// 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.
//
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// 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.Common;
using MySql.Data.Failover;
using System;
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics;
using System.Threading;

using Sog.Properties;

namespace MySql.Data.MySqlClient
{
    /// <summary>
    /// Summary description for MySqlPool.
    /// </summary>
    internal sealed class MySqlPool
    {
        private readonly List<Driver> _inUsePool;
        private readonly Queue<Driver> _idlePool;
        private readonly uint _minSize;
        private readonly uint _maxSize;
        private readonly AutoResetEvent _autoEvent;
        private int _available;

        // Object used to lock the list of host obtained from DNS SRV lookup.
        private readonly object _dnsSrvLock = new object();

        private void EnqueueIdle(Driver driver)
        {
            driver.IdleSince = DateTime.Now;
            this._idlePool.Enqueue(driver);
        }

        public MySqlPool(MySqlConnectionStringBuilder settings)
        {
            this._minSize = settings.MinimumPoolSize;
            this._maxSize = settings.MaximumPoolSize;

            this._available = (int)this._maxSize;
            this._autoEvent = new AutoResetEvent(false);

            if (this._minSize > this._maxSize)
            {
                this._minSize = this._maxSize;
            }

            this.Settings = settings;
            this._inUsePool = new List<Driver>((int)this._maxSize);
            this._idlePool = new Queue<Driver>((int)this._maxSize);

            // prepopulate the idle pool to minSize
            for (int i = 0; i < this._minSize; i++)
            {
                this.EnqueueIdle(this.CreateNewPooledConnection());
            }

            this.ProcedureCache = new ProcedureCache((int)settings.ProcedureCacheSize);
        }

        #region Properties

        public MySqlConnectionStringBuilder Settings { get; set; }

        public ProcedureCache ProcedureCache { get; }

        /// <summary>
        /// It is assumed that this property will only be used from inside an active
        /// lock.
        /// </summary>
        private bool HasIdleConnections => this._idlePool.Count > 0;

        private int NumConnections => this._idlePool.Count + this._inUsePool.Count;

        /// <summary>
        /// Indicates whether this pool is being cleared.
        /// </summary>
        public bool BeingCleared { get; private set; }

        internal Dictionary<string, string> ServerProperties { get; set; }

        #endregion

        /// <summary>
        /// It is assumed that this method is only called from inside an active lock.
        /// </summary>
        private Driver GetPooledConnection()
        {
            Driver driver = null;

            // if we don't have an idle connection but we have room for a new
            // one, then create it here.
            lock ((this._idlePool as ICollection).SyncRoot)
            {
                if (this.HasIdleConnections)
                {
                    driver = this._idlePool.Dequeue();
                }
            }

            // Obey the connection timeout
            if (driver != null)
            {
                try
                {
                    driver.ResetTimeout((int)this.Settings.ConnectionTimeout * 1000);
                }
                catch (Exception)
                {
                    driver.Close();
                    driver = null;
                }
            }

            if (driver != null)
            {
                // first check to see that the server is still alive
                if (!driver.Ping())
                {
                    driver.Close();
                    driver = null;
                }
                else if (this.Settings.ConnectionReset)
                {
                    // if the user asks us to ping/reset pooled connections
                    // do so now
                    try { driver.Reset(); }
                    catch (Exception) { this.Clear(); }
                }
            }

            if (driver == null)
            {
                driver = this.CreateNewPooledConnection();
            }

            Debug.Assert(driver != null);
            lock ((this._inUsePool as ICollection).SyncRoot)
            {
                this._inUsePool.Add(driver);
            }

            return driver;
        }

        /// <summary>
        /// It is assumed that this method is only called from inside an active lock.
        /// </summary>
        private Driver CreateNewPooledConnection()
        {
            Debug.Assert((this._maxSize - this.NumConnections) > 0, "Pool out of sync.");

            Driver driver = Driver.Create(this.Settings);
            driver.Pool = this;
            return driver;
        }

        public void ReleaseConnection(Driver driver)
        {
            lock ((this._inUsePool as ICollection).SyncRoot)
            {
                if (this._inUsePool.Contains(driver))
                {
                    this._inUsePool.Remove(driver);
                }
            }

            if (driver.ConnectionLifetimeExpired() || this.BeingCleared)
            {
                driver.Close();
                Debug.Assert(!this._idlePool.Contains(driver));
            }
            else
            {
                lock ((this._idlePool as ICollection).SyncRoot)
                {
                    this.EnqueueIdle(driver);
                }
            }

            lock (this._dnsSrvLock)
            {
                if (driver.Settings.DnsSrv)
                {
                    var dnsSrvRecords = DnsResolver.GetDnsSrvRecords(DnsResolver.ServiceName);
                    FailoverManager.SetHostList(
                        dnsSrvRecords.ConvertAll(r => new FailoverServer(r.Target, r.Port, null)),
                      FailoverMethod.Sequential);

                    foreach (var idleConnection in this._idlePool)
                    {
                        string idleServer = idleConnection.Settings.Server;
                        if (!FailoverManager.FailoverGroup.Hosts.Exists(h => h.Host == idleServer) && !idleConnection.IsInActiveUse)
                        {
                            idleConnection.Close();
                        }
                    }
                }
            }

