using System;
using System.Collections.Generic;
using System.Globalization;
using System.IO;
using System.Linq;
using System.Reflection;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Content;
using StardewModdingAPI.Framework.Content;
using StardewModdingAPI.Framework.ModLoading;
using StardewModdingAPI.Framework.Reflection;
using StardewModdingAPI.Framework.Utilities;
using StardewModdingAPI.Metadata;
using StardewValley;

namespace StardewModdingAPI.Framework
{
    /// <summary>SMAPI's implementation of the game's content manager which lets it raise content events.</summary>
    internal class SContentManager : LocalizedContentManager
    {
        /*********
        ** Properties
        *********/
        /// <summary>The possible directory separator characters in an asset key.</summary>
        private static readonly char[] PossiblePathSeparators = new[] { '/', '\\', Path.DirectorySeparatorChar, Path.AltDirectorySeparatorChar }.Distinct().ToArray();

        /// <summary>The preferred directory separator chaeacter in an asset key.</summary>
        private static readonly string PreferredPathSeparator = Path.DirectorySeparatorChar.ToString();

        /// <summary>Encapsulates monitoring and logging.</summary>
        private readonly IMonitor Monitor;

        /// <summary>The underlying content manager's asset cache.</summary>
        private readonly IDictionary<string, object> Cache;

        /// <summary>Applies platform-specific asset key normalisation so it's consistent with the underlying cache.</summary>
        private readonly Func<string, string> NormaliseAssetNameForPlatform;

        /// <summary>The private <see cref="LocalizedContentManager"/> method which generates the locale portion of an asset name.</summary>
        private readonly IPrivateMethod GetKeyLocale;

        /// <summary>The language codes used in asset keys.</summary>
        private readonly IDictionary<string, LanguageCode> KeyLocales;

        /// <summary>Provides metadata for core game assets.</summary>
        private readonly CoreAssets CoreAssets;

        /// <summary>The assets currently being intercepted by <see cref="IAssetLoader"/> instances. This is used to prevent infinite loops when a loader loads a new asset.</summary>
        private readonly ContextHash<string> AssetsBeingLoaded = new ContextHash<string>();

        /// <summary>A lookup of the content managers which loaded each asset.</summary>
        private readonly IDictionary<string, HashSet<ContentManager>> AssetLoaders = new Dictionary<string, HashSet<ContentManager>>();

        /// <summary>An object locked to prevent concurrent changes to the underlying assets.</summary>
        private readonly object Lock = new object();


        /*********
        ** Accessors
        *********/
        /// <summary>Interceptors which provide the initial versions of matching assets.</summary>
        internal IDictionary<IModMetadata, IList<IAssetLoader>> Loaders { get; } = new Dictionary<IModMetadata, IList<IAssetLoader>>();

        /// <summary>Interceptors which edit matching assets after they're loaded.</summary>
        internal IDictionary<IModMetadata, IList<IAssetEditor>> Editors { get; } = new Dictionary<IModMetadata, IList<IAssetEditor>>();

        /// <summary>The absolute path to the <see cref="ContentManager.RootDirectory"/>.</summary>
        public string FullRootDirectory => Path.Combine(Constants.ExecutionPath, this.RootDirectory);


        /*********
        ** Public methods
        *********/
        /// <summary>Construct an instance.</summary>
        /// <param name="serviceProvider">The service provider to use to locate services.</param>
        /// <param name="rootDirectory">The root directory to search for content.</param>
        /// <param name="currentCulture">The current culture for which to localise content.</param>
        /// <param name="languageCodeOverride">The current language code for which to localise content.</param>
        /// <param name="monitor">Encapsulates monitoring and logging.</param>
        public SContentManager(IServiceProvider serviceProvider, string rootDirectory, CultureInfo currentCulture, string languageCodeOverride, IMonitor monitor)
            : base(serviceProvider, rootDirectory, currentCulture, languageCodeOverride)
        {
            // validate
            if (monitor == null)
                throw new ArgumentNullException(nameof(monitor));

            // initialise
            var reflection = new Reflector();
            this.Monitor = monitor;

            // get underlying fields for interception
            this.Cache = reflection.GetPrivateField<Dictionary<string, object>>(this, "loadedAssets").GetValue();
            this.GetKeyLocale = reflection.GetPrivateMethod(this, "languageCode");

