Musify/backend/Tests/Musify.Application.Tests/Genres/GetGenresQueryHandlerTests.cs

using Musify.Application.Genres;
using Musify.Application.Tests.TestSupport;
using Musify.Domain.Entities;
using Musify.Domain.ValueObjects;
using Xunit;

namespace Musify.Application.Tests.Genres
{
    public sealed class GetGenresQueryHandlerTests : HandlerTestBase
    {
        private GetGenresQueryHandler CreateHandler() => new(Database);

        [Fact]
        public async Task Handle_NoTracks_ReturnsEmpty()
        {
            var result = await CreateHandler().Handle(new GetGenresQuery(), TestContext.Current.CancellationToken);

            Assert.Empty(result);
        }

        [Fact]
        public async Task Handle_ReturnsOnlyGenresInUse_MostPopulatedFirst()
        {
            var owner = TestEntities.User();
            var rockA = TestEntities.Track(owner, "Rock A", tags: [Genre.Rock]);
            var rockB = TestEntities.Track(owner, "Rock B", tags: [Genre.Rock, Genre.Indie]);
            var jazz = TestEntities.Track(owner, "Jazz", tags: [Genre.Jazz]);
            await SeedAsync(
                owner, rockA, rockB, jazz,
                new UserHasTrack { UserId = owner.Id, TrackId = rockA.Id },
                new UserHasTrack { UserId = owner.Id, TrackId = rockB.Id },
                new UserHasTrack { UserId = owner.Id, TrackId = jazz.Id });

            var result = await CreateHandler().Handle(new GetGenresQuery(), TestContext.Current.CancellationToken);

            Assert.Equal(
                [(Genre.Rock, 2), (Genre.Jazz, 1), (Genre.Indie, 1)],
                result.Select(r => (r.Genre, r.TrackCount)));
        }

        [Fact]
        public async Task Handle_TrackInSeveralLibraries_IsCountedOnce()
        {
            var owner = TestEntities.User();
            var other = TestEntities.User(id: 2, name: "other-user");
            var track = TestEntities.Track(owner, tags: [Genre.Pop]);
            await SeedAsync(
                owner, other, track,
                new UserHasTrack { UserId = owner.Id, TrackId = track.Id },
                new UserHasTrack { UserId = other.Id, TrackId = track.Id });

            var result = await CreateHandler().Handle(new GetGenresQuery(), TestContext.Current.CancellationToken);

            Assert.Equal(1, Assert.Single(result).TrackCount);
        }

        [Fact]
        public async Task Handle_TrackNotInAnyLibrary_IsIgnored()
        {
            var owner = TestEntities.User();
            var track = TestEntities.Track(owner, tags: [Genre.Metal]);
            await SeedAsync(owner, track);

            var result = await CreateHandler().Handle(new GetGenresQuery(), TestContext.Current.CancellationToken);

            Assert.Empty(result);
        }
    }
}