using System.Collections;
using System.Collections.Generic;
using UnityEngine;

[ExecuteInEditMode]
public class CelestialBodyGenerator : MonoBehaviour {

	public enum PreviewMode { LOD0, LOD1, LOD2 }
	public ResolutionSettings resolutionSettings;
	public PreviewMode previewMode;

	public bool logTimers;

	public CelestialBodySettings body;

	bool debugDoubleUpdate = true;
	int debug_numUpdates;

	// Private variables
	Mesh previewMesh;
	Mesh[] lodMeshes;

	ComputeBuffer vertexBuffer;

	bool shapeSettingsUpdated;
	bool shadingNoiseSettingsUpdated;
	Camera cam;

	Vector2 heightMinMax;

	// Game mode data 
	int activeLODIndex = -1;
	MeshFilter terrainMeshFilter;
	Material terrainMatInstance;

	static Dictionary<int, SphereMesh> sphereGenerators;

	void Start () {
		if (InGameMode) {
			cam = Camera.main;
			HandleGameModeGeneration ();
		}
	}

	void Update () {
		if (InEditMode) {
			HandleEditModeGeneration ();
		}
	}

	// Handles creation of celestial body when entering game mode
	// This differs from the edit-mode version in the following ways:
	// • creates all LOD meshes and stores them in mesh array (to be picked based on player position)
	// • creates its own instances of materials so multiple bodies can exist with their own shading
	// • doesn't support updating of shape/shading values once generated
	void HandleGameModeGeneration () {
		if (CanGenerateMesh ()) {
			Dummy ();

			// Generate LOD meshes
			lodMeshes = new Mesh[ResolutionSettings.numLODLevels];
			for (int i = 0; i < lodMeshes.Length; i++) {
				Vector2 lodTerrainHeightMinMax = GenerateTerrainMesh (ref lodMeshes[i], resolutionSettings.GetLODResolution (i));
				// Use min/max height of first (most detailed) LOD
				if (i == 0) {
					heightMinMax = lodTerrainHeightMinMax;
				}
			}

			// Create terrain renderer and set shading properties on the instanced material
			terrainMatInstance = new Material (body.shading.terrainMaterial);
			body.shading.Initialize (body.shape);
			body.shading.SetTerrainProperties (terrainMatInstance, heightMinMax, BodyScale);
			GameObject terrainHolder = GetOrCreateMeshObject ("Terrain Mesh", null, terrainMatInstance);
			terrainMeshFilter = terrainHolder.GetComponent<MeshFilter> ();

		} else {
			Debug.Log ("Could not generate mesh");
		}

		ReleaseAllBuffers ();
	}

	// Handles creation of celestial body in the editor
	// This allows for updating the shape/shading settings
	void HandleEditModeGeneration () {
		if (InEditMode) {
			ComputeHelper.shouldReleaseEditModeBuffers -= ReleaseAllBuffers;
			ComputeHelper.shouldReleaseEditModeBuffers += ReleaseAllBuffers;
		}

		if (CanGenerateMesh ()) {
			// Update shape settings and shading noise
			if (shapeSettingsUpdated) {
				shapeSettingsUpdated = false;
				shadingNoiseSettingsUpdated = false;
				Dummy ();

				var terrainMeshTimer = System.Diagnostics.Stopwatch.StartNew ();
				heightMinMax = GenerateTerrainMesh (ref previewMesh, PickTerrainRes ());

				LogTimer (terrainMeshTimer, "Generate terrain mesh");
				DrawEditModeMesh ();
			}
			// If only shading noise has changed, update it separately from shape to save time
			else if (shadingNoiseSettingsUpdated) {
				shadingNoiseSettingsUpdated = false;
				ComputeHelper.CreateStructuredBuffer<Vector3> (ref vertexBuffer, previewMesh.vertices);
				body.shading.Initialize (body.shape);
				Vector4[] shadingData = body.shading.GenerateShadingData (vertexBuffer);
				previewMesh.SetUVs (0, shadingData);

				// Sometimes when changing a colour property, invalid data is returned from compute shader
				// Running the shading a second time fixes it.
				// Not sure if this is my bug, or Unity's (TODO: investigate)
				debug_numUpdates++;
				if (debugDoubleUpdate && debug_numUpdates < 2) {
					shadingNoiseSettingsUpdated = true;
					HandleEditModeGeneration ();
				}
				if (debug_numUpdates == 2) {
					debug_numUpdates = 0;
				}

			}
		}

		// Update shading
		if (body && body.shading) {
			// Set material properties
			body.shading.Initialize (body.shape);
			body.shading.SetTerrainProperties (body.shading.terrainMaterial, heightMinMax, BodyScale);
		}

