module handy_http_websockets.handler;

import core.sync.rwmutex : ReadWriteMutex;
import std.uuid;

import handy_http_primitives;
import slf4d;
import streams;

import handy_http_websockets.components;
import handy_http_websockets.connection;
import handy_http_websockets.frame;

/**
 * An HTTP request handler implementation that's used as the entrypoint for
 * clients that want to establish a websocket connection. It will verify the
 * websocket request, and if successful, send back a SWITCHING_PROTOCOLS
 * response, and register a new websocket connection.
 */
class WebSocketRequestHandler : HttpRequestHandler {
    private WebSocketMessageHandler messageHandler;

    private shared WebSocketConnection[UUID] connections;
    private shared ReadWriteMutex connectionsMutex;

    /** 
     * Constructs a request handler that will use the given message handler to
     * deal with events from any websocket connections that are established.
     * Params:
     *   messageHandler = The message handler to use.
     */
    this(WebSocketMessageHandler messageHandler) {
        this.messageHandler = messageHandler;
        this.connectionsMutex = new shared ReadWriteMutex();
    }

    /** 
     * Handles an incoming HTTP request and tries to establish a websocket
     * connection by first verifying the request, then sending a switching-
     * protocols response, and finally registering the new connection with the
     * websocket manager.
     * Params:
     *   request = The request to read from.
     *   response = The response to write to.
     */
    void handle(ref ServerHttpRequest request, ref ServerHttpResponse response) {
        auto verification = verifyWebSocketRequest(request);
        if (verification == RequestVerificationResponse.INVALID_HTTP_METHOD) {
            warnF!"Received a %s request to a websocket request handler. Only GET requests are expected."(
                request.method
            );
            sendErrorResponse(response, HttpStatus.METHOD_NOT_ALLOWED, "Only GET requests are allowed.");
            return;
        }
        if (verification == RequestVerificationResponse.MISSING_KEY) {
            warn("Received a request to a websocket request handler, but is " ~
                "missing the required \"Sec-WebSocket-Key\" header.");
            sendErrorResponse(response, HttpStatus.BAD_REQUEST, "Missing Sec-WebSocket-Key header.");
            return;
        }
        sendSwitchingProtocolsResponse(request, response);
        addConnection(new WebSocketConnection(
            messageHandler,
            this,
            request.inputStream,
            response.outputStream
        ), request);
    }

    /**
     * Gets the number of active connections.
     * Returns: The number of active connections.
     */
    size_t connectionCount() {
        synchronized(connectionsMutex.reader) {
            return connections.length;
        }
    }

    /** 
     * Adds a connection to the manager and starts listening for messages.
     * Params:
     *   conn = The connection to add.
     *   request = The HTTP request that initiated the connection.
     */
    void addConnection(WebSocketConnection conn, in ServerHttpRequest request) {
        import core.thread;
        synchronized(connectionsMutex.writer) {
            connections[conn.id] = cast(shared(WebSocketConnection)) conn;
        }
        new Thread(() => connectionHandler(conn)).start();
        conn.getMessageHandler().onConnectionEstablished(conn, request);
        debugF!"Added websocket connection: %s"(conn.id.toString());
    }

    /**
     * Removes a websocket connection from the manager and closes it. This is
     * called automatically if the client sends a CLOSE frame, but you can also
     * call it yourself.
     * Params:
     *   conn = The connection to remove.
     */
    void removeConnection(WebSocketConnection conn) {
        synchronized(connectionsMutex.writer) {
            connections.remove(conn.id);
        }
        conn.close();
        debugF!"Removed websocket connection: %s"(conn.id.toString());
    }

    /**
     * Broadcasts a message to all connected clients.
     * Params:
     *   text = The text to send to all clients.
     */
    void broadcast(string text) {
        synchronized(connectionsMutex.reader) {
            debugF!"Broadcasting %d-length text message to %d clients."(text.length, connections.length);
            foreach (id, conn; connections) {
                try {
                    (cast(WebSocketConnection) conn).sendTextMessage(text);
                } catch (WebSocketException e) {
                    warnF!"Failed to broadcast to client %s: %s"(id.toString(), e.msg);
                }
            }
        }
    }

