    {
        setBlocking (inChannel, false);
    }

    static void setBlocking (int fd, bool shouldBlock)
    {
        auto flags = fcntl (fd, F_GETFL);
        fcntl (fd, F_SETFL, (shouldBlock ? (flags & ~O_NONBLOCK)
                                         : (flags | O_NONBLOCK)));
    }

    int getFd() const     { return inChannel; }

    void tryNextRead()
    {
        for (;;)
        {
            auto len = (receivingLength ? sizeof (size_t) : bufferLength.len);

            if (! receivingLength)
                buffer.realloc (len);

            auto* dst = (receivingLength ? bufferLength.data : buffer.getData());

            auto actual = read (inChannel, &dst[pos], static_cast<size_t> (len - pos));

            if (actual < 0)
            {
                if (errno == EINTR)
                    continue;

                break;
            }

            pos += static_cast<size_t> (actual);

            if (pos == len)
            {
                pos = 0;

                if (! receivingLength)
                    parseJSON (String (buffer.getData(), bufferLength.len));

                receivingLength = (! receivingLength);
            }
        }

        if (errno != EAGAIN && errno != EWOULDBLOCK && responder != nullptr)
            responder->receiverHadError();
    }

    static void sendCommand (int outChannel, const String& cmd, const var& params)
    {
        DynamicObject::Ptr obj = new DynamicObject;

        obj->setProperty (getCmdIdentifier(), cmd);

        if (! params.isVoid())
            obj->setProperty (getParamIdentifier(), params);

        auto json = JSON::toString (var (obj.get()));

        auto jsonLength = static_cast<size_t> (json.length());
        auto len        = sizeof (size_t) + jsonLength;

        HeapBlock<char> buffer (len);
        auto* dst = buffer.getData();

        memcpy (dst, &jsonLength, sizeof (size_t));
        dst += sizeof (size_t);

        memcpy (dst, json.toRawUTF8(), jsonLength);

        ssize_t ret;

        for (;;)
        {
            ret = write (outChannel, buffer.getData(), len);

            if (ret != -1 || errno != EINTR)
                break;
        }
    }

private:
    void parseJSON (const String& json)
    {
        auto object = JSON::fromString (json);

        if (! object.isVoid())
        {
            auto cmd    = object.getProperty (getCmdIdentifier(),   {}).toString();
            auto params = object.getProperty (getParamIdentifier(), {});

            if (responder != nullptr)
                responder->handleCommand (cmd, params);
        }
    }

    static Identifier getCmdIdentifier()    { static Identifier Id ("cmd");    return Id; }
    static Identifier getParamIdentifier()  { static Identifier Id ("params"); return Id; }

    Responder* responder = nullptr;
    int inChannel = 0;
    size_t pos = 0;
    bool receivingLength = true;
    union { char data [sizeof (size_t)]; size_t len; } bufferLength;
    HeapBlock<char> buffer;
};

#define juce_g_signal_connect(instance, detailed_signal, c_handler, data) \
    WebKitSymbols::getInstance()->juce_g_signal_connect_data (instance, detailed_signal, c_handler, data, nullptr, (GConnectFlags) 0)

//==============================================================================
class GtkChildProcess final : private CommandReceiver::Responder
{
public:
    //==============================================================================
    GtkChildProcess (int inChannel, int outChannelToUse, const String& userAgentToUse)
        : outChannel (outChannelToUse),
          receiver (this, inChannel),
          userAgent (userAgentToUse)
    {}

    int entry()
    {
        CommandReceiver::setBlocking (outChannel, true);

        // webkit2gtk crashes when using the wayland backend embedded into an x11 window
        WebKitSymbols::getInstance()->juce_gdk_set_allowed_backends ("x11");

        WebKitSymbols::getInstance()->juce_gtk_init (nullptr, nullptr);

        auto* settings = WebKitSymbols::getInstance()->juce_webkit_settings_new();
        WebKitSymbols::getInstance()->juce_webkit_settings_set_hardware_acceleration_policy (settings,
                                                                                             /* WEBKIT_HARDWARE_ACCELERATION_POLICY_NEVER */ 2);
        if (userAgent.isNotEmpty())
            WebKitSymbols::getInstance()->juce_webkit_settings_set_user_agent (settings, userAgent.toRawUTF8());

        auto* plug      = WebKitSymbols::getInstance()->juce_gtk_plug_new (0);
        auto* container = WebKitSymbols::getInstance()->juce_gtk_scrolled_window_new (nullptr, nullptr);

        auto* webviewWidget = WebKitSymbols::getInstance()->juce_webkit_web_view_new_with_settings (settings);
        webview = (WebKitWebView*) webviewWidget;

