const websockets = require("ws");
const { v4 } = require("uuid");
const mongoose = require("mongoose");

const { policies, gatewayPingInterval, gatewayPingCheckInterval, clientFacingPingInterval } = require("../../../config");
const { experiments } = require("../../../config");
const User = require("../../../models/User");
const Channel = require("../../../models/Channel");
const Message = require("../../../models/Message");
const { parseMessage, packet } = require("./messageparser");
const { checkToken } = require("../../../common/auth/authfunctions");

const wsCloseCodes = {
    PAYLOAD_ERROR: [4001, "Error while handling payload"],
    NOT_AUTHENTICATED: [4002, "Not authenticated"],
    SERVER_DENIED_CONNECTION: [4003, "Server denied connection"],
    AUTHENTICATION_ERROR: [4004, "Authentication error"],
    TOO_MANY_SESSIONS: [4005, "Too many sessions"],
    NOT_AUTHORIZED: [4006, "Not authorized"],
    FLOODING: [4007, "Flooding"],
    NO_PING: [4008, "No ping"],
    UNSUPPORTED_ATTRIBUTE: [4009, "Unsupported attribute."],
};

const attributes = {
    PRESENCE_UPDATES: "PRESENCE_UPDATES",
};

const supportedAttributes = [attributes.PRESENCE_UPDATES];

class GatewaySession {
    constructor() {
        this.authenticated = false;
        this.user = null;
        this.token = null;
        this.sessionId = v4();
        this.attributes = [];

        // Specific to websocket sessions
        this.isWebsocketConnection = false;
        this.ws = null;
        this.lastPing = new Date();
        this.channels = [];
    }

    hasAttribute(roleName) {
        if (roleName.length < 1) return true; // TODO: HACK
        return this.attributes.includes(roleName);
    }

    setWebsocketClient(ws) {
        this.ws = ws;
        this.isWebsocketConnection = true;
    }

    async authenticateWithToken(token) {
        let user = null;
        try {
            user = await checkToken(token);
            if (!user) return false;
            this.token = token;
            this.user = user;
            this.authenticated = true;
            return true;
        } catch(e) {
            return false;
        }
    }

    send(name, data) {
        this.ws.send(packet(name, data));
    }

    isReady() {
        return this.authenticated && this.ws;
    }
}

class GatewayHandler {
    constructor() {
        this.sessionCounters = {};
    }

    // server event handlers
    handleServerConfigRequest() {
        return {
            path: "/gateway"
        };
    }

    handleServerReady(wss) {
        this.wss = wss;

        this.pingCheckIntervalFunction = setInterval(() => {
            this.wss.clients.forEach((client) => {
                if ((new Date() - client.session.lastPing) >= gatewayPingInterval) {
                    client.close(wsCloseCodes.NO_PING[0], wsCloseCodes.NO_PING[1]);
                }
            });
        }, gatewayPingCheckInterval);
    }

    handleServerClose() {
        clearInterval(this.pingCheckIntervalFunction);
    }

    handleConnection(ws) {
        if (!policies.allowGatewayConnection) {
            return ws.close(wsCloseCodes.SERVER_DENIED_CONNECTION[0], wsCloseCodes.SERVER_DENIED_CONNECTION[1]);
        }

        const session = new GatewaySession();
        session.setWebsocketClient(ws);
        session.send("HELLO", { pingInterval: clientFacingPingInterval, supportedAttributes });
        return session;
    }

    handleConnectionClose(ws) {
        if (ws.session && ws.session.user && ws.session.channels) {
            if (this.sessionCounters[ws.session.user._id] <= 1) {
                this.eachInChannel({channelId: ws.session.channels[0], role: attributes.PRESENCE_UPDATES}, (client) => {
                    if (client.session && client.session.isReady()) {
                        client.session.send("EVENT_CHANNEL_MEMBERS", {
                            [ws.session.user._id]: {
                                _id: ws.session.user._id,
                                username: ws.session.user.username,
                                status: 0,
                                status_text: ""
                            }
                        });
                    }
                });
            }
            this.sessionCounters[ws.session.user._id]--;
            if (this.sessionCounters[ws.session.user._id] <= 0) {
                this.sessionCounters[ws.session.user._id] = null;
                delete this.sessionCounters[ws.session.user._id];
            }
        }
    }

    handleMessage(senderSession, packet) {
        return this[`handle_${packet.opcodeType}`](packet, senderSession);
    }

    // utility functions
    addSessionCounter(id) {
        if (!this.sessionCounters[id]) this.sessionCounters[id] = 0;
        this.sessionCounters[id]++;
        if (this.sessionCounters[id] > policies.perUserMaxGatewayConnections) return false;
        return true;
    }

    getClients() {
        return this.wss.clients;
    }

    eachInChannel({channelId, role=""}, callback) {
        const clients = this.getClients();
        clients.forEach((client) => {
            if (client.session && client.session.isReady() && client.session.hasAttribute(role) && client.session.channels.includes(channelId))
                callback(client);
        });
    }

