using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;
using MLEM.Textures;
using static MLEM.Textures.TextureExtensions;

namespace MLEM.Data {
    /// <summary>
    /// A runtime texture packer provides the user with the ability to combine multiple <see cref="Texture2D"/> instances into a single texture.
    /// Packing textures in this manner allows for faster rendering, as fewer texture swaps are required.
    /// The resulting texture segments are returned as <see cref="TextureRegion"/> instances.
    /// </summary>
    /// <remarks>
    /// The algorithm used by this implementation is based on the blog post "Binary Tree Bin Packing Algorithm", which can be found at https://codeincomplete.com/articles/bin-packing/.
    /// </remarks>
    public class RuntimeTexturePacker : IDisposable {

        /// <summary>
        /// The generated packed texture.
        /// This value is null before <see cref="Pack"/> is called.
        /// </summary>
        public Texture2D PackedTexture { get; private set; }
        /// <summary>
        /// The time that it took to calculate the required areas the last time that <see cref="Pack"/> was called
        /// </summary>
        public TimeSpan LastCalculationTime { get; private set; }
        /// <summary>
        /// The time that it took to copy the texture data from the invidiual textures onto the <see cref="PackedTexture"/> the last time that <see cref="Pack"/> was called
        /// </summary>
        public TimeSpan LastPackTime { get; private set; }
        /// <summary>
        /// The time that <see cref="Pack"/> took the last time it was called
        /// </summary>
        public TimeSpan LastTotalTime => this.LastCalculationTime + this.LastPackTime;
        /// <summary>
        /// The amount of currently packed texture regions.
        /// </summary>
        public int PackedTextures => this.PackedTexture != null ? this.requests.Count : 0;

        private readonly List<Request> requests = new List<Request>();
        private readonly Dictionary<Texture2D, TextureData> dataCache = new Dictionary<Texture2D, TextureData>();
        private readonly bool forcePowerOfTwo;
        private readonly bool forceSquare;
        private readonly bool disposeTextures;

        /// <summary>
        /// Creates a new runtime texture packer with the given settings.
        /// </summary>
        /// <param name="forcePowerOfTwo">Whether the resulting <see cref="PackedTexture"/> should have a width and height that is a power of two.</param>
        /// <param name="forceSquare">Whether the resulting <see cref="PackedTexture"/> should be square regardless of required size.</param>
        /// <param name="disposeTextures">Whether the original textures submitted to this texture packer should be disposed after packing.</param>
        public RuntimeTexturePacker(bool forcePowerOfTwo = false, bool forceSquare = false, bool disposeTextures = false) {
            this.forcePowerOfTwo = forcePowerOfTwo;
            this.forceSquare = forceSquare;
            this.disposeTextures = disposeTextures;
        }

        /// <summary>
        /// Adds a new <see cref="UniformTextureAtlas"/> to this texture packer to be packed.
        /// The passed <see cref="Action{T}"/> is invoked in <see cref="Pack"/> and provides the caller with the resulting dictionary of texture regions on the <see cref="PackedTexture"/>, mapped to their x and y positions on the original <see cref="UniformTextureAtlas"/>.
        /// Note that the resulting data cannot be converted back into a <see cref="UniformTextureAtlas"/>, since the resulting texture regions might be scattered throughout the <see cref="PackedTexture"/>.
        /// </summary>
        /// <param name="atlas">The texture atlas to pack.</param>
        /// <param name="result">The result callback which will receive the resulting texture regions.</param>
        /// <param name="padding">The padding that the texture should have around itself. This can be useful if texture bleeding issues occur due to texture coordinate rounding.</param>
        /// <param name="padWithPixels">Whether the texture's padding should be filled with a copy of the texture's border, rather than transparent pixels. This value only has an effect if <paramref name="padding"/> is greater than 0.</param>
        /// <param name="ignoreTransparent">Whether completely transparent texture regions in the <paramref name="atlas"/> should be ignored. If this is true, they will not be part of the <paramref name="result"/> collection either.</param>
        /// <exception cref="InvalidOperationException">Thrown when trying to add a texture width a width greater than the defined max width.</exception>
        public void Add(UniformTextureAtlas atlas, Action<Dictionary<Point, TextureRegion>> result, int padding = 0, bool padWithPixels = false, bool ignoreTransparent = false) {
            var addedRegions = new List<TextureRegion>();
            var resultRegions = new Dictionary<Point, TextureRegion>();
            for (var x = 0; x < atlas.RegionAmountX; x++) {
                for (var y = 0; y < atlas.RegionAmountY; y++) {
                    var pos = new Point(x, y);
                    var region = atlas[pos];

                    if (ignoreTransparent) {
                        if (this.IsTransparent(region))
                            continue;
                    }

                    this.Add(region, r => {
                        resultRegions.Add(pos, r);
                        if (resultRegions.Count >= addedRegions.Count)
                            result.Invoke(resultRegions);
                    }, padding, padWithPixels);
                    addedRegions.Add(region);
                }
            }
        }

