Signal.js

Elm.Native.Signal = {};

Elm.Native.Signal.make = function(localRuntime) {
	localRuntime.Native = localRuntime.Native || {};
	localRuntime.Native.Signal = localRuntime.Native.Signal || {};
	if (localRuntime.Native.Signal.values)
	{
		return localRuntime.Native.Signal.values;
	}


	var Task = Elm.Native.Task.make(localRuntime);
	var Utils = Elm.Native.Utils.make(localRuntime);


	function broadcastToKids(node, timestamp, update)
	{
		var kids = node.kids;
		for (var i = kids.length; i--; )
		{
			kids[i].notify(timestamp, update, node.id);
		}
	}


	// INPUT

	function input(name, base)
	{
		var node = {
			id: Utils.guid(),
			name: 'input-' + name,
			value: base,
			parents: [],
			kids: []
		};

		node.notify = function(timestamp, targetId, value) {
			var update = targetId === node.id;
			if (update)
			{
				node.value = value;
			}
			broadcastToKids(node, timestamp, update);
			return update;
		};

		localRuntime.inputs.push(node);

		return node;
	}

	function constant(value)
	{
		return input('constant', value);
	}


	// MAILBOX

	function mailbox(base)
	{
		var signal = input('mailbox', base);

		function send(value) {
			return Task.asyncFunction(function(callback) {
				localRuntime.setTimeout(function() {
					localRuntime.notify(signal.id, value);
				}, 0);
				callback(Task.succeed(Utils.Tuple0));
			});
		}

		return {
			signal: signal,
			address: {
				ctor: 'Address',
				_0: send
			}
		};
	}

	function sendMessage(message)
	{
		Task.perform(message._0);
	}


	// OUTPUT

	function output(name, handler, parent)
	{
		var node = {
			id: Utils.guid(),
			name: 'output-' + name,
			parents: [parent],
			isOutput: true
		};

		node.notify = function(timestamp, parentUpdate, parentID)
		{
			if (parentUpdate)
			{
				handler(parent.value);
			}
		};

		parent.kids.push(node);

		return node;
	}


	// MAP

	function mapMany(refreshValue, args)
	{
		var node = {
			id: Utils.guid(),
			name: 'map' + args.length,
			value: refreshValue(),
			parents: args,
			kids: []
		};

		var numberOfParents = args.length;
		var count = 0;
		var update = false;

		node.notify = function(timestamp, parentUpdate, parentID)
		{
			++count;

			update = update || parentUpdate;

			if (count === numberOfParents)
			{
				if (update)
				{
					node.value = refreshValue();
				}
				broadcastToKids(node, timestamp, update);
				update = false;
				count = 0;
			}
		};

		for (var i = numberOfParents; i--; )
		{
			args[i].kids.push(node);
		}

		return node;
	}


	function map(func, a)
	{
		function refreshValue()
		{
			return func(a.value);
		}
		return mapMany(refreshValue, [a]);
	}


	function map2(func, a, b)
	{
		function refreshValue()
		{
			return A2( func, a.value, b.value );
		}
		return mapMany(refreshValue, [a, b]);
	}


	function map3(func, a, b, c)
	{
		function refreshValue()
		{
			return A3( func, a.value, b.value, c.value );
		}
		return mapMany(refreshValue, [a, b, c]);
	}


	function map4(func, a, b, c, d)
	{
		function refreshValue()
		{
			return A4( func, a.value, b.value, c.value, d.value );
		}
		return mapMany(refreshValue, [a, b, c, d]);
	}


	function map5(func, a, b, c, d, e)
	{
		function refreshValue()
		{
			return A5( func, a.value, b.value, c.value, d.value, e.value );
		}
		return mapMany(refreshValue, [a, b, c, d, e]);
	}


	// FOLD

	function foldp(update, state, signal)
	{
		var node = {
			id: Utils.guid(),
			name: 'foldp',
			parents: [signal],
			kids: [],
			value: state
		};

		node.notify = function(timestamp, parentUpdate, parentID)
		{
			if (parentUpdate)
			{
				node.value = A2( update, signal.value, node.value );
			}
			broadcastToKids(node, timestamp, parentUpdate);
		};

		signal.kids.push(node);

		return node;
	}


	// TIME

	function timestamp(signal)
	{
		var node = {
			id: Utils.guid(),
			name: 'timestamp',
			value: Utils.Tuple2(localRuntime.timer.programStart, signal.value),
			parents: [signal],
			kids: []
		};

