package net.shadowfacts.cacao

import net.shadowfacts.cacao.util.KeyModifiers
import net.shadowfacts.cacao.window.Window

/**
 * A responder is an object which participates in the responder chain, a mechanism for propagating indirect events (i.e.
 * events for which there is no on-screen position to determine the targeted view, such as key presses) through the
 * view hierarchy.
 *
 * @author shadowfacts
 */
interface Responder {

	/**
	 * The window that this responder is part of.
	 */
	val window: Window?

	/**
	 * Whether this responder is the first responder of its window.
	 *
	 * `false` if [window] is null.
	 *
	 * @see Window.firstResponder
	 */
	val isFirstResponder: Boolean
		get() = window?.firstResponder === this

	/**
	 * The next responder in the chain after this. The next responder will receive an event if this responder did not
	 * accept it.
	 *
	 * The next responder may be `null` if this responder is at the end of the chain.
	 */
	val nextResponder: Responder?

	/**
	 * Makes this responder become the window's first responder.
	 * @throws RuntimeException if [window] is null
	 * @see Window.firstResponder
	 */
	fun becomeFirstResponder() {
		if (window == null) {
			throw RuntimeException("Cannot become first responder while not in Window")
		}
		window!!.firstResponder = this
	}

	/**
	 * Called immediately after this responder has become the window's first responder.
	 * @see Window.firstResponder
	 */
	fun didBecomeFirstResponder() {}

	/**
	 * Removes this object as the window's first responder.
	 * @throws RuntimeException if [window] is null
	 * @see Window.firstResponder
	 */
	fun resignFirstResponder() {
		if (window == null) {
			throw RuntimeException("Cannot resign first responder while not in Window")
		}
		window!!.firstResponder = null
	}

	/**
	 * Called immediately before this object is removed as the window's first responder.
	 * @see Window.firstResponder
	 */
	fun didResignFirstResponder() {}

	/**
	 * Called when a character has been typed.
	 *
	 * @param char The character that was typed.
	 * @param modifiers The key modifiers that were held down when the character was typed.
	 * @return Whether this responder accepted the event. If `true`, it will not be passed to the next responder.
	 */
	fun charTyped(char: Char, modifiers: KeyModifiers): Boolean {
		return false
	}

	/**
	 * Called when a keyboard key is pressed.
	 *
	 * If the pressed key is a typed character, [charTyped] will also be called. The order in which the methods are
	 * invoked is undefined and should not be relied upon.
	 *
	 * @param keyCode The integer code of the key that was pressed.
	 * @param modifiers The key modifiers that were held down when the character was typed.
	 * @return Whether this responder accepted the event. If `true`, it will not be passed to the next responder.
	 * @see org.lwjgl.glfw.GLFW for key code constants
	 */
	fun keyPressed(keyCode: Int, modifiers: KeyModifiers): Boolean {
		return false
	}

}