using System;
using System.Collections.Generic;
using System.IO;
using System.Reflection;
using System.Threading;
using System.Threading.Tasks;
using Emby.Server.Implementations.ScheduledTasks;
using MediaBrowser.Common.Configuration;
using MediaBrowser.Controller.ScheduledTasks;
using MediaBrowser.Model.Tasks;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Logging.Abstractions;
using Moq;
using Xunit;

namespace Jellyfin.Server.Implementations.Tests.ScheduledTasks;

/// <summary>
/// Tests that <see cref="ScheduledTaskWorker"/> gates the periodic (timer-driven) execution of gated
/// tasks to the scan leader, while leaving non-gated tasks and manual/API-triggered runs unaffected.
/// </summary>
public class ScheduledTaskWorkerLeaderGatingTests
{
    private const string GatedKey = "RefreshLibrary";
    private const string NonGatedKey = "DeleteTranscodeFiles";

    /// <summary>
    /// A non-leader must not enqueue a gated task when its periodic trigger fires.
    /// </summary>
    [Fact]
    [Trait("Category", "UnitTest")]
    public async Task PeriodicTrigger_NonLeader_GatedTask_DoesNotQueue()
    {
        var taskManager = new Mock<ITaskManager>();
        var lease = CreateLease(isLeader: false);
        var options = CreateOptions(GatedKey);
        var task = new StubScheduledTask(GatedKey);

        using var worker = new ScheduledTaskWorker(task, CreateAppPaths(), taskManager.Object, NullLogger.Instance, lease.Object, options);

        await FireTriggerAsync(worker);

        taskManager.Verify(t => t.QueueScheduledTask(It.IsAny<IScheduledTask>(), It.IsAny<TaskOptions>()), Times.Never);
        lease.Verify(l => l.TryAcquireOrRenewAsync(It.IsAny<CancellationToken>()), Times.Once);
    }

    /// <summary>
    /// The leader must enqueue a gated task when its periodic trigger fires.
    /// </summary>
    [Fact]
    [Trait("Category", "UnitTest")]
    public async Task PeriodicTrigger_Leader_GatedTask_Queues()
    {
        var taskManager = new Mock<ITaskManager>();
        var lease = CreateLease(isLeader: true);
        var options = CreateOptions(GatedKey);
        var task = new StubScheduledTask(GatedKey);

        using var worker = new ScheduledTaskWorker(task, CreateAppPaths(), taskManager.Object, NullLogger.Instance, lease.Object, options);

        await FireTriggerAsync(worker);

        taskManager.Verify(t => t.QueueScheduledTask(task, It.IsAny<TaskOptions>()), Times.Once);
    }

    /// <summary>
    /// A non-gated task must always enqueue when its periodic trigger fires, even for a non-leader, and
    /// must not consult the scan-leader lease at all.
    /// </summary>
    [Fact]
    [Trait("Category", "UnitTest")]
    public async Task PeriodicTrigger_NonLeader_NonGatedTask_Queues()
    {
        var taskManager = new Mock<ITaskManager>();
        var lease = CreateLease(isLeader: false);
        var options = CreateOptions(GatedKey);
        var task = new StubScheduledTask(NonGatedKey);

        using var worker = new ScheduledTaskWorker(task, CreateAppPaths(), taskManager.Object, NullLogger.Instance, lease.Object, options);

        await FireTriggerAsync(worker);

        taskManager.Verify(t => t.QueueScheduledTask(task, It.IsAny<TaskOptions>()), Times.Once);
        lease.Verify(l => l.TryAcquireOrRenewAsync(It.IsAny<CancellationToken>()), Times.Never);
    }

    /// <summary>
    /// A manual/API-triggered run goes through <see cref="ScheduledTaskWorker.Execute"/>, which must run
    /// the task regardless of leadership and must not consult the scan-leader lease.
    /// </summary>
    [Fact]
    [Trait("Category", "UnitTest")]
    public async Task Execute_NonLeader_GatedTask_RunsAndIgnoresLease()
    {
        var realTaskManager = new TaskManager(CreateAppPaths(), new Mock<ILogger<TaskManager>>().Object);
        var lease = CreateLease(isLeader: false);
        var options = CreateOptions(GatedKey);
        var task = new StubScheduledTask(GatedKey);

        using var worker = new ScheduledTaskWorker(task, CreateAppPaths(), realTaskManager, NullLogger.Instance, lease.Object, options);

        await worker.Execute(new TaskOptions());

        Assert.Equal(1, task.ExecuteCount);
        lease.Verify(l => l.TryAcquireOrRenewAsync(It.IsAny<CancellationToken>()), Times.Never);
    }

    private static Mock<IScanLeaderLease> CreateLease(bool isLeader)
    {
        var lease = new Mock<IScanLeaderLease>();
        lease
            .Setup(l => l.TryAcquireOrRenewAsync(It.IsAny<CancellationToken>()))
            .ReturnsAsync(isLeader);
        return lease;
    }

    private static ScanLeaderOptions CreateOptions(params string[] gatedKeys)
        => new ScanLeaderOptions { Enabled = true, LeaseDurationSeconds = 60, GatedTaskKeys = gatedKeys };

    private static IApplicationPaths CreateAppPaths()
    {
        var dir = Path.Combine(Path.GetTempPath(), "jf-scanleader-tests", Guid.NewGuid().ToString("N"));
        Directory.CreateDirectory(dir);

        var appPaths = new Mock<IApplicationPaths>();
        appPaths.Setup(p => p.DataPath).Returns(dir);
        appPaths.Setup(p => p.ConfigurationDirectoryPath).Returns(dir);
        return appPaths.Object;
    }

    private static async Task FireTriggerAsync(ScheduledTaskWorker worker)
    {
        var method = typeof(ScheduledTaskWorker).GetMethod(
            "OnTriggerTriggered",
            BindingFlags.NonPublic | BindingFlags.Instance);
        Assert.NotNull(method);

        method!.Invoke(worker, new object[] { new RecordingTrigger(), EventArgs.Empty });

        // OnTriggerTriggered is async void; the queue decision completes synchronously against the mocked
        // lease, so a short delay lets any continuation settle before the assertion.
        await Task.Delay(100);
    }

    private sealed class StubScheduledTask : IScheduledTask
    {
        private readonly string _key;

        public StubScheduledTask(string key)
        {
            _key = key;
        }

        public int ExecuteCount { get; private set; }

        public string Name => "Stub Task";

        public string Key => _key;

        public string Description => "Stub task for gating tests.";

        public string Category => "Tests";

        public Task ExecuteAsync(IProgress<double> progress, CancellationToken cancellationToken)
        {
            ExecuteCount++;
            return Task.CompletedTask;
        }

        public IEnumerable<TaskTriggerInfo> GetDefaultTriggers() => Array.Empty<TaskTriggerInfo>();
    }

    private sealed class RecordingTrigger : ITaskTrigger
    {
#pragma warning disable CS0067 // Required by the interface but unused in this test double.
        public event EventHandler<EventArgs>? Triggered;
#pragma warning restore CS0067

        public TaskOptions TaskOptions { get; } = new TaskOptions();

        public void Start(TaskResult? lastResult, ILogger logger, string taskName, bool isApplicationStartup)
        {
        }

        public void Stop()
        {
        }
    }
}