// <copyright file="PlugInManager.cs" company="MUnique">
// Licensed under the MIT License. See LICENSE file in the project root for full license information.
// </copyright>

namespace MUnique.OpenMU.PlugIns;

using System.Collections.Concurrent;
using System.ComponentModel.Design;
using System.Reflection;
using System.Runtime.InteropServices;
using System.Text.Json.Serialization;
using Microsoft.CodeAnalysis.CSharp;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using Nito.Disposables.Internals;

/// <summary>
/// The manager for plugins.
/// </summary>
public class PlugInManager
{
    private readonly ILogger<PlugInManager> _logger;
    private readonly ServiceContainer _serviceContainer;
    private readonly IDictionary<Type, object> _plugInPoints = new Dictionary<Type, object>();
    private readonly IDictionary<Guid, Type> _knownPlugIns = new ConcurrentDictionary<Guid, Type>();
    private readonly ConcurrentDictionary<Type, ISet<Type>> _knownPlugInsPerInterfaceType = new();
    private readonly ConcurrentDictionary<Guid, Type> _activePlugIns = new();
    private object? _lastCreatedPlugIn;

    /// <summary>
    /// Initializes a new instance of the <see cref="PlugInManager" /> class.
    /// </summary>
    /// <param name="configurations">The configurations.</param>
    /// <param name="loggerFactory">The logger factory.</param>
    /// <param name="serviceProvider">The service provider.</param>
    /// <param name="customConfigReferenceHandler">The reference handler for references in custom plugin configurations.</param>
    public PlugInManager(ICollection<PlugInConfiguration>? configurations, ILoggerFactory loggerFactory, IServiceProvider? serviceProvider, ReferenceHandler? customConfigReferenceHandler)
    {
        _ = typeof(Nito.AsyncEx.AsyncReaderWriterLock); // Ensure Nito.AsyncEx.Coordination is loaded so it will be available in proxy generation.

        this._logger = loggerFactory.CreateLogger<PlugInManager>();
        this._serviceContainer = new ServiceContainer(serviceProvider);
        this._serviceContainer.AddService(typeof(PlugInManager), this);
        this._serviceContainer.AddService(typeof(ILoggerFactory), loggerFactory);

        this.CustomConfigReferenceHandler = customConfigReferenceHandler;

        if (configurations is not null)
        {
            this.DiscoverAndRegisterPlugIns();
            var loadedAssemblies = new HashSet<string>();
            foreach (var configuration in configurations)
            {
                this.ReadConfiguration(configuration, loadedAssemblies);
            }
        }
    }

    /// <summary>
    /// Occurs when a plugin got deactivated.
    /// </summary>
    public event EventHandler<PlugInEventArgs>? PlugInDeactivated;

    /// <summary>
    /// Occurs when a plugin got activated.
    /// </summary>
    public event EventHandler<PlugInEventArgs>? PlugInActivated;

    /// <summary>
    /// Occurs when the <see cref="PlugInConfiguration.CustomConfiguration"/> has been changed.
    /// </summary>
    public event EventHandler<PlugInConfigurationChangedEventArgs>? PlugInConfigurationChanged;

    /// <summary>
    /// Gets the known plugin types.
    /// </summary>
    /// <value>
    /// The known plugin types.
    /// </value>
    public IEnumerable<Type> KnownPlugInTypes => this._knownPlugIns.Values;

    /// <summary>
    /// Gets the reference handler for references in custom plugin configurations.
    /// </summary>
    public ReferenceHandler? CustomConfigReferenceHandler { get; }

    /// <summary>
    /// Discovers and registers all plugins of all loaded assemblies.
    /// </summary>
    public void DiscoverAndRegisterPlugIns()
    {
        var plugIns = this.DiscoverNewPlugIns();
        this.ValidateNoDuplicateGuids(plugIns);
        this.RegisterPlugIns(plugIns);
    }

    /// <summary>
    /// Discovers and registers plugins of the specified assembly.
    /// </summary>
    /// <param name="assembly">The assembly.</param>
    public void DiscoverAndRegisterPlugIns(Assembly assembly)
    {
        var plugIns = this.DiscoverNewPlugIns(this.DiscoverPlugIns(assembly));
        this.ValidateNoDuplicateGuids(plugIns);
        this.RegisterPlugIns(plugIns);
    }