            // get asset key normalisation logic
            if (Constants.TargetPlatform == Platform.Windows)
            {
                IPrivateMethod method = reflection.GetPrivateMethod(typeof(TitleContainer), "GetCleanPath");
                this.NormaliseAssetNameForPlatform = path => method.Invoke<string>(path);
            }
            else
                this.NormaliseAssetNameForPlatform = key => key.Replace('\\', '/'); // based on MonoGame's ContentManager.Load<T> logic

            // get asset data
            this.CoreAssets = new CoreAssets(this.NormaliseAssetName);
            this.KeyLocales = this.GetKeyLocales(reflection);
        }

        /// <summary>Normalise path separators in a file path. For asset keys, see <see cref="NormaliseAssetName"/> instead.</summary>
        /// <param name="path">The file path to normalise.</param>
        public string NormalisePathSeparators(string path)
        {
            string[] parts = path.Split(SContentManager.PossiblePathSeparators, StringSplitOptions.RemoveEmptyEntries);
            string normalised = string.Join(SContentManager.PreferredPathSeparator, parts);
            if (path.StartsWith(SContentManager.PreferredPathSeparator))
                normalised = SContentManager.PreferredPathSeparator + normalised; // keep root slash
            return normalised;
        }

        /// <summary>Normalise an asset name so it's consistent with the underlying cache.</summary>
        /// <param name="assetName">The asset key.</param>
        public string NormaliseAssetName(string assetName)
        {
            assetName = this.NormalisePathSeparators(assetName);
            if (assetName.EndsWith(".xnb", StringComparison.InvariantCultureIgnoreCase))
                return assetName.Substring(0, assetName.Length - 4);
            return this.NormaliseAssetNameForPlatform(assetName);
        }

        /// <summary>Get whether the content manager has already loaded and cached the given asset.</summary>
        /// <param name="assetName">The asset path relative to the loader root directory, not including the <c>.xnb</c> extension.</param>
        public bool IsLoaded(string assetName)
        {
            lock (this.Lock)
            {
                assetName = this.NormaliseAssetName(assetName);
                return this.IsNormalisedKeyLoaded(assetName);
            }
        }

        /// <summary>Load an asset that has been processed by the content pipeline.</summary>
        /// <typeparam name="T">The type of asset to load.</typeparam>
        /// <param name="assetName">The asset path relative to the loader root directory, not including the <c>.xnb</c> extension.</param>
        public override T Load<T>(string assetName)
        {
            return this.LoadFor<T>(assetName, this);
        }

        /// <summary>Load an asset that has been processed by the content pipeline.</summary>
        /// <typeparam name="T">The type of asset to load.</typeparam>
        /// <param name="assetName">The asset path relative to the loader root directory, not including the <c>.xnb</c> extension.</param>
        /// <param name="instance">The content manager instance for which to load the asset.</param>
        public T LoadFor<T>(string assetName, ContentManager instance)
        {
            lock (this.Lock)
            {
                assetName = this.NormaliseAssetName(assetName);

                // skip if already loaded
                if (this.IsNormalisedKeyLoaded(assetName))
                {
                    this.TrackAssetLoader(assetName, instance);
                    return base.Load<T>(assetName);
                }

                // load asset
                T data;
                if (this.AssetsBeingLoaded.Contains(assetName))
                {
                    this.Monitor.Log($"Broke loop while loading asset '{assetName}'.", LogLevel.Warn);
                    this.Monitor.Log($"Bypassing mod loaders for this asset. Stack trace:\n{Environment.StackTrace}", LogLevel.Trace);
                    data = base.Load<T>(assetName);
                }
                else
                {
                    data = this.AssetsBeingLoaded.Track(assetName, () =>
                    {
                        IAssetInfo info = new AssetInfo(this.GetLocale(), assetName, typeof(T), this.NormaliseAssetName);
                        IAssetData asset = this.ApplyLoader<T>(info) ?? new AssetDataForObject(info, base.Load<T>(assetName), this.NormaliseAssetName);
                        asset = this.ApplyEditors<T>(info, asset);
                        return (T)asset.Data;
                    });
                }

                // update cache & return data
                this.Cache[assetName] = data;
                this.TrackAssetLoader(assetName, instance);
                return data;
            }
        }

        /// <summary>Inject an asset into the cache.</summary>
        /// <typeparam name="T">The type of asset to inject.</typeparam>
        /// <param name="assetName">The asset path relative to the loader root directory, not including the <c>.xnb</c> extension.</param>
        /// <param name="value">The asset value.</param>
        public void Inject<T>(string assetName, T value)
        {
            lock (this.Lock)
            {
                assetName = this.NormaliseAssetName(assetName);
                this.Cache[assetName] = value;
                this.TrackAssetLoader(assetName, this);
            }
        }

