/************************************************************************************
Copyright (c) Facebook Technologies, LLC and its affiliates. All rights reserved.

Your use of this SDK or tool is subject to the Oculus SDK License Agreement, available at
https://developer.oculus.com/licenses/oculussdk/

Unless required by applicable law or agreed to in writing, the Utilities SDK distributed
under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF
ANY KIND, either express or implied. See the License for the specific language governing
permissions and limitations under the License.
************************************************************************************/
using System.Collections;
using System.Collections.Generic;
using UnityEngine;

/// <summary>
/// When attached to a GameObject with an OVROverlay component, OVROverlayMeshGenerator will use a mesh renderer
/// to preview the appearance of the OVROverlay as it would appear as a TimeWarp overlay on a headset.
/// </summary>
[RequireComponent(typeof(MeshFilter))]
[RequireComponent(typeof(MeshRenderer))]
[ExecuteInEditMode]
public class OVROverlayMeshGenerator : MonoBehaviour {

	private Mesh _Mesh;
	private List<Vector3> _Verts = new List<Vector3>();
	private List<Vector2> _UV = new List<Vector2>();
	private List<int> _Tris = new List<int>();
	private OVROverlay _Overlay;
	private MeshFilter _MeshFilter;
	private MeshCollider _MeshCollider;
	private MeshRenderer _MeshRenderer;
	private Transform _CameraRoot;
	private Transform _Transform;

	private OVROverlay.OverlayShape _LastShape;
	private Vector3 _LastPosition;
	private Quaternion _LastRotation;
	private Vector3 _LastScale;
	private Rect _LastDestRectLeft;
	private Rect _LastDestRectRight;
	private Rect _LastSrcRectLeft;
	private Texture _LastTexture;

	private bool _Awake = false;

	protected void Awake()
	{
		_MeshFilter = GetComponent<MeshFilter>();
		_MeshCollider = GetComponent<MeshCollider>();
		_MeshRenderer = GetComponent<MeshRenderer>();

		_Transform = transform;
		if (Camera.main && Camera.main.transform.parent)
		{
			_CameraRoot = Camera.main.transform.parent;
		}

		_Awake = true;
	}

	public void SetOverlay(OVROverlay overlay) {
		_Overlay = overlay;
	}

	private Rect GetBoundingRect(Rect a, Rect b)
	{
		float xMin = Mathf.Min(a.x, b.x);
		float xMax = Mathf.Max(a.x + a.width, b.x + b.width);
		float yMin = Mathf.Min(a.y, b.y);
		float yMax = Mathf.Max(a.y + a.height, b.y + b.height);

		return new Rect(xMin, yMin, xMax - xMin, yMax - yMin);
	}

	protected void OnEnable() {
		#if UNITY_EDITOR
			UnityEditor.EditorApplication.update += Update;
		#endif
	}

	protected void OnDisable() {
		#if UNITY_EDITOR
			UnityEditor.EditorApplication.update -= Update;
		#endif
	}

	private void Update()
	{
		if (!Application.isEditor)
		{
			return;
		}

		if (!_Awake)
		{
			Awake();
		}

		if (_Overlay)
		{
			OVROverlay.OverlayShape shape = _Overlay.currentOverlayShape;
			Vector3 position = _CameraRoot ? (_Transform.position - _CameraRoot.position) : _Transform.position;
			Quaternion rotation = _Transform.rotation;
			Vector3 scale = _Transform.lossyScale;
			Rect destRectLeft = _Overlay.overrideTextureRectMatrix ? _Overlay.destRectLeft : new Rect(0, 0, 1, 1);
			Rect destRectRight = _Overlay.overrideTextureRectMatrix ? _Overlay.destRectRight : new Rect(0, 0, 1, 1);
			Rect srcRectLeft = _Overlay.overrideTextureRectMatrix ? _Overlay.srcRectLeft : new Rect(0, 0, 1, 1);
			Texture texture = _Overlay.textures[0];

			// Re-generate the mesh if necessary
			if (_Mesh == null ||
			    _LastShape != shape ||
			    _LastPosition != position ||
			    _LastRotation != rotation ||
			    _LastScale != scale ||
			    _LastDestRectLeft != destRectLeft ||
			    _LastDestRectRight != destRectRight)
			{
				UpdateMesh(shape, position, rotation, scale, GetBoundingRect(destRectLeft, destRectRight));
				_LastShape = shape;
				_LastPosition = position;
				_LastRotation = rotation;
				_LastScale = scale;
				_LastDestRectLeft = destRectLeft;
				_LastDestRectRight = destRectRight;
			}