    // Gateway message handlers
    async handle_YOO({ data }, session) {
        if (session.authenticated) return {error: wsCloseCodes.PAYLOAD_ERROR};
        try {
            if (!(await session.authenticateWithToken(data.token))) return {error: wsCloseCodes.AUTHENTICATION_ERROR};
        } catch(e) {
            return {error: wsCloseCodes.AUTHENTICATION_ERROR};
        }
        if (!this.addSessionCounter(session.user._id)) return {error: wsCloseCodes.TOO_MANY_SESSIONS};

        const channels = (await Channel.find().lean().sort({ _id: -1 }).limit(50).select("-posts -__v").populate("creator", User.getPulicFields(true))) || [];
        session.channels = channels.map(x => x._id.toString());

        if (data.attributes) {
            if (!Array.isArray(data.attributes) || data.attributes.length > 8) return {error: wsCloseCodes.PAYLOAD_ERROR};
            for (let i = 0; i < data.attributes.length; i++) {
                if (!supportedAttributes.includes(data.attributes[i]))
                    return {error: wsCloseCodes.UNSUPPORTED_ATTRIBUTE};
            }
            session.attributes = data.attributes;
        }

        session.send("YOO_ACK", { session_id: session.sessionId, channels, user: { username: session.user.username, _id: session.user._id }, __global_experiments: experiments });

        const channel = session.channels[0];
        if (channel) {
            const presence = {};

            this.eachInChannel({channelId: channel}, ({ session: remoteSession }) => {
                presence[remoteSession.user._id] = {
                    _id: remoteSession.user._id,
                    username: remoteSession.user.username,
                    status: 1,
                    status_text: "Online"
                };
                if (remoteSession.sessionId !== session.sessionId && remoteSession.hasAttribute(attributes.PRESENCE_UPDATES)) {
                    remoteSession.send("EVENT_CHANNEL_MEMBERS", {
                        [session.user._id]: {
                            _id: session.user._id,
                            username: session.user.username,
                            status: 1,
                            status_text: "Online"
                        }
                    });
                }
            });

            (session.hasAttribute(attributes.PRESENCE_UPDATES)) && session.send("EVENT_CHANNEL_MEMBERS", presence);
        }
    }

    async handle_ACTION_PING({ data }, session) {
        if (!session.isReady()) return {error: wsCloseCodes.NOT_AUTHENTICATED};
        if (data !== "1") throw new Error("msg: ACTION_PING payload data should be a `1`");

        const user = await checkToken(session.token);
        if (!user) return {error: wsCloseCodes.AUTHENTICATION_ERROR};
        session.lastPing = new Date();
    }

    async handle_ACTION_CREATE_MESSAGE({ data }, session) {
        if (!session.isReady()) return {error: wsCloseCodes.NOT_AUTHENTICATED};
        if (typeof data.content !== "string" || typeof data.channel !== "object" || typeof data.channel._id !== "string") throw new Error("msg: invalid fields in json payload");
        
        const messageContent = data.content.trim();
        if (messageContent.length > 2000 || messageContent.length < 1) return;
        if (data.channel._id.length !== 24) throw new Error("msg: payload has invalid id"); // MONGODB ONLY!!

        // Check if the user is in that channel before broadcasting the message
        if (!session.channels.includes(data.channel._id)) return {error: wsCloseCodes.NOT_AUTHORIZED};

        this.eachInChannel({channelId: data.channel._id}, async ({ session: remoteSession }) => {
            let id;
            if (policies.allowSavingMessages) {
                const message = await Message.create({
                    author: session.user._id,
                    channel: data.channel._id,
                    content: messageContent,
                    createdAt: new Date().getTime()
                });
                id = message._id;
            } else {
                id = new mongoose.Types.ObjectId();
            }

            remoteSession.send("EVENT_CREATE_MESSAGE", {
                content: messageContent,
                channel: {
                    _id: data.channel._id
                },
                author: {
                    _id: session.user._id,
                    username: session.user.username
                },
                _id: id
            });
        });
    }
}

class GatewayServer {
    constructor(httpServer) {
        this.httpServer = httpServer;
        this.wss = null;
        this.handler = null;
    }

    bindHandler(handler) {
        if (this.wss) throw new Error("GatewayServer: cannot bindHandler() to a server which already has a bound handler.");
        
        const newHandler = new handler();
        this.handler = newHandler;
        this.wss = new websockets.Server({ server: this.httpServer, ...(this.handler.handleServerConfigRequest()) });
        this.handler.handleServerReady(this.wss);
        this.wss.on("close", () => this.handler.handleServerClose());
        this.wss.on("connection", (ws) => {
            const session = this.handler.handleConnection(ws);
            if (!session)
                return ws.close();
            if (session.__error)
                return ws.close(session.__error[0], session.__error[1]);
            ws.session = session;
            ws.on("message", async (data, isBinary) => {
                try {
                    if (isBinary || !ws.session) return ws.close(wsCloseCodes.PAYLOAD_ERROR[0], wsCloseCodes.PAYLOAD_ERROR[1]);
                    const status = await this.handler.handleMessage(ws.session, parseMessage(data.toString()));
                    if (status && status.error) {
                        return ws.close(status.error[0], status.error[1]);
                    }
                } catch(e) {
                    console.error("GatewayServer: unexpected error while attempting to handle payload", e);
                    ws.close(wsCloseCodes.PAYLOAD_ERROR[0], wsCloseCodes.PAYLOAD_ERROR[1]);
                }
            });
            ws.on("close", (code, reason) => {
                this.handler.handleConnectionClose(ws, code, reason);
            });
        });
    }
}

module.exports = { GatewayServer, GatewayHandler };