// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
// See the LICENCE file in the repository root for full licence text.

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Reflection;
using osu.Framework;
using osu.Framework.Extensions.ObjectExtensions;
using osu.Framework.Logging;
using osu.Framework.Platform;
using osu.Game.Database;

#nullable enable

namespace osu.Game.Rulesets
{
    public class RulesetStore : IDisposable
    {
        private readonly RealmContextFactory realmFactory;

        private const string ruleset_library_prefix = @"osu.Game.Rulesets";

        private readonly Dictionary<Assembly, Type> loadedAssemblies = new Dictionary<Assembly, Type>();

        /// <summary>
        /// All available rulesets.
        /// </summary>
        public IEnumerable<RulesetInfo> AvailableRulesets => availableRulesets;

        private readonly List<RulesetInfo> availableRulesets = new List<RulesetInfo>();

        public RulesetStore(RealmContextFactory realmFactory, Storage? storage = null)
        {
            this.realmFactory = realmFactory;

            // On android in release configuration assemblies are loaded from the apk directly into memory.
            // We cannot read assemblies from cwd, so should check loaded assemblies instead.
            loadFromAppDomain();

            // This null check prevents Android from attempting to load the rulesets from disk,
            // as the underlying path "AppContext.BaseDirectory", despite being non-nullable, it returns null on android.
            // See https://github.com/xamarin/xamarin-android/issues/3489.
            if (RuntimeInfo.StartupDirectory != null)
                loadFromDisk();

            // the event handler contains code for resolving dependency on the game assembly for rulesets located outside the base game directory.
            // It needs to be attached to the assembly lookup event before the actual call to loadUserRulesets() else rulesets located out of the base game directory will fail
            // to load as unable to locate the game core assembly.
            AppDomain.CurrentDomain.AssemblyResolve += resolveRulesetDependencyAssembly;

            var rulesetStorage = storage?.GetStorageForDirectory(@"rulesets");
            if (rulesetStorage != null)
                loadUserRulesets(rulesetStorage);

            addMissingRulesets();
        }

        /// <summary>
        /// Retrieve a ruleset using a known ID.
        /// </summary>
        /// <param name="id">The ruleset's internal ID.</param>
        /// <returns>A ruleset, if available, else null.</returns>
        public RulesetInfo? GetRuleset(int id) => AvailableRulesets.FirstOrDefault(r => r.OnlineID == id);

        /// <summary>
        /// Retrieve a ruleset using a known short name.
        /// </summary>
        /// <param name="shortName">The ruleset's short name.</param>
        /// <returns>A ruleset, if available, else null.</returns>
        public RulesetInfo? GetRuleset(string shortName) => AvailableRulesets.FirstOrDefault(r => r.ShortName == shortName);

        private Assembly? resolveRulesetDependencyAssembly(object? sender, ResolveEventArgs args)
        {
            var asm = new AssemblyName(args.Name);

            // the requesting assembly may be located out of the executable's base directory, thus requiring manual resolving of its dependencies.
            // this attempts resolving the ruleset dependencies on game core and framework assemblies by returning assemblies with the same assembly name
            // already loaded in the AppDomain.
            var domainAssembly = AppDomain.CurrentDomain.GetAssemblies()
                                          // Given name is always going to be equally-or-more qualified than the assembly name.
                                          .Where(a =>
                                          {
                                              string? name = a.GetName().Name;
                                              if (name == null)
                                                  return false;

                                              return args.Name.Contains(name, StringComparison.Ordinal);
                                          })
                                          // Pick the greatest assembly version.
                                          .OrderByDescending(a => a.GetName().Version)
                                          .FirstOrDefault();

            if (domainAssembly != null)
                return domainAssembly;

            return loadedAssemblies.Keys.FirstOrDefault(a => a.FullName == asm.FullName);
        }

        private void addMissingRulesets()
        {
            using (var context = realmFactory.CreateContext())
            {
                context.Write(realm =>
                {
                    var rulesets = realm.All<RulesetInfo>();

                    List<Ruleset> instances = loadedAssemblies.Values
                                                              .Select(r => Activator.CreateInstance(r) as Ruleset)
                                                              .Where(r => r != null)
                                                              .Select(r => r.AsNonNull())
                                                              .ToList();

                    // add all legacy rulesets first to ensure they have exclusive choice of primary key.
                    foreach (var r in instances.Where(r => r is ILegacyRuleset))
                    {
                        if (realm.All<RulesetInfo>().FirstOrDefault(rr => rr.OnlineID == r.RulesetInfo.OnlineID) == null)
                            realm.Add(new RulesetInfo(r.RulesetInfo.ShortName, r.RulesetInfo.Name, r.RulesetInfo.InstantiationInfo, r.RulesetInfo.OnlineID));
                    }

                    // add any other rulesets which have assemblies present but are not yet in the database.
                    foreach (var r in instances.Where(r => !(r is ILegacyRuleset)))
                    {
                        if (rulesets.FirstOrDefault(ri => ri.InstantiationInfo.Equals(r.RulesetInfo.InstantiationInfo, StringComparison.Ordinal)) == null)
                        {
                            var existingSameShortName = rulesets.FirstOrDefault(ri => ri.ShortName == r.RulesetInfo.ShortName);