        /// <summary>
        /// Adds a new <see cref="DataTextureAtlas"/> to this texture packer to be packed.
        /// The passed <see cref="Action{T}"/> is invoked in <see cref="Pack"/> and provides the caller with the resulting dictionary of texture regions on the <see cref="PackedTexture"/>, mapped to their name on the original <see cref="DataTextureAtlas"/>.
        /// Note that the resulting data cannot be converted back into a <see cref="DataTextureAtlas"/>, since the resulting texture regions might be scattered throughout the <see cref="PackedTexture"/>.
        /// </summary>
        /// <param name="atlas">The texture atlas to pack.</param>
        /// <param name="result">The result callback which will receive the resulting texture regions.</param>
        /// <param name="padding">The padding that the texture should have around itself. This can be useful if texture bleeding issues occur due to texture coordinate rounding.</param>
        /// <param name="padWithPixels">Whether the texture's padding should be filled with a copy of the texture's border, rather than transparent pixels. This value only has an effect if <paramref name="padding"/> is greater than 0.</param>
        /// <exception cref="InvalidOperationException">Thrown when trying to add a texture width a width greater than the defined max width.</exception>
        public void Add(DataTextureAtlas atlas, Action<Dictionary<string, TextureRegion>> result, int padding = 0, bool padWithPixels = false) {
            var atlasRegions = atlas.RegionNames.ToArray();
            var resultRegions = new Dictionary<string, TextureRegion>();
            foreach (var region in atlasRegions) {
                this.Add(atlas[region], r => {
                    resultRegions.Add(region, r);
                    if (resultRegions.Count >= atlasRegions.Length)
                        result.Invoke(resultRegions);
                }, padding, padWithPixels);
            }
        }

        /// <summary>
        /// Adds a new <see cref="Texture2D"/> to this texture packer to be packed.
        /// The passed <see cref="Action{T}"/> is invoked in <see cref="Pack"/> and provides the caller with the resulting texture region on the <see cref="PackedTexture"/>.
        /// </summary>
        /// <param name="texture">The texture to pack.</param>
        /// <param name="result">The result callback which will receive the resulting texture region.</param>
        /// <param name="padding">The padding that the texture should have around itself. This can be useful if texture bleeding issues occur due to texture coordinate rounding.</param>
        /// <param name="padWithPixels">Whether the texture's padding should be filled with a copy of the texture's border, rather than transparent pixels. This value only has an effect if <paramref name="padding"/> is greater than 0.</param>
        /// <exception cref="InvalidOperationException">Thrown when trying to add a texture width a width greater than the defined max width.</exception>
        public void Add(Texture2D texture, Action<TextureRegion> result, int padding = 0, bool padWithPixels = false) {
            this.Add(new TextureRegion(texture), result, padding, padWithPixels);
        }

        /// <summary>
        /// Adds a new <see cref="TextureRegion"/> to this texture packer to be packed.
        /// The passed <see cref="Action{T}"/> is invoked in <see cref="Pack"/> and provides the caller with the resulting texture region on the <see cref="PackedTexture"/>.
        /// </summary>
        /// <param name="texture">The texture region to pack.</param>
        /// <param name="result">The result callback which will receive the resulting texture region.</param>
        /// <param name="padding">The padding that the texture should have around itself. This can be useful if texture bleeding issues occur due to texture coordinate rounding.</param>
        /// <param name="padWithPixels">Whether the texture's padding should be filled with a copy of the texture's border, rather than transparent pixels. This value only has an effect if <paramref name="padding"/> is greater than 0.</param>
        /// <exception cref="InvalidOperationException">Thrown when trying to add a texture width a width greater than the defined max width.</exception>
        public void Add(TextureRegion texture, Action<TextureRegion> result, int padding = 0, bool padWithPixels = false) {
            this.requests.Add(new Request(texture, result, padding, padWithPixels));
        }