        /// <summary>Get the current content locale.</summary>
        public string GetLocale()
        {
            return this.GetKeyLocale.Invoke<string>();
        }

        /// <summary>Get the cached asset keys.</summary>
        public IEnumerable<string> GetAssetKeys()
        {
            lock (this.Lock)
            {
                IEnumerable<string> GetAllAssetKeys()
                {
                    foreach (string cacheKey in this.Cache.Keys)
                    {
                        this.ParseCacheKey(cacheKey, out string assetKey, out string _);
                        yield return assetKey;
                    }
                }

                return GetAllAssetKeys().Distinct();
            }
        }

        /// <summary>Purge assets from the cache that match one of the interceptors.</summary>
        /// <param name="editors">The asset editors for which to purge matching assets.</param>
        /// <param name="loaders">The asset loaders for which to purge matching assets.</param>
        /// <returns>Returns whether any cache entries were invalidated.</returns>
        public bool InvalidateCacheFor(IAssetEditor[] editors, IAssetLoader[] loaders)
        {
            if (!editors.Any() && !loaders.Any())
                return false;

            // get CanEdit/Load methods
            MethodInfo canEdit = typeof(IAssetEditor).GetMethod(nameof(IAssetEditor.CanEdit));
            MethodInfo canLoad = typeof(IAssetLoader).GetMethod(nameof(IAssetLoader.CanLoad));

            // invalidate matching keys
            return this.InvalidateCache((assetName, assetType) =>
            {
                // get asset metadata
                IAssetInfo info = new AssetInfo(this.GetLocale(), assetName, assetType, this.NormaliseAssetName);

                // check loaders
                MethodInfo canLoadGeneric = canLoad.MakeGenericMethod(assetType);
                if (loaders.Any(loader => (bool)canLoadGeneric.Invoke(loader, new object[] { info })))
                    return true;

                // check editors
                MethodInfo canEditGeneric = canEdit.MakeGenericMethod(assetType);
                return editors.Any(editor => (bool)canEditGeneric.Invoke(editor, new object[] { info }));
            });
        }

        /// <summary>Purge matched assets from the cache.</summary>
        /// <param name="predicate">Matches the asset keys to invalidate.</param>
        /// <param name="dispose">Whether to dispose invalidated assets. This should only be <c>true</c> when they're being invalidated as part of a dispose, to avoid crashing the game.</param>
        /// <returns>Returns whether any cache entries were invalidated.</returns>
        public bool InvalidateCache(Func<string, Type, bool> predicate, bool dispose = false)
        {
            lock (this.Lock)
            {
                // find matching asset keys
                HashSet<string> purgeCacheKeys = new HashSet<string>(StringComparer.InvariantCultureIgnoreCase);
                HashSet<string> purgeAssetKeys = new HashSet<string>(StringComparer.InvariantCultureIgnoreCase);
                foreach (string cacheKey in this.Cache.Keys)
                {
                    this.ParseCacheKey(cacheKey, out string assetKey, out _);
                    Type type = this.Cache[cacheKey].GetType();
                    if (predicate(assetKey, type))
                    {
                        purgeAssetKeys.Add(assetKey);
                        purgeCacheKeys.Add(cacheKey);
                    }
                }

                // purge assets
                foreach (string key in purgeCacheKeys)
                {
                    if (dispose && this.Cache[key] is IDisposable disposable)
                        disposable.Dispose();
                    this.Cache.Remove(key);
                    this.AssetLoaders.Remove(key);
                }

                // reload core game assets
                int reloaded = 0;
                foreach (string key in purgeAssetKeys)
                {
                    if (this.CoreAssets.ReloadForKey(this, key))
                        reloaded++;
                }

                // report result
                if (purgeCacheKeys.Any())
                {
                    this.Monitor.Log($"Invalidated {purgeCacheKeys.Count} cache entries for {purgeAssetKeys.Count} asset keys: {string.Join(", ", purgeCacheKeys.OrderBy(p => p, StringComparer.InvariantCultureIgnoreCase))}. Reloaded {reloaded} core assets.", LogLevel.Trace);
                    return true;
                }
                this.Monitor.Log("Invalidated 0 cache entries.", LogLevel.Trace);
                return false;
            }
        }

