function UI(buttons, screen) {

	return {
		animation: animation,
		cinematic: cinematic,
		frame: frame,
		menu: menu,
		text: text
	};

	function animation(frames) {
		var frameCounter = 0;
		var scheduled;
		var step = function() {
			if(frameCounter < frames.length) {
				scheduled = null;
				frames[frameCounter].action();
				if(frames[frameCounter].delay != undefined) {
					scheduled = setTimeout(step, frames[frameCounter].delay);
				}
				frameCounter++
			}
		};
		return {
			run: step,
			pause: function() { if(scheduled != undefined) { clearTimeout(scheduled); } }
		};
	}

	function cinematic(frames, controls) {
		var remote = animation(frames);
		var mapping = {};
		for(var key in controls) {
			mapping[key] = function() {
				buttons.pop();
				remote.pause();
				controls[key]();
			};
		}
		return function(f) {
			buttons.push(mapping);
			remote.run();
			f();
		};
	}

	function frame(id) {
		screen.clear();
		screen.frame(id);
	}

	function menu(config) {
		var cursor = 0;
		var m = screen.menu(config.entries);
		var sync = function() { screen.select(cursor); };
		var mapping = {
			'Up': function() { cursor = Math.max(0, cursor - 1); sync(); },
			'Down': function() { cursor = Math.min(config.entries.length - 1, cursor + 1); sync(); },
			'A': function() { config.entries[cursor].action(); }
		};
		if(config.cancel != undefined) {
			mapping['B'] = function() { buttons.pop(); screen.clear(m); config.cancel(); }
		}
		buttons.push(mapping);
	}

	function textScreen(message) {
		var characters = message.split('');
		var frames = [];
		var ready = false;
		var append = function(c) { return function() { screen.appendText(c); }; };
		for(var i = 0; i < characters.length; i++) {
			frames.push({action: append(characters[i]), delay: 50});
		}
		frames.push({action: function() { ready = true; screen.markAsRead(); }, delay: null});
		var remote = animation(frames);
		return function(f) {
			buttons.push({
				'A': function() {
					if(ready) {
						f();
					} else {
						remote.pause();
						screen.text(message);
						ready = true;
					}
				}
			});
			screen.text('');
			remote.run();
		};
	}

	function text(message) {
		return textScreen(message);
	}
}