		node.notify = function(timestamp, parentUpdate, parentID)
		{
			if (parentUpdate)
			{
				node.value = Utils.Tuple2(timestamp, signal.value);
			}
			broadcastToKids(node, timestamp, parentUpdate);
		};

		signal.kids.push(node);

		return node;
	}


	function delay(time, signal)
	{
		var delayed = input('delay-input-' + time, signal.value);

		function handler(value)
		{
			setTimeout(function() {
				localRuntime.notify(delayed.id, value);
			}, time);
		}

		output('delay-output-' + time, handler, signal);

		return delayed;
	}


	// MERGING

	function genericMerge(tieBreaker, leftStream, rightStream)
	{
		var node = {
			id: Utils.guid(),
			name: 'merge',
			value: A2(tieBreaker, leftStream.value, rightStream.value),
			parents: [leftStream, rightStream],
			kids: []
		};

		var left = { touched: false, update: false, value: null };
		var right = { touched: false, update: false, value: null };

		node.notify = function(timestamp, parentUpdate, parentID)
		{
			if (parentID === leftStream.id)
			{
				left.touched = true;
				left.update = parentUpdate;
				left.value = leftStream.value;
			}
			if (parentID === rightStream.id)
			{
				right.touched = true;
				right.update = parentUpdate;
				right.value = rightStream.value;
			}

			if (left.touched && right.touched)
			{
				var update = false;
				if (left.update && right.update)
				{
					node.value = A2(tieBreaker, left.value, right.value);
					update = true;
				}
				else if (left.update)
				{
					node.value = left.value;
					update = true;
				}
				else if (right.update)
				{
					node.value = right.value;
					update = true;
				}
				left.touched = false;
				right.touched = false;

				broadcastToKids(node, timestamp, update);
			}
		};

		leftStream.kids.push(node);
		rightStream.kids.push(node);

		return node;
	}


	// FILTERING

	function filterMap(toMaybe, base, signal)
	{
		var maybe = toMaybe(signal.value);
		var node = {
			id: Utils.guid(),
			name: 'filterMap',
			value: maybe.ctor === 'Nothing' ? base : maybe._0,
			parents: [signal],
			kids: []
		};

		node.notify = function(timestamp, parentUpdate, parentID)
		{
			var update = false;
			if (parentUpdate)
			{
				var maybe = toMaybe(signal.value);
				if (maybe.ctor === 'Just')
				{
					update = true;
					node.value = maybe._0;
				}
			}
			broadcastToKids(node, timestamp, update);
		};

		signal.kids.push(node);

		return node;
	}


	// SAMPLING

	function sampleOn(ticker, signal)
	{
		var node = {
			id: Utils.guid(),
			name: 'sampleOn',
			value: signal.value,
			parents: [ticker, signal],
			kids: []
		};

		var signalTouch = false;
		var tickerTouch = false;
		var tickerUpdate = false;

		node.notify = function(timestamp, parentUpdate, parentID)
		{
			if (parentID === ticker.id)
			{
				tickerTouch = true;
				tickerUpdate = parentUpdate;
			}
			if (parentID === signal.id)
			{
				signalTouch = true;
			}

			if (tickerTouch && signalTouch)
			{
				if (tickerUpdate)
				{
					node.value = signal.value;
				}
				tickerTouch = false;
				signalTouch = false;

				broadcastToKids(node, timestamp, tickerUpdate);
			}
		};

		ticker.kids.push(node);
		signal.kids.push(node);

		return node;
	}


	// DROP REPEATS

	function dropRepeats(signal)
	{
		var node = {
			id: Utils.guid(),
			name: 'dropRepeats',
			value: signal.value,
			parents: [signal],
			kids: []
		};

		node.notify = function(timestamp, parentUpdate, parentID)
		{
			var update = false;
			if (parentUpdate && !Utils.eq(node.value, signal.value))
			{
				node.value = signal.value;
				update = true;
			}
			broadcastToKids(node, timestamp, update);
		};

		signal.kids.push(node);

		return node;
	}


	return localRuntime.Native.Signal.values = {
		input: input,
		constant: constant,
		mailbox: mailbox,
		sendMessage: sendMessage,
		output: output,
		map: F2(map),
		map2: F3(map2),
		map3: F4(map3),
		map4: F5(map4),
		map5: F6(map5),
		foldp: F3(foldp),
		genericMerge: F3(genericMerge),
		filterMap: F3(filterMap),
		sampleOn: F2(sampleOn),
		dropRepeats: dropRepeats,
		timestamp: timestamp,
		delay: F2(delay)
	};
};