trigram.js

(function () {

	TrigramIndex = function (inputPhrases) {

		function asTrigrams( phrase, callback ) {
			var rawData = "  ".concat( phrase , "  " );
			for( var i = rawData.length - 3; i >= 0; i = i - 1 )
				callback.call( this, rawData.slice( i, i + 3 ) );
		};

		var instance = {
			phrases : [],
			trigramIndex : [],

			index : function ( phrase ) {
				if( !phrase || phrase === "" || this.phrases.indexOf( phrase ) >= 0 ) return;
				var phraseIndex = this.phrases.push( phrase ) - 1;
				asTrigrams.call( this, phrase, function( trigram ) {
					var phrasesForTrigram = this.trigramIndex[trigram];
					if( !phrasesForTrigram ) phrasesForTrigram = [];
					if( phrasesForTrigram.indexOf( phraseIndex ) < 0 ) phrasesForTrigram.push( phraseIndex );
					this.trigramIndex[trigram] = phrasesForTrigram;
				});
			},

			find : function( phrase ) {
				var phraseMatches = [];
				var trigramsInPhrase = 0;
				asTrigrams.call( this, phrase, function( trigram ) {
					var phrasesForTrigram = this.trigramIndex[trigram];
					trigramsInPhrase += 1;
					if( phrasesForTrigram )
					for( var j in phrasesForTrigram ) {
						phraseIndex = phrasesForTrigram[j];
						if( !phraseMatches[phraseIndex] ) phraseMatches[phraseIndex] = 0;
						phraseMatches[phraseIndex] += 1;
					}
				});
				var result = [];
				for( var i in phraseMatches )
					result.push( { phrase: this.phrases[i], matches: phraseMatches[i] } );

				result.sort( function ( a, b ) {
					var diff = b.matches - a.matches;
					return diff;// == 0 ? a.phrase.localeCompare(b.phrase) : diff;
				});
				return result;
			}
		};

		for( var i in inputPhrases )
			instance.index( input[i] );
		return instance;
	};
})();