Explorer-Workbench/tests/Explorer.Application.Tests/ThumbnailSchedulerTests.cs

using Explorer.Application;

namespace Explorer.Application.Tests;

public class ThumbnailSchedulerTests
{
    [Fact]
    public void Only_window_items_are_queued_not_the_whole_directory()
    {
        var scheduler = new ThumbnailScheduler();
        scheduler.Reset(1);
        scheduler.SetEnabled(true);
        var window = Enumerable.Range(0, 40)
            .Select(i => Job($@"C:\v{i}.jpg", rank: 0))
            .Concat(Enumerable.Range(0, 24).Select(i => Job($@"C:\p{i}.jpg", rank: 1)))
            .ToList();
        scheduler.SetWindow(1, window);

        var taken = Drain(scheduler);
        Assert.Equal(64, taken.Count);
        Assert.DoesNotContain(taken, j => j.Key.Path.Contains(@"\rest", StringComparison.Ordinal));
        Assert.True(taken.Take(40).All(j => j.Rank == 0));
        Assert.Equal(0, scheduler.InFlight);
    }

    [Fact]
    public void Visible_jobs_are_taken_before_prefetch()
    {
        var scheduler = new ThumbnailScheduler();
        scheduler.Reset(1);
        scheduler.SetEnabled(true);
        scheduler.SetWindow(1,
        [
            Job(@"C:\far.jpg", rank: 1),
            Job(@"C:\near.jpg", rank: 0)
        ]);

        Assert.True(scheduler.TryTake(out var first));
        Assert.Equal(@"C:\near.jpg", first.Key.Path);
        Assert.True(scheduler.TryTake(out var second));
        Assert.Equal(@"C:\far.jpg", second.Key.Path);
        scheduler.Complete(first, generated: true, failed: false);
        scheduler.Complete(second, generated: true, failed: false);
    }

    [Fact]
    public void Scrolling_away_drops_obsolete_pending_work()
    {
        var scheduler = new ThumbnailScheduler();
        scheduler.Reset(1);
        scheduler.SetEnabled(true);
        scheduler.SetWindow(1, [Job(@"C:\old.jpg")]);
        scheduler.SetWindow(1, [Job(@"C:\new.jpg")]);

        Assert.True(scheduler.TryTake(out var job));
        Assert.Equal(@"C:\new.jpg", job.Key.Path);
        Assert.False(scheduler.TryTake(out _));
        Assert.True(scheduler.Snapshot().Cancelled > 0);
        scheduler.Complete(job, generated: true, failed: false);
    }

    [Fact]
    public void Navigation_generation_invalidates_previous_jobs()
    {
        var scheduler = new ThumbnailScheduler();
        scheduler.Reset(1);
        scheduler.SetEnabled(true);
        scheduler.SetWindow(1, [Job(@"C:\a.jpg")]);
        Assert.True(scheduler.TryTake(out var stale));
        scheduler.Reset(2);
        Assert.False(scheduler.IsCurrent(stale));
        Assert.False(scheduler.TryTake(out _));
        scheduler.SetWindow(2, [Job(@"C:\b.jpg", generation: 2)]);
        Assert.True(scheduler.TryTake(out var next));
        Assert.Equal(@"C:\b.jpg", next.Key.Path);
        scheduler.Complete(next, generated: true, failed: false);
    }

    [Fact]
    public void Cache_hit_skips_regeneration()
    {
        var scheduler = new ThumbnailScheduler();
        scheduler.Reset(1);
        scheduler.SetEnabled(true);
        var key = ThumbnailKey.From(@"C:\hit.jpg", DateTimeOffset.UnixEpoch, 128);
        scheduler.MarkCached(key);
        scheduler.SetWindow(1, [new ThumbnailJob(key, 0, 1)]);
        Assert.False(scheduler.TryTake(out _));
        scheduler.RecordCacheHit();
        Assert.Equal(1, scheduler.Snapshot().CacheHits);
    }

    [Fact]
    public void Window_is_capped_so_the_queue_cannot_hold_the_whole_directory()
    {
        var scheduler = new ThumbnailScheduler();
        scheduler.Reset(1);
        scheduler.SetEnabled(true);
        var huge = Enumerable.Range(0, 500).Select(i => Job($@"C:\{i}.jpg")).ToList();
        scheduler.SetWindow(1, huge);
        Assert.True(scheduler.Snapshot().Window <= ThumbnailScheduler.MaxPending);
        var taken = Drain(scheduler);
        Assert.Equal(ThumbnailScheduler.MaxPending, taken.Count);
    }

    [Fact]
    public void In_flight_work_is_tracked_until_complete()
    {
        var scheduler = new ThumbnailScheduler();
        scheduler.Reset(1);
        scheduler.SetEnabled(true);
        scheduler.SetWindow(1, Enumerable.Range(0, 8).Select(i => Job($@"C:\{i}.jpg")).ToList());
        Assert.True(scheduler.TryTake(out var a));
        Assert.True(scheduler.TryTake(out var b));
        Assert.Equal(2, scheduler.InFlight);
        scheduler.Complete(a, generated: true, failed: false);
        Assert.Equal(1, scheduler.InFlight);
        scheduler.Complete(b, generated: true, failed: false);
        Assert.Equal(0, scheduler.InFlight);
    }

    [Fact]
    public void Preview_disabled_cancels_window()
    {
        var scheduler = new ThumbnailScheduler();
        scheduler.Reset(1);
        scheduler.SetEnabled(true);
        scheduler.SetWindow(1, [Job(@"C:\x.jpg")]);
        scheduler.SetEnabled(false);
        Assert.False(scheduler.TryTake(out _));
    }

    [Fact]
    public void Cache_key_changes_when_file_is_modified()
    {
        var first = ThumbnailKey.From(@"C:\a.jpg", DateTimeOffset.UnixEpoch, 128);
        var second = ThumbnailKey.From(@"C:\a.jpg", DateTimeOffset.UnixEpoch.AddHours(1), 128);
        Assert.NotEqual(first, second);
    }

    [Fact]
    public void Lru_cache_evicts_oldest_when_full()
    {
        var cache = new LruCache<string, int>(2);
        cache.Set("a", 1);
        cache.Set("b", 2);
        cache.Set("c", 3);
        Assert.False(cache.TryGet("a", out _));
        Assert.True(cache.TryGet("b", out var b));
        Assert.Equal(2, b);
        cache.Set("d", 4);
        Assert.False(cache.TryGet("c", out _));
        Assert.True(cache.TryGet("b", out _));
    }

    private static ThumbnailJob Job(string path, int rank = 0, int generation = 1)
        => new(ThumbnailKey.From(path, DateTimeOffset.UnixEpoch, 128), rank, generation);

    private static List<ThumbnailJob> Drain(ThumbnailScheduler scheduler)
    {
        var taken = new List<ThumbnailJob>();
        while (scheduler.TryTake(out var job))
        {
            taken.Add(job);
            scheduler.Complete(job, generated: true, failed: false);
        }

        return taken;
    }
}