ersatztv/ErsatzTV.Tests/Application/Search/GetSearchFieldValuesHandlerTests.cs

using System.Globalization;
using ErsatzTV.Application.Search.Queries;
using ErsatzTV.Core.Api.Search;
using ErsatzTV.Core.Domain;
using ErsatzTV.Infrastructure.Data;
using ErsatzTV.Tests.Support;
using LanguageExt;
using Microsoft.EntityFrameworkCore;
using NUnit.Framework;
using Shouldly;

namespace ErsatzTV.Tests.Application.Search;

[TestFixture]
public class GetSearchFieldValuesHandlerTests
{
    private InMemoryTvContext _db = null!;

    [SetUp]
    public async Task SetUp() => _db = await InMemoryTvContext.CreateAsync();

    [TearDown]
    public async Task TearDown() => await _db.DisposeAsync();

    [Test]
    public async Task Returns_Distinct_Whole_Values_For_Genre_With_Prefix_And_Limit()
    {
        await using (TvContext context = _db.CreateContext())
        {
            context.Set<Genre>().AddRange(
                new Genre { Name = "Action" },
                new Genre { Name = "Adventure" },
                new Genre { Name = "Animation" },
                new Genre { Name = "Comedy" });
            await context.SaveChangesAsync();
        }

        var handler = new GetSearchFieldValuesHandler(_db.Factory);

        Option<SearchFieldValuesResponseModel> result = await handler.Handle(
            new GetSearchFieldValues("genre", "A", 50),
            CancellationToken.None);

        result.IsSome.ShouldBeTrue();
        result.IfSome(r => r.Values.ShouldBe(new List<string> { "Action", "Adventure", "Animation" }));

        Option<SearchFieldValuesResponseModel> limited = await handler.Handle(
            new GetSearchFieldValues("genre", "A", 2),
            CancellationToken.None);

        limited.IsSome.ShouldBeTrue();
        limited.IfSome(r => r.Values.ShouldBe(new List<string> { "Action", "Adventure" }));
    }

    [Test]
    public async Task Splits_Content_Rating_On_Slash()
    {
        await using (TvContext context = _db.CreateContext())
        {
            context.MovieMetadata.Add(new MovieMetadata
            {
                MetadataKind = MetadataKind.External,
                DateAdded = DateTime.UtcNow,
                DateUpdated = DateTime.UtcNow,
                ContentRating = "PG-13/TV-14"
            });
            await context.SaveChangesAsync();
        }

        var handler = new GetSearchFieldValuesHandler(_db.Factory);

        Option<SearchFieldValuesResponseModel> result = await handler.Handle(
            new GetSearchFieldValues("content_rating", string.Empty, 50),
            CancellationToken.None);

        result.IsSome.ShouldBeTrue();
        result.IfSome(r => r.Values.ShouldBe(new List<string> { "PG-13", "TV-14" }));
    }

    [Test]
    public async Task Returns_MediaItemState_Enum_Names_Without_Seeding()
    {
        var handler = new GetSearchFieldValuesHandler(_db.Factory);

        Option<SearchFieldValuesResponseModel> result = await handler.Handle(
            new GetSearchFieldValues("state", string.Empty, 50),
            CancellationToken.None);

        result.IsSome.ShouldBeTrue();
        result.IfSome(r => r.Values.ShouldBe(
            new List<string> { "FileNotFound", "Normal", "RemoteOnly", "Unavailable" }));
    }

    [Test]
    public async Task Returns_NotFound_For_Excluded_Text_Field_Title()
    {
        var handler = new GetSearchFieldValuesHandler(_db.Factory);

        Option<SearchFieldValuesResponseModel> result = await handler.Handle(
            new GetSearchFieldValues("title", string.Empty, 50),
            CancellationToken.None);

        result.IsNone.ShouldBeTrue();
    }

    [Test]
    public async Task Returns_NotFound_For_NonText_Field()
    {
        var handler = new GetSearchFieldValuesHandler(_db.Factory);