        /// <summary>
        /// Packs all of the textures and texture regions added using <see cref="Add(Microsoft.Xna.Framework.Graphics.Texture2D,System.Action{MLEM.Textures.TextureRegion},int,bool)"/> into one texture, which can be retrieved using <see cref="PackedTexture"/>.
        /// All of the result callbacks that were added will also be invoked.
        /// This method can be called multiple times if regions are added after <see cref="Pack"/> has already been called. When doing so, result callbacks of previous regions may be invoked again if the resulting <see cref="PackedTexture"/> has to be resized to accommodate newly added regions.
        /// </summary>
        /// <param name="device">The graphics device to use for texture generation</param>
        public void Pack(GraphicsDevice device) {
            // set pack areas for each request based on the algo in https://codeincomplete.com/articles/bin-packing/
            var stopwatch = Stopwatch.StartNew();
            RequestNode root = null;
            foreach (var request in this.requests.OrderByDescending(t => Math.Max(t.Texture.Width, t.Texture.Height) + t.Padding * 2)) {
                var size = new Point(request.Texture.Width, request.Texture.Height);
                size.X += request.Padding * 2;
                size.Y += request.Padding * 2;

                if (root == null)
                    root = new RequestNode(0, 0, size.X, size.Y);

                var node = RuntimeTexturePacker.FindNode(size, root);
                if (node == null) {
                    root = RuntimeTexturePacker.GrowNode(size, root);
                    node = RuntimeTexturePacker.FindNode(size, root);
                }

                request.Node = node;
                node.Split(size);
            }
            stopwatch.Stop();
            this.LastCalculationTime = stopwatch.Elapsed;

            // figure out texture size and regenerate texture if necessary
            var width = root.Area.Width;
            var height = root.Area.Height;
            if (this.forcePowerOfTwo) {
                width = RuntimeTexturePacker.ToPowerOfTwo(width);
                height = RuntimeTexturePacker.ToPowerOfTwo(height);
            }
            if (this.forceSquare)
                width = height = Math.Max(width, height);

            // if we don't need to regenerate, we only need to add newly added regions
            if (this.PackedTexture == null || this.PackedTexture.Width != width || this.PackedTexture.Height != height) {
                this.PackedTexture?.Dispose();
                this.PackedTexture = new Texture2D(device, width, height);
            }

            // copy texture data onto the packed texture
            stopwatch.Restart();
            using (var data = this.PackedTexture.GetTextureData()) {
                foreach (var request in this.requests)
                    this.CopyRegion(data, request);
            }
            stopwatch.Stop();
            this.LastPackTime = stopwatch.Elapsed;

            // invoke callbacks for textures we copied
            foreach (var request in this.requests) {
                var packedLoc = request.Node.Area.Location + new Point(request.Padding, request.Padding);
                var packedArea = new Rectangle(packedLoc.X, packedLoc.Y, request.Texture.Width, request.Texture.Height);
                request.Result.Invoke(new TextureRegion(this.PackedTexture, packedArea) {
                    Pivot = request.Texture.Pivot,
                    Name = request.Texture.Name,
                    Source = request.Texture
                });
                if (this.disposeTextures)
                    request.Texture.Texture.Dispose();
            }

            this.dataCache.Clear();
        }

        /// <summary>
        /// Resets this texture packer entirely, disposing its <see cref="PackedTexture"/>, clearing all previously added requests, and readying it to be re-used.
        /// </summary>
        public void Reset() {
            this.PackedTexture?.Dispose();
            this.PackedTexture = null;
            this.LastCalculationTime = TimeSpan.Zero;
            this.LastPackTime = TimeSpan.Zero;
            this.requests.Clear();
            this.dataCache.Clear();
        }

        /// <summary>Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.</summary>
        public void Dispose() {
            this.Reset();
        }

        private void CopyRegion(TextureData destination, Request request) {
            var data = this.GetCachedTextureData(request.Texture.Texture);
            var location = request.Node.Area.Location + new Point(request.Padding, request.Padding);
            for (var x = -request.Padding; x < request.Texture.Width + request.Padding; x++) {
                for (var y = -request.Padding; y < request.Texture.Height + request.Padding; y++) {
                    Color srcColor;
                    if (!request.PadWithPixels && (x < 0 || y < 0 || x >= request.Texture.Width || y >= request.Texture.Height)) {
                        // if we're out of bounds and not padding with pixels, we make it transparent
                        srcColor = Color.Transparent;
                    } else {
                        // otherwise, we just use the closest pixel that is actually in bounds, causing the border pixels to be doubled up
                        var src = new Point((int) MathHelper.Clamp(x, 0F, request.Texture.Width - 1), (int) MathHelper.Clamp(y, 0F, request.Texture.Height - 1));
                        srcColor = data[request.Texture.Position + src];
                    }
                    destination[location + new Point(x, y)] = srcColor;
                }
            }
        }

