/* 
 * FreeSWITCH Modular Media Switching Software Library / Soft-Switch Application - mod_managed
 * Copyright (C) 2008, Michael Giagnocavo <mgg@giagnocavo.net>
 *
 * Version: MPL 1.1
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 * http://www.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is FreeSWITCH Modular Media Switching Software Library / Soft-Switch Application - mod_managed
 *
 * The Initial Developer of the Original Code is
 * Michael Giagnocavo <mgg@giagnocavo.net>
 * Portions created by the Initial Developer are Copyright (C)
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 * 
 * Michael Giagnocavo <mgg@giagnocavo.net>
 * Jeff Lenk <jeff@jefflenk.com>
 * 
 * PluginManager.cs -- Plugin execution code
 *
 */

using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using System.Reflection.Emit;

namespace FreeSWITCH {

    internal abstract class PluginExecutor : MarshalByRefObject {
        public override object InitializeLifetimeService() {
            return null;
        }

        /// <summary>Names by which this plugin may be executed.</summary>
        public List<string> Aliases { get { return aliases; } }
        readonly List<string> aliases = new List<string>();
        
        /// <summary>The canonical name to identify this plugin (informative).</summary>
        public string Name { get { return name; } }
        readonly string name;

        protected PluginExecutor(string name, List<string> aliases) {
            if (string.IsNullOrEmpty(name)) throw new ArgumentException("No name provided.");
            if (aliases == null || aliases.Count == 0) throw new ArgumentException("No aliases provided.");
            this.name = name;
            this.aliases = aliases.Distinct().ToList();
        }

        int useCount = 0;
        protected void IncreaseUse() {
            System.Threading.Interlocked.Increment(ref useCount);
        }
        protected void DecreaseUse() {
            var count = System.Threading.Interlocked.Decrement(ref useCount);
            if (count == 0 && onZeroUse != null) {
                onZeroUse();
            }
        }

        Action onZeroUse;
        public void SetZeroUseNotification(Action onZeroUse) {
            this.onZeroUse = onZeroUse;
            if (useCount == 0) onZeroUse();
        }

        protected static void LogException(string action, string moduleName, Exception ex) {
            Log.WriteLine(LogLevel.Error, "{0} exception in {1}: {2}", action, moduleName, ex.Message);
            Log.WriteLine(LogLevel.Debug, "{0} exception: {1}", moduleName, ex.ToString());
        }
    }

    internal sealed class AppPluginExecutor : PluginExecutor {

        readonly Func<IAppPlugin> createPlugin;

        public AppPluginExecutor(string name, List<string> aliases, Func<IAppPlugin> creator)
            : base(name, aliases) {
            if (creator == null) throw new ArgumentNullException("Creator cannot be null.");
            this.createPlugin = creator;
        }

        public bool Execute(string args, IntPtr sessionHandle) {
            IncreaseUse();
            try {
                using (var session = new Native.ManagedSession(new Native.SWIGTYPE_p_switch_core_session(sessionHandle, false))) {
                    session.Initialize();
                    session.SetAutoHangup(false);
                    try {
                        var plugin = createPlugin();
                        var context = new AppContext(args, session);;
                        plugin.Run(context);
                        return true;
                    } catch (Exception ex) {
                        LogException("Run", Name, ex);
                        return false;
                    }
                }
            } finally {
                DecreaseUse();
            }
        }
    }

    internal sealed class ApiPluginExecutor : PluginExecutor {

        readonly Func<IApiPlugin> createPlugin;

        public ApiPluginExecutor(string name, List<string> aliases, Func<IApiPlugin> creator)
            : base(name, aliases) {
            if (creator == null) throw new ArgumentNullException("Creator cannot be null.");
            this.createPlugin = creator;
        }

        public bool ExecuteApi(string args, IntPtr streamHandle, IntPtr eventHandle) {
            IncreaseUse();
            try {
                using (var stream = new Native.Stream(new Native.switch_stream_handle(streamHandle, false)))
                using (var evt = eventHandle == IntPtr.Zero ? null : new Native.Event(new Native.switch_event(eventHandle, false), 0)) {
                    try {
                        var context = new ApiContext(args, stream, evt);
                        var plugin = createPlugin();
                        plugin.Execute(context);
                        return true;
                    } catch (Exception ex) {
                        LogException("Execute", Name, ex);
                        return false;
                    }
                }
            } finally {
                DecreaseUse();
            }
        }

        public bool ExecuteApiBackground(string args) {
            // Background doesn't affect use count
            new System.Threading.Thread(() => {
                try {
                    var context = new ApiBackgroundContext(args);
                    var plugin = createPlugin();
                    plugin.ExecuteBackground(context);
                    Log.WriteLine(LogLevel.Debug, "ExecuteBackground in {0} completed.", Name);
                } catch (Exception ex) {
                    LogException("ExecuteBackground", Name, ex);
                }
            }).Start();
            return true;
        }
    }

    internal abstract class PluginManager : MarshalByRefObject {
        public override object InitializeLifetimeService() {
            return null;
        }

        public List<ApiPluginExecutor> ApiExecutors { get { return _apiExecutors; } }
        readonly List<ApiPluginExecutor> _apiExecutors = new List<ApiPluginExecutor>();

        public List<AppPluginExecutor> AppExecutors { get { return _appExecutors; }  }

        readonly List<AppPluginExecutor> _appExecutors = new List<AppPluginExecutor>();

