using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Globalization;
using System.IO;
using System.Linq;
using System.Threading;
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;
using NPoco;
using Umbraco.Core.Cache;
using Umbraco.Core.Composing;
using Umbraco.Core.Logging;
using Umbraco.Core.Persistence;
using Umbraco.Core.Persistence.Dtos;
using Umbraco.Core.Hosting;
using Umbraco.Core.Scoping;

namespace Umbraco.Core.Sync
{
    /// <summary>
    /// An <see cref="IServerMessenger"/> that works by storing messages in the database.
    /// </summary>
    //
    // this messenger writes ALL instructions to the database,
    // but only processes instructions coming from remote servers,
    // thus ensuring that instructions run only once
    //
    public class DatabaseServerMessenger : ServerMessengerBase, IDatabaseServerMessenger
    {
        private readonly IMainDom _mainDom;
        private readonly ManualResetEvent _syncIdle;
        private readonly object _locko = new object();
        private readonly IProfilingLogger _profilingLogger;
        private readonly IServerRegistrar _serverRegistrar;
        private readonly IHostingEnvironment _hostingEnvironment;
        private readonly CacheRefresherCollection _cacheRefreshers;
        private readonly ISqlContext _sqlContext;
        private readonly Lazy<string> _distCacheFilePath;
        private int _lastId = -1;
        private DateTime _lastSync;
        private DateTime _lastPruned;
        private bool _initialized;
        private bool _syncing;
        private bool _released;

        public DatabaseServerMessengerOptions Options { get; }

        public DatabaseServerMessenger(
            IMainDom mainDom, IScopeProvider scopeProvider, ISqlContext sqlContext, IProfilingLogger proflog, IServerRegistrar serverRegistrar,
            bool distributedEnabled, DatabaseServerMessengerOptions options,  IHostingEnvironment hostingEnvironment, CacheRefresherCollection cacheRefreshers)
            : base(distributedEnabled)
        {
            ScopeProvider = scopeProvider ?? throw new ArgumentNullException(nameof(scopeProvider));
            _sqlContext = sqlContext;
            _mainDom = mainDom;
            _profilingLogger = proflog ?? throw new ArgumentNullException(nameof(proflog));
            _serverRegistrar = serverRegistrar;
            _hostingEnvironment = hostingEnvironment;
            _cacheRefreshers = cacheRefreshers;
            Logger = proflog;
            Options = options ?? throw new ArgumentNullException(nameof(options));
            _lastPruned = _lastSync = DateTime.UtcNow;
            _syncIdle = new ManualResetEvent(true);
            _distCacheFilePath = new Lazy<string>(() => GetDistCacheFilePath(hostingEnvironment));

            // See notes on LocalIdentity
            LocalIdentity = NetworkHelper.MachineName // eg DOMAIN\SERVER
                + "/" + _hostingEnvironment.ApplicationId // eg /LM/S3SVC/11/ROOT
                + " [P" + Process.GetCurrentProcess().Id // eg 1234
                + "/D" + AppDomain.CurrentDomain.Id // eg 22
                + "] " + Guid.NewGuid().ToString("N").ToUpper(); // make it truly unique
        }

        protected ILogger Logger { get; }

        protected IScopeProvider ScopeProvider { get; }

        protected Sql<ISqlContext> Sql() => _sqlContext.Sql();

        private string DistCacheFilePath => _distCacheFilePath.Value;

        #region Messenger

        protected override bool RequiresDistributed(ICacheRefresher refresher, MessageType dispatchType)
        {
            // we don't care if there's servers listed or not,
            // if distributed call is enabled we will make the call
            return _initialized && DistributedEnabled;
        }

        protected override void DeliverRemote(
            ICacheRefresher refresher,
            MessageType messageType,
            IEnumerable<object> ids = null,
            string json = null)
        {
            var idsA = ids?.ToArray();

            if (GetArrayType(idsA, out var idType) == false)
                throw new ArgumentException("All items must be of the same type, either int or Guid.", nameof(ids));

            var instructions = RefreshInstruction.GetInstructions(refresher, messageType, idsA, idType, json);

            var dto = new CacheInstructionDto
            {
                UtcStamp = DateTime.UtcNow,
                Instructions = JsonConvert.SerializeObject(instructions, Formatting.None),
                OriginIdentity = LocalIdentity,
                InstructionCount = instructions.Sum(x => x.JsonIdCount)
            };

            using (var scope = ScopeProvider.CreateScope())
            {
                scope.Database.Insert(dto);
                scope.Complete();
            }
        }