        /// <summary>Dispose assets for the given content manager shim.</summary>
        /// <param name="shim">The content manager whose assets to dispose.</param>
        internal void DisposeFor(ContentManagerShim shim)
        {
            this.Monitor.Log($"Content manager '{shim.Name}' disposed, disposing assets that aren't needed by any other asset loader.", LogLevel.Trace);

            foreach (var entry in this.AssetLoaders)
                entry.Value.Remove(shim);
            this.InvalidateCache((key, type) => !this.AssetLoaders[key].Any(), dispose: true);
        }


        /*********
        ** Private methods
        *********/
        /// <summary>Get whether an asset has already been loaded.</summary>
        /// <param name="normalisedAssetName">The normalised asset name.</param>
        private bool IsNormalisedKeyLoaded(string normalisedAssetName)
        {
            return this.Cache.ContainsKey(normalisedAssetName)
                || this.Cache.ContainsKey($"{normalisedAssetName}.{this.GetKeyLocale.Invoke<string>()}"); // translated asset
        }

        /// <summary>Track that a content manager loaded an asset.</summary>
        /// <param name="key">The asset key that was loaded.</param>
        /// <param name="manager">The content manager that loaded the asset.</param>
        private void TrackAssetLoader(string key, ContentManager manager)
        {
            if (!this.AssetLoaders.TryGetValue(key, out HashSet<ContentManager> hash))
                hash = this.AssetLoaders[key] = new HashSet<ContentManager>();
            hash.Add(manager);
        }

        /// <summary>Get the locale codes (like <c>ja-JP</c>) used in asset keys.</summary>
        /// <param name="reflection">Simplifies access to private game code.</param>
        private IDictionary<string, LanguageCode> GetKeyLocales(Reflector reflection)
        {
            // get the private code field directly to avoid changed-code logic
            IPrivateField<LanguageCode> codeField = reflection.GetPrivateField<LanguageCode>(typeof(LocalizedContentManager), "_currentLangCode");

            // remember previous settings
            LanguageCode previousCode = codeField.GetValue();
            string previousOverride = this.LanguageCodeOverride;

            // create locale => code map
            IDictionary<string, LanguageCode> map = new Dictionary<string, LanguageCode>(StringComparer.InvariantCultureIgnoreCase);
            this.LanguageCodeOverride = null;
            foreach (LanguageCode code in Enum.GetValues(typeof(LanguageCode)))
            {
                codeField.SetValue(code);
                map[this.GetKeyLocale.Invoke<string>()] = code;
            }

            // restore previous settings
            codeField.SetValue(previousCode);
            this.LanguageCodeOverride = previousOverride;

            return map;
        }

        /// <summary>Parse a cache key into its component parts.</summary>
        /// <param name="cacheKey">The input cache key.</param>
        /// <param name="assetKey">The original asset key.</param>
        /// <param name="localeCode">The asset locale code (or <c>null</c> if not localised).</param>
        private void ParseCacheKey(string cacheKey, out string assetKey, out string localeCode)
        {
            // handle localised key
            if (!string.IsNullOrWhiteSpace(cacheKey))
            {
                int lastSepIndex = cacheKey.LastIndexOf(".", StringComparison.InvariantCulture);
                if (lastSepIndex >= 0)
                {
                    string suffix = cacheKey.Substring(lastSepIndex + 1, cacheKey.Length - lastSepIndex - 1);
                    if (this.KeyLocales.ContainsKey(suffix))
                    {
                        assetKey = cacheKey.Substring(0, lastSepIndex);
                        localeCode = cacheKey.Substring(lastSepIndex + 1, cacheKey.Length - lastSepIndex - 1);
                        return;
                    }
                }
            }

            // handle simple key
            assetKey = cacheKey;
            localeCode = null;
        }

        /// <summary>Load the initial asset from the registered <see cref="Loaders"/>.</summary>
        /// <param name="info">The basic asset metadata.</param>
        /// <returns>Returns the loaded asset metadata, or <c>null</c> if no loader matched.</returns>
        private IAssetData ApplyLoader<T>(IAssetInfo info)
        {
            // find matching loaders
            var loaders = this.GetInterceptors(this.Loaders)
                .Where(entry =>
                {
                    try
                    {
                        return entry.Value.CanLoad<T>(info);
                    }
                    catch (Exception ex)
                    {
                        this.Monitor.Log($"{entry.Key.DisplayName} crashed when checking whether it could load asset '{info.AssetName}', and will be ignored. Error details:\n{ex.GetLogSummary()}", LogLevel.Error);
                        return false;
                    }
                })
                .ToArray();

