/**

 * This class provides access to device accelerometer data.

 * @constructor

 */

function Accelerometer() {

	/**

	 * The last known acceleration.

	 */

	this.lastAcceleration = null;

}

/**

 * Asynchronously aquires the current acceleration.

 * @param {Function} successCallback The function to call when the acceleration

 * data is available

 * @param {Function} errorCallback The function to call when there is an error 

 * getting the acceleration data.

 * @param {AccelerationOptions} options The options for getting the accelerometer data

 * such as timeout.

 */

Accelerometer.prototype.getCurrentAcceleration = function(successCallback, errorCallback, options) {

	// If the acceleration is available then call success

	// If the acceleration is not available then call error

	try {

		if (!this.serviceObj) 

			this.serviceObj = this.getServiceObj();

		if (this.serviceObj == null) 

			throw {

				name: "DeviceErr",

				message: "Could not initialize service object"

			};

		//get the sensor channel

		var SensorParams = {

			SearchCriterion: "AccelerometerAxis"

		};

		var returnvalue = this.serviceObj.ISensor.FindSensorChannel(SensorParams);

		var error = returnvalue["ErrorCode"];

		var errmsg = returnvalue["ErrorMessage"];

		if (!(error == 0 || error == 1012)) {

			var ex = {

				name: "Unable to find Sensor Channel: " + error,

				message: errmsg

			};

			throw ex;

		}

		var channelInfoMap = returnvalue["ReturnValue"][0];

		var criteria = {

			ChannelInfoMap: channelInfoMap,

			ListeningType: "ChannelData"

		};

		if (typeof(successCallback) != 'function') 

			successCallback = function(){

			};

		if (typeof(errorCallback) != 'function') 

			errorCallback = function(){

			};

		this.success_callback = successCallback;

		this.error_callback = errorCallback;

		//create a closure to persist this instance of Accelerometer into the RegisterForNofication callback

		var obj = this;

		// TODO: this call crashes WRT, but there is no other way to read the accel sensor

		// http://discussion.forum.nokia.com/forum/showthread.php?t=182151&highlight=memory+leak

		this.serviceObj.ISensor.RegisterForNotification(criteria, function(transId, eventCode, result){

			try {

				var criteria = {

					TransactionID: transId

				};

				obj.serviceObj.ISensor.Cancel(criteria);

				var accel = new Acceleration(result.ReturnValue.XAxisData, result.ReturnValue.YAxisData, result.ReturnValue.ZAxisData);

				Accelerometer.lastAcceleration = accel;

				obj.success_callback(accel);

			} 

			catch (ex) {

				obj.serviceObj.ISensor.Cancel(criteria);

				obj.error_callback(ex);

			}

		});

	} catch (ex) {

		errorCallback(ex);

	}

};

/**

 * Asynchronously aquires the acceleration repeatedly at a given interval.

 * @param {Function} successCallback The function to call each time the acceleration

 * data is available

 * @param {Function} errorCallback The function to call when there is an error 

 * getting the acceleration data.

 * @param {AccelerationOptions} options The options for getting the accelerometer data

 * such as timeout.

 */

Accelerometer.prototype.watchAcceleration = function(successCallback, errorCallback, options) {

	this.getCurrentAcceleration(successCallback, errorCallback, options);

	// TODO: add the interval id to a list so we can clear all watches

 	var frequency = (options != undefined)? options.frequency : 10000;

	return setInterval(function() {

		navigator.accelerometer.getCurrentAcceleration(successCallback, errorCallback, options);

	}, frequency);

};

/**

 * Clears the specified accelerometer watch.

 * @param {String} watchId The ID of the watch returned from #watchAcceleration.

 */

Accelerometer.prototype.clearWatch = function(watchId) {

	clearInterval(watchId);

};

//gets the Acceleration Service Object from WRT

Accelerometer.prototype.getServiceObj = function() {

	var so;

    try {

        so = device.getServiceObject("Service.Sensor", "ISensor");

    } catch (ex) {

		throw {

			name: "DeviceError",

			message: "Could not initialize accel service object (" + ex.name + ": " + ex.message + ")"

		};

    }		

	return so;

};

if (typeof navigator.accelerometer == "undefined") navigator.accelerometer = new Accelerometer();