            Interlocked.Increment(ref this._available);
            this._autoEvent.Set();
        }

        /// <summary>
        /// Removes a connection from the in use pool.  The only situations where this method 
        /// would be called are when a connection that is in use gets some type of fatal exception
        /// or when the connection is being returned to the pool and it's too old to be 
        /// returned.
        /// </summary>
        /// <param name="driver"></param>
        public void RemoveConnection(Driver driver)
        {
            lock ((this._inUsePool as ICollection).SyncRoot)
            {
                if (this._inUsePool.Contains(driver))
                {
                    this._inUsePool.Remove(driver);
                    Interlocked.Increment(ref this._available);
                    this._autoEvent.Set();
                }
            }

            // if we are being cleared and we are out of connections then have
            // the manager destroy us.
            if (this.BeingCleared && this.NumConnections == 0)
            {
                MySqlPoolManager.RemoveClearedPool(this);
            }
        }

        private Driver TryToGetDriver()
        {
            int count = Interlocked.Decrement(ref this._available);
            if (count < 0)
            {
                Interlocked.Increment(ref this._available);
                return null;
            }

            try
            {
                Driver driver = this.GetPooledConnection();
                return driver;
            }
            catch (Exception ex)
            {
                MySqlTrace.LogError(-1, ex.Message);
                Interlocked.Increment(ref this._available);
                throw;
            }
        }

        public Driver GetConnection()
        {
            int fullTimeOut = (int)this.Settings.ConnectionTimeout * 1000;
            int timeOut = fullTimeOut;

            DateTime start = DateTime.Now;

            while (timeOut > 0)
            {
                Driver driver = this.TryToGetDriver();
                if (driver != null)
                {
                    return driver;
                }

                // We have no tickets right now, lets wait for one.
                if (!this._autoEvent.WaitOne(timeOut, false))
                {
                    break;
                }

                timeOut = fullTimeOut - (int)DateTime.Now.Subtract(start).TotalMilliseconds;
            }

            throw new MySqlException(Resources.TimeoutGettingConnection);
        }

        /// <summary>
        /// Clears this pool of all idle connections and marks this pool and being cleared
        /// so all other connections are closed when they are returned.
        /// </summary>
        internal void Clear()
        {
            lock ((this._idlePool as ICollection).SyncRoot)
            {
                // first, mark ourselves as being cleared
                this.BeingCleared = true;

                // then we remove all connections sitting in the idle pool
                while (this._idlePool.Count > 0)
                {
                    Driver d = this._idlePool.Dequeue();
                    d.Close();
                }

                // there is nothing left to do here.  Now we just wait for all
                // in use connections to be returned to the pool.  When they are
                // they will be closed.  When the last one is closed, the pool will
                // be destroyed.
            }
        }

        /// <summary>
        /// Remove expired drivers from the idle pool
        /// </summary>
        /// <returns></returns>
        /// <remarks>
        /// Closing driver is a potentially lengthy operation involving network
        /// IO. Therefore we do not close expired drivers while holding 
        /// idlePool.SyncRoot lock. We just remove the old drivers from the idle
        /// queue and return them to the caller. The caller will need to close 
        /// them (or let GC close them)
        /// </remarks>
        internal List<Driver> RemoveOldIdleConnections()
        {
            List<Driver> oldDrivers = new List<Driver>();
            DateTime now = DateTime.Now;

            lock ((this._idlePool as ICollection).SyncRoot)
            {
                // The drivers appear to be ordered by their age, i.e it is
                // sufficient to remove them until the first element is not
                // too old.
                while (this._idlePool.Count > this._minSize)
                {
                    Driver d = this._idlePool.Peek();
                    DateTime expirationTime = d.IdleSince.Add(
                      new TimeSpan(0, 0, MySqlPoolManager.maxConnectionIdleTime));
                    if (expirationTime.CompareTo(now) < 0)
                    {
                        oldDrivers.Add(d);
                        this._idlePool.Dequeue();
                    }
                    else
                    {
                        break;
                    }
                }
            }

            return oldDrivers;
        }
    }
}