"use strict";
const events = require("events");
const WebSocket = require("ws");

const schema = require("lib/schema");
const errors = require("lib/errors");


class WebSocketBaseConnector extends events.EventEmitter {
	constructor() {
		super();

		this._socket = null;
		this._seq = 1;
		this._lastHeartbeat = null;
		this._heartbeatId = null;
		this._heartbeatInterval = null;
		this._lastReceivedSeq = null;
		this._sendBuffer = [];
	}

	_dropSendBufferSeq(seq) {
		if (seq === null) {
			return;
		}

		let dropCount = 0;
		for (let index = 0; index < this._sendBuffer.length; index++) {
			if (this._sendBuffer[index].seq <= seq) {
				dropCount++;
			} else {
				break;
			}
		}
		this._sendBuffer.splice(0, dropCount);
	}

	_doHeartbeat() {
		this._check(["connected"]);
		if (Date.now() - this._lastHeartbeat > 2000 * this._heartbeatInterval) {
			console.log("SOCKET | closing after heartbeat timed out");
			this._socket.close(1008, "Heartbeat timeout");
			clearInterval(this._heartbeatId);
			this._heartbeatId = null;

		} else {
			this._socket.send(JSON.stringify({
				seq: null,
				type: "heartbeat",
				data: { seq: this._lastReceivedSeq },
			}));
		}
	}

	_processHeartbeat(message) {
		if (!schema.heartbeat(message)) {
			console.log("SOCKET | closing after received invalid heartbeat:", message);
			this._socket.close(1002, "Invalid heartbeat");
			console.log(schema.heartbeat.errors);
			return;
		}

		this._lastHeartbeat = Date.now();
		this._dropSendBufferSeq(message.data.seq);
	}

	/**
	 * Start sending heartbeats
	 */
	startHeartbeat() {
		this._lastHeartbeat = Date.now();
		this._heartbeatId = setInterval(() => {
			this._doHeartbeat();
		}, this._heartbeatInterval * 1000);
	}

	/**
	 * Stop sending heartbeats
	 */
	stopHeartbeat() {
		if (this._heartbeatId) {
			clearInterval(this._heartbeatId);
			this._heartbeatId = null;
		}
	}

	/**
	 * Send a message over the socket
	 *
	 * @returns the sequence number of the message sent
	 */
	send(type, data) {
		this._check(["handshake", "connected", "closing"]);
		let message = { seq: this._seq, type, data };
		this._sendBuffer.push(message);
		if (["connected", "closing"].includes(this._state)) {
			this._socket.send(JSON.stringify(message));
		}
		return this._seq++;
	}

	/**
	 * Set connection state to closing
	 *
	 * Signal the connection is about tho close and that once the close
	 * frame is received it should be considered finished.
	 */
	setClosing() {
		this._state = "closing";
	}
}

/**
 * Connector for master server clients
 */
class WebSocketClientConnector extends WebSocketBaseConnector {
	constructor(url, reconnectDelay) {
		super();

		this._url = url;

		// The following states are used in the client connector
		// new: Not connected
		// handshake: Attempting to (re)connect to server.
		// connected: Connection is online
		// closing: Connection is in the process of being closed.
		this._state = "new";
		this._reconnectId = null;
		this._sessionToken = null;
		this._connected = false;
		this._reconnectDelay = reconnectDelay;
	}

	_check(expectedStates) {
		if (!expectedStates.includes(this._state)) {
			throw new Error(
				`Expected state ${expectedStates} but state is ${this._state}`
			);
		}
	}

	/**
	 * Send a handshake message over the socket
	 *
	 * Used in the register function in order to send the register handshake
	 * message over the WebSocket.
	 */
	sendHandshake(type, data) {
		this._check(["handshake"]);
		this._socket.send(JSON.stringify({ seq: null, type, data }));
	}

	/**
	 * Close the connection with the given reason.
	 *
	 * Sends a close frame and disconnects the connector.
	 */
	close(code, reason) {
		if (this._state === "new") {
			return;
		}

		if (this._reconnectId) {
			clearTimeout(this._reconnectId);
			this._reconnectId = null;
		}

		this.stopHeartbeat();
		this._state = "closing";
		this._socket.close(code, reason);
	}

	/**
	 * Connect to the master server
	 */
	async connect() {
		this._check(["new"]);
		this._state = "handshake";

		this._doConnect();

		// Wait for the connection to be ready
		await events.once(this, "connected");
	}

	async _doConnect() {
		let url = new URL(this._url);
		url.pathname += "api/socket";

		// Open WebSocket to master
		console.log(`SOCKET | connecting to ${url}`)

		this._socket = new WebSocket(url, {
			// For now we do not verify TLS certificates since the default setup is
			// to create a self-signed certificate.
			rejectUnauthorized: false,
		});

		this._attachSocketHandlers();
	}

	/**
	 * Attempt re-establishing the connecting again
	 */
	reconnect() {
		if (this._reconnectId !== null) {
			return;
		}

		let delay = Math.random() * this._reconnectDelay;
		console.log(`SOCKET | waiting ${delay.toLocaleString("en", { maximumFractionDigits: 2 })} seconds for reconnect`)
		this._reconnectId = setTimeout(() => {
			this._reconnectId = null;
			this._doConnect();
		}, delay * 1000);
	}

