using System;
using System.Collections.Generic;
using System.Threading;
using Hangfire.Raven.Entities;
using Hangfire.Raven.Storage;
using Hangfire.Logging;
using Hangfire.Storage;
using Raven.Abstractions.Exceptions;

namespace Hangfire.Raven.DistributedLocks
{
    public class RavenDistributedLock : IDisposable
    {
        private static readonly ILog Logger = LogProvider.For<RavenDistributedLock>();

        private static readonly ThreadLocal<Dictionary<string, int>> AcquiredLocks
                    = new ThreadLocal<Dictionary<string, int>>(() => new Dictionary<string, int>());

        private RavenStorage _storage;

        private string _resource;

        private readonly RavenStorageOptions _options;

        private DistributedLock _distributedLock;

        private Timer _heartbeatTimer;

        private bool _completed;

        private readonly object _lockObject = new object();

        private string EventWaitHandleName => $@"{GetType().FullName}.{_resource}";

        public RavenDistributedLock(RavenStorage storage, string resource, TimeSpan timeout, RavenStorageOptions options)
        {
            storage.ThrowIfNull("storage");
            if (string.IsNullOrEmpty(resource))
            {
                throw new ArgumentNullException(nameof(resource));
            }
            if (timeout.TotalSeconds > int.MaxValue)
            {
                throw new ArgumentException($"The timeout specified is too large. Please supply a timeout equal to or less than {int.MaxValue} seconds", nameof(timeout));
            }
            options.ThrowIfNull("options");

            _storage = storage;
            _resource = resource;
            _options = options;

            if (!AcquiredLocks.Value.ContainsKey(_resource) || AcquiredLocks.Value[_resource] == 0)
            {
                Acquire(timeout);
                AcquiredLocks.Value[_resource] = 1;
                StartHeartBeat();
            }
            else
            {
                AcquiredLocks.Value[_resource]++;
            }
        }

        public void Dispose()
        {
            if (_completed)
            {
                return;
            }
            _completed = true;

            if (!AcquiredLocks.Value.ContainsKey(_resource))
            {
                return;
            }

            AcquiredLocks.Value[_resource]--;

            if (AcquiredLocks.Value[_resource] > 0)
            {
                return;
            }

            lock (_lockObject)
            {
                AcquiredLocks.Value.Remove(_resource);

                if (_heartbeatTimer != null)
                {
                    _heartbeatTimer.Dispose();
                    _heartbeatTimer = null;
                }

                Release();
            }
        }

        private void Acquire(TimeSpan timeout)
        {
            try
            {
                var isLockAcquired = false;
                var now = DateTime.Now;
                var lockTimeoutTime = now.Add(timeout);

                while (!isLockAcquired && (lockTimeoutTime >= now))
                {
                    using (var session = _storage.Repository.OpenSession())
                    {
                        _distributedLock = new DistributedLock()
                        {
                            ClientId = _storage.Options.ClientId,
                            Resource = _resource
                        };

                        session.Store(_distributedLock);
                        session.Advanced.AddExpire(_distributedLock, DateTime.UtcNow.Add(_options.DistributedLockLifetime));

                        try
                        {
                            // Blocking session!
                            session.Advanced.UseOptimisticConcurrency = true;
                            session.SaveChanges();
                            isLockAcquired = true;
                        }
                        catch (ConcurrencyException)
                        {
                            _distributedLock = null;
                            try
                            {
                                var eventWaitHandle = new EventWaitHandle(false, EventResetMode.AutoReset, EventWaitHandleName);
                                eventWaitHandle.WaitOne((int)timeout.TotalMilliseconds / 10);
                            }
                            catch (PlatformNotSupportedException)
                            {
                                Thread.Sleep((int)timeout.TotalMilliseconds / 10);
                            }
                            now = DateTime.Now;
                        }
                    }
                }

                if (!isLockAcquired)
                {
                    throw new DistributedLockTimeoutException(_resource);
                }
            }
            catch (DistributedLockTimeoutException)
            {
                throw;
            }
            catch (Exception ex)
            {
                throw new RavenDistributedLockException($"Could not place a lock on the resource \'{_resource}\': Check inner exception for details.", ex);
            }
        }

        private void Release()
        {
            try
            {
                if (_distributedLock != null)
                {
                    // Non blocking session!
                    using (var session = _storage.Repository.OpenSession())
                    {
                        session.Delete(_distributedLock.Id);
                        session.SaveChanges();
                        _distributedLock = null;
                    }
                }
                EventWaitHandle eventWaitHandler;
                if (EventWaitHandle.TryOpenExisting(EventWaitHandleName, out eventWaitHandler))
                {
                    eventWaitHandler.Set();
                }
            }
            catch (PlatformNotSupportedException)
            {
            }
            catch (Exception ex)
            {
                _distributedLock = null;
                throw new RavenDistributedLockException($"Could not release a lock on the resource \'{_resource}\': Check inner exception for details.", ex);
            }
        }

        private void StartHeartBeat()
        {
            Logger.InfoFormat(".Starting heartbeat for resource: {0}", _resource);

            TimeSpan timerInterval = TimeSpan.FromMilliseconds(_options.DistributedLockLifetime.TotalMilliseconds / 5);

            _heartbeatTimer = new Timer(state =>
            {
                lock (_lockObject)
                {
                    try
                    {
                        Logger.InfoFormat("..Heartbeat for resource {0}", _resource);

                        using (var session = _storage.Repository.OpenSession())
                        {
                            var distributedLock = session.Load<DistributedLock>(_distributedLock.Id);

                            session.Advanced.AddExpire(distributedLock, DateTime.UtcNow.Add(_options.DistributedLockLifetime));
                            session.SaveChanges();
                        }
                    }
                    catch (Exception ex)
                    {
                        Logger.ErrorFormat("...Unable to update heartbeat on the resource '{0}'. {1}", _resource, ex);
                        Release();
                    }
                }
            }, null, timerInterval, timerInterval);
        }
    }
}