        WebKitSymbols::getInstance()->juce_gtk_container_add ((GtkContainer*) container, webviewWidget);
        WebKitSymbols::getInstance()->juce_gtk_container_add ((GtkContainer*) plug,      container);

        WebKitSymbols::getInstance()->juce_webkit_web_view_load_uri (webview, "about:blank");

        juce_g_signal_connect (webview, "decide-policy",
                               (GCallback) decidePolicyCallback, this);

        juce_g_signal_connect (webview, "load-changed",
                               (GCallback) loadChangedCallback, this);

        juce_g_signal_connect (webview, "load-failed",
                               (GCallback) loadFailedCallback, this);

        WebKitSymbols::getInstance()->juce_gtk_widget_show_all (plug);
        auto wID = (unsigned long) WebKitSymbols::getInstance()->juce_gtk_plug_get_id ((GtkPlug*) plug);

        ssize_t ret;

        for (;;)
        {
            ret = write (outChannel, &wID, sizeof (wID));

            if (ret != -1 || errno != EINTR)
                break;
        }

        WebKitSymbols::getInstance()->juce_g_unix_fd_add (receiver.getFd(), G_IO_IN, pipeReadyStatic, this);
        receiver.tryNextRead();

        WebKitSymbols::getInstance()->juce_gtk_main();

        WebKitSymbols::getInstance()->deleteInstance();
        return 0;
    }

    void goToURL (const var& params)
    {
        static Identifier urlIdentifier ("url");
        auto url = params.getProperty (urlIdentifier, var()).toString();

        WebKitSymbols::getInstance()->juce_webkit_web_view_load_uri (webview, url.toRawUTF8());
    }

    void handleDecisionResponse (const var& params)
    {
        auto* decision = (WebKitPolicyDecision*) ((int64) params.getProperty ("decision_id", var (0)));
        bool allow = params.getProperty ("allow", var (false));

        if (decision != nullptr && decisions.contains (decision))
        {
            if (allow)
                WebKitSymbols::getInstance()->juce_webkit_policy_decision_use (decision);
            else
                WebKitSymbols::getInstance()->juce_webkit_policy_decision_ignore (decision);

            decisions.removeAllInstancesOf (decision);
            WebKitSymbols::getInstance()->juce_g_object_unref (decision);
        }
    }

    //==============================================================================
    void handleCommand (const String& cmd, const var& params) override
    {
        if      (cmd == "quit")      quit();
        else if (cmd == "goToURL")   goToURL (params);
        else if (cmd == "goBack")    WebKitSymbols::getInstance()->juce_webkit_web_view_go_back      (webview);
        else if (cmd == "goForward") WebKitSymbols::getInstance()->juce_webkit_web_view_go_forward   (webview);
        else if (cmd == "refresh")   WebKitSymbols::getInstance()->juce_webkit_web_view_reload       (webview);
        else if (cmd == "stop")      WebKitSymbols::getInstance()->juce_webkit_web_view_stop_loading (webview);
        else if (cmd == "decision")  handleDecisionResponse (params);
    }

    void receiverHadError() override
    {
        exit (-1);
    }

    //==============================================================================
    bool pipeReady (gint fd, GIOCondition)
    {
        if (fd == receiver.getFd())
        {
            receiver.tryNextRead();
            return true;
        }

        return false;
    }

    void quit()
    {
        WebKitSymbols::getInstance()->juce_gtk_main_quit();
    }

    String getURIStringForAction (WebKitNavigationAction* action)
    {
        auto* request = WebKitSymbols::getInstance()->juce_webkit_navigation_action_get_request (action);
        return WebKitSymbols::getInstance()->juce_webkit_uri_request_get_uri (request);
    }

    bool onNavigation (String frameName,
                       WebKitNavigationAction* action,
                       WebKitPolicyDecision* decision)
    {
        if (decision != nullptr && frameName.isEmpty())
        {
            WebKitSymbols::getInstance()->juce_g_object_ref (decision);
            decisions.add (decision);

