/*
 *
 * (c) Copyright Ascensio System Limited 2010-2018
 *
 * This program is freeware. You can redistribute it and/or modify it under the terms of the GNU 
 * General Public License (GPL) version 3 as published by the Free Software Foundation (https://www.gnu.org/copyleft/gpl.html). 
 * In accordance with Section 7(a) of the GNU GPL its Section 15 shall be amended to the effect that 
 * Ascensio System SIA expressly excludes the warranty of non-infringement of any third-party rights.
 *
 * THIS PROGRAM IS DISTRIBUTED WITHOUT ANY WARRANTY; WITHOUT EVEN THE IMPLIED WARRANTY OF MERCHANTABILITY OR
 * FITNESS FOR A PARTICULAR PURPOSE. For more details, see GNU GPL at https://www.gnu.org/copyleft/gpl.html
 *
 * You can contact Ascensio System SIA by email at sales@onlyoffice.com
 *
 * The interactive user interfaces in modified source and object code versions of ONLYOFFICE must display 
 * Appropriate Legal Notices, as required under Section 5 of the GNU GPL version 3.
 *
 * Pursuant to Section 7 § 3(b) of the GNU GPL you must retain the original ONLYOFFICE logo which contains 
 * relevant author attributions when distributing the software. If the display of the logo in its graphic 
 * form is not reasonably feasible for technical reasons, you must include the words "Powered by ONLYOFFICE" 
 * in every copy of the program you distribute. 
 * Pursuant to Section 7 § 3(e) we decline to grant you any rights under trademark law for use of our trademarks.
 *
*/


using System;
using System.Configuration;
using System.IO;
using System.Linq;
using System.Net.Mail;
using System.Text;
using System.Threading;
using ASC.Common.Utils;
using Amazon.SimpleEmail;
using Amazon.SimpleEmail.Model;
using log4net;

namespace ASC.Common.Notify
{
    public class AWSEmail
    {
        public enum SendStatus
        {
            Ok,
            Failed,
            QuotaLimit
        }

        private readonly AmazonSimpleEmailServiceClient _emailService;
        private readonly ILog _log = LogHolder.Log("ASC.Notify.AmazonSES");

        //Static fields
        private static readonly TimeSpan RefreshTimeout;
        private static DateTime _lastRefresh;
        private static DateTime _lastSend;
        private static TimeSpan _sendWindow = TimeSpan.MinValue;
        private static GetSendQuotaResult _quota;
        private static readonly object SynchRoot = new object();


        static AWSEmail()
        {
            RefreshTimeout = TimeSpan.FromMinutes(30);
            if (!string.IsNullOrEmpty(ConfigurationManager.AppSettings["ses.refreshTimeout"]))
            {
                TimeSpan.TryParse(ConfigurationManager.AppSettings["ses.refreshTimeout"], out RefreshTimeout);
            }
            _lastRefresh = DateTime.UtcNow - RefreshTimeout;//Set to refresh on first send
        }

        public AWSEmail()
        {
            var accessKey = ConfigurationManager.AppSettings["ses.accessKey"];
            var secretKey = ConfigurationManager.AppSettings["ses.secretKey"];

            _emailService = new AmazonSimpleEmailServiceClient(accessKey, secretKey);


        }

        public SendStatus SendEmail(MailMessage mailMessage)
        {
            //Check if we need to query stats
            RefreshQuotaIfNeeded();
            if (_quota != null)
            {
                lock (SynchRoot)
                {
                    if (_quota.Max24HourSend <= _quota.SentLast24Hours)
                    {
                        //Quota exceeded
                        //Queu next refresh to +24 hours
                        _lastRefresh = DateTime.UtcNow.AddHours(24);
                        _log.WarnFormat("quota limit reached. setting next check to: {0}", _lastRefresh);
                        return SendStatus.QuotaLimit;
                    }
                }
            }



            var destination = new Destination
            {
                ToAddresses = mailMessage.To.Select(adresses => adresses.Address).ToList(),
                BccAddresses = mailMessage.Bcc.Select(adresses => adresses.Address).ToList(),
                CcAddresses = mailMessage.CC.Select(adresses => adresses.Address).ToList(),

            };

            var body = new Body(new Content(mailMessage.Body) { Charset = Encoding.UTF8.WebName });

            if (mailMessage.AlternateViews.Count > 0)
            {
                //Get html body
                foreach (var alternateView in mailMessage.AlternateViews)
                {
                    if ("text/html".Equals(alternateView.ContentType.MediaType, StringComparison.OrdinalIgnoreCase))
                    {
                        var stream = alternateView.ContentStream;
                        var buf = new byte[stream.Length];
                        stream.Read(buf, 0, buf.Length);
                        stream.Seek(0, SeekOrigin.Begin);//NOTE:seek to begin to keep HTML body
                        body.Html = new Content(Encoding.UTF8.GetString(buf)) { Charset = Encoding.UTF8.WebName };
                        break;
                    }
                }
            }

            var message = new Message(new Content(mailMessage.Subject), body);

            var seRequest = new SendEmailRequest(mailMessage.From.ToEncodedStringEx(), destination, message);
            if (mailMessage.ReplyTo != null)
                seRequest.ReplyToAddresses.Add(mailMessage.ReplyTo.Address);

            ThrottleIfNeeded();

            var response = _emailService.SendEmail(seRequest);
            _lastSend = DateTime.UtcNow;
            return response != null ? SendStatus.Ok : SendStatus.Failed;
        }

        private void ThrottleIfNeeded()
        {
            //Check last send and throttle if needed
            if (_sendWindow != TimeSpan.MinValue)
            {
                if (DateTime.UtcNow - _lastSend <= _sendWindow)
                //Possible BUG: at high frequncies maybe bug with to little differences
                {
                    //This means that time passed from last send is less then message per second
                    _log.DebugFormat("send rate doesn't fit in send window. sleeping for:{0}", _sendWindow);
                    Thread.Sleep(_sendWindow);
                }
            }
        }

        private void RefreshQuotaIfNeeded()
        {
            if (!IsRefreshNeeded()) return;

            lock (SynchRoot)
            {
                if (IsRefreshNeeded())//Double check
                {
                    _log.DebugFormat("refreshing qouta. interval: {0} Last refresh was at: {1}", RefreshTimeout,
                                     _lastRefresh);

                    //Do quota refresh
                    _lastRefresh = DateTime.UtcNow.AddMinutes(1);
                    try
                    {
                        var quotaRequest = new GetSendQuotaRequest();
                        _quota = _emailService.GetSendQuota(quotaRequest).GetSendQuotaResult;
                        _sendWindow = TimeSpan.FromSeconds(1.0 / _quota.MaxSendRate);
                        _log.DebugFormat("quota: {0}/{1} at {2} mps. send window:{3}", _quota.SentLast24Hours,
                                         _quota.Max24HourSend, _quota.MaxSendRate, _sendWindow);
                    }
                    catch (Exception e)
                    {
                        _log.Error("error refreshing quota", e);
                    }
                }
            }
        }

        private static bool IsRefreshNeeded()
        {
            return (DateTime.UtcNow - _lastRefresh) > RefreshTimeout || _quota == null;
        }
    }
}