using System;
using System.Text.Json;
using Jellyfin.Extensions.Json;
using MediaBrowser.Common.Configuration;
using Microsoft.Extensions.Logging;
using StackExchange.Redis;

namespace Emby.Server.Implementations.Configuration
{
    /// <summary>
    /// A Redis pub/sub <see cref="IConfigurationInvalidationBus"/>. Notices are broadcast on one channel
    /// and every instance but the publisher applies them.
    /// </summary>
    public sealed class RedisConfigurationInvalidationBus : IConfigurationInvalidationBus
    {
        private const string ChannelName = "jellyfin:configinvalidation";

        private static readonly JsonSerializerOptions _jsonOptions = JsonDefaults.Options;

        private readonly ISubscriber _subscriber;
        private readonly ILogger<RedisConfigurationInvalidationBus> _logger;
        private readonly string _originId;

        /// <summary>
        /// Initializes a new instance of the <see cref="RedisConfigurationInvalidationBus"/> class.
        /// </summary>
        /// <param name="redis">The Redis connection multiplexer.</param>
        /// <param name="logger">The logger.</param>
        public RedisConfigurationInvalidationBus(IConnectionMultiplexer redis, ILogger<RedisConfigurationInvalidationBus> logger)
        {
            ArgumentNullException.ThrowIfNull(redis);

            _subscriber = redis.GetSubscriber();
            _logger = logger;
            _originId = Environment.GetEnvironmentVariable("JELLYFIN_INSTANCE_ID") ?? Environment.MachineName;
        }

        /// <inheritdoc />
        public void Publish(ConfigurationInvalidationScope scope, string? target)
        {
            var invalidation = new ConfigurationInvalidation
            {
                Scope = scope,
                Target = target,
                OriginId = _originId
            };

            try
            {
                // Fire and forget: an admin saving configuration must never wait on, or fail because of,
                // the bus. The write has already reached the shared directory by this point.
                _subscriber.Publish(
                    RedisChannel.Literal(ChannelName),
                    JsonSerializer.Serialize(invalidation, _jsonOptions),
                    CommandFlags.FireAndForget);
            }
            catch (Exception ex)
            {
                _logger.LogWarning(ex, "Failed to publish {Scope} invalidation for {Target}; other instances keep their cached copy until they restart.", scope, target);
            }
        }

        /// <inheritdoc />
        public void Subscribe(Action<ConfigurationInvalidation> handler)
        {
            ArgumentNullException.ThrowIfNull(handler);

            try
            {
                _subscriber.Subscribe(RedisChannel.Literal(ChannelName), (_, value) => Dispatch(handler, value));
            }
            catch (Exception ex)
            {
                _logger.LogWarning(ex, "Failed to subscribe to configuration invalidations; this instance keeps its cached configuration until it restarts.");
            }
        }

        private void Dispatch(Action<ConfigurationInvalidation> handler, RedisValue value)
        {
            try
            {
                var invalidation = JsonSerializer.Deserialize<ConfigurationInvalidation>(value.ToString(), _jsonOptions);
                if (invalidation is null || string.Equals(invalidation.OriginId, _originId, StringComparison.Ordinal))
                {
                    return;
                }

                handler(invalidation);
            }
            catch (Exception ex)
            {
                _logger.LogWarning(ex, "Failed to apply a configuration invalidation.");
            }
        }
    }
}