    /// <summary>
    /// Discovers and register plugins of type <typeparamref name="T"/>.
    /// </summary>
    /// <typeparam name="T">The type of the plugins that should be discovered.</typeparam>
    public void DiscoverAndRegisterPlugInsOf<T>()
    {
        var plugIns = this.DiscoverAllPlugIns().Where(type => typeof(T).IsAssignableFrom(type));
        this.RegisterPlugIns(plugIns);
    }

    /// <summary>
    /// Gets the known plugins of the given interface type.
    /// </summary>
    /// <typeparam name="T">The plugin interface type. Type parameter of a <see cref="CustomPlugInContainerBase{TPlugIn}"/>.</typeparam>
    /// <returns>The known plugins of the given interface type.</returns>
    public IEnumerable<Type> GetKnownPlugInsOf<T>()
    {
        if (this._knownPlugInsPerInterfaceType.TryGetValue(typeof(T), out var result))
        {
            return result;
        }

        return this._knownPlugIns.Values.Where(p => typeof(T).IsAssignableFrom(p));
    }

    /// <summary>
    /// Gets the active plugins of the specified type.
    /// </summary>
    /// <typeparam name="TPlugIn">The type of the plugin.</typeparam>
    /// <returns>The active plugins of the specified type.</returns>
    public IEnumerable<TPlugIn> GetActivePlugInsOf<TPlugIn>()
    {
        if (this._plugInPoints.TryGetValue(typeof(TPlugIn), out var point) && point is IPlugInContainer<TPlugIn> container)
        {
            return container.ActivePlugIns;
        }

        return Enumerable.Empty<TPlugIn>();
    }

    /// <summary>
    /// Deactivates the plugin of type <typeparamref name="TPlugIn"/>.
    /// </summary>
    /// <typeparam name="TPlugIn">The type of the plugin.</typeparam>
    public void DeactivatePlugIn<TPlugIn>() => this.DeactivatePlugIn(typeof(TPlugIn));

    /// <summary>
    /// Deactivates the plugin of the specified type.
    /// </summary>
    /// <param name="plugIn">The plugin.</param>
    public void DeactivatePlugIn(Type plugIn) => this.DeactivatePlugIn(plugIn.GUID);

    /// <summary>
    /// Deactivates the plugin with the specified type id.
    /// </summary>
    /// <param name="plugInId">The plugin identifier.</param>
    public void DeactivatePlugIn(Guid plugInId)
    {
        if (this._knownPlugIns.TryGetValue(plugInId, out var plugInType))
        {
            this._activePlugIns.TryRemove(plugInId, out _);
            this.PlugInDeactivated?.Invoke(this, new PlugInEventArgs(plugInType));
        }
    }

    /// <summary>
    /// Activates the plugin of type <typeparamref name="TPlugIn"/>.
    /// </summary>
    /// <typeparam name="TPlugIn">The type of the plugin.</typeparam>
    public void ActivatePlugIn<TPlugIn>() => this.ActivatePlugIn(typeof(TPlugIn));

    /// <summary>
    /// Activates the plugin of the specified type.
    /// </summary>
    /// <param name="plugIn">The plugin.</param>
    public void ActivatePlugIn(Type plugIn) => this.ActivatePlugIn(plugIn.GUID);

    /// <summary>
    /// Activates the plugin with the specified type id.
    /// </summary>
    /// <param name="plugInId">The plugin identifier.</param>
    public void ActivatePlugIn(Guid plugInId)
    {
        if (this._knownPlugIns.TryGetValue(plugInId, out var plugInType))
        {
            this._activePlugIns.TryAdd(plugInId, plugInType);
            this.PlugInActivated?.Invoke(this, new PlugInEventArgs(plugInType));
        }
    }

