// Example 1 (from the spec):
let chosenHeartRateService: BluetoothRemoteGATTService = null;

navigator.bluetooth.requestDevice({
	filters: [{
		services: ['heart_rate'],
	}]
}).then((device: BluetoothDevice) => device.gatt.connect())
	.then((server: BluetoothRemoteGATTServer) => server.getPrimaryService('heart_rate'))
	.then((service: BluetoothRemoteGATTService) => {
		chosenHeartRateService = service;
		return Promise.all([
			service.getCharacteristic('body_sensor_location')
				.then(handleBodySensorLocationCharacteristic),
			service.getCharacteristic('heart_rate_measurement')
				.then(handleHeartRateMeasurementCharacteristic),
		]);
	});

function handleBodySensorLocationCharacteristic(characteristic: BluetoothRemoteGATTCharacteristic) {
	if (characteristic === null) {
		console.log("Unknown sensor location.");
		return Promise.resolve();
	}
	return characteristic.readValue()
		.then(sensorLocationData => {
			let sensorLocation = sensorLocationData.getUint8(0);
			switch (sensorLocation) {
				case 0: return 'Other';
				case 1: return 'Chest';
				case 2: return 'Wrist';
				case 3: return 'Finger';
				case 4: return 'Hand';
				case 5: return 'Ear Lobe';
				case 6: return 'Foot';
				default: return 'Unknown';
			}
		}).then(location => console.log(location));
}

function handleHeartRateMeasurementCharacteristic(characteristic: BluetoothRemoteGATTCharacteristic) {
	return characteristic.startNotifications()
		.then(char => {
			characteristic.addEventListener('characteristicvaluechanged',
				onHeartRateChanged);
		});
}

function onHeartRateChanged(event: Event) {
	let characteristic = event.target as BluetoothRemoteGATTCharacteristic;
	console.log(parseHeartRate(characteristic.value));
}

function parseHeartRate(data: DataView) {
	let flags = data.getUint8(0);
	let rate16Bits = flags & 0x1;
	let result: any = {};
	let index = 1;
	if (rate16Bits) {
		result.heartRate = data.getUint16(index, /*littleEndian=*/true);
		index += 2;
	} else {
		result.heartRate = data.getUint8(index);
		index += 1;
	}
	let contactDetected = flags & 0x2;
	let contactSensorPresent = flags & 0x4;
	if (contactSensorPresent) {
		result.contactDetected = !!contactDetected;
	}
	let energyPresent = flags & 0x8;
	if (energyPresent) {
		result.energyExpended = data.getUint16(index, /*littleEndian=*/true);
		index += 2;
	}
	let rrIntervalPresent = flags & 0x10;
	if (rrIntervalPresent) {
		let rrIntervals: number[] = [];
		for (; index + 1 < data.byteLength; index += 2) {
			rrIntervals.push(data.getUint16(index, /*littleEndian=*/true));
		}
		result.rrIntervals = rrIntervals;
	}
	return result;
}