function Buttons(session) {
	var mapping;
	var mappingsStack = [];
	var buttons = {
		'A': 0,
		'B': 1,
		'Left': 2,
		'Right': 3,
		'Up': 4,
		'Down': 5,
		'Start': 6,
		'Select': 7
	};

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

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

	function assign(key, button) {
		var layoutDiff = {};
		var layout = session.get('options').layout;
		for(var currentKey in layout) {
			if(layout[currentKey] == button) {
				layoutDiff[currentKey] = undefined;
				break;
			}
		}
		layoutDiff[key] = button;
		return {layoutDiff: layoutDiff, button: layout[key] != button ? layout[key] : null};
	}

	function code(button) {
		return buttons[button];
	}

	function map(newMapping) {
		mapping = newMapping;
	}

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

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