using System;
using System.Collections.Generic;
using System.Diagnostics.CodeAnalysis;
using System.Linq;
using System.Net.Http.Headers;
using System.Reflection;
using System.Reflection.Metadata.Ecma335;
using System.Text;
using System.Threading.Tasks;

namespace Pilz.Plugins
{
    public class PluginManager<TPluginInterface, TPluginRuntimeInfo> where TPluginInterface : class where TPluginRuntimeInfo : PluginRuntimeInfo<TPluginInterface>
    {
        protected readonly List<TPluginRuntimeInfo> loadedPlugins = [];

        /// <summary>
        /// The default initialization parameters used when no parameters passed. Commonly used for dynamically loading assemblies.
        /// </summary>
        public virtual object?[] DefaultParameters { get; set; } = [];

        /// <summary>
        /// Returns a list of all currently loaded plugins.
        /// </summary>
        public virtual IEnumerable<TPluginRuntimeInfo> LoadedPlugins => loadedPlugins.AsReadOnly();

        protected void OnCurrentAppDomainAssemblyLoad(object? sender, AssemblyLoadEventArgs args)
        {
            LoadPlugins(args.LoadedAssembly);
        }

        /// <summary>
        /// Loads assembly from the given file paths and then loads the plugins from the assemblies.
        /// </summary>
        /// <param name="paths"></param>
        /// <param name="parameters"></param>
        /// <returns></returns>
        public virtual IEnumerable<PluginLoadInfo<TPluginInterface, TPluginRuntimeInfo>> LoadPlugins(string[] paths, params object?[]? parameters)
        {
            var results = new List<PluginLoadInfo<TPluginInterface, TPluginRuntimeInfo>>();

            foreach (var path in paths)
                results.Add(LoadPlugin(path, parameters));

            return results;
        }

        /// <summary>
        /// Loads plugins from the given assemblies.
        /// </summary>
        /// <param name="paths"></param>
        /// <param name="parameters"></param>
        /// <returns></returns>
        public virtual IEnumerable<PluginLoadInfo<TPluginInterface, TPluginRuntimeInfo>> LoadPlugins(Assembly[] assemblies, params object?[]? parameters)
        {
            var results = new List<PluginLoadInfo<TPluginInterface, TPluginRuntimeInfo>>();

            foreach (var assembly in assemblies)
                results.Add(LoadPlugins(assembly, parameters));

            return results;
        }

        /// <summary>
        /// Loads plugins from already loaded assemblies for the current <see cref="AppDomain.CurrentDomain"/>.
        /// </summary>
        /// <returns></returns>
        public virtual IEnumerable<PluginLoadInfo<TPluginInterface, TPluginRuntimeInfo>> LoadOwnPlugins(params object?[]? parameters)
        {
            return LoadOwnPlugins(false, parameters);
        }

        /// <summary>
        /// Loads plugins from already loaded assemblies for the current <see cref="AppDomain.CurrentDomain"/>.
        /// </summary>
        /// <param name="listenAssemblyLoadContext">Do also load plugins from all yet not loaded assemblies by listening the event <see cref="AppDomain.AssemblyLoad"/>.
        /// <returns></returns>
        public virtual IEnumerable<PluginLoadInfo<TPluginInterface, TPluginRuntimeInfo>> LoadOwnPlugins(bool listenAssemblyLoadContext, params object?[]? parameters)
        {
            var results = new List<PluginLoadInfo<TPluginInterface, TPluginRuntimeInfo>>();

            if (listenAssemblyLoadContext)
                AppDomain.CurrentDomain.AssemblyLoad += OnCurrentAppDomainAssemblyLoad;

            foreach (var assembly in AppDomain.CurrentDomain.GetAssemblies())
                results.Add(LoadPlugins(assembly, parameters));

            return results;
        }

        /// <summary>
        /// Loads an assembly from the given file path and then loads plugins from the assembly.
        /// </summary>
        /// <param name="path"></param>
        /// <param name="parameters"></param>
        /// <returns></returns>
        public virtual PluginLoadInfo<TPluginInterface, TPluginRuntimeInfo> LoadPlugin(string path, params object?[]? parameters)
        {
            var result = new PluginLoadInfo<TPluginInterface, TPluginRuntimeInfo>();
            var loadContext = new PluginLoadContext(path);

