using System;
using System.Collections.Generic;
using UnityEngine;
#if UNITY_2017_2_OR_NEWER
using UnityEngine.XR;
#endif

namespace ZenFulcrum.EmbeddedBrowser {

/// <summary>
/// Base class that handles input for mouse/touch/pointer/VR/nose inputs.
/// The concept is thus:
///   You have an arbitrary number of 3D (FPS player, VR pointer, and world ray) and
///   2D (mouse, touch, and screen position) pointers and you want any of them
///   to be able to interact with the Browser.
/// 
/// Concrete implementations of this class handle interacting with different rendered mediums
/// (such as a mesh or a GUI renderer).
/// </summary>
[RequireComponent(typeof(Browser))]
public abstract class PointerUIBase : MonoBehaviour, IBrowserUI {
	public readonly KeyEvents keyEvents = new KeyEvents();


	protected Browser browser;
	protected bool appFocused = true;

	/// <summary>
	/// Called once per tick. Handlers registered here should look at the pointers they have
	/// and tell us about them.
	/// </summary>
	public event Action onHandlePointers = () => {};

	protected int currentPointerId;

	protected readonly List<PointerState> currentPointers = new List<PointerState>();

	[Tooltip(
		"When clicking, how far (in browser-space pixels) must the cursor be moved before we send this movement to the browser backend? " +
		"This helps keep us from unintentionally dragging when we meant to just click, esp. under VR where it's hard to hold the cursor still."
	)]
	public float dragMovementThreshold = 0;
	/// <summary>
	/// Cursor location when we most recently went from 0 buttons to any buttons down.
	/// </summary>
	protected Vector2 mouseDownPosition;
	/// <summary>
	/// True when we have the any mouse button down AND we've moved at least dragMovementThreshold after that.
	/// </summary>
	protected bool dragging = false;

#region Pointer Core

	public struct PointerState {
		/// <summary>
		/// Unique value for this pointer, to distinguish it by. Must be > 0.
		/// </summary>
		public int id;
		/// <summary>
		/// Is the pointer a 2d or 3d pointer?
		/// </summary>
		public bool is2D;
		public Vector2 position2D;
		public Ray position3D;
		/// <summary>
		/// Currently depressed "buttons" on this pointer.
		/// </summary>
		public MouseButton activeButtons;
		/// <summary>
		/// If the pointer can scroll, delta scrolling values since last frame.
		/// </summary>
		public Vector2 scrollDelta;
	}

	/// <summary>
	/// Called when the browser gets clicked with any mouse button.
	/// (More precisely, when we go from having no buttons down to 1+ buttons down.)
	/// </summary>
	public event Action onClick = () => {};


	public virtual void Awake() {
		BrowserCursor = new BrowserCursor();
		BrowserCursor.cursorChange += CursorUpdated;

		InputSettings = new BrowserInputSettings();

		browser = GetComponent<Browser>();
		browser.UIHandler = this;


		onHandlePointers += OnHandlePointers;

		if (disableMouseEmulation) Input.simulateMouseWithTouches = false;
	}

	public virtual void InputUpdate() {
		keyEvents.InputUpdate();

		p_currentDown = p_anyDown = p_currentOver = p_anyOver = -1;
		currentPointers.Clear();

		onHandlePointers();

		CalculatePointer();
	}

	public void OnApplicationFocus(bool focused) {
		appFocused = focused;
	}


	/// <summary>
	/// Converts a 2D screen-space coordinate to browser-space coordinates.
	/// If the given point doesn't map to the browser, return float.NaN for the position.
	/// </summary>
	/// <param name="screenPosition"></param>
	/// <param name="pointerId"></param>
	/// <returns></returns>
	protected abstract Vector2 MapPointerToBrowser(Vector2 screenPosition, int pointerId);

	/// <summary>
	/// Converts a 3D world-space ray to a browser-space coordinate.
	/// If the given ray doesn't map to the browser, return float.NaN for the position.
	/// </summary>
	/// <param name="worldRay"></param>
	/// <param name="pointerId"></param>
	/// <returns></returns>
	protected abstract Vector2 MapRayToBrowser(Ray worldRay, int pointerId);

	/// <summary>
	/// Returns the current position+rotation of the active pointer in world space.
	/// If there is none, or it doesn't make sense to map to world space, position will
	/// be NaNs.
	/// 
	/// Coordinates are in world space. The rotation should point up in the direction the browser sees as up.
	/// Z+ should go "into" the browser surface.
	/// </summary>
	/// <param name="pos"></param>
	/// <param name="rot"></param>
	public abstract void GetCurrentHitLocation(out Vector3 pos, out Quaternion rot);

	/** Indexes into currentPointers for useful items this frame. -1 if N/A. */
	protected int p_currentDown, p_anyDown, p_currentOver, p_anyOver;

