using LiteDB;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Tango.Core;
using Tango.Core.ExtensionMethods;
using Tango.Logging;
using Tango.Telemetry.Helpers;

namespace Tango.Telemetry
{
    public class TelemetryLiteDBStorageManager : ExtendedObject, ITelemetryStorageManager
    {
        public class PublishedTelemetry
        {
            public String ID { get; set; }
            public DateTime CreatedAt { get; set; }
        }

        private bool _disposed;
        private LiteDatabase _database;
        private static Object _lock = new object();
        private ITelemetryCheckpointsRecoveryClient _checkpointsRecoveryClient;
        private HashSet<String> _publishedTelemetriesIDs;

        private DateTime _lastCloudBackupTime = DateTime.MinValue;
        private TimeSpan _checkpointsBackupInterval = TimeSpan.FromMinutes(1);

        public TimeSpan CheckpointsBackupInterval { get => _checkpointsBackupInterval; set => _checkpointsBackupInterval = value >= TimeSpan.FromMinutes(1) ? value : TimeSpan.FromMinutes(1); }
        public String DatabasePath { get; private set; }

        public bool EnableCheckPointsRecovery { get; set; }
        public bool EnforceCheckpointsRecovery { get; set; }

        public TelemetryLiteDBStorageManager()
        {
            _publishedTelemetriesIDs = new HashSet<string>();
            EnableCheckPointsRecovery = true;
            EnforceCheckpointsRecovery = true;
            DatabasePath = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData), "Twine", "Tango", "Telemetry", Path.GetFileNameWithoutExtension(AppDomain.CurrentDomain.FriendlyName) + ".telemetry");
        }

        public TelemetryLiteDBStorageManager(String databaseFile) : this()
        {
            DatabasePath = databaseFile;
        }

        public async Task Init(ITelemetryCheckpointsRecoveryClient checkpointsRecoveryClient)
        {
            LogManager.Log("Initializing telemetry database...");

            _checkpointsRecoveryClient = checkpointsRecoveryClient;

            Directory.CreateDirectory(Path.GetDirectoryName(DatabasePath));

            if (!File.Exists(DatabasePath))
            {
                LogManager.Log("Telemetry database was not found. A new one will be created and source checkpoints will be recovered from the remote service if required.", LogCategory.Critical);

                if (_checkpointsRecoveryClient == null && EnableCheckPointsRecovery && EnforceCheckpointsRecovery)
                {
                    throw new NullReferenceException("No TelemetryCheckpointsRecoveryClient was introduced. Telemetry Storage manager should not operate.");
                }
            }

            _database = new LiteDatabase($"Filename={DatabasePath}");
            _database.Pragma("TIMEOUT", 10); //Read Timeout
            _database.Pragma("UTC_DATE", true); //Keep time as UTC when getting data
            _database.Commit();

            var checkPointsCollection = GetSourcesCheckpointCollection();
            var localCheckPoints = checkPointsCollection.FindAll().ToList();

            if (localCheckPoints.Count == 0)
            {
                if (EnableCheckPointsRecovery)
                {
                    try
                    {
                        LogManager.Log("Attempting to retrieve sources checkpoints from backup...");
                        var remoteCheckPoints = await _checkpointsRecoveryClient.GetCheckpointsBackup();
                        if (remoteCheckPoints.Count > 0)
                        {
                            checkPointsCollection.InsertBulk(remoteCheckPoints);
                            LogManager.Log($"Sources checkpoints successfully recovered.\n{remoteCheckPoints.ToJsonString()}");
                        }
                        else
                        {
                            LogManager.Log("No sources checkpoint found on backup. Assuming first operation...");
                        }
                    }
                    catch (Exception ex)
                    {
                        if (EnforceCheckpointsRecovery)
                        {
                            LogManager.Log(ex, LogCategory.Critical, "Could not retrieve sources checkpoints from backup. Telemetry storage manager should not operate.");
                            throw;
                        }
                        else
                        {
                            LogManager.Log(ex, LogCategory.Warning, "Could not retrieve sources checkpoints from backup. No Checkpoints available!");
                        }
                    }
                }
            }
            else
            {
                var minDateTime = localCheckPoints.Min(x => x.Time);
                PerformPublishedTelemetriesCleanUp(minDateTime);
            }

            LogManager.Log("Loading published telemetries cache...");
            _publishedTelemetriesIDs = new HashSet<string>(GetPublishedTelemetriesCollection().FindAll().Select(x => x.ID).ToList());