        bool isLoaded = false;

        public bool Load(string file) {
            Console.WriteLine("Loading {0} from domain {1}", file, AppDomain.CurrentDomain.FriendlyName);
            if (isLoaded) throw new InvalidOperationException("PluginManager has already been loaded.");
            if (string.IsNullOrEmpty(file)) throw new ArgumentNullException("file cannot be null or empty.");
            if (AppDomain.CurrentDomain.IsDefaultAppDomain()) throw new InvalidOperationException("PluginManager must load in its own AppDomain.");
            var res = LoadInternal(file);
            isLoaded = true;

            if (res) {
                res = (AppExecutors.Count > 0 || ApiExecutors.Count > 0);
                if (!res) Log.WriteLine(LogLevel.Info, "No App or Api plugins found in {0}.", file);
            }
            return res;
        }

        protected abstract bool LoadInternal(string fileName);

        protected bool RunLoadNotify(Type[] allTypes) {
            // Run Load on all the load plugins
            var ty = typeof(ILoadNotificationPlugin);
            var pluginTypes = allTypes.Where(x => ty.IsAssignableFrom(x) && !x.IsAbstract).ToList();
            if (pluginTypes.Count == 0) return true;
            foreach (var pt in pluginTypes) {
                var load = ((ILoadNotificationPlugin)Activator.CreateInstance(pt, false));
                if (!load.Load()) {
                    Log.WriteLine(LogLevel.Notice, "Type {0} requested no loading. Assembly will not be loaded.", pt.FullName);
                    return false;
                }
            }
            return true;
        }

        protected void AddApiPlugins(Type[] allTypes) {
            var iApiTy = typeof(IApiPlugin);
            foreach (var ty in allTypes.Where(x => iApiTy.IsAssignableFrom(x) && !x.IsAbstract)) {
                var del = CreateConstructorDelegate<IApiPlugin>(ty);
                var exec = new ApiPluginExecutor(ty.FullName, new List<string> { ty.FullName, ty.Name }, del);
                this.ApiExecutors.Add(exec);
            }
        }

        protected void AddAppPlugins(Type[] allTypes) {
            var iAppTy = typeof(IAppPlugin);
            foreach (var ty in allTypes.Where(x => iAppTy.IsAssignableFrom(x) && !x.IsAbstract)) {
                var del = CreateConstructorDelegate<IAppPlugin>(ty);
                var exec = new AppPluginExecutor(ty.FullName, new List<string> { ty.FullName, ty.Name }, del);
                this.AppExecutors.Add(exec);
            }
        }

        #region Unload

        bool isUnloading = false;
        int unloadCount;
        System.Threading.ManualResetEvent unloadSignal = new System.Threading.ManualResetEvent(false);
        void decreaseUnloadCount() {
            if (System.Threading.Interlocked.Decrement(ref unloadCount) == 0) {
                unloadSignal.Set();
            }
        }

        public void BlockUntilUnloadIsSafe() {
            if (isUnloading) throw new InvalidOperationException("PluginManager is already unloading.");
            isUnloading = true;
            unloadCount = ApiExecutors.Count + AppExecutors.Count;
            ApiExecutors.ForEach(x => x.SetZeroUseNotification(decreaseUnloadCount));
            AppExecutors.ForEach(x => x.SetZeroUseNotification(decreaseUnloadCount));
            unloadSignal.WaitOne();
        }

        #endregion

        public static Func<T> CreateConstructorDelegate<T>(Type ty) {
            var destTy = typeof(T);
            if (!destTy.IsAssignableFrom(ty)) throw new ArgumentException(string.Format("Type {0} is not assignable from {1}.", destTy.FullName, ty.FullName));
            var con = ty.GetConstructor(Type.EmptyTypes);
            if (con == null) throw new ArgumentException(string.Format("Type {0} doesn't have an accessible parameterless constructor.", ty.FullName));

            var rand = Guid.NewGuid().ToString().Replace("-", "");
            var dm = new DynamicMethod("CREATE_" + ty.FullName.Replace('.', '_') + rand, ty, null, true);
            var il = dm.GetILGenerator();
            il.Emit(OpCodes.Newobj, ty.GetConstructor(Type.EmptyTypes));
            il.Emit(OpCodes.Ret);

            return (Func<T>)dm.CreateDelegate(typeof(Func<T>));
        }
    }

    internal class AsmPluginManager : PluginManager {

        protected override bool LoadInternal(string fileName) {
            Assembly asm;
            try {
                asm = Assembly.LoadFrom(fileName);
            } catch (Exception ex) {
                Log.WriteLine(LogLevel.Info, "Couldn't load {0}: {1}", fileName, ex.Message);
                return false;
            }

            // Ensure it's a plugin assembly
            var ourName = Assembly.GetExecutingAssembly().GetName().Name;
            if (!asm.GetReferencedAssemblies().Any(n => n.Name == ourName)) {
                Log.WriteLine(LogLevel.Debug, "Assembly {0} doesn't reference FreeSWITCH.Managed, not loading.");
                return false; 
            }

            // See if it wants to be loaded
            var allTypes = asm.GetExportedTypes();
            if (!RunLoadNotify(allTypes)) return false;

            AddApiPlugins(allTypes);
            AddAppPlugins(allTypes);

            return true;
        }

    }

}
