function Buttons(session) {
	var mapping;
	var mappingsStack = [];

	document.addEventListener('keydown', function(event) {
		var button = session.getOptions().layout[event.key];
		if(button != undefined && mapping[button] != undefined) {
			mapping[button]();
		}
	});

	return {
		map: map,
		pop: pop,
		push: push
	};

	function map(newMapping) {
		mapping = newMapping;
	}

	function pop() {
		mappingsStack.pop();
		map(mappingsStack[mappingsStack.length-1]);
	}

	function push(newMapping) {
		mappingsStack.push(newMapping);
		map(newMapping);
	}
}