			// Generate the material and update textures if necessary
			if (_MeshRenderer.sharedMaterial == null)
			{
				Material previewMat = new Material(Shader.Find("Unlit/Transparent"));
				_MeshRenderer.sharedMaterial = previewMat;
			}

			if (_MeshRenderer.sharedMaterial.mainTexture != texture && !_Overlay.isExternalSurface)
			{
				_MeshRenderer.sharedMaterial.mainTexture = texture;
			}

			if (_LastSrcRectLeft != srcRectLeft)
			{
				_MeshRenderer.sharedMaterial.mainTextureOffset = srcRectLeft.position;
				_MeshRenderer.sharedMaterial.mainTextureScale = srcRectLeft.size;
				_LastSrcRectLeft = srcRectLeft;
			}
		}
	}

	private void UpdateMesh(OVROverlay.OverlayShape shape, Vector3 position, Quaternion rotation, Vector3 scale, Rect rect)
	{
		if (_MeshFilter)
		{
			if (_Mesh == null)
			{
				_Mesh = new Mesh() { name = "Overlay" };
				_Mesh.hideFlags = HideFlags.DontSaveInBuild | HideFlags.DontSaveInEditor;
			}
			_Mesh.Clear();
			_Verts.Clear();
			_UV.Clear();
			_Tris.Clear();

			GenerateMesh(_Verts, _UV, _Tris, shape, position, rotation, scale, rect);

			_Mesh.SetVertices(_Verts);
			_Mesh.SetUVs(0, _UV);
			_Mesh.SetTriangles(_Tris, 0);
			_Mesh.UploadMeshData(false);

			_MeshFilter.sharedMesh = _Mesh;

			if (_MeshCollider)
			{
				_MeshCollider.sharedMesh = _Mesh;
			}
		}
	}


	public static void GenerateMesh(List<Vector3> verts, List<Vector2> uvs, List<int> tris, OVROverlay.OverlayShape shape, Vector3 position, Quaternion rotation, Vector3 scale, Rect rect)
	{
		switch (shape)
		{
			case OVROverlay.OverlayShape.Equirect:
				BuildSphere(verts, uvs, tris, position, rotation, scale, rect);
				break;
			case OVROverlay.OverlayShape.Cubemap:
			case OVROverlay.OverlayShape.OffcenterCubemap:
				BuildCube(verts, uvs, tris, position, rotation, scale);
				break;
			case OVROverlay.OverlayShape.Quad:
				BuildQuad(verts, uvs, tris, rect);
				break;
			case OVROverlay.OverlayShape.Cylinder:
				BuildHemicylinder(verts, uvs, tris, scale, rect);
				break;
		}
	}

	private static Vector2 GetSphereUV(float theta, float phi, float expand_coef)
	{
		float thetaU = ((theta / (2 * Mathf.PI) - 0.5f) / expand_coef) + 0.5f;
		float phiV = ((phi / Mathf.PI) / expand_coef) + 0.5f;
		return new Vector2(thetaU, phiV);
	}

	private static Vector3 GetSphereVert(float theta, float phi)
	{
		return new Vector3(-Mathf.Sin(theta) * Mathf.Cos(phi), Mathf.Sin(phi), -Mathf.Cos(theta) * Mathf.Cos(phi));
	}

	public static void BuildSphere(List<Vector3> verts, List<Vector2> uv, List<int> triangles, Vector3 position, Quaternion rotation, Vector3 scale, Rect rect, float worldScale = 800, int latitudes = 128, int longitudes = 128, float expand_coef = 1.0f)
	{
		position = Quaternion.Inverse(rotation) * position;

		latitudes = Mathf.CeilToInt(latitudes * rect.height);
		longitudes = Mathf.CeilToInt(longitudes * rect.width);

		float minTheta = Mathf.PI * 2 * ( rect.x);
		float minPhi = Mathf.PI * (0.5f - rect.y - rect.height);

		float thetaScale = Mathf.PI * 2 * rect.width / longitudes;
		float phiScale = Mathf.PI * rect.height / latitudes;

		for (int j = 0; j < latitudes + 1; j += 1)
		{
			for (int k = 0; k < longitudes + 1; k++)
			{
				float theta = minTheta + k * thetaScale;
				float phi = minPhi + j * phiScale;