        #endregion

        #region Sync

        /// <summary>
        /// Boots the messenger.
        /// </summary>
        /// <remarks>
        /// Thread safety: this is NOT thread safe. Because it is NOT meant to run multi-threaded.
        /// Callers MUST ensure thread-safety.
        /// </remarks>
        protected void Boot()
        {
            // weight:10, must release *before* the published snapshot service, because once released
            // the service will *not* be able to properly handle our notifications anymore
            const int weight = 10;


            var registered = _mainDom.Register(
                () =>
                {
                    lock (_locko)
                    {
                        _released = true; // no more syncs
                    }

                    // wait a max of 5 seconds and then return, so that we don't block
                    // the entire MainDom callbacks chain and prevent the AppDomain from
                    // properly releasing MainDom - a timeout here means that one refresher
                    // is taking too much time processing, however when it's done we will
                    // not update lastId and stop everything
                    var idle =_syncIdle.WaitOne(5000);
                    if (idle == false)
                    {
                        Logger.Warn<DatabaseServerMessenger>("The wait lock timed out, application is shutting down. The current instruction batch will be re-processed.");
                    }
                },
                weight);

            if (registered == false)
                return;

            ReadLastSynced(); // get _lastId
            using (var scope = ScopeProvider.CreateScope())
            {
                EnsureInstructions(scope.Database); // reset _lastId if instructions are missing
                Initialize(scope.Database); // boot

                scope.Complete();
            }
        }

        /// <summary>
        /// Initializes a server that has never synchronized before.
        /// </summary>
        /// <remarks>
        /// Thread safety: this is NOT thread safe. Because it is NOT meant to run multi-threaded.
        /// Callers MUST ensure thread-safety.
        /// </remarks>
        private void Initialize(IUmbracoDatabase database)
        {
            lock (_locko)
            {
                if (_released) return;

                var coldboot = false;
                if (_lastId < 0) // never synced before
                {
                    // we haven't synced - in this case we aren't going to sync the whole thing, we will assume this is a new
                    // server and it will need to rebuild it's own caches, eg Lucene or the xml cache file.
                    Logger.Warn<DatabaseServerMessenger>("No last synced Id found, this generally means this is a new server/install."
                        + " The server will build its caches and indexes, and then adjust its last synced Id to the latest found in"
                        + " the database and maintain cache updates based on that Id.");

                    coldboot = true;
                }
                else
                {
                    //check for how many instructions there are to process, each row contains a count of the number of instructions contained in each
                    //row so we will sum these numbers to get the actual count.
                    var count = database.ExecuteScalar<int>("SELECT SUM(instructionCount) FROM umbracoCacheInstruction WHERE id > @lastId", new {lastId = _lastId});
                    if (count > Options.MaxProcessingInstructionCount)
                    {
                        //too many instructions, proceed to cold boot
                        Logger.Warn<DatabaseServerMessenger>(
                            "The instruction count ({InstructionCount}) exceeds the specified MaxProcessingInstructionCount ({MaxProcessingInstructionCount})."
                            + " The server will skip existing instructions, rebuild its caches and indexes entirely, adjust its last synced Id"
                            + " to the latest found in the database and maintain cache updates based on that Id.",
                            count, Options.MaxProcessingInstructionCount);

                        coldboot = true;
                    }
                }

                if (coldboot)
                {
                    // go get the last id in the db and store it
                    // note: do it BEFORE initializing otherwise some instructions might get lost
                    // when doing it before, some instructions might run twice - not an issue
                    var maxId = database.ExecuteScalar<int>("SELECT MAX(id) FROM umbracoCacheInstruction");

