const express = require('express');
const http    = require( 'http');
const WebSocket  = require('ws');
const cors       = require('cors');

const app = express();

//initialize a simple http server
const server = http.createServer(app);

//initialize the WebSocket server instance
const wss = new WebSocket.Server({ server });

const messages = [];
var   sockets  = [];


/**
 * openPromise  returns promise with resolve and reject callbacks available in object
 * 
 * @access public
 * @return promise
 */
function openPromise(){
    let resolve, reject;

    let np = new Promise((ok, fail) => {resolve = ok; reject = fail});

    np.resolve = resolve;
    np.reject  = reject;

    return np
}


/**
 * asynchronize returns generator of promises of chunks or messages
 * 
 * @param s - Stream or Socket to generate promises
 * @param chunkEventName="message" stream event for data chunk or message
 *        Use 'message' for ws or `data` for node Streams
 * @param endEventName="close" stream event for end/close of stream/socket
 * @access public
 * @return function*
 */
function asynchronize({s, chunkEventName="message", endEventName="close"}){
    return function*(){
        //buffer of chunks incoming from stream
        const chunks        = {};
        //buffer of promises yielding outside
        const promises      = {};

        const clear         = i => (delete chunks[i], delete promises[i])


        let   chunkCount    = 0; //autoincrement of chunks
        let   promiseCount  = 0; //autoincrement of promises
        let   end           = false; //flag

        //check availability of chunk and promise. If any, resolve promise, and clear both from queue 
        const chunkAndPromise = i  =>   (i in chunks) && 
                                        (i in promises) && (
                                            promises[i].resolve(chunks[i]),
                                            clear(i))

        s.on(chunkEventName, data => {
            chunks[chunkCount] = data
            chunkAndPromise(chunkCount)

            chunkCount++
        })

        //when end of stream becomes
        s.on(endEventName, () => {
            end = true;

            //all pending promises should be rejected
            for (let i in promises){
                promises[i].reject(new Error('End Of S'))
            }
        })

        while (!end){
            let p;
            promises[promiseCount] = p = openPromise();

            chunkAndPromise(promiseCount)

            promiseCount++;
            yield p; //yield promise outside
        }
    }
}


/**
 * broadcast sends same message to socket list
 * 
 * @param data message to send
 * @access public
 * @return undefined
 */
function broadcast(data){
    for (s of sockets){
        console.log(data)
        s.send(JSON.stringify(data))
    }
}


/**
 * Collection of remote available functions 
 */
let RPC = {
    /**
     * addMessage - saves message in history, broadcast it then returns length of history
     */
    addMessage({nick, message}){
        messages.push({nick, message, timestamp: (new Date).getTime()})
        broadcast({func: 'addMessage', nick, message})
        return messages.length;
    },

    /**
     *  getMessages - returns messages younger than offset
     */
    getMessages({offset=0}){
        return messages.slice(offset)
    },

    /**
     * getUserCount - returns length of socket array (current online users)
     */
    getUserCount(){
        return sockets.length;
    }
}





wss.on('connection', async ws => {

    let gena = asynchronize({s:ws})

    sockets.push(ws)

    //broadcast new usercount after connect
    broadcast({func:'getUserCount', value: sockets.length})

    //main loop, iterating incoming messages
    for (let p of gena()){
        try {
            let message = await p;
            let data    = JSON.parse(message)

            if (data.func in RPC){
                //run function from RPC if any, and send to socket result of it 
                ws.send(JSON.stringify(RPC[data.func](data)))
            }
        }
        catch(e){
            //catching known rejection 
            if (e.message === 'End Of S'){
                console.log('client OTPAL')
                //break loop when connection closed
                break;
            }
            // otherwise print error, but it should be throw e there
            console.log(e)
        }
    }

    //clear closed socket from list of sockets
    sockets = sockets.filter(s => s !== ws)

    //broadcast new usercount after disconnect
    broadcast({func:'getUserCount', value: sockets.length})
});

app.use(express.static('public'));
app.use(cors());

//start our server
server.listen(process.env.PORT || 8999, () => {
    console.log(`Server started on port ${server.address().port} :)`);
});