		ReleaseAllBuffers (); //
	}

	public void SetLOD (int lodIndex) {
		if (lodIndex != activeLODIndex && terrainMeshFilter) {
			activeLODIndex = lodIndex;
			terrainMeshFilter.sharedMesh = lodMeshes[lodIndex];
		}
	}

	public void OnShapeSettingChanged () {
		shapeSettingsUpdated = true;
	}

	public void OnShadingNoiseSettingChanged () {
		shadingNoiseSettingsUpdated = true;
	}

	void OnValidate () {
		if (body) {
			if (body.shape) {
				body.shape.OnSettingChanged -= OnShapeSettingChanged;
				body.shape.OnSettingChanged += OnShapeSettingChanged;
			}
			if (body.shading) {
				body.shading.OnSettingChanged -= OnShadingNoiseSettingChanged;
				body.shading.OnSettingChanged += OnShadingNoiseSettingChanged;
			}
		}

		if (resolutionSettings != null) {
			resolutionSettings.ClampResolutions ();
		}
		OnShapeSettingChanged ();
	}

	void Dummy () {
		// Crude fix for a problem I was having where the values in the vertex buffer were *occasionally* all zero at start of game
		// This function runs the compute shader once with single dummy input, after which it seems the problem doesn't occur
		// (Waiting until Time.frameCount > 3 before generating is another gross hack that seems to fix the problem)
		// I don't know why...
		Vector3[] vertices = new Vector3[] { Vector3.zero };
		ComputeHelper.CreateStructuredBuffer<Vector3> (ref vertexBuffer, vertices);
		body.shape.CalculateHeights (vertexBuffer);
	}

	// Generates terrain mesh based on heights generated by the Shape object
	// Shading data from the Shading object is stored in the mesh uvs
	// Returns the min/max height of the terrain
	Vector2 GenerateTerrainMesh (ref Mesh mesh, int resolution) {
		var (vertices, triangles) = CreateSphereVertsAndTris (resolution);
		ComputeHelper.CreateStructuredBuffer<Vector3> (ref vertexBuffer, vertices);

		float edgeLength = (vertices[triangles[0]] - vertices[triangles[1]]).magnitude;

		// Set heights
		float[] heights = body.shape.CalculateHeights (vertexBuffer);

		// Perturb vertices to give terrain a less perfectly smooth appearance
		if (body.shape.perturbVertices && body.shape.perturbCompute) {
			ComputeShader perturbShader = body.shape.perturbCompute;
			float maxperturbStrength = body.shape.perturbStrength * edgeLength / 2;

			perturbShader.SetBuffer (0, "points", vertexBuffer);
			perturbShader.SetInt ("numPoints", vertices.Length);
			perturbShader.SetFloat ("maxStrength", maxperturbStrength);

			ComputeHelper.Run (perturbShader, vertices.Length);
			Vector3[] pertData = new Vector3[vertices.Length];
			vertexBuffer.GetData (vertices);
		}

		// Calculate terrain min/max height and set heights of vertices
		float minHeight = float.PositiveInfinity;
		float maxHeight = float.NegativeInfinity;
		for (int i = 0; i < heights.Length; i++) {
			float height = heights[i];
			vertices[i] *= height;
			minHeight = Mathf.Min (minHeight, height);
			maxHeight = Mathf.Max (maxHeight, height);
		}

		// Create mesh
		CreateMesh (ref mesh, vertices.Length);
		mesh.SetVertices (vertices);
		mesh.SetTriangles (triangles, 0, true);
		mesh.RecalculateNormals (); //

		// Shading noise data
		body.shading.Initialize (body.shape);
		Vector4[] shadingData = body.shading.GenerateShadingData (vertexBuffer);
		mesh.SetUVs (0, shadingData);

		// Create crude tangents (vectors perpendicular to surface normal)
		// This is needed (even though normal mapping is being done with triplanar)
		// because surfaceshader wants normals in tangent space
		var normals = mesh.normals;
		var crudeTangents = new Vector4[mesh.vertices.Length];
		for (int i = 0; i < vertices.Length; i++) {
			Vector3 normal = normals[i];
			crudeTangents[i] = new Vector4 (-normal.z, 0, normal.x, 1);
		}
		mesh.SetTangents (crudeTangents);

		return new Vector2 (minHeight, maxHeight);
	}

	void CreateMesh (ref Mesh mesh, int numVertices) {
		const int vertexLimit16Bit = 1 << 16 - 1; // 65535
		if (mesh == null) {
			mesh = new Mesh ();
		} else {
			mesh.Clear ();
		}
		mesh.indexFormat = (numVertices < vertexLimit16Bit) ? UnityEngine.Rendering.IndexFormat.UInt16 : UnityEngine.Rendering.IndexFormat.UInt32;
	}

	void DrawEditModeMesh () {
		GameObject terrainHolder = GetOrCreateMeshObject ("Terrain Mesh", previewMesh, body.shading.terrainMaterial);
	}