            DynamicObject::Ptr params = new DynamicObject;

            params->setProperty ("url", getURIStringForAction (action));
            params->setProperty ("decision_id", (int64) decision);
            CommandReceiver::sendCommand (outChannel, "pageAboutToLoad", var (params.get()));

            return true;
        }

        return false;
    }

    bool onNewWindow (String /*frameName*/,
                      WebKitNavigationAction* action,
                      WebKitPolicyDecision* decision)
    {
        if (decision != nullptr)
        {
            DynamicObject::Ptr params = new DynamicObject;

            params->setProperty ("url", getURIStringForAction (action));
            CommandReceiver::sendCommand (outChannel, "newWindowAttemptingToLoad", var (params.get()));

            // never allow new windows
            WebKitSymbols::getInstance()->juce_webkit_policy_decision_ignore (decision);

            return true;
        }

        return false;
    }

    void onLoadChanged (WebKitLoadEvent loadEvent)
    {
        if (loadEvent == WEBKIT_LOAD_FINISHED)
        {
            DynamicObject::Ptr params = new DynamicObject;

            params->setProperty ("url", String (WebKitSymbols::getInstance()->juce_webkit_web_view_get_uri (webview)));
            CommandReceiver::sendCommand (outChannel, "pageFinishedLoading", var (params.get()));
        }
    }

    bool onDecidePolicy (WebKitPolicyDecision*    decision,
                         WebKitPolicyDecisionType decisionType)
    {
        switch (decisionType)
        {
        case WEBKIT_POLICY_DECISION_TYPE_NAVIGATION_ACTION:
            {
                auto* navigationDecision = (WebKitNavigationPolicyDecision*) decision;
                auto* frameName = WebKitSymbols::getInstance()->juce_webkit_navigation_policy_decision_get_frame_name (navigationDecision);

                return onNavigation (String (frameName != nullptr ? frameName : ""),
                                     WebKitSymbols::getInstance()->juce_webkit_navigation_policy_decision_get_navigation_action (navigationDecision),
                                     decision);
            }
            break;
        case WEBKIT_POLICY_DECISION_TYPE_NEW_WINDOW_ACTION:
            {
                auto* navigationDecision = (WebKitNavigationPolicyDecision*) decision;
                auto* frameName = WebKitSymbols::getInstance()->juce_webkit_navigation_policy_decision_get_frame_name (navigationDecision);

                return onNewWindow  (String (frameName != nullptr ? frameName : ""),
                                     WebKitSymbols::getInstance()->juce_webkit_navigation_policy_decision_get_navigation_action (navigationDecision),
                                     decision);
            }
            break;
        case WEBKIT_POLICY_DECISION_TYPE_RESPONSE:
            {
                [[maybe_unused]] auto* response = (WebKitNavigationPolicyDecision*) decision;

                // for now just always allow response requests
                WebKitSymbols::getInstance()->juce_webkit_policy_decision_use (decision);
                return true;
            }
            break;
        default:
            break;
        }

        return false;
    }

    void onLoadFailed (GError* error)
    {
        DynamicObject::Ptr params = new DynamicObject;

        params->setProperty ("error", String (error != nullptr ? error->message : "unknown error"));
        CommandReceiver::sendCommand (outChannel, "pageLoadHadNetworkError", var (params.get()));
    }

private:
    static gboolean pipeReadyStatic (gint fd, GIOCondition condition, gpointer user)
    {
        return (reinterpret_cast<GtkChildProcess*> (user)->pipeReady (fd, condition) ? TRUE : FALSE);
    }

    static gboolean decidePolicyCallback (WebKitWebView*,
                                          WebKitPolicyDecision*    decision,
                                          WebKitPolicyDecisionType decisionType,
                                          gpointer user)
    {
        auto& owner = *reinterpret_cast<GtkChildProcess*> (user);
        return (owner.onDecidePolicy (decision, decisionType) ? TRUE : FALSE);
    }

    static void loadChangedCallback (WebKitWebView*,
                                     WebKitLoadEvent loadEvent,
                                     gpointer        user)
    {
        auto& owner = *reinterpret_cast<GtkChildProcess*> (user);
        owner.onLoadChanged (loadEvent);
    }

    static void loadFailedCallback (WebKitWebView*,
                                    WebKitLoadEvent /*loadEvent*/,
                                    gchar*          /*failing_uri*/,
                                    GError*         error,
                                    gpointer        user)
    {
        auto& owner = *reinterpret_cast<GtkChildProcess*> (user);
        owner.onLoadFailed (error);
    }

    int outChannel = 0;
    CommandReceiver receiver;
    String userAgent;
    WebKitWebView* webview = nullptr;
    Array<WebKitPolicyDecision*> decisions;
};

