time-to-botec

limit.js (4342B)

---

 /**
 * @license Apache-2.0
 *
 * Copyright (c) 2018 The Stdlib Authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
 
 'use strict';
 
 // MODULES //
 
 var logger = require( 'debug' );
 
 
 // VARIABLES //
 
 var debug = logger( 'bifurcate-by-async:limit' );
 
 
 // MAIN //
 
 /**
 * Invokes a predicate function once for each element in a collection, limiting the number of concurrently pending functions.
 *
 * ## Notes
 *
 * -   We need to cache the collection value to prevent the edge case where, during the invocation of the predicate function, the element at index `i` is swapped for some other value. For some, that might be a feature; here, we take the stance that one should be less clever.
 *
 *
 * @private
 * @param {Collection} collection - input collection
 * @param {Options} opts - function options
 * @param {*} [opts.thisArg] - execution context
 * @param {PositiveInteger} [opts.limit] - maximum number of pending function invocations
 * @param {string} [options.returns] - output format
 * @param {Function} predicate - predicate function
 * @param {Callback} done - function to invoke upon completion or upon encountering an error
 * @returns {void}
 */
 function limit( collection, opts, predicate, done ) {
 	var maxIndex;
 	var count;
 	var flg;
 	var lim;
 	var len;
 	var idx;
 	var out;
 	var i;
 
 	len = collection.length;
 	debug( 'Collection length: %d', len );
 
 	out = [];
 	if ( len === 0 ) {
 		debug( 'Finished processing a collection.' );
 		return done( null, out );
 	}
 	out.push( [], [] );
 	if ( len < opts.limit ) {
 		lim = len;
 	} else {
 		lim = opts.limit;
 	}
 	debug( 'Concurrency limit: %d', lim );
 	debug( 'Number of arguments: %d', predicate.length );
 
 	maxIndex = len - 1;
 	count = 0;
 	idx = -1;
 	for ( i = 0; i < lim; i++ ) {
 		// This guard is necessary to protect against synchronous functions which exhaust all collection elements...
 		if ( idx < maxIndex ) {
 			next(); // eslint-disable-line callback-return
 		}
 	}
 	/**
 	* Callback to invoke a provided function for the next element in a collection.
 	*
 	* @private
 	*/
 	function next() {
 		var v;
 		var j;
 
 		idx += 1;
 		j = idx;
 		v = collection[ j ];
 
 		debug( 'Collection element %d: %s.', j, JSON.stringify( v ) );
 		if ( predicate.length === 2 ) {
 			predicate.call( opts.thisArg, v, cb );
 		} else if ( predicate.length === 3 ) {
 			predicate.call( opts.thisArg, v, j, cb );
 		} else {
 			predicate.call( opts.thisArg, v, j, collection, cb );
 		}
 		/**
 		* Callback invoked once a provided function finishes processing a collection element.
 		*
 		* @private
 		* @param {*} [error] - error
 		* @param {*} [bool] - group indicator
 		* @returns {void}
 		*/
 		function cb( error, bool ) {
 			if ( flg ) {
 				// Prevent further processing of collection elements:
 				return;
 			}
 			if ( error ) {
 				flg = true;
 				return clbk( error );
 			}
 			debug( 'Collection element %d group: %s.', j, ( bool ) ? '0' : '1' );
 
 			// Default is to return values...
 			if ( opts.returns === 'indices' ) {
 				if ( bool ) {
 					out[ 0 ].push( j );
 				} else {
 					out[ 1 ].push( j );
 				}
 			} else if ( opts.returns === '*' ) {
 				if ( bool ) {
 					out[ 0 ].push( [ j, v ] );
 				} else {
 					out[ 1 ].push( [ j, v ] );
 				}
 			} else if ( bool ) {
 				out[ 0 ].push( v );
 			} else {
 				out[ 1 ].push( v );
 			}
 			clbk();
 		}
 	}
 
 	/**
 	* Callback invoked once ready to process the next collection element.
 	*
 	* @private
 	* @param {*} [error] - error
 	* @returns {void}
 	*/
 	function clbk( error ) {
 		if ( error ) {
 			debug( 'Encountered an error: %s', error.message );
 			return done( error );
 		}
 		count += 1;
 		debug( 'Processed %d of %d collection elements.', count, len );
 		if ( idx < maxIndex ) {
 			return next();
 		}
 		if ( count === len ) {
 			debug( 'Finished processing a collection.' );
 			return done( null, out );
 		}
 	}
 }
 
 
 // EXPORTS //
 
 module.exports = limit;