/*
 * Copyright (c) Contributors, http://opensimulator.org/
 * See CONTRIBUTORS.TXT for a full list of copyright holders.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *     * Redistributions of source code must retain the above copyright
 *       notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above copyright
 *       notice, this list of conditions and the following disclaimer in the
 *       documentation and/or other materials provided with the distribution.
 *     * Neither the name of the OpenSimulator Project nor the
 *       names of its contributors may be used to endorse or promote products
 *       derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE CONTRIBUTORS BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
using OpenSim.Framework;
using System.Collections.Generic;
using System.IO;
using System.Reflection;
using log4net;

namespace OpenSim.Framework.Servers.HttpServer
{
    /// <summary>
    /// BaseStreamHandlerBasicDOSProtector Base streamed request handler.
    /// </summary>
    /// <remarks>
    /// Inheriting classes should override ProcessRequest() rather than Handle()
    /// </remarks>
    public abstract class BaseStreamHandlerBasicDOSProtector : BaseRequestHandler, IStreamedRequestHandler
    {
        private readonly CircularBuffer<int> _generalRequestTimes;
        private readonly BasicDosProtectorOptions _options;
        private readonly Dictionary<string, CircularBuffer<int>> _deeperInspection;
        private readonly Dictionary<string, int> _tempBlocked;
        private readonly System.Timers.Timer _forgetTimer;
        private static readonly ILog m_log = LogManager.GetLogger(MethodBase.GetCurrentMethod().DeclaringType);
        private readonly System.Threading.ReaderWriterLockSlim _lockSlim = new System.Threading.ReaderWriterLockSlim();

        protected BaseStreamHandlerBasicDOSProtector(string httpMethod, string path, BasicDosProtectorOptions options) : this(httpMethod, path, null, null, options) {}

        protected BaseStreamHandlerBasicDOSProtector(string httpMethod, string path, string name, string description, BasicDosProtectorOptions options)
            : base(httpMethod, path, name, description)
        {
            _generalRequestTimes = new CircularBuffer<int>(options.MaxRequestsInTimeframe + 1, true);
            _generalRequestTimes.Put(0);
            _options = options;
            _deeperInspection = new Dictionary<string, CircularBuffer<int>>();
            _tempBlocked = new Dictionary<string, int>();
            _forgetTimer = new System.Timers.Timer();
            _forgetTimer.Elapsed += delegate
            {
                _forgetTimer.Enabled = false;

                List<string> removes = new List<string>();
                _lockSlim.EnterReadLock();
                foreach (string str in _tempBlocked.Keys)
                {
                    if (
                        Util.EnvironmentTickCountSubtract(Util.EnvironmentTickCount(),
                                                          _tempBlocked[str]) > 0)
                        removes.Add(str);
                }
                _lockSlim.ExitReadLock();
                lock (_deeperInspection)
                {
                    _lockSlim.EnterWriteLock();
                    for (int i = 0; i < removes.Count; i++)
                    {
                        _tempBlocked.Remove(removes[i]);
                        _deeperInspection.Remove(removes[i]);
                    }
                    _lockSlim.ExitWriteLock();
                }
                foreach (string str in removes)
                {
                    m_log.InfoFormat("[{0}] client: {1} is no longer blocked.",
                                     _options.ReportingName, str);
                }
                _lockSlim.EnterReadLock();
                if (_tempBlocked.Count > 0)
                    _forgetTimer.Enabled = true;
                _lockSlim.ExitReadLock();
            };

            _forgetTimer.Interval = _options.ForgetTimeSpan.TotalMilliseconds;
        }

        public virtual byte[] Handle(
            string path, Stream request, IOSHttpRequest httpRequest, IOSHttpResponse httpResponse)
        {
            byte[] result;
            RequestsReceived++;
            //httpRequest.Headers

            if (_options.MaxRequestsInTimeframe < 1 || _options.RequestTimeSpan.TotalMilliseconds < 1)
            {
                result = ProcessRequest(path, request, httpRequest, httpResponse);
                RequestsHandled++;
                return result;
                
            }

            string clientstring = GetClientString(httpRequest);