    /// <summary>
    /// Gets the plugin point which implements <typeparamref name="TPlugIn"/>.
    /// </summary>
    /// <typeparam name="TPlugIn">The type of the plugin.</typeparam>
    /// <returns>The plugin point which implements <typeparamref name="TPlugIn"/>, if available; Otherwise, <c>null</c>.</returns>
    public TPlugIn? GetPlugInPoint<TPlugIn>()
        where TPlugIn : class
    {
        if (this._plugInPoints.TryGetValue(typeof(TPlugIn), out var obj) && obj is TPlugIn plugIn)
        {
            return plugIn;
        }

        return null;
    }

    /// <summary>
    /// Gets the strategy plugin.
    /// </summary>
    /// <typeparam name="TKey">The type of the key.</typeparam>
    /// <typeparam name="TStrategy">The type of the strategy.</typeparam>
    /// <returns>The strategy plugin.</returns>
    public IStrategyPlugInProvider<TKey, TStrategy>? GetStrategyProvider<TKey, TStrategy>()
        where TStrategy : class, IStrategyPlugIn<TKey>
    {
        if (this._plugInPoints.TryGetValue(typeof(TStrategy), out var obj) && obj is IStrategyPlugInProvider<TKey, TStrategy> plugIn)
        {
            return plugIn;
        }

        return null;
    }

    /// <summary>
    /// Gets the strategy plugin.
    /// </summary>
    /// <typeparam name="TKey">The type of the key.</typeparam>
    /// <typeparam name="TStrategy">The type of the strategy.</typeparam>
    /// <param name="key">The key.</param>
    /// <returns>The strategy plugin of the specified key, if available; Otherwise, <c>null</c>.</returns>
    public TStrategy? GetStrategy<TKey, TStrategy>(TKey key)
        where TStrategy : class, IStrategyPlugIn<TKey>
    {
        return this.GetStrategyProvider<TKey, TStrategy>()?[key];
    }

    /// <summary>
    /// Gets the strategy plugin.
    /// </summary>
    /// <typeparam name="TStrategy">The type of the strategy.</typeparam>
    /// <param name="key">The key.</param>
    /// <returns>The strategy plugin of the specified key, if available; Otherwise, <c>null</c>.</returns>
    public TStrategy? GetStrategy<TStrategy>(string key)
        where TStrategy : class, IStrategyPlugIn<string>
    {
        return this.GetStrategy<string, TStrategy>(key);
    }

    /// <summary>
    /// Determines whether the specified plugin type is configured as active.
    /// </summary>
    /// <param name="plugInType">Type of the plugin.</param>
    /// <returns>
    ///   <c>true</c> if the specified plugin type is configured as active; otherwise, <c>false</c>.
    /// </returns>
    public bool IsPlugInActive(Type plugInType)
    {
        return this.IsPlugInActive(plugInType.GUID);
    }

    /// <summary>
    /// Determines whether the specified plugin type is configured as active.
    /// </summary>
    /// <param name="plugInTypeId">Identifier of the type of the plugin.</param>
    /// <returns>
    ///   <c>true</c> if the specified plugin type is configured as active; otherwise, <c>false</c>.
    /// </returns>
    public bool IsPlugInActive(Guid plugInTypeId)
    {
        return this._activePlugIns.ContainsKey(plugInTypeId);
    }

    /// <summary>
    /// Registers the plugin class for the specified plugin interface.
    /// </summary>
    /// <typeparam name="TPlugInInterface">The type of the plugin interface.</typeparam>
    /// <typeparam name="TPlugInClass">The type of the plugin class.</typeparam>
    public void RegisterPlugIn<TPlugInInterface, TPlugInClass>()
        where TPlugInInterface : class
        where TPlugInClass : class, TPlugInInterface
    {
        this.RegisterPlugInType(typeof(TPlugInClass));
        if (typeof(TPlugInInterface).GetCustomAttribute(typeof(PlugInPointAttribute)) != null)
        {
            var plugIn = this._lastCreatedPlugIn as TPlugInClass ?? this.CreatePlugInInstance<TPlugInClass>();
            this._lastCreatedPlugIn = plugIn;
            this.RegisterPlugInAtPlugInPoint<TPlugInInterface>(plugIn);
        }
        else if (this.GetCustomPlugInPointType(typeof(TPlugInInterface)) is { } customPlugInPointType)
        {
            if (!this._knownPlugInsPerInterfaceType.TryGetValue(customPlugInPointType, out var plugInList))
            {
                plugInList = new HashSet<Type>();
                this._knownPlugInsPerInterfaceType.TryAdd(customPlugInPointType, plugInList);
            }

