using System;
using System.Collections.Generic;
using System.IO;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Content;
using Microsoft.Xna.Framework.Graphics;

#if NET6_0_OR_GREATER
using System.Diagnostics.CodeAnalysis;
#endif

namespace MLEM.Data.Content {
    /// <summary>
    /// Represents a version of <see cref="ContentManager"/> that doesn't load content binary <c>xnb</c> files, but rather as their regular formats.
    /// </summary>
    public class RawContentManager : ContentManager, IGameComponent {

        /// <summary>
        /// The graphics device that this content manager uses
        /// </summary>
        public readonly GraphicsDevice GraphicsDevice;

        private readonly List<IDisposable> disposableAssets = new List<IDisposable>();
        private readonly List<RawContentReader> readers;

#if FNA
        private Dictionary<string, object> LoadedAssets { get; } = new Dictionary<string, object>(StringComparer.OrdinalIgnoreCase);
#endif

        /// <summary>
        /// Creates a new content manager with an optionally specified root directory.
        /// Each <see cref="RawContentReader"/> required for asset loading is gathered and instantiated automatically from the loaded assemblies.
        /// </summary>
        /// <param name="serviceProvider">The service provider of your game</param>
        /// <param name="rootDirectory">The root directory. Defaults to "Content"</param>
#if NET6_0_OR_GREATER
        [RequiresUnreferencedCode("Automatically gathered RawContentReader types might be removed, use other constructor to add readers manually")]
#endif
        public RawContentManager(IServiceProvider serviceProvider, string rootDirectory = "Content") :
            this(serviceProvider, RawContentManager.CollectContentReaders(), rootDirectory) {}

        /// <summary>
        /// Creates a new content manager with an optionally specified root directory.
        /// Each <see cref="RawContentReader"/> required for asset loading has to be passed using <paramref name="readers"/>.
        /// </summary>
        /// <param name="serviceProvider">The service provider of your game</param>
        /// <param name="readers">The raw content readers to use, which can be modified externally afterwards to add additional readers if desired.</param>
        /// <param name="rootDirectory">The root directory. Defaults to "Content"</param>
        public RawContentManager(IServiceProvider serviceProvider, List<RawContentReader> readers, string rootDirectory) :
            base(serviceProvider, rootDirectory) {
            if (serviceProvider.GetService(typeof(IGraphicsDeviceService)) is IGraphicsDeviceService s)
                this.GraphicsDevice = s.GraphicsDevice;
            this.readers = readers;
        }

        /// <summary>
        /// Loads a raw asset with the given name, based on the <see cref="ContentManager.RootDirectory"/>.
        /// If the asset was previously loaded using this method, the cached asset is merely returned.
        /// </summary>
        /// <param name="assetName">The path and name of the asset to load, without extension.</param>
        /// <typeparam name="T">The type of asset to load</typeparam>
        /// <returns>The asset, either loaded from the cache, or from disk.</returns>
        public override T Load<T>(string assetName) {
            if (this.LoadedAssets.TryGetValue(assetName, out var ret) && ret is T t)
                return t;
            return this.Read<T>(assetName, default);
        }

        /// <summary>
        /// Reloads the asset of the given type, with the given original name.
        /// </summary>
        /// <param name="originalAssetName">The original name of the asset.</param>
        /// <param name="currentAsset">The current asset instance.</param>
        /// <typeparam name="T">The asset's type.</typeparam>
        protected
#if !FNA
            override
#endif
            void ReloadAsset<T>(string originalAssetName, T currentAsset) {
            this.Read(originalAssetName, currentAsset);
        }

        private T Read<T>(string assetName, T existing) {
            var triedFiles = new List<string>();
            foreach (var reader in this.readers) {
                if (!reader.CanRead(typeof(T)))
                    continue;
                foreach (var ext in reader.GetFileExtensions()) {
                    var file = Path.Combine(this.RootDirectory, $"{assetName}.{ext}");
                    triedFiles.Add(file);
                    try {
                        using (var stream = Path.IsPathRooted(file) ? File.OpenRead(file) : TitleContainer.OpenStream(file)) {
                            var read = reader.Read(this, assetName, stream, typeof(T), existing);
                            if (!(read is T t))
                                throw new ContentLoadException($"{reader} returned non-{typeof(T)} for asset {assetName}");
                            this.LoadedAssets[assetName] = t;
                            if (t is IDisposable d && !this.disposableAssets.Contains(d))
                                this.disposableAssets.Add(d);
                            if (t is GraphicsResource r)
                                r.Name = assetName;
                            return t;
                        }
                    } catch (FileNotFoundException) {}
                }
            }
            throw new ContentLoadException($"Asset {assetName} not found. Tried files {string.Join(", ", triedFiles)}");
        }

        /// <summary>
        /// Unloads this content manager, disposing all of the assets that it loaded.
        /// </summary>
        public override void Unload() {
            foreach (var d in this.disposableAssets)
                d.Dispose();
            this.disposableAssets.Clear();
            base.Unload();
        }

        /// <summary>
        /// Initializes the component. Used to load non-graphical resources.
        /// </summary>
        public void Initialize() {}

#if NET6_0_OR_GREATER
        [RequiresUnreferencedCode("Automatically gathered RawContentReader types might be removed, use other constructor to add readers manually")]
#endif
        private static List<RawContentReader> CollectContentReaders() {
            var ret = new List<RawContentReader>();
            var assemblyExceptions = new List<Exception>();
            foreach (var assembly in AppDomain.CurrentDomain.GetAssemblies()) {
                try {
                    if (assembly.IsDynamic)
                        continue;
                    foreach (var type in assembly.GetExportedTypes()) {
                        try {
                            if (type.IsAbstract)
                                continue;
                            if (!type.IsSubclassOf(typeof(RawContentReader)))
                                continue;
                            ret.Add((RawContentReader) Activator.CreateInstance(type));
                        } catch (Exception e) {
                            throw new NotSupportedException($"The type {type} cannot be constructed by a RawContentManager. Does it have a visible parameterless constructor?", e);
                        }
                    }
                } catch (Exception e) {
                    assemblyExceptions.Add(e);
                }
            }
            if (ret.Count <= 0)
                throw new AggregateException("Failed to construct any RawContentReader instances", assemblyExceptions);
            return ret;
        }

    }
}