        // "minutes" is a "number" field in SearchFieldCatalog, not "text"
        Option<SearchFieldValuesResponseModel> result = await handler.Handle(
            new GetSearchFieldValues("minutes", string.Empty, 50),
            CancellationToken.None);

        result.IsNone.ShouldBeTrue();
    }

    [Test]
    public async Task Returns_NotFound_For_Unknown_Field()
    {
        var handler = new GetSearchFieldValuesHandler(_db.Factory);

        Option<SearchFieldValuesResponseModel> result = await handler.Handle(
            new GetSearchFieldValues("nope", string.Empty, 50),
            CancellationToken.None);

        result.IsNone.ShouldBeTrue();
    }

    [Test]
    public async Task Matches_Case_Insensitive_Prefix()
    {
        await using (TvContext context = _db.CreateContext())
        {
            context.Set<Genre>().AddRange(
                new Genre { Name = "Action" },
                new Genre { Name = "Comedy" });
            await context.SaveChangesAsync();
        }

        var handler = new GetSearchFieldValuesHandler(_db.Factory);

        Option<SearchFieldValuesResponseModel> result = await handler.Handle(
            new GetSearchFieldValues("genre", "a", 50),
            CancellationToken.None);

        result.IsSome.ShouldBeTrue();
        result.IfSome(r => r.Values.ShouldBe(new List<string> { "Action" }));
    }

    [Test]
    public async Task Excludes_Network_And_Country_Tags_From_Tag_Field_And_Routes_Network_Tags_To_Network_Field()
    {
        await using (TvContext context = _db.CreateContext())
        {
            context.Set<Tag>().AddRange(
                new Tag { Name = "PlainTag" },
                new Tag { Name = "HBO", ExternalTypeId = Tag.PlexNetworkTypeId },
                new Tag { Name = "USA", ExternalTypeId = Tag.NfoCountryTypeId });
            await context.SaveChangesAsync();
        }

        var handler = new GetSearchFieldValuesHandler(_db.Factory);

        Option<SearchFieldValuesResponseModel> tagResult = await handler.Handle(
            new GetSearchFieldValues("tag", string.Empty, 50),
            CancellationToken.None);

        tagResult.IsSome.ShouldBeTrue();
        tagResult.IfSome(r => r.Values.ShouldBe(new List<string> { "PlainTag" }));

        Option<SearchFieldValuesResponseModel> networkResult = await handler.Handle(
            new GetSearchFieldValues("network", string.Empty, 50),
            CancellationToken.None);

        networkResult.IsSome.ShouldBeTrue();
        networkResult.IfSome(r => r.Values.ShouldBe(new List<string> { "HBO" }));
    }

    [Test]
    public async Task Artist_Merges_Entity_Artists_Music_Video_Credits_And_Song_Credits()
    {
        await using (TvContext context = _db.CreateContext())
        {
            context.ArtistMetadata.Add(Artist("Alpha Entity"));

            // negative control: an entity artist that must NOT match the "al" prefix
            context.ArtistMetadata.Add(Artist("Zeta Entity"));

            context.MusicVideoMetadata.AddRange(
                MusicVideo("MV One", "Alpha Credit", "Alpha Shared"),
                // "Alpha Shared" appears in two rows, so DISTINCT has something to collapse
                MusicVideo("MV Two", "Alpha Shared"),
                MusicVideo("MV Three", "Zeta Credit"));

            context.SongMetadata.AddRange(
                Song("Song One", ["Alpha Song", "Zeta Song"]),
                Song("Song Two", ["Alpha Song"]),
                Song("Song Three", ["Zeta Only"]));

            await context.SaveChangesAsync();
        }

        var handler = new GetSearchFieldValuesHandler(_db.Factory);

