using System.Collections.Generic;
using UnityEngine;

namespace Assets.ThoMagic.Renderer
{
    /// <summary>
    /// Subdivides a terrain into smaller 2d-cells in the xz-plane based on terrain settings. Only cells in range 'maxDetailDistance' of the camera
    /// are alive. 
    /// </summary>
    public class GrassStreamer : InstanceStreamer
    {
        /// <summary>
        /// The limit of how many instances are created per frame. 
        /// TODO: While the setting is global, the budget is per streamer and each
        /// terrain has it's own streamer. This should be a real global budget.
        /// </summary>
        static int globalStreamingBudget = 10000;

        protected List<int> grassPrefabs;
        protected List<bool> grassPrefabSet;

        private readonly Terrain terrain;
        private readonly TerrainData terrainData;

        /// <summary>
        /// Used to find cells in range of the camera.
        /// </summary>
        private float maxDetailDistance;
        private Bounds worldBounds;
        private int layerCount;

        private Cell[] Cells;
        private float cellSizeX, cellSizeZ;
        private int cellsX, cellsZ;

        /// <summary>
        /// A queue with a list of cells to load. Cells are loaded per frame
        /// til the streaming budget is spent.
        /// </summary>
        private Queue<int> cellsToLoad = new Queue<int>();
        /// <summary>
        /// List of cells unloaded in a frame, only temporary list used to remove from loadedCells.
        /// </summary>
        private List<int> cellsToUnloaded = new List<int>();
        //A map of loaded cells. The cell index is z * cellCountX + x.
        private Dictionary<int, Cell> loadedCells = new Dictionary<int, Cell>();

        public static void SetStreamingBudget(int budget) => globalStreamingBudget = budget;

        private static float CalculatePatchSizeX(TerrainData terrainData) => (float)((double)terrainData.detailResolutionPerPatch / (double)terrainData.detailResolution * terrainData.size.x);

        private static float CalculatePatchSizeZ(TerrainData terrainData) => (float)((double)terrainData.detailResolutionPerPatch / (double)terrainData.detailResolution * terrainData.size.z);

        public GrassStreamer(
          Terrain terrain)
          : base()
        {
            this.terrain = terrain;
            terrainData = terrain.terrainData;
        }

        /// <summary>        
        /// Update loaded cells. Called by renderer. The renderer calls this once each frame.
        /// </summary>
        public void Update()
        {
            //Load cells until either all cells are loaded or budget is spent.
            //Returns the budget left.
            int streamingBudget = UpdateLoadCellsAsync();

            //Go through all loaded cells and reduce 'inRangeOfAnyCamera'.
            //If 'inRangeOfAnyCamera' is equal or below zero unload the cell.
            //'inRangeOfAnyCamera' is reset to x if a camera renders and this
            //cell is in range.
            foreach (var cellIndex in loadedCells.Keys)
            {
                var cell = loadedCells[cellIndex];

                //If cell is out of range and budget exist, unload.
                if (cell.inRangeOfAnyCamera <= 0 && streamingBudget > 0)
                {
                    streamingBudget -= UnloadCell(cellIndex);
                    cellsToUnloaded.Add(cellIndex);
                }
                
                --cell.inRangeOfAnyCamera;
            }

            //Remove all cells unloaded from 'loadedCells'.
            if (cellsToUnloaded.Count > 0)
            {
                foreach (var id in cellsToUnloaded)
                    loadedCells.Remove(id);
                cellsToUnloaded.Clear();
            }
        }

        /// <summary>
        /// Rebuild the cell layout. Called on initialize and on certain terrain changes.
        /// </summary>
        /// <param name="maxDistance">Max distance where a cell is in range</param>
        /// <param name="layerCount">Count of detail layers</param>
        public void Build(float maxDistance, int layerCount)
        {
            maxDetailDistance = maxDistance;
            this.layerCount = layerCount;

            cellSizeX = CalculatePatchSizeX(terrainData);
            cellSizeZ = CalculatePatchSizeZ(terrainData);

            Vector3 position = terrain.GetPosition();
            worldBounds = new Bounds(terrainData.bounds.center + position, terrainData.bounds.size);

            cellsX = Mathf.CeilToInt(worldBounds.size.x / cellSizeX);
            cellsZ = Mathf.CeilToInt(worldBounds.size.z / cellSizeZ);
            Cells = new Cell[cellsX * cellsZ];

            float cellSizeX_2 = cellSizeX * 0.5f;
            float cellSizeZ_2 = cellSizeZ * 0.5f;
            for (int indexZ = 0; indexZ < cellsZ; ++indexZ)
            {
                for (int indexX = 0; indexX < cellsX; ++indexX)
                {                    
                    int cellIndex = indexZ * cellsX + indexX;
                    Cells[cellIndex] = new Cell();
                    float cellCenterX = indexX * cellSizeX + cellSizeX_2;
                    float cellCenterZ = indexZ * cellSizeZ + cellSizeZ_2;
                    Cells[cellIndex].CenterX = cellCenterX;
                    Cells[cellIndex].CenterZ = cellCenterZ;
                }
            }
        }

