@barchart/common-node-js/stream/GroupTransformer.js

Common classes, utilities, and functions for building Node.js servers

const log4js = require('log4js'),
	Stream = require('stream');

const assert = require('@barchart/common-js/lang/assert'),
	is = require('@barchart/common-js/lang/is'),
	object = require('@barchart/common-js/lang/object');

module.exports = (() => {
	'use strict';

	const logger = log4js.getLogger('common-node/stream/GroupTransformer');

	/**
	 * Groups items into arrays, based on key (selected by delegate). Stream must be sorted.
	 *
	 * @public
	 * @extends {Steam.Transform}
	 * @param {Function} keySelector
	 * @param {String=} description
	 * @param {Boolean=} silent
	 */
	class GroupTransformer extends Stream.Transform {
		constructor(keySelector, description, silent) {
			super({ objectMode: true });

			assert.argumentIsRequired(keySelector, 'keySelector', Function);
			assert.argumentIsOptional(description, 'description', String);
			assert.argumentIsOptional(silent, 'silent', Boolean);

			this._keySelector = keySelector;

			this._description = description || 'Group Transformer';
			this._silent = is.boolean(silent) && silent;

			this._counter = 0;

			this._batch = null;
			this._key = null;
		}

		_transform(chunk, encoding, callback) {
			this._counter = this._counter + 1;

			let error = null;

			if (is.object(chunk)) {
				let key;

				try {
					key = this._keySelector(chunk);
				} catch (e) {
					error = e;
				}

				if (error === null) {
					if (!object.equals(this._key, key)) {
						publish.call(this);

						this._key = key;
					}

					this._batch.push(chunk);
				}
			} else {
				error = new Error(`Transformation [ ${this._counter} ] for [ ${this._description} ] failed, unexpected input type.`);
			}

			if (error === null) {
				callback();
			} else {
				if (this._silent) {
					logger.warn(`Transformation [ ${this._counter} ] for [ ${this._description} ] failed.`);

					if (logger.isTraceEnabled() && chunk) {
						logger.trace(chunk);
					}

					error = null;
				}

				callback(error, null);
			}
		}

		_flush(callback) {
			publish.call(this);

			callback();
		}

		toString() {
			return '[GroupTransformer]';
		}
	}

	function publish() {
		if (is.array(this._batch) && this._batch.length !== 0) {
			this.push(this._batch);
		}

		this._batch = [ ];
	}

	return GroupTransformer;
})();