        Option<SearchFieldValuesResponseModel> result = await handler.Handle(
            new GetSearchFieldValues("artist", "al", 50),
            CancellationToken.None);

        result.IsSome.ShouldBeTrue();
        result.IfSome(r => r.Values.ShouldBe(
            new List<string> { "Alpha Credit", "Alpha Entity", "Alpha Shared", "Alpha Song" }));
    }

    [Test]
    public async Task Artist_Returns_Every_Source_For_Empty_Query()
    {
        await using (TvContext context = _db.CreateContext())
        {
            context.ArtistMetadata.Add(Artist("Entity"));
            context.MusicVideoMetadata.Add(MusicVideo("MV", "Credit"));
            context.SongMetadata.Add(Song("Song", ["SongArtist"]));
            await context.SaveChangesAsync();
        }

        var handler = new GetSearchFieldValuesHandler(_db.Factory);

        Option<SearchFieldValuesResponseModel> result = await handler.Handle(
            new GetSearchFieldValues("artist", string.Empty, 50),
            CancellationToken.None);

        result.IsSome.ShouldBeTrue();
        result.IfSome(r => r.Values.ShouldBe(new List<string> { "Credit", "Entity", "SongArtist" }));
    }

    [Test]
    public async Task Album_Artist_Returns_Song_Album_Artists_Instead_Of_NotFound()
    {
        await using (TvContext context = _db.CreateContext())
        {
            context.SongMetadata.AddRange(
                Song("One", ["Performer"], ["Alpha Album Artist", "Beta Album Artist"]),
                // repeated across rows so DISTINCT is exercised
                Song("Two", ["Performer"], ["Alpha Album Artist"]),
                // negative control: a row whose album artists are absent entirely
                Song("Three", ["Performer"], null));
            await context.SaveChangesAsync();
        }

        var handler = new GetSearchFieldValuesHandler(_db.Factory);

        Option<SearchFieldValuesResponseModel> result = await handler.Handle(
            new GetSearchFieldValues("album_artist", string.Empty, 50),
            CancellationToken.None);

        result.IsSome.ShouldBeTrue();
        result.IfSome(r => r.Values.ShouldBe(new List<string> { "Alpha Album Artist", "Beta Album Artist" }));

        // the performers on the same rows must not leak into album_artist
        result.IfSome(r => r.Values.ShouldNotContain("Performer"));
    }

    [Test]
    public async Task List_Valued_Fields_Match_Whole_Elements_Not_Substrings_And_Ignore_Neighbours()
    {
        await using (TvContext context = _db.CreateContext())
        {
            context.SongMetadata.AddRange(
                // "Neighbour" arrives on the same row as "Radiohead" -- rows are read whole -- and must be
                // dropped by the in-memory exact prefix filter.
                Song("One", ["Radiohead", "Neighbour"]),
                // "The Radio Dept." contains "radio" but does not start with it
                Song("Two", ["The Radio Dept."]),
                Song("Three", ["Radio Birdman"]));
            await context.SaveChangesAsync();
        }

        var handler = new GetSearchFieldValuesHandler(_db.Factory);

        Option<SearchFieldValuesResponseModel> result = await handler.Handle(
            new GetSearchFieldValues("artist", "radio", 50),
            CancellationToken.None);

        result.IsSome.ShouldBeTrue();
        result.IfSome(r => r.Values.ShouldBe(new List<string> { "Radio Birdman", "Radiohead" }));
    }

    [Test]
    public async Task List_Valued_Fields_Match_Literally_Including_Json_Escaped_And_Wildcard_Characters()
    {
        await using (TvContext context = _db.CreateContext())
        {
            context.SongMetadata.AddRange(
                // non-ASCII: stored on disk JSON-escaped as \u00E9, and must survive the round trip
                Song("One", ["Beyoncé"]),
                // an embedded quote is stored as \u0022
                Song("Two", ["\"Weird Al\" Yankovic"]),
                // SQL wildcards must be ordinary characters here, matched literally
                Song("Three", ["50% Off"]),
                Song("Four", ["50 Cent"]));
            await context.SaveChangesAsync();
        }

        var handler = new GetSearchFieldValuesHandler(_db.Factory);