//==============================================================================
class WebBrowserComponent::Pimpl  : private Thread,
                                    private CommandReceiver::Responder
{
public:
    Pimpl (WebBrowserComponent& parent, const String& userAgentToUse)
        : Thread ("Webview"), owner (parent), userAgent (userAgentToUse)
    {
        webKitIsAvailable = WebKitSymbols::getInstance()->isWebKitAvailable();
    }

    ~Pimpl() override
    {
        quit();
    }

    //==============================================================================
    void init()
    {
        if (! webKitIsAvailable)
            return;

        launchChild();

        [[maybe_unused]] auto ret = pipe (threadControl);

        jassert (ret == 0);

        CommandReceiver::setBlocking (inChannel,        true);
        CommandReceiver::setBlocking (outChannel,       true);
        CommandReceiver::setBlocking (threadControl[0], false);
        CommandReceiver::setBlocking (threadControl[1], true);

        unsigned long windowHandle;
        auto actual = read (inChannel, &windowHandle, sizeof (windowHandle));

        if (actual != (ssize_t) sizeof (windowHandle))
        {
            killChild();
            return;
        }

        receiver.reset (new CommandReceiver (this, inChannel));

        pfds.push_back ({ threadControl[0],  POLLIN, 0 });
        pfds.push_back ({ receiver->getFd(), POLLIN, 0 });

        startThread();

        xembed.reset (new XEmbedComponent (windowHandle));
        owner.addAndMakeVisible (xembed.get());
    }

    void quit()
    {
        if (! webKitIsAvailable)
            return;

        if (isThreadRunning())
        {
            signalThreadShouldExit();

            char ignore = 0;
            ssize_t ret;

            for (;;)
            {
                ret = write (threadControl[1], &ignore, 1);

                if (ret != -1 || errno != EINTR)
                    break;
            }

            waitForThreadToExit (-1);
            receiver = nullptr;
        }

        if (childProcess != 0)
        {
            CommandReceiver::sendCommand (outChannel, "quit", {});
            killChild();
        }
    }

    //==============================================================================
    void goToURL (const String& url, const StringArray* headers, const MemoryBlock* postData)
    {
        if (! webKitIsAvailable)
            return;

        DynamicObject::Ptr params = new DynamicObject;

        params->setProperty ("url", url);

        if (headers != nullptr)
            params->setProperty ("headers", var (*headers));

        if (postData != nullptr)
            params->setProperty ("postData", var (*postData));

        CommandReceiver::sendCommand (outChannel, "goToURL", var (params.get()));
    }

    void goBack()      { if (webKitIsAvailable) CommandReceiver::sendCommand (outChannel, "goBack",    {}); }
    void goForward()   { if (webKitIsAvailable) CommandReceiver::sendCommand (outChannel, "goForward", {}); }
    void refresh()     { if (webKitIsAvailable) CommandReceiver::sendCommand (outChannel, "refresh",   {}); }
    void stop()        { if (webKitIsAvailable) CommandReceiver::sendCommand (outChannel, "stop",      {}); }

    void resized()
    {
        if (xembed != nullptr)
            xembed->setBounds (owner.getLocalBounds());
    }

private:
    //==============================================================================
    void killChild()
    {
        if (childProcess != 0)
        {
            xembed = nullptr;

            int status = 0, result = 0;

            result = waitpid (childProcess, &status, WNOHANG);
            for (int i = 0; i < 15 && (! WIFEXITED (status) || result != childProcess); ++i)
            {
                Thread::sleep (100);
                result = waitpid (childProcess, &status, WNOHANG);
            }