        /// <summary>
        /// Is this streamer within range?
        /// </summary>
        /// <param name="camera">The camera to check for</param>
        /// <param name="planes">Planes of the camera frustum</param>
        /// <returns></returns>
        public override bool IsInRange(Camera camera, Plane[] planes)
        {
            if (layerCount == 0)
                return false;

            if (!terrain.editorRenderFlags.HasFlag(TerrainRenderFlags.Details))
                return false;

            var eyePos = camera.transform.position;
            
            if ((eyePos - worldBounds.ClosestPoint(eyePos)).magnitude <= Mathf.Min(camera.farClipPlane, maxDetailDistance))
                return true;

            return false;
        }

        /// <summary>
        /// Load cells until either all cells are loaded from the cellsToLoad list
        /// or the budget is spent.
        /// </summary>
        /// <returns>Unspent budget</returns>
        private int UpdateLoadCellsAsync()
        {
            int streamingBudget = globalStreamingBudget;

            if (globalStreamingBudget <= 0 || Cells == null || Cells.Length == 0)
                return streamingBudget;

            while(streamingBudget > 0 && cellsToLoad.TryDequeue(out var cellIndex))
            {                
                streamingBudget -= LoadCell(cellIndex);
            }

            return streamingBudget;
        }

        public virtual void Recycle()
        {
            UnloadAll();
        }

        private void UnloadAll()
        {
            if (Cells == null || Cells.Length == 0)
                return;

            for (int cellIndex = 0; cellIndex < Cells.Length; ++cellIndex)
            {
                UnloadCell(cellIndex);
            }

            loadedCells.Clear();
        }

        /// <summary>
        /// Remove all instances of a cell. 
        /// </summary>
        /// <param name="cellIndex"></param>
        /// <returns>The amount of deleted instances</returns>
        private int UnloadCell(int cellIndex)
        {
            if (cellIndex < 0 || cellIndex >= Cells.Length || !Cells[cellIndex].IsLoaded)
                return 0;

            var cell = Cells[cellIndex];
            cell.IsLoaded = false;
            cell.IsLoading = false;

            int deletedInstances = cell.loadedInstances.Count;

            foreach (var instanceInfo in cell.loadedInstances)
                RemoveInstance(instanceInfo.objectId, instanceInfo.instanceId);

            cell.loadedInstances.Clear();

            return deletedInstances;
        }

        /// <summary>
        /// Load all instances for a cell.
        /// </summary>
        /// <param name="cellIndex"></param>
        /// <returns>The amount of loaded instances</returns>
        private int LoadCell(int cellIndex)
        {            
            if (cellIndex < 0 || cellIndex >= Cells.Length || Cells[cellIndex].IsLoaded)
                return 0;

            var cell = Cells[cellIndex];
            cell.IsLoaded = true;
            cell.IsLoading = false;

            loadedCells.Add(cellIndex, cell);
            int x = Mathf.FloorToInt(cell.CenterX / cellSizeX);
            int z = Mathf.FloorToInt(cell.CenterZ / cellSizeZ);
            Vector3 size = terrainData.size;
            Vector3 terrainOffset = terrain.transform.position;
            Quaternion terrainRotation = terrain.transform.rotation;
            float detailObjectDensity = terrain.detailObjectDensity;

            for (int layer = 0; layer < layerCount; layer++)
            {
                var instanceTransforms = terrainData.ComputeDetailInstanceTransforms(x, z, layer, detailObjectDensity, out var _);
                
                for (int index = 0; index < instanceTransforms.Length; ++index)
                {
                    var local = instanceTransforms[index];

                    Vector3 interpolatedNormal = terrainData.GetInterpolatedNormal((local.posX / size.x), (local.posZ / size.z));
                    Quaternion rotation = terrainRotation * Quaternion.FromToRotation(Vector3.up, interpolatedNormal) * Quaternion.AngleAxis((local.rotationY * 57.2957801818848f), Vector3.up);

                    var instanceId = AddInstance(grassPrefabs[layer], new Vector3(local.posX, local.posY, local.posZ) + terrainOffset, rotation, local.scaleXZ, local.scaleY);
                    cell.loadedInstances.Add(new InstanceInfo { instanceId = instanceId, objectId = grassPrefabs[layer] });
                }
            }
            
            return cell.loadedInstances.Count;
        }

        /// <summary>
        /// Called by each camera at the start of a frame.
        /// Finds all cells visible in range of a camera. Either
        /// resets the 'inRangeOfAnyCamera' counter or adds the cell
        /// to the load list.
        /// </summary>
        /// <param name="camera"></param>
        /// <param name="planes"></param>
        public override void UpdateForCamera(Camera camera, Plane[] planes)
        {
            if (Cells == null || Cells.Length == 0)
                return;

            var range = Mathf.Min(camera.farClipPlane, maxDetailDistance);
            var rangeX = Mathf.CeilToInt((range + cellSizeX * 0.5f) / cellSizeX);
            var rangeZ = Mathf.CeilToInt((range + cellSizeZ * 0.5f) / cellSizeZ);

            var eyePos = camera.transform.position - worldBounds.min;
            var eyeCellX = Mathf.FloorToInt(eyePos.x / cellSizeX);
            var eyeCellZ = Mathf.FloorToInt(eyePos.z / cellSizeZ);

            for(int indexZ = eyeCellZ - rangeZ; indexZ < eyeCellZ + rangeZ; indexZ++)
                for (int indexX = eyeCellX - rangeX; indexX < eyeCellX + rangeX; indexX++)
                {
                    if(indexZ >= 0 && indexZ < cellsZ &&
                        indexX >= 0 && indexX < cellsX)
                    {
                        int cellIndex = indexZ * cellsX + indexX;
                        if (Cells[cellIndex].IsLoaded || Cells[cellIndex].IsLoading)
                        {
                            Cells[cellIndex].inRangeOfAnyCamera = 2;
                        }
                        else
                        {
                            Cells[cellIndex].IsLoading = true;
                            Cells[cellIndex].inRangeOfAnyCamera = 2;
                            cellsToLoad.Enqueue(cellIndex);
                        }
                    }
                }
        }
    }
}