                    //if there is a max currently, or if we've never synced
                    if (maxId > 0 || _lastId < 0)
                        SaveLastSynced(maxId);

                    // execute initializing callbacks
                    if (Options.InitializingCallbacks != null)
                        foreach (var callback in Options.InitializingCallbacks)
                            callback();
                }

                _initialized = true;
            }
        }

        /// <summary>
        /// Synchronize the server (throttled).
        /// </summary>
        public void Sync()
        {
            lock (_locko)
            {
                if (_syncing)
                    return;

                //Don't continue if we are released
                if (_released)
                    return;

                if ((DateTime.UtcNow - _lastSync).TotalSeconds <= Options.ThrottleSeconds)
                    return;

                //Set our flag and the lock to be in it's original state (i.e. it can be awaited)
                _syncing = true;
                _syncIdle.Reset();
                _lastSync = DateTime.UtcNow;
            }

            try
            {
                using (_profilingLogger.DebugDuration<DatabaseServerMessenger>("Syncing from database..."))
                using (var scope = ScopeProvider.CreateScope())
                {
                    ProcessDatabaseInstructions(scope.Database);

                    //Check for pruning throttling
                    if (_released || (DateTime.UtcNow - _lastPruned).TotalSeconds <= Options.PruneThrottleSeconds)
                    {
                        scope.Complete();
                        return;
                    }

                    _lastPruned = _lastSync;

                    switch (_serverRegistrar.GetCurrentServerRole())
                    {
                        case ServerRole.Single:
                        case ServerRole.Master:
                            PruneOldInstructions(scope.Database);
                            break;
                    }

                    scope.Complete();
                }
            }
            finally
            {
                lock (_locko)
                {
                    //We must reset our flag and signal any waiting locks
                    _syncing = false;
                }

                _syncIdle.Set();
            }
        }

        /// <summary>
        /// Process instructions from the database.
        /// </summary>
        /// <remarks>
        /// Thread safety: this is NOT thread safe. Because it is NOT meant to run multi-threaded.
        /// </remarks>
        /// <returns>
        /// Returns the number of processed instructions
        /// </returns>
        private void ProcessDatabaseInstructions(IUmbracoDatabase database)
        {
            // NOTE
            // we 'could' recurse to ensure that no remaining instructions are pending in the table before proceeding but I don't think that
            // would be a good idea since instructions could keep getting added and then all other threads will probably get stuck from serving requests
            // (depending on what the cache refreshers are doing). I think it's best we do the one time check, process them and continue, if there are
            // pending requests after being processed, they'll just be processed on the next poll.
            //
            // TODO: not true if we're running on a background thread, assuming we can?

            var sql = Sql().SelectAll()
                .From<CacheInstructionDto>()
                .Where<CacheInstructionDto>(dto => dto.Id > _lastId)
                .OrderBy<CacheInstructionDto>(dto => dto.Id);

            //only retrieve the top 100 (just in case there's tons)
            // even though MaxProcessingInstructionCount is by default 1000 we still don't want to process that many
            // rows in one request thread since each row can contain a ton of instructions (until 7.5.5 in which case
            // a row can only contain MaxProcessingInstructionCount)
            var topSql = sql.SelectTop(100);

            // only process instructions coming from a remote server, and ignore instructions coming from
            // the local server as they've already been processed. We should NOT assume that the sequence of
            // instructions in the database makes any sense whatsoever, because it's all async.
            var localIdentity = LocalIdentity;

            var lastId = 0;

            //tracks which ones have already been processed to avoid duplicates
            var processed = new HashSet<RefreshInstruction>();