            plugInList.Add(typeof(TPlugInClass));
            this.PlugInActivated?.Invoke(this, new PlugInEventArgs(typeof(TPlugInClass)));
        }
        else
        {
            this._logger.LogWarning("Plugin {PlugInClass} wasn't registered, because it's not an implementation of an interface which is marked with PlugInPointAttribute or CustomPlugInContainerAttribute.", typeof(TPlugInClass));
        }
    }

    /// <summary>
    /// Registers the plugin instance for the specified plugin point interface.
    /// </summary>
    /// <typeparam name="TPlugInInterface">The type of the plugin interface.</typeparam>
    /// <param name="instance">The instance.</param>
    /// <exception cref="ArgumentException">Plugin Type {instance.GetType()} - instance.</exception>
    public void RegisterPlugInAtPlugInPoint<TPlugInInterface>(TPlugInInterface instance)
        where TPlugInInterface : class
    {
        if (instance.GetType().GetCustomAttribute<GuidAttribute>() is null)
        {
            throw new ArgumentException($"Plugin Type {instance.GetType()} is missing a {typeof(GuidAttribute)}. It's required to identify the plugin in the configuration. Otherwise, the plugin would get a different Guid every time it gets compiled.", nameof(instance));
        }

        if (!this._plugInPoints.TryGetValue(typeof(TPlugInInterface), out var point))
        {
            var proxy = this.CreateProxy<TPlugInInterface>();
            proxy.AddPlugIn(instance, true);
            this._plugInPoints.Add(typeof(TPlugInInterface), proxy);
        }
        else if (point is IPlugInContainer<TPlugInInterface> proxy)
        {
            proxy.AddPlugIn(instance, true);
        }
        else
        {
            throw new InvalidPlugInProxyException(point.GetType(), typeof(IPlugInContainer<TPlugInInterface>));
        }

        this.RegisterPlugInType(instance.GetType());
    }

    /// <summary>
    /// Configures the plugin.
    /// </summary>
    /// <param name="plugInId">The plugin identifier.</param>
    /// <param name="configuration">The configuration.</param>
    public void ConfigurePlugIn(Guid plugInId, PlugInConfiguration configuration)
    {
        if (this._knownPlugIns.TryGetValue(plugInId, out var plugInType))
        {
            this.ConfigurePlugIn(plugInType, configuration);
        }
    }

    private void ValidateNoDuplicateGuids(IEnumerable<Type> plugIns)
    {
        var allPlugIns = plugIns.Concat(this._knownPlugIns.Values).Distinct();
        var duplicates = allPlugIns.GroupBy(t => t.GUID).Where(g => g.Count() > 1).ToList();
        if (duplicates.Count == 0)
        {
            return;
        }

        var message = string.Join("; ", duplicates.Select(g =>
            $"{g.Key} used by {string.Join(", ", g.Select(t => t.FullName ?? t.Name))}"));
        throw new DuplicatePlugInGuidException(message);
    }

    private Type? GetCustomPlugInPointType(Type interfaceType)
    {
        if (interfaceType.GetCustomAttribute<CustomPlugInContainerAttribute>() != null)
        {
            return interfaceType;
        }

        return interfaceType.GetInterfaces().FirstOrDefault(i => i.GetCustomAttribute<CustomPlugInContainerAttribute>() != null);
    }

    private void RegisterPlugInType(Type plugInType)
    {
        var plugInTypeId = plugInType.GUID;
        if (!this._knownPlugIns.ContainsKey(plugInTypeId))
        {
            this._knownPlugIns.Add(plugInTypeId, plugInType);
            this._activePlugIns.TryAdd(plugInTypeId, plugInType); // registered plugins are by default active
            this._logger.LogDebug("Added known plugin {0}, {1}", plugInTypeId, plugInType);
        }
    }