        (await handler.Handle(new GetSearchFieldValues("artist", "beyoncé", 50), CancellationToken.None))
            .IfSome(r => r.Values.ShouldBe(new List<string> { "Beyoncé" }));

        (await handler.Handle(new GetSearchFieldValues("artist", "\"weird", 50), CancellationToken.None))
            .IfSome(r => r.Values.ShouldBe(new List<string> { "\"Weird Al\" Yankovic" }));

        // "50%" must not behave as the wildcard "50<anything>" — "50 Cent" must not come back
        (await handler.Handle(new GetSearchFieldValues("artist", "50%", 50), CancellationToken.None))
            .IfSome(r => r.Values.ShouldBe(new List<string> { "50% Off" }));
    }

    /// <summary>
    ///     Seeds <paramref name="fillerRows" /> non-matching songs through raw SQL — 20k rows via the change
    ///     tracker is minutes, this is milliseconds.
    /// </summary>
    private static Task SeedFiller(TvContext context, int fillerRows) =>
        context.Database.ExecuteSqlRawAsync(
            $"""
             WITH RECURSIVE seq(n) AS (SELECT 1 UNION ALL SELECT n + 1 FROM seq WHERE n < {fillerRows})
             INSERT INTO SongMetadata (SongId, MetadataKind, Title, Artists, DateAdded, DateUpdated)
             SELECT 0, 0, 'Filler ' || n, '["zzz-filler"]', '2026-01-01', '2026-01-01' FROM seq
             """);

    [Test]
    public async Task List_Valued_Walk_Reads_At_Most_20000_Rows()
    {
        // Pinned in both directions so the ceiling itself is nailed down: a match in row 20000 is read, the same
        // match in row 20001 is not. The query has no RESIDUAL predicate -- only the cursor -- so "rows read" is
        // what LIMIT returns. That bounds LOGICAL rows, not physical work: the engine may still traverse more
        // index records than it returns (MySQL purge lag), and row width is unbounded.
        const string needle = "\u00E9clair-the-needle";

        await using (TvContext context = _db.CreateContext())
        {
            await SeedFiller(context, 19999);
            context.SongMetadata.Add(Song("Needle", [needle]));
            await context.SaveChangesAsync();

            (await context.SongMetadata.CountAsync()).ShouldBe(20000);
        }

        var handler = new GetSearchFieldValuesHandler(_db.Factory);

        (await handler.Handle(new GetSearchFieldValues("artist", "\u00E9", 50), CancellationToken.None))
            .IfSome(r => r.Values.ShouldBe(new List<string> { needle }, "row 20000 is inside the ceiling"));

        await using (TvContext context = _db.CreateContext())
        {
            SongMetadata existing = await context.SongMetadata.SingleAsync(m => m.Title == "Needle");
            context.SongMetadata.Remove(existing);
            await SeedFiller(context, 1);
            await context.SaveChangesAsync();
            context.SongMetadata.Add(Song("Needle", [needle]));
            await context.SaveChangesAsync();

            (await context.SongMetadata.CountAsync()).ShouldBe(20001);
        }

        (await handler.Handle(new GetSearchFieldValues("artist", "\u00E9", 50), CancellationToken.None))
            .IfSome(
                r => r.Values.ShouldBeEmpty(
                    "row 20001 is past the ceiling; this false negative is the documented bounded-best-effort "
                    + "contract, deliberately pinned rather than papered over"));
    }