	/// <summary>
	/// Feeds the state of the given pointer into the handler.
	/// </summary>
	/// <param name="state"></param>
	public virtual void FeedPointerState(PointerState state) {
		if (state.is2D) state.position2D = MapPointerToBrowser(state.position2D, state.id);
		else {
			Debug.DrawRay(state.position3D.origin, state.position3D.direction * (Mathf.Min(500, maxDistance)), Color.cyan);
			state.position2D = MapRayToBrowser(state.position3D, state.id);
			//Debug.Log("Pointer " + state.id + " at " + state.position3D.origin + " pointing " + state.position3D.direction + " maps to  " + state.position2D);
		}

		if (float.IsNaN(state.position2D.x)) return;

		if (state.id == currentPointerId) {
			p_currentOver = currentPointers.Count;

			if (state.activeButtons != 0) p_currentDown = currentPointers.Count;
		} else {
			p_anyOver = currentPointers.Count;

			if (state.activeButtons != 0) p_anyDown = currentPointers.Count;
		}

		currentPointers.Add(state);
	}

	protected virtual void CalculatePointer() {
//		if (!appFocused) {
//			MouseIsOff();
//			return;
//		}

		/*
		 * The position/priority we feed to the browser is determined in this order:
		 *   - Pointer we used earlier with a button down
		 *   - Pointer with a button down
		 *   - Pointer we used earlier 
		 *   - Any pointer that is over the browser
		 * Pointers that aren't over the browser are ignored.
		 * If multiple pointers meet the criteria we may pick any that qualify.
		 */

		PointerState stateToUse;
		if (p_currentDown >= 0) {
			//last frame's pointer with a button down
			stateToUse = currentPointers[p_currentDown];
		} else if (p_anyDown >= 0) {
			//mouse button count became > 0 this frame
			stateToUse = currentPointers[p_anyDown];
		} else if (p_currentOver >= 0) {
			//just hovering (use the pointer from last frame)
			stateToUse = currentPointers[p_currentOver];
		} else if (p_anyOver >= 0) {
			//just hovering (use any pointer over us)
			stateToUse = currentPointers[p_anyOver];
		} else {
			//no pointers over us
			MouseIsOff();
			return;
		}

		MouseIsOver();

		if (MouseButtons == 0 && stateToUse.activeButtons != 0) {
			//no buttons -> 1+ buttons
			onClick();
			//start drag prevention
			dragging = false;
			mouseDownPosition = stateToUse.position2D;
		}

		if (float.IsNaN(stateToUse.position2D.x)) Debug.LogError("Using an invalid pointer");// "shouldn't happen"

		if (stateToUse.activeButtons != 0 || MouseButtons != 0) {
			//Button(s) held or being released, do some extra logic to prevent unintentional dragging during clicks.

			if (!dragging && stateToUse.activeButtons != 0) {//only check distance if buttons(s) held and not already dragging
				//Check to see if we passed the drag threshold.
				var size = browser.Size;
				var distance = Vector2.Distance(
					Vector2.Scale(stateToUse.position2D, size),//convert from [0, 1] to pixels
					Vector2.Scale(mouseDownPosition, size)//convert from [0, 1] to pixels
				);

				if (distance > dragMovementThreshold) {
					dragging = true;
				}
			}

			if (dragging) MousePosition = stateToUse.position2D;
			else MousePosition = mouseDownPosition;
		} else {
			//no buttons held (or being release), no need to fiddle with the position
			MousePosition = stateToUse.position2D;
		}

		MouseButtons = stateToUse.activeButtons;
		MouseScroll = stateToUse.scrollDelta;
		currentPointerId = stateToUse.id;
	}


	public void OnGUI() {
		keyEvents.Feed(Event.current);
	}

	protected bool mouseWasOver = false;
	protected void MouseIsOver() {
		MouseHasFocus = true;
		KeyboardHasFocus = true;

		if (BrowserCursor != null) {
			CursorUpdated();
		}

		mouseWasOver = true;
	}

	protected void MouseIsOff() {
//		if (BrowserCursor != null && mouseWasOver) {
//			SetCursor(null);
//		}
		mouseWasOver = false;

		MouseHasFocus = false;
		if (focusForceCount <= 0) KeyboardHasFocus = false;
		MouseButtons = 0;
		MouseScroll = Vector2.zero;

		currentPointerId = 0;
	}

	protected void CursorUpdated() {
//		SetCursor(BrowserCursor);
	}

	private int focusForceCount = 0;

	/// <summary>
	/// Sets a flag to keep the keyboard focus on this browser, even if it has no pointers.
	/// Useful for focusing it to type things in via external keyboard.
	/// 
	/// Call again with force = false to return to the default behavior. (You must call force
	/// on and force off an equal number of times to revert to the default behavior.)
	/// 
	/// </summary>
	/// <param name="force"></param>
	public void ForceKeyboardHasFocus(bool force) {
		if (force) ++focusForceCount;
		else --focusForceCount;
		if (focusForceCount == 1) KeyboardHasFocus = true;
		else if (focusForceCount == 0) KeyboardHasFocus = false;
	}