        private TextureData GetCachedTextureData(Texture2D texture) {
            // we cache texture data in case multiple requests use the same underlying texture
            // this collection doesn't need to be disposed since we don't actually edit these textures
            if (!this.dataCache.TryGetValue(texture, out var data)) {
                data = texture.GetTextureData();
                this.dataCache.Add(texture, data);
            }
            return data;
        }

        private bool IsTransparent(TextureRegion region) {
            var data = this.GetCachedTextureData(region.Texture);
            for (var rX = 0; rX < region.Width; rX++) {
                for (var rY = 0; rY < region.Height; rY++) {
                    if (data[region.U + rX, region.V + rY] != Color.Transparent)
                        return false;
                }
            }
            return true;
        }

        private static int ToPowerOfTwo(int value) {
            var ret = 1;
            while (ret < value)
                ret <<= 1;
            return ret;
        }

        private static RequestNode FindNode(Point requestSize, RequestNode node) {
            if (node.Down != null && node.Right != null) {
                return RuntimeTexturePacker.FindNode(requestSize, node.Right) ?? RuntimeTexturePacker.FindNode(requestSize, node.Down);
            } else if (requestSize.X <= node.Area.Width && requestSize.Y <= node.Area.Height) {
                return node;
            } else {
                return null;
            }
        }

        private static RequestNode GrowNode(Point requestSize, RequestNode node) {
            var canGrowDown = requestSize.X <= node.Area.Width;
            var canGrowRight = requestSize.Y <= node.Area.Height;

            var shouldGrowRight = canGrowRight && node.Area.Height >= node.Area.Width + requestSize.X;
            var shouldGrowDown = canGrowDown && node.Area.Width >= node.Area.Height + requestSize.Y;

            if (shouldGrowRight) {
                return RuntimeTexturePacker.GrowNodeRight(requestSize, node);
            } else if (shouldGrowDown) {
                return RuntimeTexturePacker.GrowNodeDown(requestSize, node);
            } else if (canGrowRight) {
                return RuntimeTexturePacker.GrowNodeRight(requestSize, node);
            } else if (canGrowDown) {
                return RuntimeTexturePacker.GrowNodeDown(requestSize, node);
            } else {
                return null;
            }
        }

        private static RequestNode GrowNodeRight(Point requestSize, RequestNode node) {
            return new RequestNode(0, 0, node.Area.Width + requestSize.X, node.Area.Height) {
                Right = new RequestNode(node.Area.Width, 0, requestSize.X, node.Area.Height),
                Down = node
            };
        }

        private static RequestNode GrowNodeDown(Point requestSize, RequestNode node) {
            return new RequestNode(0, 0, node.Area.Width, node.Area.Height + requestSize.Y) {
                Right = node,
                Down = new RequestNode(0, node.Area.Height, node.Area.Width, requestSize.Y)
            };
        }

        private class Request {

            public readonly TextureRegion Texture;
            public readonly Action<TextureRegion> Result;
            public readonly int Padding;
            public readonly bool PadWithPixels;
            public RequestNode Node;

            public Request(TextureRegion texture, Action<TextureRegion> result, int padding, bool padWithPixels) {
                this.Texture = texture;
                this.Result = result;
                this.Padding = padding;
                this.PadWithPixels = padWithPixels;
            }

        }

        private class RequestNode {

            public readonly Rectangle Area;
            public RequestNode Down;
            public RequestNode Right;

            public RequestNode(int x, int y, int width, int height) {
                this.Area = new Rectangle(x, y, width, height);
            }

            public void Split(Point requestSize) {
                this.Down = new RequestNode(this.Area.X, this.Area.Y + requestSize.Y, this.Area.Width, this.Area.Height - requestSize.Y);
                this.Right = new RequestNode(this.Area.X + requestSize.X, this.Area.Y, this.Area.Width - requestSize.X, requestSize.Y);
            }

        }

    }
}