            if (File.Exists(path))
            {
                try
                {
                    result.Assembly = loadContext.LoadFromAssemblyName(new AssemblyName(Path.GetFileNameWithoutExtension(path)));
                }
                catch
                {
                    result.Status = PluginLoadStatus.ErrorAtLoading;
                }
            }
            else
                result.Status = PluginLoadStatus.FileNotFound;
            
            if (result.Assembly != null)
                LoadPlugin(result, parameters);

            return result;
        }

        /// <summary>
        /// Load plugins from a given assembly.
        /// </summary>
        /// <param name="assembly"></param>
        /// <param name="parameters"></param>
        /// <returns></returns>
        public virtual PluginLoadInfo<TPluginInterface, TPluginRuntimeInfo> LoadPlugins(Assembly assembly, params object?[]? parameters)
        {
            var result = new PluginLoadInfo<TPluginInterface, TPluginRuntimeInfo>
            {
                Assembly = assembly
            };

            LoadPlugin(result);
            
            return result;
        }

        /// <summary>
        /// Loads the plugin from a given type.
        /// <br/>Commonly used to ensure loading core plugins.
        /// </summary>
        /// <typeparam name="TPlugin"></typeparam>
        /// <param name="parameters"></param>
        /// <returns></returns>
        public virtual PluginLoadInfo<TPluginInterface, TPluginRuntimeInfo> LoadPlugin<TPlugin>(params object?[]? parameters) where TPlugin : TPluginInterface
        {
            var result = new PluginLoadInfo<TPluginInterface, TPluginRuntimeInfo>
            {
                Assembly = typeof(TPlugin).Assembly
            };

            LoadPlugin(result, typeof(TPlugin), parameters);

            return result;
        }

        protected virtual void LoadPlugin(PluginLoadInfo<TPluginInterface, TPluginRuntimeInfo> result, params object?[]? parameters)
        {
            if (result.Assembly == null)
                result.Status = PluginLoadStatus.NoValidPlugin;
            else if (loadedPlugins.Any(n => n.Assembly == result.Assembly))
                result.Status = PluginLoadStatus.AlreadyLoaded;
            else
            {
                foreach (var type in result.Assembly.GetTypes())
                    LoadPlugin(result, type, parameters);
            }

            if (result.PluginsInternal.Count == 0)
                result.Status = PluginLoadStatus.NoValidPlugin;
        }

        protected virtual void LoadPlugin(PluginLoadInfo<TPluginInterface, TPluginRuntimeInfo> result, Type type, params object?[]? parameters)
        {
            if (parameters == null || parameters.Length == 0)
                parameters = DefaultParameters;

            if (loadedPlugins.Any(n => n.Plugin != null && n.Plugin.GetType() == type))
                result.Status = PluginLoadStatus.AlreadyLoaded;
            else if (type.IsAssignableTo(typeof(TPluginInterface)))
            {
                var info = Activator.CreateInstance<TPluginRuntimeInfo>();
                info.Assembly = result.Assembly;
                result.PluginsInternal.Add(info);

                try
                {
                    if (Activator.CreateInstance(type,  null, parameters, null) is TPluginInterface plugin)
                    {
                        if (plugin is IPluginLateInitialization pluginLateInit)
                            pluginLateInit.LateInit();

                        info.Plugin = plugin;
                        info.Status = PluginStatus.Success;
                        loadedPlugins.Add(info);
                    }
                }
                catch (Exception ex)
                {
                    info.Exception = ex;
                    info.Status = PluginStatus.ErrorAtInitializing;
                }
            }
            else
                result.Status = PluginLoadStatus.NoValidPlugin;
        }

        protected virtual BindingFlags GetConstructorFlags()
        {
            return BindingFlags.Instance | BindingFlags.Public | BindingFlags.CreateInstance;
        }
    }
}