            // clean-up any zombies
            status = 0;
            if (! WIFEXITED (status) || result != childProcess)
            {
                for (;;)
                {
                    kill (childProcess, SIGTERM);
                    waitpid (childProcess, &status, 0);

                    if (WIFEXITED (status))
                        break;
                }
            }

            childProcess = 0;
        }
    }

    void launchChild()
    {
        int inPipe[2], outPipe[2];

        [[maybe_unused]] auto ret = pipe (inPipe);
        jassert (ret == 0);

        ret = pipe (outPipe);
        jassert (ret == 0);

        std::vector<String> arguments;

       #if JUCE_USE_EXTERNAL_TEMPORARY_SUBPROCESS
        if (! JUCEApplicationBase::isStandaloneApp())
        {
            subprocessFile.emplace ("_juce_linux_subprocess");

            const auto externalSubprocessAvailable = subprocessFile->getFile().replaceWithData (LinuxSubprocessHelperBinaryData::juce_linux_subprocess_helper,
                                                                                                LinuxSubprocessHelperBinaryData::juce_linux_subprocess_helperSize)
                                                     && subprocessFile->getFile().setExecutePermission (true);

            ignoreUnused (externalSubprocessAvailable);
            jassert (externalSubprocessAvailable);

            /*  The external subprocess will load the .so specified as its first argument and execute
                the function specified by the second. The remaining arguments will be passed on to
                the function.
            */
            arguments.emplace_back (subprocessFile->getFile().getFullPathName());
            arguments.emplace_back (File::getSpecialLocation (File::currentExecutableFile).getFullPathName());
            arguments.emplace_back ("juce_gtkWebkitMain");
        }
       #endif

        arguments.emplace_back (File::getSpecialLocation (File::currentExecutableFile).getFullPathName());
        arguments.emplace_back ("--juce-gtkwebkitfork-child");
        arguments.emplace_back (outPipe[0]);
        arguments.emplace_back (inPipe [1]);

        if (userAgent.isNotEmpty())
            arguments.emplace_back (userAgent);

        std::vector<const char*> argv (arguments.size() + 1, nullptr);
        std::transform (arguments.begin(), arguments.end(), argv.begin(), [] (const auto& arg)
        {
            return arg.toRawUTF8();
        });

        auto pid = fork();

        if (pid == 0)
        {
            close (inPipe[0]);
            close (outPipe[1]);

            if (JUCEApplicationBase::isStandaloneApp())
            {
                execv (arguments[0].toRawUTF8(), (char**) argv.data());
            }
            else
            {
               #if JUCE_USE_EXTERNAL_TEMPORARY_SUBPROCESS
                execv (arguments[0].toRawUTF8(), (char**) argv.data());
               #else
                // After a fork in a multithreaded program, the child can only safely call
                // async-signal-safe functions until it calls execv, but if we reached this point
                // then execv won't be called at all! The following call is unsafe, and is very
                // likely to lead to unexpected behaviour.
                jassertfalse;
                juce_gtkWebkitMain ((int) arguments.size(), argv.data());
               #endif
            }

            exit (0);
        }

        close (inPipe[1]);
        close (outPipe[0]);

        inChannel  = inPipe[0];
        outChannel = outPipe[1];

        childProcess = pid;
    }

    void run() override
    {
        while (! threadShouldExit())
        {
            if (shouldExit())
                return;

            receiver->tryNextRead();

            int result = 0;

            while (result == 0 || (result < 0 && errno == EINTR))
                result = poll (&pfds.front(), static_cast<nfds_t> (pfds.size()), 10);

            if (result < 0)
                break;
        }
    }

    bool shouldExit()
    {
        char ignore;
        auto result = read (threadControl[0], &ignore, 1);

        return (result != -1 || (errno != EAGAIN && errno != EWOULDBLOCK));
    }

    //==============================================================================
    void handleCommandOnMessageThread (const String& cmd, const var& params)
    {
        auto url = params.getProperty ("url", var()).toString();

        if      (cmd == "pageAboutToLoad")           handlePageAboutToLoad (url, params);
        else if (cmd == "pageFinishedLoading")       owner.pageFinishedLoading (url);
        else if (cmd == "windowCloseRequest")        owner.windowCloseRequest();
        else if (cmd == "newWindowAttemptingToLoad") owner.newWindowAttemptingToLoad (url);
        else if (cmd == "pageLoadHadNetworkError")   handlePageLoadHadNetworkError (params);
    }

    void handlePageAboutToLoad (const String& url, const var& inputParams)
    {
        int64 decision_id = inputParams.getProperty ("decision_id", var (0));

        if (decision_id != 0)
        {
            DynamicObject::Ptr params = new DynamicObject;

            params->setProperty ("decision_id", decision_id);
            params->setProperty ("allow", owner.pageAboutToLoad (url));

