// Copyright © 2004, 2011, Oracle and/or its affiliates. All rights reserved.
//
// MySQL Connector/NET is licensed under the terms of the GPLv2
// <http://www.gnu.org/licenses/old-licenses/gpl-2.0.html>, like most 
// MySQL Connectors. There are special exceptions to the terms and 
// conditions of the GPLv2 as it is applied to this software, see the 
// FLOSS License Exception
// <http://www.mysql.com/about/legal/licensing/foss-exception.html>.
//
// This program 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; version 2 of the License.
//
// 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 
// 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 System;
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics;
using System.Threading;
using MySql.Data.MySqlClient.Properties;

namespace MySql.Data.MySqlClient
{
    /// <summary>
    /// Summary description for MySqlPool.
    /// </summary>
    internal sealed class MySqlPool
    {
        private List<Driver> inUsePool;
        private Stack<Driver> idlePool;
        private MySqlConnectionStringBuilder settings;
        private uint minSize;
        private uint maxSize;
        private ProcedureCache procedureCache;
        private bool beingCleared;
        private int available;
        private AutoResetEvent autoEvent;

        internal object lockServerProperties = new object();

        private void PushIdle(Driver driver)
        {
            driver.IdleSince = DateTime.Now;
            idlePool.Push(driver);
        }

        public MySqlPool(MySqlConnectionStringBuilder settings)
        {
            minSize = settings.MinimumPoolSize;
            maxSize = settings.MaximumPoolSize;

            available = (int)maxSize;
            autoEvent = new AutoResetEvent(false);

            if (minSize > maxSize)
                minSize = maxSize;
            this.settings = settings;
            inUsePool = new List<Driver>((int)maxSize);
            idlePool = new Stack<Driver>((int)maxSize);

            // prepopulate the idle pool to minSize
            for (int i = 0; i < minSize; i++)
                PushIdle(CreateNewPooledConnection());

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

        #region Properties

        public MySqlConnectionStringBuilder Settings
        {
            get
            {
                return settings;
            }
            set
            {
                settings = value;
            }
        }

        public ProcedureCache ProcedureCache
        {
            get
            {
                return procedureCache;
            }
        }

        /// <summary>
        /// It is assumed that this property will only be used from inside an active
        /// lock.
        /// </summary>
        private bool HasIdleConnections
        {
            get
            {
                return idlePool.Count > 0;
            }
        }

        private int NumConnections
        {
            get
            {
                return idlePool.Count + inUsePool.Count;
            }
        }

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

        internal Hashtable ServerProperties
        {
            get;
            set;
        }

        internal Hashtable CharacterSets
        {
            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 ((idlePool as ICollection).SyncRoot)
            {
                if (HasIdleConnections)
                    driver = idlePool.Pop();
            }

            // Obey the connection timeout
            if (driver != null)
            {
                try
                {
                    driver.ResetTimeout((int)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 (settings.ConnectionReset)
                    // if the user asks us to ping/reset pooled connections
                    // do so now
                    driver.Reset();
            }
            if (driver == null)
                driver = CreateNewPooledConnection();

            Debug.Assert(driver != null);
            lock ((inUsePool as ICollection).SyncRoot)
            {
                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((maxSize - NumConnections) > 0, "Pool out of sync.");

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

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

            if (driver.ConnectionLifetimeExpired() || beingCleared)
            {
                driver.Close();
                Debug.Assert(!idlePool.Contains(driver));
            }
            else
            {
                lock ((idlePool as ICollection).SyncRoot)
                {
                    PushIdle(driver);
                }
            }

            Interlocked.Increment(ref available);
            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 ((inUsePool as ICollection).SyncRoot)
            {
                if (inUsePool.Contains(driver))
                {
                    inUsePool.Remove(driver);
                    Interlocked.Increment(ref available);
                    autoEvent.Set();
                }
            }

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

        private Driver TryToGetDriver()
        {
            int count = Interlocked.Decrement(ref available);
            if (count < 0)
            {
                Interlocked.Increment(ref available);
                return null;
            }
            try
            {
                Driver driver = GetPooledConnection();
                return driver;
            }
            catch (Exception ex)
            {
                MySqlTrace.LogError(-1, ex.Message);
                Interlocked.Increment(ref available);
                throw;
            }
        }

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

            DateTime start = DateTime.Now;

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

                // We have no tickets right now, lets wait for one.
                if (!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 ((idlePool as ICollection).SyncRoot)
            {
                // first, mark ourselves as being cleared
                beingCleared = true;

                // then we remove all connections sitting in the idle pool
                while (idlePool.Count > 0)
                {
                    Driver d = idlePool.Pop();
                    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()
        {
            DateTime now = DateTime.Now;

            lock ((idlePool as ICollection).SyncRoot)
            {
                // Rebuild the Stack with only newly used drivers, 
                // and return old idle drivers
                List<Driver> oldDrivers = new List<Driver>(idlePool.ToArray());
                idlePool.Clear();
                // Newest driver at index 0, iterate in reverse order
                for (int i = oldDrivers.Count - 1; i >= 0; i--)
                {
                    Driver d = oldDrivers[i];
                    DateTime expirationTime = d.IdleSince.Add(
                        TimeSpan.FromSeconds(MySqlPoolManager.maxConnectionIdleTime));
                    if ((i < minSize) || (expirationTime > now))
                    {
                        idlePool.Push(d);
                        oldDrivers.Remove(d);
                    }
                }
                return oldDrivers;
            }
        }
    }
}