using System;
using System.Threading;
using System.Threading.Tasks;
using MediaBrowser.Controller.MediaEncoding;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using StackExchange.Redis;

namespace Emby.Server.Implementations.MediaEncoding;

/// <summary>
/// Reports the round trip to the configured Redis transcode session store once at startup, so the
/// state of cross-pod takeover is visible where the server is started.
/// </summary>
/// <remarks>
/// This reports, it does not gate. <see cref="ApplicationHost.InitializeServices"/> has already read the
/// same connection for quick connect by the time this runs and has stopped startup if it could not be
/// reached, so the error branch here only covers a store that went away in between.
/// </remarks>
public sealed class TranscodeStoreConnectivityProbe : IHostedService
{
    private readonly IServiceProvider _serviceProvider;
    private readonly ILogger<TranscodeStoreConnectivityProbe> _logger;

    /// <summary>
    /// Initializes a new instance of the <see cref="TranscodeStoreConnectivityProbe"/> class.
    /// </summary>
    /// <param name="serviceProvider">The service provider used to resolve the Redis connection.</param>
    /// <param name="logger">The logger.</param>
    public TranscodeStoreConnectivityProbe(IServiceProvider serviceProvider, ILogger<TranscodeStoreConnectivityProbe> logger)
    {
        _serviceProvider = serviceProvider;
        _logger = logger;
    }

    /// <inheritdoc />
    public async Task StartAsync(CancellationToken cancellationToken)
    {
        try
        {
            // Resolved here rather than injected so a store lost after the quick connect gate is reported.
            var redis = _serviceProvider.GetRequiredService<IConnectionMultiplexer>();
            var roundTrip = await redis.GetDatabase().PingAsync().ConfigureAwait(false);

            _logger.LogInformation(
                "Redis transcode session store is reachable ({RoundTripMs}ms round trip). HA transcode takeover is active.",
                (long)roundTrip.TotalMilliseconds);
        }
        catch (Exception ex)
        {
            _logger.LogError(
                ex,
                "Redis transcode session store is configured but UNREACHABLE. HA transcode takeover is not working: sessions stay local to this instance and are lost when it restarts. Check {Key}.",
                TranscodeStoreOptions.RedisConnectionStringKey);
        }
    }

    /// <inheritdoc />
    public Task StopAsync(CancellationToken cancellationToken) => Task.CompletedTask;
}