using UnityEditor;
using UnityEngine;
using UnityEngine.EventSystems;
using UnityEngine.UI;

namespace UiParticles.Editor
{
	/// <summary>
	/// Add Particle System to UI menu option to the Unity Editor
	/// </summary>
	public class MenuOption 
	{

		[MenuItem("GameObject/UI/Particle System", false, 2101)]
		public static void AddScrollView(MenuCommand menuCommand)
		{
			GameObject gameObject = new GameObject("Particle System");
			gameObject.AddComponent<RectTransform>().sizeDelta = new Vector2(100f, 100f);
			gameObject.AddComponent<UiParticles>();
			PlaceUIElementRoot(gameObject, menuCommand);
		}
		
		// ReSharper disable once InconsistentNaming
		private static void PlaceUIElementRoot(GameObject element, MenuCommand menuCommand)
		{
			GameObject parent = menuCommand.context as GameObject;
			if (parent == null || parent.GetComponentInParent<Canvas>() == null)
			{
				parent = GetOrCreateCanvasGameObject();
			}
			string uniqueName = GameObjectUtility.GetUniqueNameForSibling(parent.transform, element.name);
			element.name = uniqueName;
			Undo.RegisterCreatedObjectUndo(element, "Create " + element.name);
			Undo.SetTransformParent(element.transform, parent.transform, "Parent " + element.name);
			GameObjectUtility.SetParentAndAlign(element, parent);
			if (parent != menuCommand.context) // not a context click, so center in sceneview
				SetPositionVisibleinSceneView(parent.GetComponent<RectTransform>(), element.GetComponent<RectTransform>());

			Selection.activeGameObject = element;
		}
		
		
		private static GameObject GetOrCreateCanvasGameObject()
		{
			GameObject selectedGo = Selection.activeGameObject;

			// Try to find a gameobject that is the selected GO or one if its parents.
			Canvas canvas = (selectedGo != null) ? selectedGo.GetComponentInParent<Canvas>() : null;
			if (canvas != null && canvas.gameObject.activeInHierarchy)
				return canvas.gameObject;

			// No canvas in selection or its parents? Then use just any canvas..
			canvas = Object.FindObjectOfType(typeof(Canvas)) as Canvas;
			if (canvas != null && canvas.gameObject.activeInHierarchy)
				return canvas.gameObject;

			// No canvas in the scene at all? Then create a new one.
			return CreateNewUI();
		}
		
		private static void SetPositionVisibleinSceneView(RectTransform canvasRTransform, RectTransform itemTransform)
		{
			// Find the best scene view
			SceneView sceneView = SceneView.lastActiveSceneView;
			if (sceneView == null && SceneView.sceneViews.Count > 0)
				sceneView = SceneView.sceneViews[0] as SceneView;

			// Couldn't find a SceneView. Don't set position.
			if (sceneView == null || sceneView.camera == null)
				return;

			// Create world space Plane from canvas position.
			Vector2 localPlanePosition;
			Camera camera = sceneView.camera;
			Vector3 position = Vector3.zero;
			if (RectTransformUtility.ScreenPointToLocalPointInRectangle(canvasRTransform, new Vector2(camera.pixelWidth / 2f, camera.pixelHeight / 2f), camera, out localPlanePosition))
			{
				// Adjust for canvas pivot
				localPlanePosition.x = localPlanePosition.x + canvasRTransform.sizeDelta.x * canvasRTransform.pivot.x;
				localPlanePosition.y = localPlanePosition.y + canvasRTransform.sizeDelta.y * canvasRTransform.pivot.y;

				localPlanePosition.x = Mathf.Clamp(localPlanePosition.x, 0, canvasRTransform.sizeDelta.x);
				localPlanePosition.y = Mathf.Clamp(localPlanePosition.y, 0, canvasRTransform.sizeDelta.y);

				// Adjust for anchoring
				position.x = localPlanePosition.x - canvasRTransform.sizeDelta.x * itemTransform.anchorMin.x;
				position.y = localPlanePosition.y - canvasRTransform.sizeDelta.y * itemTransform.anchorMin.y;

				Vector3 minLocalPosition;
				minLocalPosition.x = canvasRTransform.sizeDelta.x * (0 - canvasRTransform.pivot.x) + itemTransform.sizeDelta.x * itemTransform.pivot.x;
				minLocalPosition.y = canvasRTransform.sizeDelta.y * (0 - canvasRTransform.pivot.y) + itemTransform.sizeDelta.y * itemTransform.pivot.y;

				Vector3 maxLocalPosition;
				maxLocalPosition.x = canvasRTransform.sizeDelta.x * (1 - canvasRTransform.pivot.x) - itemTransform.sizeDelta.x * itemTransform.pivot.x;
				maxLocalPosition.y = canvasRTransform.sizeDelta.y * (1 - canvasRTransform.pivot.y) - itemTransform.sizeDelta.y * itemTransform.pivot.y;

				position.x = Mathf.Clamp(position.x, minLocalPosition.x, maxLocalPosition.x);
				position.y = Mathf.Clamp(position.y, minLocalPosition.y, maxLocalPosition.y);
			}

			itemTransform.anchoredPosition = position;
			itemTransform.localRotation = Quaternion.identity;
			itemTransform.localScale = Vector3.one;
		}
		
		// ReSharper disable once InconsistentNaming
		private static GameObject CreateNewUI()
		{
			// Root for the UI
			var root = new GameObject("Canvas")
			{
				layer = LayerMask.NameToLayer("UI")
			};
			Canvas canvas = root.AddComponent<Canvas>();
			canvas.renderMode = RenderMode.ScreenSpaceOverlay;
			root.AddComponent<CanvasScaler>();
			root.AddComponent<GraphicRaycaster>();
			Undo.RegisterCreatedObjectUndo(root, "Create " + root.name);

			// if there is no event system add one...
			CreateEventSystem(false);
			return root;
		}

		private static void CreateEventSystem(bool select, GameObject parent = null)
		{
			var esys = Object.FindObjectOfType<EventSystem>();
			if (esys == null)
			{
				var eventSystem = new GameObject("EventSystem");
				GameObjectUtility.SetParentAndAlign(eventSystem, parent);
				esys = eventSystem.AddComponent<EventSystem>();
				eventSystem.AddComponent<StandaloneInputModule>();
				Undo.RegisterCreatedObjectUndo(eventSystem, "Create " + eventSystem.name);
			}

			if (select && esys != null)
			{
				Selection.activeGameObject = esys.gameObject;
			}
		}
	}
}