            //It would have been nice to do this in a Query instead of Fetch using a data reader to save
            // some memory however we cannot do that because inside of this loop the cache refreshers are also
            // performing some lookups which cannot be done with an active reader open
            foreach (var dto in database.Fetch<CacheInstructionDto>(topSql))
            {
                //If this flag gets set it means we're shutting down! In this case, we need to exit asap and cannot
                // continue processing anything otherwise we'll hold up the app domain shutdown
                if (_released)
                {
                    break;
                }

                if (dto.OriginIdentity == localIdentity)
                {
                    // just skip that local one but update lastId nevertheless
                    lastId = dto.Id;
                    continue;
                }

                // deserialize remote instructions & skip if it fails
                JArray jsonA;
                try
                {
                    jsonA = JsonConvert.DeserializeObject<JArray>(dto.Instructions);
                }
                catch (JsonException ex)
                {
                    Logger.Error<DatabaseServerMessenger>(ex, "Failed to deserialize instructions ({DtoId}: '{DtoInstructions}').",
                        dto.Id,
                        dto.Instructions);

                    lastId = dto.Id; // skip
                    continue;
                }

                var instructionBatch = GetAllInstructions(jsonA);

                //process as per-normal
                var success = ProcessDatabaseInstructions(instructionBatch, dto, processed, ref lastId);

                //if they couldn't be all processed (i.e. we're shutting down) then exit
                if (success == false)
                {
                    Logger.Info<DatabaseServerMessenger>("The current batch of instructions was not processed, app is shutting down");
                    break;
                }

            }

            if (lastId > 0)
                SaveLastSynced(lastId);
        }

        /// <summary>
        /// Processes the instruction batch and checks for errors
        /// </summary>
        /// <param name="instructionBatch"></param>
        /// <param name="dto"></param>
        /// <param name="processed">
        /// Tracks which instructions have already been processed to avoid duplicates
        /// </param>
        /// <param name="lastId"></param>
        /// <returns>
        /// returns true if all instructions in the batch were processed, otherwise false if they could not be due to the app being shut down
        /// </returns>
        private bool ProcessDatabaseInstructions(IReadOnlyCollection<RefreshInstruction> instructionBatch, CacheInstructionDto dto, HashSet<RefreshInstruction> processed, ref int lastId)
        {
            // execute remote instructions & update lastId
            try
            {
                var result = NotifyRefreshers(instructionBatch, processed);
                if (result)
                {
                    //if all instructions we're processed, set the last id
                    lastId = dto.Id;
                }
                return result;
            }
            //catch (ThreadAbortException ex)
            //{
            //    //This will occur if the instructions processing is taking too long since this is occurring on a request thread.
            //    // Or possibly if IIS terminates the appdomain. In any case, we should deal with this differently perhaps...
            //}
            catch (Exception ex)
            {
                    Logger.Error<DatabaseServerMessenger>(
                        ex,
                        "DISTRIBUTED CACHE IS NOT UPDATED. Failed to execute instructions ({DtoId}: '{DtoInstructions}'). Instruction is being skipped/ignored",
                        dto.Id,
                        dto.Instructions);

                //we cannot throw here because this invalid instruction will just keep getting processed over and over and errors
                // will be thrown over and over. The only thing we can do is ignore and move on.
                lastId = dto.Id;
                return false;
            }

            ////if this is returned it will not be saved
            //return -1;
        }

        /// <summary>
        /// Remove old instructions from the database
        /// </summary>
        /// <remarks>
        /// Always leave the last (most recent) record in the db table, this is so that not all instructions are removed which would cause
        /// the site to cold boot if there's been no instruction activity for more than DaysToRetainInstructions.
        /// See: http://issues.umbraco.org/issue/U4-7643#comment=67-25085
        /// </remarks>
        private void PruneOldInstructions(IUmbracoDatabase database)
        {
            var pruneDate = DateTime.UtcNow.AddDays(-Options.DaysToRetainInstructions);

