// This function is called every time `component.updateState` is called.
func renderApp(component: Component<Int>, count: Int) -> Element {
	return View()
		// The view itself should be centered.
		.justification(.Center)
		// The children should be centered in the view.
		.childAlignment(.Center)
		// Layout children in a column.
		.direction(.Column)
		.children([
			Label("You've clicked \(count) times!"),
			Button(title: "Click me!", action: {
					component.updateState { $0 + 1 }
				})
				.margin(Edges(uniform: 10))
				.width(100),
		])
}

class AppDelegate: NSObject, NSApplicationDelegate {
	@IBOutlet weak var window: NSWindow!

	private let appComponent = Component(initialState: 0, render: renderApp)

	func applicationDidFinishLaunching(notification: NSNotification) {
		let contentView = window.contentView as NSView
		appComponent.addToView(contentView)
	}
}

struct ConverterState {
	static let defaultFahrenheit: CGFloat = 32

	let fahrenheit = defaultFahrenheit
	let celcius = f2c(defaultFahrenheit)
}

private func c2f(c: CGFloat) -> CGFloat {
	return (c * 9/5) + 32
}

private func f2c(f: CGFloat) -> CGFloat {
	return (f - 32) * 5/9
}

private func renderLabeledInput(label: String, value: String, autofocus: Bool, fn: String -> ()) -> Element {
	return View()
		// Layout children in a row.
		.direction(.Row)
		.padding(Edges(bottom: 4))
		.children([
			Label(label).width(75),
			Input(
				text: value,
				placeholder: label,
				action: fn)
				// Autofocus means that the Input will become the first responder when
				// it is first added to the window.
				.autofocus(autofocus)
				.width(100),
		])
}

private func render(component: Component<ConverterState>, state: ConverterState) -> Element {
	let numberFormatter = NSNumberFormatter()
	let parseNumber: String -> CGFloat? = { str in
		return (numberFormatter.numberFromString(str)?.doubleValue).map { CGFloat($0) }
	}
	return View()
		// Center the view.
		.justification(.Center)
		// Center the children.
		.childAlignment(.Center)
		.direction(.Column)
		.children([
			// Each time the text fields change, we re-render. But note that Few.swift
			// is smart enough not to interrupt the user's editing or selection.
			renderLabeledInput("Fahrenheit", "\(state.fahrenheit)", true) {
				if let f = parseNumber($0) {
					component.updateState { _ in ConverterState(fahrenheit: f, celcius: f2c(f)) }
				}
			},
			renderLabeledInput("Celcius", "\(state.celcius)", false) {
				if let c = parseNumber($0) {
					component.updateState { _ in ConverterState(fahrenheit: c2f(c), celcius: c) }
				}
			},
		])
}