using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Reflection;
using System.Runtime.CompilerServices;
using Emby.Server.Implementations.ScheduledTasks.Tasks;
using MediaBrowser.Controller.ScheduledTasks;
using MediaBrowser.Model.Tasks;
using Xunit;

namespace Jellyfin.Server.Implementations.Tests.ScheduledTasks;

public class ScanLeaderOptionsTests
{
    private static readonly Assembly[] _taskAssemblies =
    {
        typeof(DeleteTranscodeFileTask).Assembly,
        typeof(MediaBrowser.Providers.Lyric.LyricScheduledTask).Assembly,
        typeof(Jellyfin.LiveTv.Guide.RefreshGuideScheduledTask).Assembly,
        typeof(Jellyfin.MediaEncoding.Hls.ScheduledTasks.KeyframeExtractionScheduledTask).Assembly
    };

    /// <summary>
    /// A gated key that matches no registered task silently stops gating anything, so the default
    /// set is pinned to the task keys that actually exist in the build.
    /// </summary>
    [Fact]
    public void DefaultGatedTaskKeys_Should_MatchRegisteredScheduledTasks()
    {
        var registeredKeys = DiscoverScheduledTaskKeys(_taskAssemblies);

        Assert.NotEmpty(registeredKeys);

        var unmatched = new ScanLeaderOptions().GatedTaskKeys.Except(registeredKeys, StringComparer.Ordinal).ToList();
        Assert.True(
            unmatched.Count == 0,
            $"Gated keys match no scheduled task: {string.Join(", ", unmatched)}. Known keys: {string.Join(", ", registeredKeys.Order(StringComparer.Ordinal))}");
    }

    /// <summary>
    /// A key dropped from the default set silently un-gates that task on every replica, so the whole
    /// set is pinned against a hand-maintained expectation rather than read back from the options.
    /// </summary>
    [Fact]
    public void DefaultGatedTaskKeys_Should_BeTheExpectedSet()
    {
        string[] expected =
        {
            "AudioNormalization",
            "CleanupUserDataTask",
            "DownloadLyrics",
            "DownloadSubtitles",
            "KeyframeExtraction",
            "MoveTrickplayImages",
            "OptimizeDatabaseTask",
            "PluginUpdates",
            "RefreshChapterImages",
            "RefreshGuide",
            "RefreshInternetChannels",
            "RefreshLibrary",
            "RefreshPeople",
            "RefreshTrickplayImages",
            "TaskExtractMediaSegments",
            "TmdbRefreshUpcomingEpisodes"
        };

        var actual = new ScanLeaderOptions().GatedTaskKeys;
        var missing = expected.Except(actual, StringComparer.Ordinal).ToList();
        var unexpected = actual.Except(expected, StringComparer.Ordinal).ToList();

        Assert.True(
            missing.Count == 0 && unexpected.Count == 0,
            $"Default gated task keys drifted. Missing: {Describe(missing)}. Unexpected: {Describe(unexpected)}.");
    }

    /// <summary>
    /// The key universe is only as complete as the assemblies it is read from, so a task added to an
    /// unscanned assembly must fail here rather than narrow what the previous test can catch.
    /// </summary>
    [Fact]
    public void TaskAssemblies_Should_CoverEveryAssemblyDeclaringScheduledTasks()
    {
        var scanned = _taskAssemblies.Select(a => a.GetName().Name).ToHashSet(StringComparer.Ordinal);
        var missing = new List<string>();

        foreach (var path in Directory.EnumerateFiles(AppContext.BaseDirectory, "*.dll"))
        {
            var name = Path.GetFileNameWithoutExtension(path);
            if (scanned.Contains(name)
                || name.EndsWith(".Tests", StringComparison.Ordinal)
                || !(name.StartsWith("Jellyfin.", StringComparison.Ordinal)
                    || name.StartsWith("Emby.", StringComparison.Ordinal)
                    || name.StartsWith("MediaBrowser.", StringComparison.Ordinal)))
            {
                continue;
            }

            if (GetScheduledTaskTypes(Assembly.LoadFrom(path)).Any())
            {
                missing.Add(name);
            }
        }

        Assert.True(missing.Count == 0, $"Assemblies declaring scheduled tasks but not scanned: {string.Join(", ", missing)}");
    }

    private static string Describe(IReadOnlyCollection<string> keys)
        => keys.Count == 0 ? "none" : string.Join(", ", keys.Order(StringComparer.Ordinal));

    private static HashSet<string> DiscoverScheduledTaskKeys(IEnumerable<Assembly> assemblies)
    {
        var keys = new HashSet<string>(StringComparer.Ordinal);

        foreach (var type in assemblies.SelectMany(GetScheduledTaskTypes))
        {
            // Task keys are constant expressions, so an uninitialised instance is enough to read
            // them without standing up each task's dependency graph.
            var task = (IScheduledTask)RuntimeHelpers.GetUninitializedObject(type);
            keys.Add(task.Key);
        }

        return keys;
    }

    private static IEnumerable<Type> GetScheduledTaskTypes(Assembly assembly)
    {
        Type?[] types;
        try
        {
            types = assembly.GetTypes();
        }
        catch (ReflectionTypeLoadException ex)
        {
            types = ex.Types;
        }

        return types
            .Where(t => t is not null && !t.IsAbstract && !t.IsInterface && typeof(IScheduledTask).IsAssignableFrom(t))
            .Select(t => t!);
    }
}