            // using 2 queries is faster than convoluted joins

            var maxId = database.ExecuteScalar<int>("SELECT MAX(id) FROM umbracoCacheInstruction;");

            var delete = new Sql().Append(@"DELETE FROM umbracoCacheInstruction WHERE utcStamp < @pruneDate AND id < @maxId",
                new { pruneDate, maxId });

            database.Execute(delete);
        }

        /// <summary>
        /// Ensure that the last instruction that was processed is still in the database.
        /// </summary>
        /// <remarks>
        /// If the last instruction is not in the database anymore, then the messenger
        /// should not try to process any instructions, because some instructions might be lost,
        /// and it should instead cold-boot.
        /// However, if the last synced instruction id is '0' and there are '0' records, then this indicates
        /// that it's a fresh site and no user actions have taken place, in this circumstance we do not want to cold
        /// boot. See: http://issues.umbraco.org/issue/U4-8627
        /// </remarks>
        private void EnsureInstructions(IUmbracoDatabase database)
        {
            if (_lastId == 0)
            {
                var sql = Sql().Select("COUNT(*)")
                    .From<CacheInstructionDto>();

                var count = database.ExecuteScalar<int>(sql);

                //if there are instructions but we haven't synced, then a cold boot is necessary
                if (count > 0)
                    _lastId = -1;
            }
            else
            {
                var sql = Sql().SelectAll()
                    .From<CacheInstructionDto>()
                    .Where<CacheInstructionDto>(dto => dto.Id == _lastId);

                var dtos = database.Fetch<CacheInstructionDto>(sql);

                //if the last synced instruction is not found in the db, then a cold boot is necessary
                if (dtos.Count == 0)
                    _lastId = -1;
            }
        }

        /// <summary>
        /// Reads the last-synced id from file into memory.
        /// </summary>
        /// <remarks>
        /// Thread safety: this is NOT thread safe. Because it is NOT meant to run multi-threaded.
        /// </remarks>
        private void ReadLastSynced()
        {
            if (File.Exists(DistCacheFilePath) == false) return;

            var content = File.ReadAllText(DistCacheFilePath);
            if (int.TryParse(content, out var last))
                _lastId = last;
        }

        /// <summary>
        /// Updates the in-memory last-synced id and persists it to file.
        /// </summary>
        /// <param name="id">The id.</param>
        /// <remarks>
        /// Thread safety: this is NOT thread safe. Because it is NOT meant to run multi-threaded.
        /// </remarks>
        private void SaveLastSynced(int id)
        {
            File.WriteAllText(DistCacheFilePath, id.ToString(CultureInfo.InvariantCulture));
            _lastId = id;
        }

        /// <summary>
        /// Gets the unique local identity of the executing AppDomain.
        /// </summary>
        /// <remarks>
        /// <para>It is not only about the "server" (machine name and appDomainappId), but also about
        /// an AppDomain, within a Process, on that server - because two AppDomains running at the same
        /// time on the same server (eg during a restart) are, practically, a LB setup.</para>
        /// <para>Practically, all we really need is the guid, the other infos are here for information
        /// and debugging purposes.</para>
        /// </remarks>
        protected string LocalIdentity { get; }

        private string GetDistCacheFilePath(IHostingEnvironment hostingEnvironment)
        {
            var fileName = _hostingEnvironment.ApplicationId.ReplaceNonAlphanumericChars(string.Empty) + "-lastsynced.txt";

            var distCacheFilePath = Path.Combine(hostingEnvironment.LocalTempPath, "DistCache", fileName);

            //ensure the folder exists
            var folder = Path.GetDirectoryName(distCacheFilePath);
            if (folder == null)
                throw new InvalidOperationException("The folder could not be determined for the file " + distCacheFilePath);
            if (Directory.Exists(folder) == false)
                Directory.CreateDirectory(folder);

            return distCacheFilePath;
        }

        #endregion

        #region Notify refreshers

        private ICacheRefresher GetRefresher(Guid id)
        {
            var refresher = _cacheRefreshers[id];
            if (refresher == null)
                throw new InvalidOperationException("Cache refresher with ID \"" + id + "\" does not exist.");
            return refresher;
        }

        private IJsonCacheRefresher GetJsonRefresher(Guid id)
        {
            return GetJsonRefresher(GetRefresher(id));
        }

        private static IJsonCacheRefresher GetJsonRefresher(ICacheRefresher refresher)
        {
            var jsonRefresher = refresher as IJsonCacheRefresher;
            if (jsonRefresher == null)
                throw new InvalidOperationException("Cache refresher with ID \"" + refresher.RefresherUniqueId + "\" does not implement " + typeof(IJsonCacheRefresher) + ".");
            return jsonRefresher;
        }