				Vector2 suv = GetSphereUV(theta, phi, expand_coef);
				uv.Add(new Vector2((suv.x - rect.x) / rect.width, (suv.y - rect.y) / rect.height));
				Vector3 vert = GetSphereVert(theta, phi);
				vert.x = (worldScale * vert.x - position.x) / scale.x;
				vert.y = (worldScale * vert.y - position.y) / scale.y;
				vert.z = (worldScale * vert.z - position.z) / scale.z;
				verts.Add(vert);
			}
		}

		for (int j = 0; j < latitudes; j++)
		{
			for (int k = 0; k < longitudes; k++)
			{
				triangles.Add((j * (longitudes + 1)) + k);
				triangles.Add(((j + 1) * (longitudes + 1)) + k);
				triangles.Add(((j + 1) * (longitudes + 1)) + k + 1);
				triangles.Add(((j + 1) * (longitudes + 1)) + k + 1);
				triangles.Add((j * (longitudes + 1)) + k + 1);
				triangles.Add((j * (longitudes + 1)) + k);
			}
		}
	}

	private enum CubeFace
	{
		Right,
		Left,
		Top,
		Bottom,
		Front,
		Back,
		COUNT
	}

	private static readonly Vector3[] BottomLeft = new Vector3[]
		{
			new Vector3(-0.5f, -0.5f, -0.5f),
			new Vector3(0.5f, -0.5f, 0.5f),
			new Vector3(0.5f, 0.5f, -0.5f),
			new Vector3(0.5f, -0.5f, 0.5f),
			new Vector3(0.5f, -0.5f, -0.5f),
			new Vector3(-0.5f, -0.5f, 0.5f)
		};

	private static readonly Vector3[] RightVector = new Vector3[]
		{
			Vector3.forward,
			Vector3.back,
			Vector3.left,
			Vector3.left,
			Vector3.left,
			Vector3.right
		};

	private static readonly Vector3[] UpVector = new Vector3[]
		{
			Vector3.up,
			Vector3.up,
			Vector3.forward,
			Vector3.back,
			Vector3.up,
			Vector3.up
		};

	private static Vector2 GetCubeUV(CubeFace face, Vector2 sideUV, float expand_coef)
	{
		sideUV = (sideUV - 0.5f * Vector2.one) / expand_coef + 0.5f * Vector2.one;
		switch (face)
		{
			case CubeFace.Bottom:
				return new Vector2(sideUV.x / 3, sideUV.y / 2);
			case CubeFace.Front:
				return new Vector2((1 + sideUV.x) / 3, sideUV.y / 2);
			case CubeFace.Back:
				return new Vector2((2 + sideUV.x) / 3, sideUV.y / 2);
			case CubeFace.Right:
				return new Vector2(sideUV.x / 3, (1 + sideUV.y) / 2);
			case CubeFace.Left:
				return new Vector2((1 + sideUV.x) / 3, (1 + sideUV.y) / 2);
			case CubeFace.Top:
				return new Vector2((2 + sideUV.x) / 3, (1 + sideUV.y) / 2);
			default:
				return Vector2.zero;
		}
	}

	private static Vector3 GetCubeVert(CubeFace face, Vector2 sideUV, float expand_coef)
	{
		return BottomLeft[(int)face] + sideUV.x * RightVector[(int)face] + sideUV.y * UpVector[(int)face];
	}

	public static void BuildCube(List<Vector3> verts, List<Vector2> uv, List<int> triangles, Vector3 position, Quaternion rotation, Vector3 scale, float worldScale = 800, int subQuads = 1, float expand_coef = 1.01f)
	{
		position = Quaternion.Inverse(rotation) * position;

		int vertsPerSide = (subQuads + 1) * (subQuads + 1);

		for (int i = 0; i < (int)CubeFace.COUNT; i++)
		{
			for(int j = 0; j < subQuads + 1; j++)
			{
				for(int k = 0; k < subQuads + 1; k++)
				{
					float u = j / (float)subQuads;
					float v = k / (float)subQuads;