    /**
     * Broadcasts a binary message to all connected clients.
     * Params:
     *   data = The binary data to send to all clients.
     */
    void broadcast(ubyte[] data) {
        synchronized(connectionsMutex.reader) {
            debugF!"Broadcasting %d bytes of binary data to %d clients."(data.length, connections.length);
            foreach (id, conn; connections) {
                try {
                    (cast(WebSocketConnection) conn).sendBinaryMessage(data);
                } catch (WebSocketException e) {
                    warnF!"Failed to broadcast to client %s: %s"(id.toString(), e.msg);
                }
            }
        }
    }

    /**
     * Internal routine that runs in a fiber, and handles an individual websocket
     * connection by listening for messages.
     * Params:
     *   conn = The connection to handle.
     */
    private void connectionHandler(WebSocketConnection conn) {
        debugF!"Started routine to monitor websocket connection %s."(conn.id.toString());
        bool running = true;
        while (running) {
            try {
                WebSocketFrame f = receiveWebSocketFrame(conn.inputStream);
                switch (f.opcode) {
                    case WebSocketFrameOpcode.CONNECTION_CLOSE:
                        removeConnection(conn);
                        running = false;
                        break;
                    case WebSocketFrameOpcode.PING:
                        sendWebSocketPongFrame(conn.outputStream, f.payload);
                        break;
                    case WebSocketFrameOpcode.TEXT_FRAME:
                    case WebSocketFrameOpcode.BINARY_FRAME:
                        handleClientDataFrame(conn, f);
                        break;
                    case WebSocketFrameOpcode.CONTINUATION:
                        warn("Got websocket CONTINUATION frame when not expecting one. Ignoring.");
                        break;
                    default:
                        break;
                }
            } catch (Exception e) {
                error(e);
                running = false;
            }
        }
        debugF!"Routine to monitor websocket connection %s has ended."(conn.id.toString());
    }

    /** 
     * Handles a websocket data frame (text or binary).
     * Params:
     *   conn = The connection from which the frame was received.
     *   f = The frame that was received.
     */
    private void handleClientDataFrame(WebSocketConnection conn, WebSocketFrame f) {
        bool isText = f.opcode == WebSocketFrameOpcode.TEXT_FRAME;
        ubyte[] payload = f.payload.dup;
        while (!f.finalFragment) {
            f = receiveWebSocketFrame(conn.inputStream);
            if (f.opcode != WebSocketFrameOpcode.CONTINUATION) {
                removeConnection(conn);
                warnF!"Received invalid websocket frame opcode %s when expecting a CONTINUATION frame."(
                    f.opcode
                );
                return;
            }
            payload ~= f.payload;
        }
        if (isText) {
            conn.getMessageHandler().onTextMessage(WebSocketTextMessage(conn, cast(string) payload));
        } else {
            conn.getMessageHandler().onBinaryMessage(WebSocketBinaryMessage(conn, payload));
        }
    }
}

private enum RequestVerificationResponse {
    INVALID_HTTP_METHOD,
    MISSING_KEY,
    VALID
}

private RequestVerificationResponse verifyWebSocketRequest(in ServerHttpRequest r) {
    if (r.method != HttpMethod.GET) {
        return RequestVerificationResponse.INVALID_HTTP_METHOD;
    }
    if ("Sec-WebSocket-Key" !in r.headers || r.headers["Sec-WebSocket-Key"].length == 0) {
        return RequestVerificationResponse.MISSING_KEY;
    }
    return RequestVerificationResponse.VALID;
}

private void sendErrorResponse(ref ServerHttpResponse response, HttpStatus status, string msg) {
    response.status = status;
    response.writeBodyString(msg);
}

private void sendSwitchingProtocolsResponse(in ServerHttpRequest request, ref ServerHttpResponse response) {
    string key = request.headers["Sec-WebSocket-Key"][0];
    response.status = HttpStatus.SWITCHING_PROTOCOLS;
    response.headers.add("Upgrade", "websocket");
    response.headers.add("Connection", "Upgrade");
    response.headers.add("Sec-WebSocket-Accept", generateWebSocketAcceptHeader(key));
    response.outputStream.writeToStream([]); // Trigger this to flush the response.
}

private string generateWebSocketAcceptHeader(string key) {
    import std.digest.sha : sha1Of;
    import std.base64;
    ubyte[20] hash = sha1Of(key ~ "258EAFA5-E914-47DA-95CA-C5AB0DC85B11");
    return Base64.encode(hash);
}

unittest {
    string result = generateWebSocketAcceptHeader("dGhlIHNhbXBsZSBub25jZQ==");
    assert(result == "s3pPLMBiTxaQ9kYGzzhZRbK+xOo=");
}