    private IPlugInContainer<TPlugInInterface> CreateProxy<TPlugInInterface>()
        where TPlugInInterface : class
    {
        IPlugInContainer<TPlugInInterface> proxy;
        var strategyPlugInInterface = typeof(TPlugInInterface).GetInterfaces().FirstOrDefault(i => i.IsGenericType && i.GetGenericTypeDefinition() == typeof(IStrategyPlugIn<>));
        if (strategyPlugInInterface != null)
        {
            var keyType = strategyPlugInInterface.GetGenericArguments()[0];
            var providerType = typeof(StrategyPlugInProvider<,>).MakeGenericType(keyType, typeof(TPlugInInterface));
            proxy = (IPlugInContainer<TPlugInInterface>)ActivatorUtilities.CreateInstance(this._serviceContainer, providerType);
        }
        else
        {
            var proxyGenerator = new PlugInProxyTypeGenerator();
            proxy = proxyGenerator.GenerateProxy<TPlugInInterface>(this);
        }

        return proxy;
    }

    private TPlugInClass CreatePlugInInstance<TPlugInClass>()
    {
        return ActivatorUtilities.CreateInstance<TPlugInClass>(this._serviceContainer);
    }

    private void ReadConfiguration(PlugInConfiguration configuration, HashSet<string> loadedAssemblies)
    {
        if (!this._knownPlugIns.ContainsKey(configuration.TypeId))
        {
            if (!string.IsNullOrEmpty(configuration.ExternalAssemblyName)
                && !loadedAssemblies.Contains(configuration.ExternalAssemblyName.ToLower()))
            {
                loadedAssemblies.Add(configuration.ExternalAssemblyName.ToLower());

                try
                {
                    var assembly = Assembly.LoadFile("plugins\\" + configuration.ExternalAssemblyName);
                    this.DiscoverAndRegisterPlugIns(assembly);
                }
                catch (Exception e)
                {
                    this._logger.LogError(e, "Error while loading external plugin assembly {ExternalAssemblyName} for plugin {TypeId}.", configuration.ExternalAssemblyName, configuration.TypeId);
                    return;
                }
            }
            else if (!string.IsNullOrEmpty(configuration.CustomPlugInSource))
            {
                this._logger.LogWarning("Custom plugin source found at plugin configuration: {Configuration}", configuration);
                /* TODO: Implement code signing, if we really need this feature.
                Assembly customPlugInAssembly = this.CompileCustomPlugInAssembly(configuration);
                this.DiscoverAndRegisterPlugIns(customPlugInAssembly);*/
            }
            else
            {
                // nothing we can do
            }
        }

        if (this._knownPlugIns.TryGetValue(configuration.TypeId, out var plugInType))
        {
            if (!configuration.IsActive)
            {
                this.DeactivatePlugIn(plugInType);
            }

            this.ConfigurePlugIn(plugInType, configuration);

            // When the IsActive property changed, we activate/deactivate accordingly.
            // Currently, property changes are only fired for IsActive, so we don't need to check it.
            configuration.PropertyChanged += (sender, args) => this.OnConfigurationChanged(configuration, plugInType, args.PropertyName);
        }
        else
        {
            this._logger.LogWarning("Unknown plugin type for id {TypeId}", configuration.TypeId);
        }
    }

    private void OnConfigurationChanged(PlugInConfiguration configuration, Type plugInType, string? propertyName)
    {
        if (propertyName == nameof(PlugInConfiguration.IsActive))
        {
            if (configuration.IsActive)
            {
                this.ActivatePlugIn(plugInType);
                this.ConfigurePlugIn(plugInType, configuration);
            }
            else
            {
                this.DeactivatePlugIn(plugInType);
            }
        }

        if (propertyName == nameof(PlugInConfiguration.CustomConfiguration))
        {
            this.ConfigurePlugIn(plugInType, configuration);
        }
    }

    private void ConfigurePlugIn(Type plugInType, PlugInConfiguration configuration)
    {
        this.PlugInConfigurationChanged?.Invoke(this, new PlugInConfigurationChangedEventArgs(plugInType, configuration));
    }

    private IEnumerable<Type> DiscoverNewPlugIns()
    {
        return this.DiscoverNewPlugIns(this.DiscoverAllPlugIns());
    }

