// Copyright (c) 2004, 2019, Oracle and/or its affiliates. All rights reserved.
//
// This program is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License, version 2.0, as
// published by the Free Software Foundation.
//
// This program is also distributed with certain software (including
// but not limited to OpenSSL) that is licensed under separate terms,
// as designated in a particular file or component or in included license
// documentation.  The authors of MySQL hereby grant you an
// additional permission to link the program and your derivative works
// with the separately licensed software that they have included with
// MySQL.
//
// Without limiting anything contained in the foregoing, this file,
// which is part of MySQL Connector/NET, is also subject to the
// Universal FOSS Exception, version 1.0, a copy of which can be found at
// http://oss.oracle.com/licenses/universal-foss-exception.
//
// This program 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, version 2.0, for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software Foundation, Inc.,
// 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA

using MySql.Data.Failover;
using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Threading;


namespace MySql.Data.MySqlClient
{
    /// <summary>
    /// Summary description for MySqlPoolManager.
    /// </summary>
    internal class MySqlPoolManager
    {
        private static readonly Dictionary<string, MySqlPool> Pools = new Dictionary<string, MySqlPool>();
        private static readonly List<MySqlPool> ClearingPools = new List<MySqlPool>();
        internal const int DEMOTED_TIMEOUT = 120000;

#region Properties

        /// <summary>
        /// Queue of demoted hosts.
        /// </summary>
        internal static ConcurrentQueue<FailoverServer> DemotedHosts { get; set; }

        /// <summary>
        /// List of hosts that will be attempted to connect to.
        /// </summary>
        internal static List<FailoverServer> Hosts { get; set; }

        /// <summary>
        /// Timer to be used when a host have been demoted.
        /// </summary>
        internal static Timer DemotedServersTimer { get; set; }
#endregion

        // Timeout in seconds, after which an unused (idle) connection 
        // should be closed.
        internal static int maxConnectionIdleTime = 180;

        static MySqlPoolManager()
        {
            AppDomain.CurrentDomain.ProcessExit += EnsureClearingPools;
            AppDomain.CurrentDomain.DomainUnload += EnsureClearingPools;
        }

        private static void EnsureClearingPools(object sender, EventArgs e)
        {
            ClearAllPools();
        }

        // we add a small amount to the due time to let the cleanup detect
        // expired connections in the first cleanup.
        private static Timer timer = new Timer(
            CleanIdleConnections,
          null, (maxConnectionIdleTime * 1000) + 8000, maxConnectionIdleTime * 1000);

        private static string GetKey(MySqlConnectionStringBuilder settings)
        {
            string key = "";
            lock (settings)
            {
                key = settings.ConnectionString;
            }

            if (!settings.IntegratedSecurity || settings.ConnectionReset)
            {
                return key;
            }
#if !CF && !RT && !NETCOREAPP

      try
      {
                // Append SID to the connection string to generate a key
                // With Integrated security different Windows users with the same
                // connection string may be mapped to different MySQL accounts.
                System.Security.Principal.WindowsIdentity id =
          System.Security.Principal.WindowsIdentity.GetCurrent();

        key += ";" + id.User;

      }
      catch (System.Security.SecurityException ex)
      {
        // Documentation for WindowsIdentity.GetCurrent() states 
        // SecurityException can be thrown. In this case the 
        // connection can only be pooled if reset is done.
        throw new MySqlException(Resources.NoWindowsIdentity, ex);
      }
#endif

            return key;
        }

        public static MySqlPool GetPool(MySqlConnectionStringBuilder settings)
        {
            string text = GetKey(settings);

            lock (Pools)
            {
                MySqlPool pool;
                Pools.TryGetValue(text, out pool);

                if (pool == null)
                {
                    pool = new MySqlPool(settings);
                    Pools.Add(text, pool);
                }
                else
                {
                    pool.Settings = settings;
                }

                return pool;
            }
        }

        public static void RemoveConnection(Driver driver)
        {
            Debug.Assert(driver != null);

            MySqlPool pool = driver.Pool;

            pool?.RemoveConnection(driver);
        }

        public static void ReleaseConnection(Driver driver)
        {
            Debug.Assert(driver != null);

            MySqlPool pool = driver.Pool;

            pool?.ReleaseConnection(driver);
        }

        public static void ClearPool(MySqlConnectionStringBuilder settings)
        {
            Debug.Assert(settings != null);
            string text;
            try
            {
                text = GetKey(settings);
            }
            catch (MySqlException)
            {
                // Cannot retrieve windows identity for IntegratedSecurity=true
                // This can be ignored.
                return;
            }

            ClearPoolByText(text);
        }

        private static void ClearPoolByText(string key)
        {
            lock (Pools)
            {
                // if pools doesn't have it, then this pool must already have been cleared
                if (!Pools.ContainsKey(key))
                {
                    return;
                }

                // add the pool to our list of pools being cleared
                MySqlPool pool = (Pools[key] as MySqlPool);
                ClearingPools.Add(pool);

                // now tell the pool to clear itself
                pool.Clear();

                // and then remove the pool from the active pools list
                Pools.Remove(key);
            }
        }

        public static void ClearAllPools()
        {
            lock (Pools)
            {
                // Create separate keys list.
                List<string> keys = new List<string>(Pools.Count);
                keys.AddRange(Pools.Keys);

                // Remove all pools by key.
                foreach (string key in keys)
                {
                    ClearPoolByText(key);
                }
            }

            if (DemotedServersTimer != null)
            {
                DemotedServersTimer.Dispose();
                Hosts?.Clear();
                while (!DemotedHosts.IsEmpty)
                {
                    DemotedHosts.TryDequeue(out _);
                }
            }
        }

        public static void RemoveClearedPool(MySqlPool pool)
        {
            Debug.Assert(ClearingPools.Contains(pool));
            ClearingPools.Remove(pool);
        }

        /// <summary>
        /// Remove drivers that have been idle for too long.
        /// </summary>
        public static void CleanIdleConnections(object obj)
        {
            List<Driver> oldDrivers = new List<Driver>();
            lock (Pools)
            {
                foreach (MySqlPool pool in Pools.Keys.Select(key => Pools[key]))
                {
                    oldDrivers.AddRange(pool.RemoveOldIdleConnections());
                }
            }

            foreach (Driver driver in oldDrivers)
            {
                driver.Close();
            }
        }

        /// <summary>
        /// Remove hosts that have been on the demoted list for more
        /// than 120,000 milliseconds and add them to the available hosts list.
        /// </summary>
        internal static void ReleaseDemotedHosts(object state)
        {
            while (!DemotedHosts.IsEmpty)
            {
                if (DemotedHosts.TryPeek(out FailoverServer demotedServer) &&
                demotedServer.DemotedTime.AddMilliseconds(DEMOTED_TIMEOUT) < DateTime.Now)
                {
                    demotedServer.Attempted = false;
                    Hosts?.Add(demotedServer);
                    DemotedHosts.TryDequeue(out demotedServer);
                }
                else
                {
                    break;
                }
            }

            DemotedServersTimer.Change(DEMOTED_TIMEOUT, Timeout.Infinite);
        }
    }
}