                            if (existingSameShortName != null)
                            {
                                // even if a matching InstantiationInfo was not found, there may be an existing ruleset with the same ShortName.
                                // this generally means the user or ruleset provider has renamed their dll but the underlying ruleset is *likely* the same one.
                                // in such cases, update the instantiation info of the existing entry to point to the new one.
                                existingSameShortName.InstantiationInfo = r.RulesetInfo.InstantiationInfo;
                            }
                            else
                                realm.Add(new RulesetInfo(r.RulesetInfo.ShortName, r.RulesetInfo.Name, r.RulesetInfo.InstantiationInfo, r.RulesetInfo.OnlineID));
                        }
                    }

                    List<RulesetInfo> detachedRulesets = new List<RulesetInfo>();

                    // perform a consistency check and detach final rulesets from realm for cross-thread runtime usage.
                    foreach (var r in rulesets)
                    {
                        try
                        {
                            var resolvedType = Type.GetType(r.InstantiationInfo)
                                               ?? throw new RulesetLoadException(@"Type could not be resolved");

                            var instanceInfo = (Activator.CreateInstance(resolvedType) as Ruleset)?.RulesetInfo
                                               ?? throw new RulesetLoadException(@"Instantiation failure");

                            r.Name = instanceInfo.Name;
                            r.ShortName = instanceInfo.ShortName;
                            r.InstantiationInfo = instanceInfo.InstantiationInfo;
                            r.Available = true;

                            detachedRulesets.Add(r.Clone());
                        }
                        catch (Exception ex)
                        {
                            r.Available = false;
                            Logger.Log($"Could not load ruleset {r}: {ex.Message}");
                        }
                    }

                    availableRulesets.AddRange(detachedRulesets);
                });
            }
        }

        private void loadFromAppDomain()
        {
            foreach (var ruleset in AppDomain.CurrentDomain.GetAssemblies())
            {
                string? rulesetName = ruleset.GetName().Name;

                if (rulesetName == null)
                    continue;

                if (!rulesetName.StartsWith(ruleset_library_prefix, StringComparison.InvariantCultureIgnoreCase) || rulesetName.Contains(@"Tests"))
                    continue;

                addRuleset(ruleset);
            }
        }

        private void loadUserRulesets(Storage rulesetStorage)
        {
            var rulesets = rulesetStorage.GetFiles(@".", @$"{ruleset_library_prefix}.*.dll");

            foreach (string? ruleset in rulesets.Where(f => !f.Contains(@"Tests")))
                loadRulesetFromFile(rulesetStorage.GetFullPath(ruleset));
        }

        private void loadFromDisk()
        {
            try
            {
                string[] files = Directory.GetFiles(RuntimeInfo.StartupDirectory, @$"{ruleset_library_prefix}.*.dll");

                foreach (string file in files.Where(f => !Path.GetFileName(f).Contains("Tests")))
                    loadRulesetFromFile(file);
            }
            catch (Exception e)
            {
                Logger.Error(e, $"Could not load rulesets from directory {RuntimeInfo.StartupDirectory}");
            }
        }

        private void loadRulesetFromFile(string file)
        {
            string? filename = Path.GetFileNameWithoutExtension(file);

            if (loadedAssemblies.Values.Any(t => Path.GetFileNameWithoutExtension(t.Assembly.Location) == filename))
                return;

            try
            {
                addRuleset(Assembly.LoadFrom(file));
            }
            catch (Exception e)
            {
                Logger.Error(e, $"Failed to load ruleset {filename}");
            }
        }

        private void addRuleset(Assembly assembly)
        {
            if (loadedAssemblies.ContainsKey(assembly))
                return;

            // the same assembly may be loaded twice in the same AppDomain (currently a thing in certain Rider versions https://youtrack.jetbrains.com/issue/RIDER-48799).
            // as a failsafe, also compare by FullName.
            if (loadedAssemblies.Any(a => a.Key.FullName == assembly.FullName))
                return;

            try
            {
                loadedAssemblies[assembly] = assembly.GetTypes().First(t => t.IsPublic && t.IsSubclassOf(typeof(Ruleset)));
            }
            catch (Exception e)
            {
                Logger.Error(e, $"Failed to add ruleset {assembly}");
            }
        }

        public void Dispose()
        {
            Dispose(true);
            GC.SuppressFinalize(this);
        }

        protected virtual void Dispose(bool disposing)
        {
            AppDomain.CurrentDomain.AssemblyResolve -= resolveRulesetDependencyAssembly;
        }

        #region Implementation of IRulesetStore

        IRulesetInfo IRulesetStore.GetRuleset(int id) => GetRuleset(id);
        IRulesetInfo IRulesetStore.GetRuleset(string shortName) => GetRuleset(shortName);
        IEnumerable<IRulesetInfo> IRulesetStore.AvailableRulesets => AvailableRulesets;

        #endregion
    }
}