	_attachSocketHandlers() {
		this._socket.on("close", (code, reason) => {
			console.log(`SOCKET | Close (code: ${code}, reason: ${reason})`);
			// Authentication failed
			if (code === 4003) {
				this.emit("error", new errors.AuthenticationFailed("Authentication failed"));
				this._state = "closing";
			}

			if (this._state === "closing") {
				this._lastReceivedSeq = null;
				this._sessionToken = null;
				this._sendBuffer.length = 0;
				this._state = "new";

				if (this._connected) {
					this.emit("close");
					this._connected = false;
				}

			} else {
				this._state = "handshake";
				this.reconnect();

				if (this._connected) {
					this.emit("dropped");
					this._connected = false;
				}
			}

			this.stopHeartbeat();
		});

		this._socket.on("error", err => {
			// It's assumed that close is always called by ws
			console.error("SOCKET | Error:", err);
		});

		/*
		this._socket.on("unexpected-response", (req, res) => {
			let data = "";
			res.on('data', (chunk) => { data += chunk; });
			res.on('end', () => {
				console.error(`SOCKET | Unexpeced Response ${res.statusCode}`);
				console.error(data);
				this._socket.emit("error", new Error(`Unexpected Response ${res.statusCode}`));
			});
		});
		*/

		this._socket.on("open", () => {
			console.log("SOCKET | Open");
		});
		this._socket.on("ping", data => {
			console.log(`SOCKET | Ping (data: ${data}`);
		});
		this._socket.on("pong", data => {
			console.log(`SOCKET | Pong (data: ${data}`);
		});

		// Handle messages
		this._socket.on("message", data => {
			let message = JSON.parse(data);
			if (this._state === "handshake") {
				this._processHandshake(message);

			} else if (["connected", "closing"].includes(this._state)) {
				if (message.seq !== null) {
					this._lastReceivedSeq = message.seq;
				}

				if (message.type === "heartbeat") {
					this._processHeartbeat(message);

				} else {
					this.emit("message", message);
				}

			} else {
				throw new Error(`Received message in unexpected state ${this._state}`);
			}
		});
	}

	_processHandshake(message) {
		if (!schema.serverHandshake(message)) {
			console.log("SOCKET | closing after received invalid handshake:", message);
			this._socket.close(1002, "Invalid handshake");
			return;
		}

		let { seq, type, data } = message;
		if (type == 'hello') {
			console.log(`SOCKET | received hello from master version ${data.version}`);
			if (this._sessionToken) {
				console.log("SOCKET | Attempting resume");
				this.sendHandshake("resume", {
					session_token: this._sessionToken,
					last_seq: this._lastReceivedSeq,
				});
			} else {
				this.register();
			}

		} else if (type === 'ready') {
			console.log("SOCKET | received ready from master");
			this._state = "connected";
			this._sessionToken = data.session_token;
			this._heartbeatInterval = data.heartbeat_interval;
			this.startHeartbeat();
			this._connected = true;
			this.emit("connected");

		} else if (type === "continue") {
			console.log("SOCKET | resuming existing session");
			this._state = "connected";
			this._heartbeatInterval = data.heartbeat_interval;
			this.startHeartbeat();
			this._dropSendBufferSeq(data.last_seq);
			for (let message of this._sendBuffer) {
				this._socket.send(JSON.stringify(message));
			}
			this._connected = true;
			this.emit("connected");

		} else if (type === "invalidate") {
			this._heartbeatInterval = null;
			this._lastReceivedSeq = null;
			this._sessionToken = null;
			this._sendBuffer.length = 0;
			this.emit("invalidate");
			this.register();
		}
	}

	/**
	 * Register the link with the server
	 *
	 * This function is expected to be overriden by sub-classes and send the
	 * register message over the socket when invoked.
	 */
	register() {
		throw Error("Abstract function");
	}
}

class VirtualConnector extends events.EventEmitter {
	constructor() {
		super();

		this.other = this;
		this._seq = 1;
	}

	/**
	 * Create a pair of virtual connector hooked into each other
	 *
	 * Creates two virtual connectors that are liked to each othes such that
	 * a message sent on one is received by the other.
	 *
	 * @returns {Array} two virtuarl connectors.
	 */
	static makePair() {
		let first = new this();
		let second = new this();
		first.other = second;
		second.other = first;
		return [first, second];
	}

	/**
	 * Send a message to the other end of the connector
	 *
	 * @returns the sequence number of the message sent
	 */
	send(type, data) {
		this.other.emit('message', { seq: this._seq, type, data });
		return this._seq++;
	}
}

module.exports = {
	WebSocketBaseConnector,
	WebSocketClientConnector,
	VirtualConnector,
};