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

Stream Flow Control

const {Writable, Readable} = require('stream');
const {Manager} = require('../manager/manager.js');

/**
 * Stream every element of an array individually.
 * 
 * @extends Writable
 */
class FlowEach extends Writable {

    /** 
     * Create a FlowEach stream
     * @param {object} [options] Global options
     * @param {string} [options.name] Name for this stream
     */
    constructor(options) {
        options = {...options, objectMode: true};
        super(options);
        this.options = options;
        this.type = 'FlowEach';
        if(this.options.name) Manager.set(this.type, this);
        this._reader = null;
        this._corking_readers = {};
        this._reader_messages = [];
        this._none_reader = null;
    }

    /**
     * Set stream(s) to pipe to
     * @param {(Writable|Writable[])} dst 
     * @returns {(Writable|FlowAll)} if dst is an array, then returns "this", else dst is returned
     */
    pipe(dst) {
        if(!this._reader) {
            const self = this;
            this._reader = new Readable({
                objectMode: true,
                read() {
                    if(self._writableState.corked && self._corking_readers['reader']) {
                        self.uncork();
                        delete self._corking_readers['reader'];
                        self._deliver_messages();
                    }
                }
            });
            this._reader.options = {...this._reader.options||{}, name: this.options.name};
            this._reader._readableState.sync = false;
        }

        const pipes = Array.isArray(dst)?dst:[dst];
        pipes.forEach(dst=>this._reader.pipe(dst));
        return Array.isArray(dst)?this:dst;
    }

    /**
     * Set stream(s) to pipe to when no other stream was piped
     * @param {(Writable|Writable[])} dst Destination stream
     * @returns {(Writable|FlowAll)} if dst is an array, then returns "this", else dst is returned
     */
    none(dst) {
        if(!this._none_reader) {
            const self = this;
            this._none_reader = new Readable({
                objectMode: true,
                read() {
                    if(self._writableState.corked && self._corking_readers['reader']) {
                        self.uncork();
                        delete self._corking_readers['reader'];
                    }
                }
            });
            this._none_reader.options = {...this._none_reader.options||{}, name: this.options.name, port: 'none'};
            this._none_reader._readableState.sync = false;
        }

        const pipes = Array.isArray(dst)?dst:[dst];
        pipes.forEach(dst=>this._none_reader.pipe(dst));
        return Array.isArray(dst)?this:dst;
    }

    _deliver_messages() {
        if(this._reader) {
            while(this._reader_messages.length) {
                if(!this._reader.push(this._reader_messages.shift()) && !this._corking_readers['reader']) {
                    this.cork();
                    this._corking_readers['reader'] = true;
                    break;
                }
            }
        }
        if(!this._reader_messages.length && this._needsEnd) {
            this._reader && this._reader.push(null);
            this._none_reader && this._none_reader.push(null);
        }
    }

    _write(payload, encoding, cb) {
        let data;
        if(this.goal) {
            // Is goal player
            data = payload.data;
        } else {
            data = payload;
        }
        
        if(this._reader) {
            this._reader_messages = this._reader_messages.concat((!Array.isArray(data)?[data]:data));
            if(this.goal) {
                this._reader_messages = this._reader_messages.map(data=>payload.getChild(this).setData(data));   
            };
            this._deliver_messages();
        }

        if(!this._reader && this._none_reader) {
            if(this.options.none_reason) {
                let data = typeof this.options.none_reason == 'function'?this.options.none_reason(payload):this.options.none_reason;
                payload = (this.goal)?payload.getChild(this).setData(data):data;
            } else {
                payload = this.goal?payload.getChild(this):payload
            }
            if(!this._none_reader.push(payload) && !this._corking_readers['none']) {
                this.cork();
                this._corking_readers['none'] = true;
            }
        }

        cb();

    }

    end() {
        if(!this._reader_messages.length) {
            this._reader && this._reader.push(null);
            this._none_reader && this._none_reader.push(null);
        } else {
            this._needsEnd = true;
        }
    }

}

module.exports.FlowEach = FlowEach;