#endregion

#region Input Handlers

	[Tooltip("Camera to use to interpret 2D inputs and to originate FPS rays from. Defaults to Camera.main.")]
	public Camera viewCamera;

	public bool enableMouseInput = true;
	public bool enableTouchInput = true;
	public bool enableFPSInput = false;
	public bool enableVRInput = false;

	[Tooltip("(For ray-based interaction) How close must you be to the browser to be able to interact with it?")]
	public float maxDistance = float.PositiveInfinity;

	[Space(5)]
	[Tooltip("Disable Input.simulateMouseWithTouches globally. This will prevent touches from appearing as mouse events.")]
	public bool disableMouseEmulation = false;

	protected virtual void OnHandlePointers() {
		if (enableFPSInput) FeedFPS();

		//special case to avoid duplicate pointer from the first touch (ignore mouse)
		if (enableMouseInput && enableTouchInput && Input.simulateMouseWithTouches && Input.touchCount > 0) {
			FeedTouchPointers();
			return;
		}

		if (enableMouseInput) FeedMousePointer();
		if (enableTouchInput) FeedTouchPointers();
		#if UNITY_2017_2_OR_NEWER
			if (enableVRInput) FeedVRPointers();
		#endif
	}

	/// <summary>
	/// Calls FeedPointerState with all the items in Input.touches.
	/// (Does not happen automatically, call when desired.)
	/// </summary>
	protected virtual void FeedTouchPointers() {
		for (int i = 0; i < Input.touchCount; i++) {
			var touch = Input.GetTouch(i);

			FeedPointerState(new PointerState {
				id = 10 + touch.fingerId,
				is2D = true,
				position2D = touch.position,
				activeButtons = (touch.phase == TouchPhase.Began || touch.phase == TouchPhase.Moved || touch.phase == TouchPhase.Stationary) ? MouseButton.Left : 0,
			});
		}
	}

	/// <summary>
	/// Calls FeedPointerState with the current mouse state.
	/// (Does not happen automatically, call when desired.)
	/// </summary>
	protected virtual void FeedMousePointer() {
		var buttons = (MouseButton)0;
		if (Input.GetMouseButton(0)) buttons |= MouseButton.Left;
		if (Input.GetMouseButton(1)) buttons |= MouseButton.Right;
		if (Input.GetMouseButton(2)) buttons |= MouseButton.Middle;

		FeedPointerState(new PointerState {
			id = 1,
			is2D = true,
			position2D = Input.mousePosition,
			activeButtons = buttons,
			scrollDelta = Input.mouseScrollDelta,
		});
	}


	protected virtual void FeedFPS() {
		var buttons =
			(Input.GetButton("Fire1") ? MouseButton.Left : 0) |
			(Input.GetButton("Fire2") ? MouseButton.Right : 0) |
			(Input.GetButton("Fire3") ? MouseButton.Middle : 0)
		;

		var camera = viewCamera ? viewCamera : Camera.main;

		var scrollDelta = Input.mouseScrollDelta;

		//Don't double-count scrolling if we are processing the mouse too.
		if (enableMouseInput) scrollDelta = Vector2.zero;

		FeedPointerState(new PointerState {
			id = 2,
			is2D = false,
			position3D = new Ray(camera.transform.position, camera.transform.forward),
			activeButtons = buttons,
			scrollDelta = scrollDelta,
		});
	}

#if UNITY_2017_2_OR_NEWER
	protected VRBrowserHand[] vrHands = null;
	protected virtual void FeedVRPointers() {
		if (vrHands == null) {
			vrHands = FindObjectsOfType<VRBrowserHand>();
			if (vrHands.Length == 0 && XRSettings.enabled) {
				Debug.LogWarning("VR input is enabled, but no VRBrowserHands were found in the scene", this);
			}
		}

		for (int i = 0; i < vrHands.Length; i++) {
			if (!vrHands[i].Tracked) continue;

			FeedPointerState(new PointerState {
				id = 100 + i,
				is2D = false,
				position3D = new Ray(vrHands[i].transform.position, vrHands[i].transform.forward),
				activeButtons = vrHands[i].DepressedButtons,
				scrollDelta = vrHands[i].ScrollDelta,
			});
		}

	}
#endif

#endregion

	public virtual bool MouseHasFocus { get; protected set; }
	public virtual Vector2 MousePosition { get; protected set; }
	public virtual MouseButton MouseButtons { get; protected set; }
	public virtual Vector2 MouseScroll { get; protected set; }
	public virtual bool KeyboardHasFocus { get; protected set; }
	public virtual List<Event> KeyEvents { get { return keyEvents.Events; } }
	public virtual BrowserCursor BrowserCursor { get; protected set; }
	public virtual BrowserInputSettings InputSettings { get; protected set; }

}

}