text: /**
  * @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' );
  var indexOf = require( '@stdlib/utils-index-of' );
  
  
  // VARIABLES //
  
  var debug = logger( 'tabulate-by-async:limit' );
  
  
  // MAIN //
  
  /**
  * Invokes an indicator function once for each element in a collection, limiting the number of concurrently pending functions.
  *
  * @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 {Function} indicator - indicator function
  * @param {Callback} done - function to invoke upon completion or upon encountering an error
  * @returns {void}
  */
  function limit( collection, opts, indicator, done ) {
  	var maxIndex;
  	var count;
  	var flg;
  	var lim;
  	var len;
  	var idx;
  	var out;
  	var tmp;
  	var i;
  
  	len = collection.length;
  	debug( 'Collection length: %d', len );
  
  	out = [];
  	if ( len === 0 ) {
  		debug( 'Finished processing a collection.' );
  		return done( null, out );
  	}
  	tmp = [];
  	if ( len < opts.limit ) {
  		lim = len;
  	} else {
  		lim = opts.limit;
  	}
  	debug( 'Concurrency limit: %d', lim );
  	debug( 'Number of arguments: %d', indicator.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 node/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 ( indicator.length === 2 ) {
  			indicator.call( opts.thisArg, v, cb );
  		} else if ( indicator.length === 3 ) {
  			indicator.call( opts.thisArg, v, j, cb );
  		} else {
  			indicator.call( opts.thisArg, v, j, collection, cb );
  		}
  		/**
  		* Callback invoked once a provided function finishes processing a collection element.
  		*
  		* @private
  		* @param {*} [error] - error
  		* @param {*} [group] - group
  		* @returns {void}
  		*/
  		function cb( error, group ) {
  			var i;
  			if ( flg ) {
  				// Prevent further processing of collection elements:
  				return;
  			}
  			if ( error ) {
  				flg = true;
  				return clbk( error );
  			}
  			debug( 'Collection element %d group: %s.', j, group );
  
  			// Determine if we've seen the group/category before. If not, cache a reference which points to its location in the output array; otherwise, update the running count.
  			i = indexOf( tmp, group );
  			if ( i === -1 ) {
  				tmp.push( group );
  				out.push( [ group, 1, 0 ] );
  			} else {
  				out[ i ][ 1 ] += 1;
  			}
  			clbk();
  		}
  	}
  
  	/**
  	* Callback invoked once ready to process the next collection element.
  	*
  	* @private
  	* @param {*} [error] - error
  	* @returns {void}
  	*/
  	function clbk( error ) {
  		var i;
  		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 ) {
  			// Compute percentages...
  			for ( i = 0; i < out.length; i++ ) {
  				out[ i ][ 2 ] = out[ i ][ 1 ] / count;
  			}
  			debug( 'Finished processing a collection.' );
  			return done( null, out );
  		}
  	}
  }
  
  
  // EXPORTS //
  
  module.exports = limit;
  