// ----------------------------------------------------------------------------
// -                        Open3D: www.open3d.org                            -
// ----------------------------------------------------------------------------
// Copyright (c) 2018-2023 www.open3d.org
// SPDX-License-Identifier: MIT
// ----------------------------------------------------------------------------
/// \file WebRTCWindowSystem.h
///
/// The main header file for WebRTC visualizer.

#pragma once

#include <functional>
#include <memory>
#include <string>
#include <vector>

#include "open3d/visualization/gui/BitmapWindowSystem.h"

namespace open3d {
namespace visualization {
namespace webrtc_server {

/// \brief WebRTCWindowSystem is a BitmapWindowSystem with a WebRTC server that
/// sends video frames to remote clients for visualization.
///
/// WebRTCWindowSystem owns a PeerConnectionManager, which manages all things
/// related to the WebRTC connections, e.g. get media lists, get and add ICE
/// candidates, connect to a media and hangup.
///
/// When the client visit a Open3D visualizer's website for visualization
/// (a.k.a. standalone mode), an HTTP handshake server will be used to serve the
/// website and perform handshake to establish the WebRTC connection. In Jupyter
/// mode, the HTTP handshake server is disabled and the handshake is done via
/// Jupyter's JavaScript<->Python communication channel.
///
/// WebRTCWindowSystem shall be used as a global singleton. Both the
/// PeerConnectionManager and the HTTP handshake server runs on different
/// threads.
class WebRTCWindowSystem : public gui::BitmapWindowSystem {
public:
    static std::shared_ptr<WebRTCWindowSystem> GetInstance();
    virtual ~WebRTCWindowSystem();
    OSWindow CreateOSWindow(gui::Window* o3d_window,
                            int width,
                            int height,
                            const char* title,
                            int flags) override;
    void DestroyWindow(OSWindow w) override;

    /// List available windows.
    std::vector<std::string> GetWindowUIDs() const;
    std::string GetWindowUID(OSWindow w) const;
    OSWindow GetOSWindowByUID(const std::string& uid) const;

    /// Start WebRTC server in a background thread.
    void StartWebRTCServer();

    /// Client -> server message.
    /// \return Message reply that should be sent back to the client.
    std::string OnDataChannelMessage(const std::string& message);

    /// When the data channel receives a valid JSON string, the \p class_name
    /// property of the JSON object will be examined and the corresponding
    /// callback function will be called. The callback should return a string
    /// reply, which will be sent back to the client.
    ///
    /// \param class_name The value of the \p class_name property of the JSON
    /// object.
    /// \param callback The callback function that will be called when a JSON
    /// object with the matching \p class_name is received via the data channel.
    ///
    /// \code{.cpp}
    /// // Register callback in C++
    /// auto ws =
    /// visualization::webrtc_server::WebRTCWindowSystem::GetInstance();
    /// ws->EnableWebRTC();
    /// ws->RegisterDataChannelMessageCallback("webapp/input", "input",
    ///     [](const std::string &data) {
    ///         std::string reply = fmt::format("Received dataChannel message"
    ///         " for class_name 'webapp/input' with data: {}", data);
    ///         utility::LogInfo(reply);
    ///         return reply;
    ///     });
    /// \endcode
    /// \n
    /// \code{.js}
    /// /* Send message in JavaScript to trigger callback. this is
    /// WebRTCStreamer object */
    /// this.dataChannel.send('{"class_name":"webapp/input",
    ///     "data":"Test event"}');
    /// \endcode
    void RegisterDataChannelMessageCallback(
            const std::string& class_name,
            const std::function<std::string(const std::string&)> callback);

    /// Server -> client frame.
    void OnFrame(const std::string& window_uid,
                 const std::shared_ptr<core::Tensor>& im);

    /// Send initial frames. This flushes the WebRTC video stream. After the
    /// initial frames, new frames will only be sent at triggered events.
    void SendInitFrames(const std::string& window_uid);

    /// \brief Call PeerConnectionManager's web request API.
    ///
    /// This function is called in JavaScript via Python binding to mimic the
    /// behavior of sending HTTP request via fetch() in JavaScript.
    ///
    /// With fetch:
    /// data = {method: "POST", body: JSON.stringify(candidate)};
    /// fetch("/api/addIceCandidate?peerid=" + peerid, data);
    ///
    /// Now with CallHttpAPI:
    /// open3d.visualization.webrtc_server("/api/addIceCandidate",
    ///                                    "?peerid=" + peerid,
    ///                                    data["body"]);
    ///
    /// \param entry_point URL part before '?'.
    /// \param query_string URL part after '?', including '?'. If '?' is not the
    /// first character or if the string is empty, the query_string is ignored.
    /// \param data JSON-encoded string.
    std::string CallHttpAPI(const std::string& entry_point,
                            const std::string& query_string = "",
                            const std::string& data = "") const;

    /// Sets WebRTCWindowSystem as the default window system in Application.
    /// This enables a global WebRTC server and each gui::Window will be
    /// rendered to a WebRTC video stream.
    void EnableWebRTC();

    /// HTTP handshake server is enabled by default. In Jupyter environment,
    /// call DisableHttpHandshake() before StartWebRTCServer().
    void DisableHttpHandshake();

    /// Close all WebRTC connections that correspond to a Window.
    void CloseWindowConnections(const std::string& window_uid);

private:
    WebRTCWindowSystem();
    struct Impl;
    std::unique_ptr<Impl> impl_;
};

}  // namespace webrtc_server
}  // namespace visualization
}  // namespace open3d