            LogManager.Log("Telemetry LiteDB storage manager initialized...");
        }

        private ILiteCollection<PublishedTelemetry> GetPublishedTelemetriesCollection()
        {
            return _database.GetCollection<PublishedTelemetry>("PublishedTelemetries");
        }

        private ILiteCollection<PendingTelemetry> GetPendingTelemetriesCollection()
        {
            return _database.GetCollection<PendingTelemetry>("PendingTelemetries");
        }

        private ILiteCollection<TelemetryHistorySourceCheckPoint> GetSourcesCheckpointCollection()
        {
            return _database.GetCollection<TelemetryHistorySourceCheckPoint>("SourcesCheckPoints");
        }

        public void UpsertPendingTelemetry(PendingTelemetry pendingTelemetry)
        {
            lock (_lock)
            {
                var collection = GetPendingTelemetriesCollection();

                //Ensure all datetimes "Kind" is UTC so LiteDB won't change them on query.
                DateTimeUtcFixer.EnsureDateTimeUTC(pendingTelemetry.TelemetryObject);

                collection.Upsert(pendingTelemetry);
            }
        }

        public void DeletePendingTelemetry(PendingTelemetry pendingTelemetry)
        {
            lock (_lock)
            {
                var collection = GetPendingTelemetriesCollection();
                collection.Delete(pendingTelemetry.Id);
            }
        }

        public List<PendingTelemetry> GetPendingTelemetries(int maxCount)
        {
            lock (_lock)
            {
                var collection = GetPendingTelemetriesCollection();
                var pendingTelemetries = collection.FindAll().OrderBy(x => x.TelemetryObject.Time).Take(Math.Max(maxCount, 1)).ToList();
                return pendingTelemetries;
            }
        }

        public TelemetryHistorySourceCheckPoint GetHistorySourceCheckPoint(ITelemetryHistorySource source)
        {
            lock (_lock)
            {
                var collection = GetSourcesCheckpointCollection();
                var checkpoint = collection.FindOne(x => x.SourceName == source.Name);
                return checkpoint;
            }
        }

        public List<TelemetryHistorySourceCheckPoint> GetHistorySourcesCheckPoints()
        {
            lock (_lock)
            {
                var collection = GetSourcesCheckpointCollection();
                var checkpoints = collection.FindAll().ToList();
                return checkpoints;
            }
        }

        public void SetHistorySourceCheckPoint(ITelemetryHistorySource source, DateTime time, int totalCount)
        {
            var a = time.Kind;
            lock (_lock)
            {
                DateTime utcTime = DateTime.SpecifyKind(time, DateTimeKind.Utc);

                var collection = GetSourcesCheckpointCollection();
                collection.Upsert(new TelemetryHistorySourceCheckPoint() { SourceName = source.Name, Time = utcTime, TotalCount = totalCount });

                if (_checkpointsRecoveryClient != null && DateTime.UtcNow - _lastCloudBackupTime > CheckpointsBackupInterval)
                {
                    _lastCloudBackupTime = DateTime.UtcNow;
                    Task.Run(async () =>
                    {
                        try
                        {
                            var allCheckpoints = collection.FindAll().ToList();
                            await _checkpointsRecoveryClient.SaveCheckpointsBackup(allCheckpoints);
                            LogManager.Log("Sources checkpoints successfully backed up to remote service.");
                        }
                        catch (Exception ex)
                        {
                            LogManager.Log(ex, LogCategory.Warning, "Failed to back up checkpoints to remote service.");
                        }
                    });
                }
            }
        }

        public int GetPendingTelemetriesCount()
        {
            lock (_lock)
            {
                var collection = GetPendingTelemetriesCollection();
                var count = collection.Count();
                return count;
            }
        }

        public void AddToPublishedTelemetryCache(ITelemetry telemetry)
        {
            _publishedTelemetriesIDs.Add(telemetry.ID);
            GetPublishedTelemetriesCollection().Insert(new PublishedTelemetry() { CreatedAt = DateTime.UtcNow, ID = telemetry.ID });
        }

        public bool IsTelemetryInPublishedCache(ITelemetry telementry)
        {
            return _publishedTelemetriesIDs.Contains(telementry.ID);
        }

        public void PerformPublishedTelemetriesCleanUp(DateTime olderThan)
        {
            LogManager.Log("Performing published telemetries cache cleanup...");
            var collection = GetPublishedTelemetriesCollection();
            int deleted = collection.DeleteMany(x => x.CreatedAt < olderThan);
            LogManager.Log($"Published telemetries cleanup completed. {deleted} cleaned.");
        }

        public virtual void Dispose()
        {
            if (_database != null && !_disposed)
            {
                try
                {
                    _disposed = true;
                    _database.Dispose();
                    _database = null;
                }
                catch { }
            }
        }

        ~TelemetryLiteDBStorageManager()
        {
            Dispose();
        }
    }
}