	// Gets child object with specified name.
	// If it doesn't exist, then creates object with that name, adds mesh renderer/filter and attaches mesh and material
	GameObject GetOrCreateMeshObject (string name, Mesh mesh, Material material) {
		// Find/create object
		var child = transform.Find (name);
		if (!child) {
			child = new GameObject (name).transform;
			child.parent = transform;
			child.localPosition = Vector3.zero;
			child.localRotation = Quaternion.identity;
			child.localScale = Vector3.one;
			child.gameObject.layer = gameObject.layer;
		}

		// Add mesh components
		MeshFilter filter;
		if (!child.TryGetComponent<MeshFilter> (out filter)) {
			filter = child.gameObject.AddComponent<MeshFilter> ();
		}
		filter.sharedMesh = mesh;

		MeshRenderer renderer;
		if (!child.TryGetComponent<MeshRenderer> (out renderer)) {
			renderer = child.gameObject.AddComponent<MeshRenderer> ();
		}
		renderer.sharedMaterial = material;

		return child.gameObject;
	}

	public int PickTerrainRes () {
		if (!Application.isPlaying) {
			switch (previewMode) {
				case PreviewMode.LOD0:
					return resolutionSettings.lod0;
				case PreviewMode.LOD1:
					return resolutionSettings.lod1;
				case PreviewMode.LOD2:
					return resolutionSettings.lod2;
			}
		}

		return 0;

	}

	// Radius of the ocean (0 if no ocean exists)
	// public float GetOceanRadius () {
	// 	if (!body.shading.hasOcean) {
	// 		return 0;
	// 	}
	// 	return UnscaledOceanRadius * BodyScale;
	// }

	// float UnscaledOceanRadius {
	// 	get {
	// 		return Mathf.Lerp (heightMinMax.x, 1, body.shading.oceanLevel);
	// 	}
	// }

	public float BodyScale {
		get {
			// Body radius is determined by the celestial body class,
			// which sets the local scale of the generator object (this object)
			return transform.localScale.x;
		}
	}

	// Generate sphere (or reuse if already generated) and return a copy of the vertices and triangles
	(Vector3[] vertices, int[] triangles) CreateSphereVertsAndTris (int resolution) {
		if (sphereGenerators == null) {
			sphereGenerators = new Dictionary<int, SphereMesh> ();
		}

		if (!sphereGenerators.ContainsKey (resolution)) {
			sphereGenerators.Add (resolution, new SphereMesh (resolution));
		}

		var generator = sphereGenerators[resolution];

		var vertices = new Vector3[generator.Vertices.Length];
		var triangles = new int[generator.Triangles.Length];
		System.Array.Copy (generator.Vertices, vertices, vertices.Length);
		System.Array.Copy (generator.Triangles, triangles, triangles.Length);
		return (vertices, triangles);
	}

	void ReleaseAllBuffers () {
		ComputeHelper.Release (vertexBuffer);
		if (body && body.shape) {
			body.shape.ReleaseBuffers ();
		}
		if (body && body.shading) {
			body.shading.ReleaseBuffers ();
		}
	}

	void OnDestroy () {
		ReleaseAllBuffers ();
	}

	bool CanGenerateMesh () {
		if (body == null) return false;
		return ComputeHelper.CanRunEditModeCompute && body.shape && body.shape.heightMapCompute;
	}

	void LogTimer (System.Diagnostics.Stopwatch sw, string text) {
		if (logTimers) {
			Debug.Log (text + " " + sw.ElapsedMilliseconds + " ms.");
		}
	}

	bool InGameMode {
		get {
			return Application.isPlaying;
		}
	}

	bool InEditMode {
		get {
			return !Application.isPlaying;
		}
	}

	public class TerrainData {
		public float[] heights;
		public Vector4[] uvs;
	}

	[System.Serializable]
	public class ResolutionSettings {

		public const int numLODLevels = 3;
		const int maxAllowedResolution = 500;

		public int lod0 = 300;
		public int lod1 = 100;
		public int lod2 = 50;

		public int GetLODResolution (int lodLevel) {
			switch (lodLevel) {
				case 0:
					return lod0;
				case 1:
					return lod1;
				case 2:
					return lod2;
			}
			return lod2;
		}

		public void ClampResolutions () {
			lod0 = Mathf.Min (maxAllowedResolution, lod0);
			lod1 = Mathf.Min (maxAllowedResolution, lod1);
			lod2 = Mathf.Min (maxAllowedResolution, lod2);
		}
	}

}