            _lockSlim.EnterReadLock();
            if (_tempBlocked.ContainsKey(clientstring))
            {
                _lockSlim.ExitReadLock();

                if (_options.ThrottledAction == ThrottleAction.DoThrottledMethod)
                {
                    result = ThrottledRequest(path, request, httpRequest, httpResponse);
                    RequestsHandled++;
                    return result;
                }
                else
                    throw new System.Security.SecurityException("Throttled");
            }
            _lockSlim.ExitReadLock();

            _generalRequestTimes.Put(Util.EnvironmentTickCount());

            if (_generalRequestTimes.Size == _generalRequestTimes.Capacity &&
                (Util.EnvironmentTickCountSubtract(Util.EnvironmentTickCount(), _generalRequestTimes.Get()) <
                 _options.RequestTimeSpan.TotalMilliseconds))
            {
                //Trigger deeper inspection
                if (DeeperInspection(httpRequest))
                {
                    result = ProcessRequest(path, request, httpRequest, httpResponse);
                    RequestsHandled++;
                    return result;
                }
                if (_options.ThrottledAction == ThrottleAction.DoThrottledMethod)
                {
                    result = ThrottledRequest(path, request, httpRequest, httpResponse);
                    RequestsHandled++;
                    return result;
                }
                else
                    throw new System.Security.SecurityException("Throttled");
            }
           
            result =ProcessRequest(path, request, httpRequest, httpResponse);
            RequestsHandled++;

            return result;
        }

        protected virtual byte[] ProcessRequest(
            string path, Stream request, IOSHttpRequest httpRequest, IOSHttpResponse httpResponse)
        {
            return null;
        }

        protected virtual byte[] ThrottledRequest(
            string path, Stream request, IOSHttpRequest httpRequest, IOSHttpResponse httpResponse)
        {
            return new byte[0];
        }

        private bool DeeperInspection(IOSHttpRequest httpRequest)
        {
            lock (_deeperInspection)
            {
                string clientstring = GetClientString(httpRequest);


                if (_deeperInspection.ContainsKey(clientstring))
                {
                    _deeperInspection[clientstring].Put(Util.EnvironmentTickCount());
                    if (_deeperInspection[clientstring].Size == _deeperInspection[clientstring].Capacity &&
                        (Util.EnvironmentTickCountSubtract(Util.EnvironmentTickCount(), _deeperInspection[clientstring].Get()) <
                         _options.RequestTimeSpan.TotalMilliseconds))
                    {
                        _lockSlim.EnterWriteLock();
                        if (!_tempBlocked.ContainsKey(clientstring))
                            _tempBlocked.Add(clientstring, Util.EnvironmentTickCount() + (int)_options.ForgetTimeSpan.TotalMilliseconds);
                        else
                            _tempBlocked[clientstring] = Util.EnvironmentTickCount() + (int)_options.ForgetTimeSpan.TotalMilliseconds;
                        _lockSlim.ExitWriteLock();

                        m_log.WarnFormat("[{0}]: client: {1} is blocked for {2} milliseconds, X-ForwardedForAllowed status is {3}, endpoint:{4}", _options.ReportingName, clientstring, _options.ForgetTimeSpan.TotalMilliseconds, _options.AllowXForwardedFor, GetRemoteAddr(httpRequest));
                        return false;
                    }
                    //else
                    //   return true;
                }
                else
                {
                    _deeperInspection.Add(clientstring, new CircularBuffer<int>(_options.MaxRequestsInTimeframe + 1, true));
                    _deeperInspection[clientstring].Put(Util.EnvironmentTickCount());
                    _forgetTimer.Enabled = true;
                }

            }
            return true;
        }
        private string GetRemoteAddr(IOSHttpRequest httpRequest)
        {
            string remoteaddr = string.Empty;
            if (httpRequest.Headers["remote_addr"] != null)
                remoteaddr = httpRequest.Headers["remote_addr"];

            return remoteaddr;
        }

        private string GetClientString(IOSHttpRequest httpRequest)
        {
            string clientstring = string.Empty;

            if (_options.AllowXForwardedFor && httpRequest.Headers["x-forwarded-for"] != null)
                clientstring = httpRequest.Headers["x-forwarded-for"];
            else
                clientstring = GetRemoteAddr(httpRequest);

            return clientstring;
           
        }
    }
}