            // validate loaders
            if (!loaders.Any())
                return null;
            if (loaders.Length > 1)
            {
                string[] loaderNames = loaders.Select(p => p.Key.DisplayName).ToArray();
                this.Monitor.Log($"Multiple mods want to provide the '{info.AssetName}' asset ({string.Join(", ", loaderNames)}), but an asset can't be loaded multiple times. SMAPI will use the default asset instead; uninstall one of the mods to fix this. (Message for modders: you should usually use {typeof(IAssetEditor)} instead to avoid conflicts.)", LogLevel.Warn);
                return null;
            }

            // fetch asset from loader
            IModMetadata mod = loaders[0].Key;
            IAssetLoader loader = loaders[0].Value;
            T data;
            try
            {
                data = loader.Load<T>(info);
                this.Monitor.Log($"{mod.DisplayName} loaded asset '{info.AssetName}'.", LogLevel.Trace);
            }
            catch (Exception ex)
            {
                this.Monitor.Log($"{mod.DisplayName} crashed when loading asset '{info.AssetName}'. SMAPI will use the default asset instead. Error details:\n{ex.GetLogSummary()}", LogLevel.Error);
                return null;
            }

            // validate asset
            if (data == null)
            {
                this.Monitor.Log($"{mod.DisplayName} incorrectly set asset '{info.AssetName}' to a null value; ignoring override.", LogLevel.Error);
                return null;
            }

            // return matched asset
            return new AssetDataForObject(info, data, this.NormaliseAssetName);
        }

        /// <summary>Apply any <see cref="Editors"/> to a loaded asset.</summary>
        /// <typeparam name="T">The asset type.</typeparam>
        /// <param name="info">The basic asset metadata.</param>
        /// <param name="asset">The loaded asset.</param>
        private IAssetData ApplyEditors<T>(IAssetInfo info, IAssetData asset)
        {
            IAssetData GetNewData(object data) => new AssetDataForObject(info, data, this.NormaliseAssetName);

            // edit asset
            foreach (var entry in this.GetInterceptors(this.Editors))
            {
                // check for match
                IModMetadata mod = entry.Key;
                IAssetEditor editor = entry.Value;
                try
                {
                    if (!editor.CanEdit<T>(info))
                        continue;
                }
                catch (Exception ex)
                {
                    this.Monitor.Log($"{mod.DisplayName} crashed when checking whether it could edit asset '{info.AssetName}', and will be ignored. Error details:\n{ex.GetLogSummary()}", LogLevel.Error);
                    continue;
                }

                // try edit
                object prevAsset = asset.Data;
                try
                {
                    editor.Edit<T>(asset);
                    this.Monitor.Log($"{mod.DisplayName} intercepted {info.AssetName}.", LogLevel.Trace);
                }
                catch (Exception ex)
                {
                    this.Monitor.Log($"{mod.DisplayName} crashed when editing asset '{info.AssetName}', which may cause errors in-game. Error details:\n{ex.GetLogSummary()}", LogLevel.Error);
                }

                // validate edit
                if (asset.Data == null)
                {
                    this.Monitor.Log($"{mod.DisplayName} incorrectly set asset '{info.AssetName}' to a null value; ignoring override.", LogLevel.Warn);
                    asset = GetNewData(prevAsset);
                }
                else if (!(asset.Data is T))
                {
                    this.Monitor.Log($"{mod.DisplayName} incorrectly set asset '{asset.AssetName}' to incompatible type '{asset.Data.GetType()}', expected '{typeof(T)}'; ignoring override.", LogLevel.Warn);
                    asset = GetNewData(prevAsset);
                }
            }

            // return result
            return asset;
        }

        /// <summary>Get all registered interceptors from a list.</summary>
        private IEnumerable<KeyValuePair<IModMetadata, T>> GetInterceptors<T>(IDictionary<IModMetadata, IList<T>> entries)
        {
            foreach (var entry in entries)
            {
                IModMetadata metadata = entry.Key;
                IList<T> interceptors = entry.Value;

                // special case if mod is an interceptor
                if (metadata.Mod is T modAsInterceptor)
                    yield return new KeyValuePair<IModMetadata, T>(metadata, modAsInterceptor);

                // registered editors
                foreach (T interceptor in interceptors)
                    yield return new KeyValuePair<IModMetadata, T>(metadata, interceptor);
            }
        }

        /// <summary>Dispose held resources.</summary>
        /// <param name="disposing">Whether the content manager is disposing (rather than finalising).</param>
        protected override void Dispose(bool disposing)
        {
            this.Monitor.Log("Disposing SMAPI's main content manager. It will no longer be usable after this point.", LogLevel.Trace);
            base.Dispose(disposing);
        }
    }
}