1 files changed, 110 insertions, 0 deletions
diff --git a/resources/src/mediawiki/mediawiki.experiments.js b/resources/src/mediawiki/mediawiki.experiments.js
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+++ b/resources/src/mediawiki/mediawiki.experiments.js
@@ -0,0 +1,110 @@
+/* jshint bitwise:false */
+( function ( mw, $ ) {
+
+	var CONTROL_BUCKET = 'control',
+		MAX_INT32_UNSIGNED = 4294967295;
+
+	/**
+	 * An implementation of Jenkins' one-at-a-time hash.
+	 *
+	 * @see http://en.wikipedia.org/wiki/Jenkins_hash_function
+	 *
+	 * @param {String} string String to hash
+	 * @return {Number} The hash as a 32-bit unsigned integer
+	 * @ignore
+	 *
+	 * @author Ori Livneh <ori@wikimedia.org>
+	 * @see http://jsbin.com/kejewi/4/watch?js,console
+	 */
+	function hashString( string ) {
+		var hash = 0,
+			i = string.length;
+
+		while ( i-- ) {
+			hash += string.charCodeAt( i );
+			hash += ( hash << 10 );
+			hash ^= ( hash >> 6 );
+		}
+		hash += ( hash << 3 );
+		hash ^= ( hash >> 11 );
+		hash += ( hash << 15 );
+
+		return hash >>> 0;
+	}
+
+	/**
+	 * Provides an API for bucketing users in experiments.
+	 *
+	 * @class mw.experiments
+	 * @singleton
+	 */
+	mw.experiments = {
+
+		/**
+		 * Gets the bucket for the experiment given the token.
+		 *
+		 * The name of the experiment and the token are hashed. The hash is converted
+		 * to a number which is then used to get a bucket.
+		 *
+		 * Consider the following experiment specification:
+		 *
+		 * ```
+		 * {
+		 *   name: 'My first experiment',
+		 *   enabled: true,
+		 *   buckets: {
+		 *     control: 0.5
+		 *     A: 0.25,
+		 *     B: 0.25
+		 *   }
+		 * }
+		 * ```
+		 *
+		 * The experiment has three buckets: control, A, and B. The user has a 50%
+		 * chance of being assigned to the control bucket, and a 25% chance of being
+		 * assigned to either the A or B buckets. If the experiment were disabled,
+		 * then the user would always be assigned to the control bucket.
+		 *
+		 * This function is based on the deprecated `mw.user.bucket` function.
+		 *
+		 * @param {Object} experiment
+		 * @param {String} experiment.name The name of the experiment
+		 * @param {Boolean} experiment.enabled Whether or not the experiment is
+		 *  enabled. If the experiment is disabled, then the user is always assigned
+		 *  to the control bucket
+		 * @param {Object} experiment.buckets A map of bucket name to probability
+		 *  that the user will be assigned to that bucket
+		 * @param {String} token A token that uniquely identifies the user for the
+		 *  duration of the experiment
+		 * @returns {String} The bucket
+		 */
+		getBucket: function ( experiment, token ) {
+			var buckets = experiment.buckets,
+				key,
+				range = 0,
+				hash,
+				max,
+				acc = 0;
+
+			if ( !experiment.enabled || $.isEmptyObject( experiment.buckets ) ) {
+				return CONTROL_BUCKET;
+			}
+
+			for ( key in buckets ) {
+				range += buckets[ key ];
+			}
+
+			hash = hashString( experiment.name + ':' + token );
+			max = ( hash / MAX_INT32_UNSIGNED ) * range;
+
+			for ( key in buckets ) {
+				acc += buckets[ key ];
+
+				if ( max <= acc ) {
+					return key;
+				}
+			}
+		}
+	};
+
+}( mediaWiki, jQuery ) );