Musify/backend/Tests/Musify.Application.Tests/Mixes/GenerateMixesForUserCommandHandlerTests.cs

using ErrorOr;
using Microsoft.EntityFrameworkCore;
using Musify.Application.Contracts;
using Musify.Application.Mixes;
using Musify.Application.Tests.TestSupport;
using Musify.Domain.Entities;
using Musify.Domain.ValueObjects;
using NSubstitute;
using Xunit;

namespace Musify.Application.Tests.Mixes
{
    public sealed class GenerateMixesForUserCommandHandlerTests : HandlerTestBase
    {
        private readonly IYouTubeMusicService youTubeMusicService = Substitute.For<IYouTubeMusicService>();

        private GenerateMixesForUserCommandHandler CreateHandler() => new(
            Database, youTubeMusicService, TestConfigurations.Mix(), NoOpLogger<GenerateMixesForUserCommandHandler>());

        [Fact]
        public async Task Handle_NoListeningHistory_DoesNotCreateAnyMix()
        {
            var user = TestEntities.User();
            await SeedAsync(user);

            var result = await CreateHandler().Handle(new GenerateMixesForUserCommand(user.Id), TestContext.Current.CancellationToken);

            Assert.False(result.IsError);
            Assert.Empty(await Database.Mixes.ToListAsync(TestContext.Current.CancellationToken));
        }

        [Fact]
        public async Task Handle_HistoryWithNoKnownArtists_DoesNotCreateAnyMix()
        {
            var user = TestEntities.User();
            var track = TestEntities.LocalTrack(user);
            await SeedAsync(user, track, TestEntities.ListeningHistory(user.Id, track.Id));

            var result = await CreateHandler().Handle(new GenerateMixesForUserCommand(user.Id), TestContext.Current.CancellationToken);

            Assert.False(result.IsError);
            Assert.Empty(await Database.Mixes.ToListAsync(TestContext.Current.CancellationToken));
        }

        [Fact]
        public async Task Handle_SeedArtistWithYouTubeAndLocalCandidates_ReplacesPreviousMixes()
        {
            youTubeMusicService
                .SearchSongsAsync(Arg.Any<string>(), Arg.Any<string>(), Arg.Any<CancellationToken>())
                .Returns(new YouTubeSearchResult(
                    [new YouTubeSongResult("yt-1", "YouTube Song", "Seed Artist", "Album", 200, "https://img/thumb.jpg", IsExplicit: false, [] )],
                    ContinuationToken: string.Empty));
            youTubeMusicService.ResolveArtworkUrl(Arg.Any<string>()).Returns(callInfo => callInfo.Arg<string>());

            var user = TestEntities.User();
            var artist = TestEntities.Artist("Seed Artist");
            var listenedTrack = TestEntities.ExternalTrack(externalId: "listened", title: "Listened Track");
            var otherTrackByArtist = TestEntities.ExternalTrack(externalId: "not-listened", title: "Other Track");

            var staleMix = TestEntities.Mix(user.Id, "Stale Mix");
            var staleItem = TestEntities.MixItem(staleMix.Id, title: "Stale Item");

            await SeedAsync(
                user, artist, listenedTrack, otherTrackByArtist, staleMix, staleItem,
                new TrackArtist { TrackId = listenedTrack.Id, ArtistId = artist.Id, Position = 0 },
                new TrackArtist { TrackId = otherTrackByArtist.Id, ArtistId = artist.Id, Position = 0 },
                TestEntities.ListeningHistory(user.Id, listenedTrack.Id));

            var result = await CreateHandler().Handle(new GenerateMixesForUserCommand(user.Id), TestContext.Current.CancellationToken);

            Assert.False(result.IsError);
            var mixes = await Database.Mixes.ToListAsync(TestContext.Current.CancellationToken);
            Assert.NotEmpty(mixes);
            Assert.DoesNotContain(mixes, mix => mix.Title == "Stale Mix");
            Assert.Empty(await Database.MixItems.Where(item => item.MixId == staleMix.Id).ToListAsync(TestContext.Current.CancellationToken));
        }

        [Fact]
        public async Task Handle_YouTubeSourceUnavailable_StillCreatesMixesFromLocalCandidatesOnly()
        {
            // Simulates IYouTubeMusicService.SearchSongsAsync as it behaves when the YouTube source is
            // disabled (DisabledYouTubeMusicService, see Infrastructure): every call fails. Mix
            // generation must degrade to local-only candidates instead of failing the whole command.
            youTubeMusicService
                .SearchSongsAsync(Arg.Any<string>(), Arg.Any<string>(), Arg.Any<CancellationToken>())
                .Returns(Error.Forbidden(description: "The YouTube Music source is disabled."));

            var user = TestEntities.User();
            var artist = TestEntities.Artist("Seed Artist");
            var listenedTrack = TestEntities.ExternalTrack(externalId: "listened", title: "Listened Track");
            var otherTrackByArtist = TestEntities.ExternalTrack(externalId: "not-listened", title: "Other Track");

            await SeedAsync(
                user, artist, listenedTrack, otherTrackByArtist,
                new TrackArtist { TrackId = listenedTrack.Id, ArtistId = artist.Id, Position = 0 },
                new TrackArtist { TrackId = otherTrackByArtist.Id, ArtistId = artist.Id, Position = 0 },
                TestEntities.ListeningHistory(user.Id, listenedTrack.Id));

            var result = await CreateHandler().Handle(new GenerateMixesForUserCommand(user.Id), TestContext.Current.CancellationToken);

            Assert.False(result.IsError);
            var items = await Database.MixItems.ToListAsync(TestContext.Current.CancellationToken);
            Assert.NotEmpty(items);
            Assert.All(items, item => Assert.Equal(MixItemSource.Musify, item.Source));
        }
    }
}