stream-flow-control/lib/flows/first.js

Stream Flow Control

const {Readable} = require('stream');
const {Manager} = require('../manager/manager.js');
const uuid = require('uuid');
const {DataWrapper} = require('../wrapper/data_wrapper.js')

/**
 * Flow the first message from multiple source streams and discard the rest.
 * 
 * @extends Readable
 */
class FlowFirst extends Readable {

    /** 
     * Create a FlowFirst stream
     * @param {object} options Global options
     * @param {string} [options.name] Name for this stream
     * @param {Identify} options.identify Function that returns a message id to match
     * @param {Condition} [options.criteria] Add an extra criteria for message to match. Return false to discard the message.
     * @param {Process} [options.match] How messages are matched according to _options.identify_ function.
     */
    constructor(options) {
        options = {...options, objectMode: true};
        super(options);
        this.options = options;
        /** @property Source streams */
        this._sources = {};
        this._readableState.sync = false;
        this.type = 'FlowFirst';
        if(this.options.name) Manager.set(this.type, this);
        if(this.options.match && typeof this.options.match == 'function') this._match = this.options.match;
        if(this.options.identify && typeof this.options.identify == 'function') this._identify = this.options.identify;
        this._identities={};

        //Delete used identities every 5 seconds
        setInterval(()=>{
            Object.keys(this._identities).forEach(key => {
                const ts = Date.now() - 1000;
                if(this._identities[key] < ts) delete this._identities[key];
            });
        }, 5000);


        this.on('pipe', (src)=>{
            src.on('data', (data)=>{
                //console.log('hay data');
                this._match(data);
            });
            this.on('pause', ()=>{
                src.pause();
            });
            this.on('resume', ()=>{
                src.resume();
            });
        });
    }

    _identify(data) {
        throw 'METHOD NOT IMPLEMENTED _identify()';
    }

    _criteria(data) {
        return true;
    }

    _match(data) {
        if(!this._criteria(data)) return;
        const id = this._identify(data);
        if(!this._identities[id]) {
            this._identities[id] = Date.now();
            if(!this.push(data)) this.pause();
        }
    }

    write(payload) {

    }

    end() {
        this.push(null);
    }

    _read() {
        this.resume();
    }

}

module.exports.FlowFirst = FlowFirst;