            CommandReceiver::sendCommand (outChannel, "decision", var (params.get()));
        }
    }

    void handlePageLoadHadNetworkError (const var& params)
    {
        String error = params.getProperty ("error", "Unknown error");

        if (owner.pageLoadHadNetworkError (error))
            goToURL (String ("data:text/plain,") + error, nullptr, nullptr);
    }

    void handleCommand (const String& cmd, const var& params) override
    {
        MessageManager::callAsync ([liveness = std::weak_ptr (livenessProbe), this, cmd, params]
                                   {
                                       if (liveness.lock() != nullptr)
                                           handleCommandOnMessageThread (cmd, params);
                                   });
    }

    void receiverHadError() override {}

    //==============================================================================
    bool webKitIsAvailable = false;

    WebBrowserComponent& owner;
    String userAgent;
    std::unique_ptr<CommandReceiver> receiver;
    int childProcess = 0, inChannel = 0, outChannel = 0;
    int threadControl[2];
    std::unique_ptr<XEmbedComponent> xembed;
    std::shared_ptr<int> livenessProbe = std::make_shared<int> (0);
    std::vector<pollfd> pfds;
    std::optional<TemporaryFile> subprocessFile;
};

//==============================================================================
WebBrowserComponent::WebBrowserComponent (const Options& options)
    : browser (new Pimpl (*this, options.getUserAgent()))
{
    ignoreUnused (blankPageShown);
    ignoreUnused (unloadPageWhenHidden);

    setOpaque (true);

    browser->init();
}

WebBrowserComponent::~WebBrowserComponent()
{
}

//==============================================================================
void WebBrowserComponent::goToURL (const String& url,
                                   const StringArray* headers,
                                   const MemoryBlock* postData)
{
    lastURL = url;

    if (headers != nullptr)
        lastHeaders = *headers;
    else
        lastHeaders.clear();

    if (postData != nullptr)
        lastPostData = *postData;
    else
        lastPostData.reset();

    browser->goToURL (url, headers, postData);
}

void WebBrowserComponent::stop()
{
    browser->stop();
}

void WebBrowserComponent::goBack()
{
    lastURL.clear();

    browser->goBack();
}

void WebBrowserComponent::goForward()
{
    lastURL.clear();
    browser->goForward();
}

void WebBrowserComponent::refresh()
{
    browser->refresh();
}

//==============================================================================
void WebBrowserComponent::paint (Graphics& g)
{
    g.fillAll (Colours::white);
}

void WebBrowserComponent::checkWindowAssociation()
{
}

void WebBrowserComponent::reloadLastURL()
{
    if (lastURL.isNotEmpty())
    {
        goToURL (lastURL, &lastHeaders, &lastPostData);
        lastURL.clear();
    }
}

void WebBrowserComponent::parentHierarchyChanged()
{
    checkWindowAssociation();
}

void WebBrowserComponent::resized()
{
    if (browser != nullptr)
        browser->resized();
}

void WebBrowserComponent::visibilityChanged()
{
    checkWindowAssociation();
}

void WebBrowserComponent::focusGainedWithDirection (FocusChangeType, FocusChangeDirection)
{
}

void WebBrowserComponent::clearCookies()
{
    // Currently not implemented on linux as WebBrowserComponent currently does not
    // store cookies on linux
    jassertfalse;
}

bool WebBrowserComponent::areOptionsSupported (const Options& options)
{
    return (options.getBackend() == Options::Backend::defaultBackend);
}

extern "C" __attribute__ ((visibility ("default"))) int juce_gtkWebkitMain (int argc, const char* const* argv)
{
    if (argc < 4)
        return -1;

    GtkChildProcess child (String (argv[2]).getIntValue(),
                           String (argv[3]).getIntValue(),
                           argc >= 5 ? String (argv[4]) : String());

    return child.entry();
}

} // namespace juce