    private IEnumerable<Type> DiscoverNewPlugIns(IEnumerable<Type> allPlugIns)
    {
        var newPlugIns = allPlugIns.Where(plugIn => !this._knownPlugIns.ContainsKey(plugIn.GUID)).ToList();
        return newPlugIns;
    }

    private IEnumerable<Type> DiscoverAllPlugIns()
    {
        return AppDomain.CurrentDomain.GetAssemblies()
            .Where(assembly => assembly.FullName is not null)
            .Where(assembly => !assembly.FullName!.StartsWith("System"))
            .Where(assembly => !assembly.FullName!.StartsWith("Microsoft"))
            .Where(assembly => !assembly.FullName!.StartsWith("Nito"))
            .Where(assembly => !assembly.FullName!.StartsWith("Blazor"))
            .SelectMany(assembly =>
                {
                    try
                    {
                        return assembly.DefinedTypes.Where(type => type.GetCustomAttribute<PlugInAttribute>() != null);
                    }
                    catch (ReflectionTypeLoadException ex)
                    {
                        return ex.Types.WhereNotNull();
                    }
                    catch (Exception)
                    {
                        return Enumerable.Empty<Type>();
                    }
                });
    }

    private IEnumerable<Type> DiscoverPlugIns(Assembly assembly)
    {
        return assembly.DefinedTypes.Where(type => type.GetCustomAttribute<PlugInAttribute>() != null);
    }

    private void RegisterPlugIns(IEnumerable<Type> plugIns)
    {
        foreach (var plugIn in plugIns)
        {
            try
            {
                // A plugin usually should be small, but it should be possible that one plugin can implement more than one plugin interface.
                // In this case, we need to register it at every plugin point
                var plugInInterfaces = plugIn.GetInterfaces().Where(t => t.IsInterface && (t.GetCustomAttribute<PlugInPointAttribute>() != null || t.GetCustomAttribute<CustomPlugInContainerAttribute>() != null));
                foreach (var plugInInterface in plugInInterfaces)
                {
                    var genericMethod = this.GetType().GetMethods().FirstOrDefault(mi => mi.IsGenericMethod && mi.Name == nameof(this.RegisterPlugIn))?.MakeGenericMethod(plugInInterface, plugIn);
                    genericMethod?.Invoke(this, []);
                }
            }
            catch (Exception e)
            {
                this._logger.LogError(e, "Couldn't register plugin type {PlugIn}", plugIn);
                this._logger.LogError("TODO: Use ServiceContainer");
            }

            this._lastCreatedPlugIn = null;
        }
    }

    /// <summary>
    /// Exception that is thrown when two different plugin types share the same <see cref="GuidAttribute"/>.
    /// </summary>
    public class DuplicatePlugInGuidException : InvalidOperationException
    {
        /// <summary>
        /// Initializes a new instance of the <see cref="DuplicatePlugInGuidException"/> class.
        /// </summary>
        /// <param name="message">The message.</param>
        public DuplicatePlugInGuidException(string message)
            : base(message)
        {
        }
    }

    /// <summary>
    /// Exception that occurs when the created proxy doesn't implement the expected interface <see cref="IPlugInContainer{TPlugIn}"/>.
    /// </summary>
    /// <seealso cref="System.Exception" />
    public class InvalidPlugInProxyException : Exception
    {
        /// <summary>
        /// Initializes a new instance of the <see cref="InvalidPlugInProxyException"/> class.
        /// </summary>
        /// <param name="type">The actual class type of the proxy.</param>
        /// <param name="expectedType">The expected interface type of the proxy.</param>
        public InvalidPlugInProxyException(Type type, Type expectedType)
        {
            this.Type = type;
            this.ExpectedType = expectedType;
        }

        /// <summary>
        /// Gets the actual class type of the proxy.
        /// </summary>
        /// <value>
        /// The type.
        /// </value>
        public Type Type { get; }

        /// <summary>
        /// Gets the expected interface type of the proxy.
        /// </summary>
        public Type ExpectedType { get; }

        /// <inheritdoc />
        public override string ToString()
        {
            return $"Unexpected plugin proxy type {this.Type}. Expected one of {this.ExpectedType}";
        }
    }
}