					uv.Add(GetCubeUV((CubeFace)i, new Vector2(u, v), expand_coef));
					Vector3 vert = GetCubeVert((CubeFace)i, new Vector2(u, v), expand_coef);
					vert.x = (worldScale * vert.x - position.x) / scale.x;
					vert.y = (worldScale * vert.y - position.y) / scale.y;
					vert.z = (worldScale * vert.z - position.z) / scale.z;
					verts.Add(vert);
				}
			}

			for(int j = 0; j < subQuads; j++)
			{
				for(int k = 0; k < subQuads; k++)
				{
					triangles.Add(vertsPerSide * i + ((j + 1) * (subQuads + 1)) + k);
					triangles.Add(vertsPerSide * i + (j * (subQuads + 1)) + k);
					triangles.Add(vertsPerSide * i + ((j + 1) * (subQuads + 1)) + k + 1);
					triangles.Add(vertsPerSide * i + ((j + 1) * (subQuads + 1)) + k + 1);
					triangles.Add(vertsPerSide * i + (j * (subQuads + 1)) + k);
					triangles.Add(vertsPerSide * i + (j * (subQuads + 1)) + k + 1);
				}
			}
		}
	}


	public static void BuildQuad(List<Vector3> verts, List<Vector2> uv, List<int> triangles, Rect rect)
	{
		verts.Add(new Vector3(rect.x - 0.5f, (1 - rect.y - rect.height) - 0.5f, 0));
		verts.Add(new Vector3(rect.x - 0.5f, (1 - rect.y) - 0.5f, 0));
		verts.Add(new Vector3(rect.x + rect.width - 0.5f, (1 - rect.y) - 0.5f, 0));
		verts.Add(new Vector3(rect.x + rect.width - 0.5f, (1 - rect.y - rect.height) - 0.5f, 0));

		uv.Add(new Vector2(0, 0));
		uv.Add(new Vector2(0, 1));
		uv.Add(new Vector2(1, 1));
		uv.Add(new Vector2(1, 0));

		triangles.Add(0);
		triangles.Add(1);
		triangles.Add(2);
		triangles.Add(2);
		triangles.Add(3);
		triangles.Add(0);
	}

	public static void BuildHemicylinder(List<Vector3> verts, List<Vector2> uv, List<int> triangles, Vector3 scale, Rect rect, int longitudes = 128)
	{
		float height = Mathf.Abs(scale.y) * rect.height;
		float radius = scale.z;
		float arcLength = scale.x * rect.width;

		float arcAngle = arcLength / radius;
		float minAngle = scale.x * (-0.5f + rect.x) / radius;

		int columns = Mathf.CeilToInt(longitudes * arcAngle / (2 * Mathf.PI));

		// we don't want super tall skinny triangles because that can lead to artifacting.
		// make triangles no more than 2x taller than wide

		float triangleWidth = arcLength / columns;
		float ratio = height / triangleWidth;

		int rows = Mathf.CeilToInt(ratio / 2);

		for (int j = 0; j < rows + 1; j += 1)
		{
			for (int k = 0; k < columns + 1; k++)
			{
				uv.Add(new Vector2((k / (float)columns), 1 - (j / (float)rows)));

				Vector3 vert = Vector3.zero;
				// because the scale is used to control the parameters, we need
				// to reverse multiply by scale to appear correctly
				vert.x = (Mathf.Sin(minAngle + (k * arcAngle / columns)) * radius) / scale.x;

				vert.y = (0.5f - rect.y - rect.height + rect.height * (1 - j / (float)rows));
				vert.z = (Mathf.Cos(minAngle + (k * arcAngle / columns)) * radius) / scale.z;
				verts.Add(vert);
			}
		}

		for (int j = 0; j < rows; j++)
		{
			for (int k = 0; k < columns; k++)
			{
				triangles.Add((j * (columns + 1)) + k);
				triangles.Add(((j + 1) * (columns + 1)) + k + 1);
				triangles.Add(((j + 1) * (columns + 1)) + k);
				triangles.Add(((j + 1) * (columns + 1)) + k + 1);
				triangles.Add((j * (columns + 1)) + k);
				triangles.Add((j * (columns + 1)) + k + 1);
			}
		}
	}
}