// <copyright file="CacheCoordinator.cs" company="PlaceholderCompany">
// Copyright (c) PlaceholderCompany. All rights reserved.
// </copyright>

namespace Jellyfin.Server.Implementations.Clustering
{
    using System;
    using System.Text.Json;
    using System.Threading;
    using System.Threading.Tasks;
    using MediaBrowser.Controller.Library;
    using Microsoft.Extensions.Logging;

    /// <summary>
    /// Coordinates cache invalidation across multiple Jellyfin instances using PostgreSQL LISTEN/NOTIFY.
    /// </summary>
    public sealed class CacheCoordinator : ICacheCoordinator, IAsyncDisposable
    {
        private const string CacheInvalidationChannel = "jellyfin_cache_invalidation";

        private readonly IPostgresNotificationListener _notificationListener;
        private readonly IInstanceRegistry _instanceRegistry;
        private readonly ILogger<CacheCoordinator> _logger;
        private readonly ILibraryManager? _libraryManager;
        private bool _disposed;
        private bool _started;

        /// <summary>
        /// Initializes a new instance of the <see cref="CacheCoordinator"/> class.
        /// </summary>
        /// <param name="notificationListener">The PostgreSQL notification listener.</param>
        /// <param name="instanceRegistry">The instance registry.</param>
        /// <param name="logger">The logger.</param>
        /// <param name="libraryManager">The library manager (optional).</param>
        public CacheCoordinator(
            IPostgresNotificationListener notificationListener,
            IInstanceRegistry instanceRegistry,
            ILogger<CacheCoordinator> logger,
            ILibraryManager? libraryManager = null)
        {
            _notificationListener = notificationListener;
            _instanceRegistry = instanceRegistry;
            _logger = logger;
            _libraryManager = libraryManager;
        }

        /// <inheritdoc/>
        public async Task StartAsync(CancellationToken cancellationToken = default)
        {
            if (_started)
            {
                _logger.LogWarning("Cache coordinator already started");
                return;
            }

            try
            {
                _notificationListener.NotificationReceived += OnNotificationReceived;
                await _notificationListener.StartListeningAsync(CacheInvalidationChannel, cancellationToken).ConfigureAwait(false);
                _started = true;

                _logger.LogInformation("Cache coordinator started successfully");
            }
            catch (Exception ex)
            {
                _logger.LogError(ex, "Failed to start cache coordinator");
                throw;
            }
        }

        /// <inheritdoc/>
        public async Task StopAsync(CancellationToken cancellationToken = default)
        {
            if (!_started)
            {
                return;
            }

            try
            {
                _notificationListener.NotificationReceived -= OnNotificationReceived;
                await _notificationListener.StopListeningAsync(cancellationToken).ConfigureAwait(false);
                _started = false;

                _logger.LogInformation("Cache coordinator stopped");
            }
            catch (Exception ex)
            {
                _logger.LogError(ex, "Error stopping cache coordinator");
            }
        }

        /// <inheritdoc/>
        public async Task InvalidateItemAsync(Guid itemId, CancellationToken cancellationToken = default)
        {
            var message = new CacheInvalidationMessage
            {
                Type = CacheInvalidationType.Item,
                EntityId = itemId,
                Timestamp = DateTime.UtcNow,
                SourceInstanceId = _instanceRegistry.CurrentInstanceId
            };

            await SendInvalidationMessageAsync(message, cancellationToken).ConfigureAwait(false);
        }

        /// <inheritdoc/>
        public async Task InvalidateUserDataAsync(Guid userId, CancellationToken cancellationToken = default)
        {
            var message = new CacheInvalidationMessage
            {
                Type = CacheInvalidationType.UserData,
                EntityId = userId,
                Timestamp = DateTime.UtcNow,
                SourceInstanceId = _instanceRegistry.CurrentInstanceId
            };

            await SendInvalidationMessageAsync(message, cancellationToken).ConfigureAwait(false);
        }

        /// <inheritdoc/>
        public async Task InvalidateImageAsync(Guid itemId, CancellationToken cancellationToken = default)
        {
            var message = new CacheInvalidationMessage
            {
                Type = CacheInvalidationType.Image,
                EntityId = itemId,
                Timestamp = DateTime.UtcNow,
                SourceInstanceId = _instanceRegistry.CurrentInstanceId
            };

            await SendInvalidationMessageAsync(message, cancellationToken).ConfigureAwait(false);
        }

        /// <inheritdoc/>
        public async Task InvalidateAllAsync(CacheInvalidationType cacheType, CancellationToken cancellationToken = default)
        {
            var message = new CacheInvalidationMessage
            {
                Type = cacheType,
                EntityId = null,
                Timestamp = DateTime.UtcNow,
                SourceInstanceId = _instanceRegistry.CurrentInstanceId
            };

            await SendInvalidationMessageAsync(message, cancellationToken).ConfigureAwait(false);
        }

