using UnityEngine;
using System.Collections;

namespace DynamicFogAndMist {

    [ExecuteInEditMode]
    public class DynamicFogOfWar : MonoBehaviour {

        public int fogOfWarTextureSize = 512;


        Material fogMat;
        static DynamicFogOfWar _instance;
        Texture2D fogOfWarTexture;
        Color32[] fogOfWarColorBuffer;

        public static DynamicFogOfWar instance {
            get {
                if (_instance == null) {
                    _instance = FindObjectOfType<DynamicFogOfWar>();
                }
                return _instance;
            }
        }

        void OnEnable() {
            fogMat = GetComponent<MeshRenderer>().sharedMaterial;
            UpdateFogOfWarTexture();
        }

        void OnDisable() {
            if (fogOfWarTexture != null) {
                DestroyImmediate(fogOfWarTexture);
                fogOfWarTexture = null;
            }
        }

        void Update() {
            fogMat.SetVector("_FogOfWarData", new Vector4(transform.position.x, transform.position.z, transform.localScale.x, transform.localScale.y));
        }


        void UpdateFogOfWarTexture() {
            int size = GetScaledSize(fogOfWarTextureSize, 1.0f);
            fogOfWarTexture = new Texture2D(size, size, TextureFormat.ARGB32, false);
            fogOfWarTexture.hideFlags = HideFlags.DontSave;
            fogOfWarTexture.filterMode = FilterMode.Bilinear;
            fogOfWarTexture.wrapMode = TextureWrapMode.Clamp;
            fogMat.mainTexture = fogOfWarTexture;
            ResetFogOfWar();
        }

        int GetScaledSize(int size, float factor) {
            size = (int)(size / factor);
            size /= 4;
            if (size < 1)
                size = 1;
            return size * 4;
        }


        #region Fog of War Public API


        /// <summary>
        /// Returns the alpha value of fog of war at a given world space position
        /// </summary>
        /// <param name="worldPosition">in world space coordinates.</param>
        public float GetFogOfWarAlpha(Vector3 worldPosition) {
            if (fogOfWarTexture == null)
                return 1;

            float tx = (worldPosition.x - transform.position.x) / transform.localScale.x + 0.5f;
            if (tx < 0 || tx > 1f)
                return 1;
            float tz = (worldPosition.z - transform.position.z) / transform.localScale.y + 0.5f;
            if (tz < 0 || tz > 1f)
                return 1;

            int tw = fogOfWarTexture.width;
            int th = fogOfWarTexture.height;
            int px = (int)(tx * tw);
            int pz = (int)(tz * th);
            int colorBufferPos = pz * tw + px;
            return fogOfWarColorBuffer[colorBufferPos].a / 255f;
        }


        /// <summary>
        /// Changes the alpha value of the fog of war at world position. It takes into account FogOfWarCenter and FogOfWarSize.
        /// Note that only x and z coordinates are used. Y (vertical) coordinate is ignored.
        /// </summary>
        /// <param name="worldPosition">in world space coordinates.</param>
        /// <param name="radius">radius of application in world units.</param>
        public void SetFogOfWarAlpha(Vector3 worldPosition, float radius, float fogNewAlpha) {
            if (fogOfWarTexture == null)
                return;

            float tx = (worldPosition.x - transform.position.x) / transform.localScale.x + 0.5f;
            if (tx < 0 || tx > 1f)
                return;
            float tz = (worldPosition.z - transform.position.z) / transform.localScale.y + 0.5f;
            if (tz < 0 || tz > 1f)
                return;

            int tw = fogOfWarTexture.width;
            int th = fogOfWarTexture.height;
            int px = (int)(tx * tw);
            int pz = (int)(tz * th);
            int colorBufferPos = pz * tw + px;
            byte newAlpha8 = (byte)(fogNewAlpha * 255);
            Color32 existingColor = fogOfWarColorBuffer[colorBufferPos];
            if (newAlpha8 != existingColor.a) { // just to avoid over setting the texture in an Update() loop
                float tr = radius / transform.localScale.y;
                int delta = Mathf.FloorToInt(th * tr);
                for (int r = pz - delta; r <= pz + delta; r++) {
                    if (r >= 0 && r < th) {
                        for (int c = px - delta; c <= px + delta; c++) {
                            if (c >= 0 && c < tw) {
                                int distance = (int)(Mathf.Sqrt((pz - r) * (pz - r) + (px - c) * (px - c)));
                                if (distance <= delta) {
                                    colorBufferPos = r * tw + c;
                                    Color32 colorBuffer = fogOfWarColorBuffer[colorBufferPos];
                                    colorBuffer.a = (byte)Mathf.Lerp(newAlpha8, colorBuffer.a, (float)distance / delta);
                                    fogOfWarColorBuffer[colorBufferPos] = colorBuffer;
                                    fogOfWarTexture.SetPixel(c, r, colorBuffer);
                                }
                            }
                        }
                    }
                }
                fogOfWarTexture.Apply();
            }
        }

        public void ResetFogOfWar() {
            if (fogOfWarTexture == null)
                return;
            int h = fogOfWarTexture.height;
            int w = fogOfWarTexture.width;
            int newLength = h * w;
            if (fogOfWarColorBuffer == null || fogOfWarColorBuffer.Length != newLength) {
                fogOfWarColorBuffer = new Color32[newLength];
            }
            Color32 opaque = new Color32(255, 255, 255, 255);
            for (int k = 0; k < newLength; k++)
                fogOfWarColorBuffer[k] = opaque;
            fogOfWarTexture.SetPixels32(fogOfWarColorBuffer);
            fogOfWarTexture.Apply();
        }

        public void SetFogOfWarTerrainBoundary(Terrain terrain, float borderWidth) {
            TerrainData td = terrain.terrainData;
            int tw = td.heightmapResolution;
            int th = td.heightmapResolution;
            float ta = td.size.y;
            float[,] heights = td.GetHeights(0, 0, tw, th);
            float y0 = transform.position.y - 1f;
            float y1 = transform.position.y + 10f;
            //Vector3 halfSize = new Vector3(-td.size.x * 0.5f, 0, -td.size.z * 0.5f);
            Vector3 terrainPos = terrain.GetPosition();
            for (int j = 0; j < th; j++) {
                for (int k = 0; k < tw; k++) {
                    float h = heights[j, k] * ta + terrain.transform.position.y;
                    if (h > y0 && h < y1) {
                        Vector3 wpos = terrainPos + new Vector3(td.size.x * (k + 0.5f) / tw, 0, td.size.z * (j + 0.5f) / th);
                        SetFogOfWarAlpha(wpos, borderWidth, 0);
                    }
                }
            }
        }


        #endregion


    }

}