/*
* Copyright (c) 2022 Vaughn Nugent
* 
* Library: VNLib
* Package: VNLib.Plugins.Runtime
* File: LivePlugin.cs 
*
* LivePlugin.cs is part of VNLib.Plugins.Runtime which is part of the larger 
* VNLib collection of libraries and utilities.
*
* VNLib.Plugins.Runtime is free software: you can redistribute it and/or modify 
* it under the terms of the GNU General Public License as published
* by the Free Software Foundation, either version 2 of the License,
* or (at your option) any later version.
*
* VNLib.Plugins.Runtime is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License 
* along with VNLib.Plugins.Runtime. If not, see http://www.gnu.org/licenses/.
*/

using System;
using System.Linq;
using System.Reflection;
using System.Text.Json;

using VNLib.Utils.Logging;
using VNLib.Utils.Extensions;
using VNLib.Plugins.Attributes;

namespace VNLib.Plugins.Runtime
{
    /// <summary>
    /// <para>
    /// Wrapper for a loaded <see cref="IPlugin"/> instance, used internally 
    /// for a single instance. 
    /// </para>
    /// <para>
    /// Lifetime: for the existance of a single loaded 
    /// plugin instance. Created once per loaded plugin instance. Once the plugin
    /// is unloaded, it is no longer useable.
    /// </para>
    /// </summary>
    public class LivePlugin : IEquatable<IPlugin>, IEquatable<LivePlugin>
    {
        /// <summary>
        /// The plugin's <see cref="IPlugin.PluginName"/> property during load time
        /// </summary>
        /// <exception cref="InvalidOperationException"></exception>
        public string PluginName => Plugin?.PluginName ?? throw new InvalidOperationException("Plugin is not loaded");

        /// <summary>
        /// The underlying <see cref="IPlugin"/> that is warpped
        /// by he current instance
        /// </summary>
        public IPlugin? Plugin { get; private set; }
        
        private readonly Type PluginType;
       
        private ConsoleEventHandlerSignature? PluginConsoleHandler;

        internal LivePlugin(IPlugin plugin)
        {
            Plugin = plugin;
            PluginType = plugin.GetType();
            GetConsoleHandler();
        }

        private void GetConsoleHandler()
        {
            //Get the console handler method from the plugin instance
            MethodInfo? handler = (from m in PluginType.GetMethods()
                                   where m.GetCustomAttribute<ConsoleEventHandlerAttribute>() != null
                                   select m)
                                   .FirstOrDefault();
            //Get a delegate handler for the plugin
            PluginConsoleHandler = handler?.CreateDelegate<ConsoleEventHandlerSignature>(Plugin);
        }

        /// <summary>
        /// Sets the plugin's configuration if it defines a <see cref="ConfigurationInitalizerAttribute"/>
        /// on an instance method
        /// </summary>
        /// <param name="hostConfig">The host configuration DOM</param>
        /// <param name="pluginConf">The plugin local configuration DOM</param>
        internal void InitConfig(JsonDocument hostConfig, JsonDocument pluginConf)
        {
            //Get the console handler method from the plugin instance
            MethodInfo? confHan = PluginType.GetMethods().Where(static m => m.GetCustomAttribute<ConfigurationInitalizerAttribute>() != null)
                                  .FirstOrDefault();
            //Get a delegate handler for the plugin
            ConfigInitializer? configInit = confHan?.CreateDelegate<ConfigInitializer>(Plugin);
            if (configInit == null)
            {
                return;
            }
            //Merge configurations before passing to plugin
            JsonDocument merged = hostConfig.Merge(pluginConf, "host", PluginType.Name);
            try
            {
                //Invoke
                configInit.Invoke(merged);
            }
            catch
            {
                merged.Dispose();
                throw;
            }
        }
        
        /// <summary>
        /// Invokes the plugin's log initalizer method if it defines a <see cref="LogInitializerAttribute"/>
        /// on an instance method
        /// </summary>
        /// <param name="cliArgs">The current process's CLI args</param>
        internal void InitLog(string[] cliArgs)
        {
            //Get the console handler method from the plugin instance
            MethodInfo? logInit = (from m in PluginType.GetMethods()
                                   where m.GetCustomAttribute<LogInitializerAttribute>() != null
                                   select m)
                                   .FirstOrDefault();
            //Get a delegate handler for the plugin
            LogInitializer? logFunc = logInit?.CreateDelegate<LogInitializer>(Plugin);
            //Invoke
            logFunc?.Invoke(cliArgs);
        }

        /// <summary>
        /// Invokes the plugins console event handler if the type has one 
        /// and the plugin is loaded.
        /// </summary>
        /// <param name="message">The message to pass to the plugin handler</param>
        /// <returns>
        /// True if the command was sent to the plugin, false if the plugin is
        /// unloaded or did not export a console event handler
        /// </returns>
        public bool SendConsoleMessage(string message)
        {
            //Make sure plugin is loaded and has a console handler
            if (PluginConsoleHandler == null)
            {
                return false;
            }
            //Invoke plugin console handler
            PluginConsoleHandler(message);
            return true;
        }

        /// <summary>
        /// Calls the <see cref="IPlugin.Load"/> method on the plugin if its loaded
        /// </summary>
        internal void LoadPlugin() => Plugin?.Load();

        /// <summary>
        /// Unloads all loaded endpoints from 
        /// that they were loaded to, then unloads the plugin.
        /// </summary>
        /// <param name="logSink">An optional log provider to write unload exceptions to</param>
        /// <remarks>
        /// If <paramref name="logSink"/> is no null unload exceptions are swallowed and written to the log
        /// </remarks>
        internal void UnloadPlugin(ILogProvider? logSink)
        {
            /*
             * We need to swallow plugin unload errors to avoid 
             * unknown state, making sure endpoints are properly 
             * unloaded!
             */
            try
            {
                //Unload the plugin
                Plugin?.Unload();
            }
            catch (Exception ex)
            {
                //Create an unload wrapper for the exception
                PluginUnloadException wrapper = new("Exception raised during plugin unload", ex);
                if (logSink == null)
                {
                    throw wrapper;
                }
                //Write error to log sink
                logSink.Error(wrapper);
            }
            Plugin = null;
            PluginConsoleHandler = null;
        }
        ///<inheritdoc/>
        public override bool Equals(object? obj)
        {
            Type? pluginType = Plugin?.GetType();
            Type? otherType = obj?.GetType();
            if(pluginType == null || otherType == null)
            {
                return false;
            }
            //If the other plugin is the same type as the current instance return true
            return pluginType.FullName == otherType.FullName;
        }
        ///<inheritdoc/>
        public bool Equals(LivePlugin? other)
        {
            return Equals(other?.Plugin);
        }
        ///<inheritdoc/>
        public bool Equals(IPlugin? other)
        {
            return Equals((object?)other);
        }
        ///<inheritdoc/>
        public override int GetHashCode()
        {
            return Plugin?.GetHashCode() ?? throw new InvalidOperationException("Plugin is null");
        }       
    }
}