        /// <inheritdoc/>
        public async Task InvalidateLibraryAsync(Guid libraryId, CancellationToken cancellationToken = default)
        {
            var message = new CacheInvalidationMessage
            {
                Type = CacheInvalidationType.Library,
                EntityId = libraryId,
                Timestamp = DateTime.UtcNow,
                SourceInstanceId = _instanceRegistry.CurrentInstanceId
            };

            await SendInvalidationMessageAsync(message, cancellationToken).ConfigureAwait(false);
        }

        /// <inheritdoc/>
        public async Task InvalidatePersonAsync(Guid personId, CancellationToken cancellationToken = default)
        {
            var message = new CacheInvalidationMessage
            {
                Type = CacheInvalidationType.Person,
                EntityId = personId,
                Timestamp = DateTime.UtcNow,
                SourceInstanceId = _instanceRegistry.CurrentInstanceId
            };

            await SendInvalidationMessageAsync(message, cancellationToken).ConfigureAwait(false);
        }

        /// <inheritdoc/>
        public async Task InvalidateMetadataAsync(Guid itemId, CancellationToken cancellationToken = default)
        {
            var message = new CacheInvalidationMessage
            {
                Type = CacheInvalidationType.Metadata,
                EntityId = itemId,
                Timestamp = DateTime.UtcNow,
                SourceInstanceId = _instanceRegistry.CurrentInstanceId
            };

            await SendInvalidationMessageAsync(message, cancellationToken).ConfigureAwait(false);
        }

        /// <inheritdoc/>
        public async ValueTask DisposeAsync()
        {
            if (_disposed)
            {
                return;
            }

            _disposed = true;

            await StopAsync(CancellationToken.None).ConfigureAwait(false);
        }

        private async Task SendInvalidationMessageAsync(CacheInvalidationMessage message, CancellationToken cancellationToken)
        {
            try
            {
                var json = JsonSerializer.Serialize(message);
                await _notificationListener.NotifyAsync(CacheInvalidationChannel, json, cancellationToken).ConfigureAwait(false);

                _logger.LogDebug(
                    "Sent cache invalidation: Type={Type}, EntityId={EntityId}",
                    message.Type,
                    message.EntityId);
            }
            catch (Exception ex)
            {
                _logger.LogError(
                    ex,
                    "Failed to send cache invalidation message: Type={Type}, EntityId={EntityId}",
                    message.Type,
                    message.EntityId);
            }
        }

        private void OnNotificationReceived(object? sender, PostgresNotificationEventArgs e)
        {
            try
            {
                var message = JsonSerializer.Deserialize<CacheInvalidationMessage>(e.Payload);

                if (message is null)
                {
                    _logger.LogWarning("Received invalid cache invalidation message");
                    return;
                }

                // Don't process messages from this instance
                if (message.SourceInstanceId.Equals(_instanceRegistry.CurrentInstanceId))
                {
                    return;
                }

                _logger.LogDebug(
                    "Processing cache invalidation from instance {SourceInstanceId}: Type={Type}, EntityId={EntityId}",
                    message.SourceInstanceId,
                    message.Type,
                    message.EntityId);

                ProcessInvalidationMessage(message);
            }
            catch (Exception ex)
            {
                _logger.LogError(ex, "Error processing cache invalidation notification");
            }
        }

        private void ProcessInvalidationMessage(CacheInvalidationMessage message)
        {
            // TODO: Actual cache invalidation logic would go here
            // This is a placeholder that demonstrates the pattern
            // The actual implementation would call into Jellyfin's cache managers

            switch (message.Type)
            {
                case CacheInvalidationType.Item:
                    if (message.EntityId.HasValue && _libraryManager is not null)
                    {
                        // Example: _libraryManager.InvalidateItemCache(message.EntityId.Value);
                        _logger.LogDebug("Invalidating item cache for {ItemId}", message.EntityId.Value);
                    }

                    break;

                case CacheInvalidationType.UserData:
                    if (message.EntityId.HasValue)
                    {
                        _logger.LogDebug("Invalidating user data cache for {UserId}", message.EntityId.Value);
                    }

                    break;

                case CacheInvalidationType.Image:
                    if (message.EntityId.HasValue)
                    {
                        _logger.LogDebug("Invalidating image cache for {ItemId}", message.EntityId.Value);
                    }

                    break;

                case CacheInvalidationType.Library:
                    if (message.EntityId.HasValue)
                    {
                        _logger.LogDebug("Invalidating library cache for {LibraryId}", message.EntityId.Value);
                    }

                    break;

                case CacheInvalidationType.All:
                    _logger.LogDebug("Invalidating all caches of type {CacheType}", message.Type);
                    break;

                default:
                    _logger.LogWarning("Unknown cache invalidation type: {Type}", message.Type);
                    break;
            }
        }
    }
}