        /// <summary>
        /// Parses out the individual instructions to be processed
        /// </summary>
        /// <param name="jsonArray"></param>
        /// <returns></returns>
        private static List<RefreshInstruction> GetAllInstructions(IEnumerable<JToken> jsonArray)
        {
            var result = new List<RefreshInstruction>();
            foreach (var jsonItem in jsonArray)
            {
                // could be a JObject in which case we can convert to a RefreshInstruction,
                // otherwise it could be another JArray - in which case we'll iterate that.
                var jsonObj = jsonItem as JObject;
                if (jsonObj != null)
                {
                    var instruction = jsonObj.ToObject<RefreshInstruction>();
                    result.Add(instruction);
                }
                else
                {
                    var jsonInnerArray = (JArray)jsonItem;
                    result.AddRange(GetAllInstructions(jsonInnerArray)); // recurse
                }
            }
            return result;
        }

        /// <summary>
        /// executes the instructions against the cache refresher instances
        /// </summary>
        /// <param name="instructions"></param>
        /// <param name="processed"></param>
        /// <returns>
        /// Returns true if all instructions were processed, otherwise false if the processing was interrupted (i.e. app shutdown)
        /// </returns>
        private bool NotifyRefreshers(IEnumerable<RefreshInstruction> instructions, HashSet<RefreshInstruction> processed)
        {
            foreach (var instruction in instructions)
            {
                //Check if the app is shutting down, we need to exit if this happens.
                if (_released)
                {
                    return false;
                }

                //this has already been processed
                if (processed.Contains(instruction))
                    continue;

                switch (instruction.RefreshType)
                {
                    case RefreshMethodType.RefreshAll:
                        RefreshAll(instruction.RefresherId);
                        break;
                    case RefreshMethodType.RefreshByGuid:
                        RefreshByGuid(instruction.RefresherId, instruction.GuidId);
                        break;
                    case RefreshMethodType.RefreshById:
                        RefreshById(instruction.RefresherId, instruction.IntId);
                        break;
                    case RefreshMethodType.RefreshByIds:
                        RefreshByIds(instruction.RefresherId, instruction.JsonIds);
                        break;
                    case RefreshMethodType.RefreshByJson:
                        RefreshByJson(instruction.RefresherId, instruction.JsonPayload);
                        break;
                    case RefreshMethodType.RemoveById:
                        RemoveById(instruction.RefresherId, instruction.IntId);
                        break;
                }

                processed.Add(instruction);
            }
            return true;
        }

        private void RefreshAll(Guid uniqueIdentifier)
        {
            var refresher = GetRefresher(uniqueIdentifier);
            refresher.RefreshAll();
        }

        private void RefreshByGuid(Guid uniqueIdentifier, Guid id)
        {
            var refresher = GetRefresher(uniqueIdentifier);
            refresher.Refresh(id);
        }

        private void RefreshById(Guid uniqueIdentifier, int id)
        {
            var refresher = GetRefresher(uniqueIdentifier);
            refresher.Refresh(id);
        }

        private void RefreshByIds(Guid uniqueIdentifier, string jsonIds)
        {
            var refresher = GetRefresher(uniqueIdentifier);
            foreach (var id in JsonConvert.DeserializeObject<int[]>(jsonIds))
                refresher.Refresh(id);
        }

        private void RefreshByJson(Guid uniqueIdentifier, string jsonPayload)
        {
            var refresher = GetJsonRefresher(uniqueIdentifier);
            refresher.Refresh(jsonPayload);
        }

        private void RemoveById(Guid uniqueIdentifier, int id)
        {
            var refresher = GetRefresher(uniqueIdentifier);
            refresher.Remove(id);
        }

        #endregion
    }
}