    [Test]
    public async Task List_Valued_Walk_Reads_Live_Rows_Regardless_Of_Id_Density()
    {
        // Bounding the Id KEYSPACE is the killer here: keyspace is not rows — with 20,000
        // historical rows deleted and one live song at Id 20001, the walk spent its whole allowance on empty
        // ranges and returned [] for a table containing exactly one row. Capacity degraded linearly with
        // deletion ratio, and no ratio was safe -- one placed gap hid the next match.
        //
        // Paging by row position rather than Id value makes density irrelevant: LIMIT @Batch returns @Batch
        // ROWS, wherever they sit in the keyspace.
        await using (TvContext context = _db.CreateContext())
        {
            await SeedFiller(context, 20000);
            await context.Database.ExecuteSqlRawAsync("DELETE FROM SongMetadata");
            context.SongMetadata.Add(Song("Survivor", ["Queen"]));
            await context.SaveChangesAsync();

            // one live row, sitting past the old keyspace allowance
            (await context.SongMetadata.CountAsync()).ShouldBe(1);
            (await context.SongMetadata.Select(m => m.Id).SingleAsync()).ShouldBeGreaterThan(20000);
        }

        var handler = new GetSearchFieldValuesHandler(_db.Factory);

        (await handler.Handle(new GetSearchFieldValues("artist", "que", 50), CancellationToken.None))
            .IfSome(
                r => r.Values.ShouldBe(
                    new List<string> { "Queen" },
                    "a one-row table must be fully readable no matter where its Id sits"));

        // and a leading gap must not hide a later match either
        await using (TvContext context = _db.CreateContext())
        {
            context.SongMetadata.Add(Song("Second", ["Queens of the Stone Age"]));
            await context.SaveChangesAsync();
        }

        (await handler.Handle(new GetSearchFieldValues("artist", "que", 50), CancellationToken.None))
            .IfSome(r => r.Values.ShouldBe(new List<string> { "Queen", "Queens of the Stone Age" }));
    }

    [Test]
    [TestCase("é", "\u00C9dith Piaf")]
    [TestCase("\u00C9", "\u00C9dith Piaf")]
    [TestCase("\u00E9dith", "\u00C9dith Piaf")]
    [TestCase("bj", "Bj\u00F6rk")]
    [TestCase("bj\u00F6", "Bj\u00F6rk")]
    [TestCase("BJ\u00D6RK", "Bj\u00F6rk")]
    [TestCase("beyonc\u00E9", "Beyonc\u00E9")]
    [TestCase("sigur r", "Sigur R\u00F3s")]
    [TestCase("\u00D6", "\u00D6zdemir")]
    public async Task Matches_NonAscii_Values_In_Any_Casing(string query, string stored)
    {
        // Accented artists are the common case in a music library, so non-ASCII matching is pinned end to
        // end, in both casings of the query.
        //
        // Historical note, because it is why this suite exists: revision 1b78dc9e narrowed rows in SQL
        // with a LIKE built by JSON-encoding the query, which cannot work -- non-ASCII is stored escaped
        // (\u00C9) and SQL LOWER() folds the escape TEXT, not the codepoint it denotes. THREE of these nine
        // cases fail against that revision (the ones where query and stored casing differ, so \u00e9 and
        // \u00C9 diverge); the other six pass it, because when the casings agree the escape texts line up.
        // The SQL now has no residual predicate at all -- matching happens in memory, where a string is just
        // a string -- so these cases pin current behaviour rather than guard that revision.
        await using (TvContext context = _db.CreateContext())
        {
            context.SongMetadata.AddRange(
                Song("Hit", [stored]),
                // negative control: a row that must never come back for any of these queries
                Song("Other", ["Nothing Relevant"]));
            await context.SaveChangesAsync();
        }

        var handler = new GetSearchFieldValuesHandler(_db.Factory);

        Option<SearchFieldValuesResponseModel> result = await handler.Handle(
            new GetSearchFieldValues("artist", query, 50),
            CancellationToken.None);

        result.IsSome.ShouldBeTrue();
        result.IfSome(r => r.Values.ShouldBe(new List<string> { stored }));
    }

    [Test]
    public async Task Results_Do_Not_Depend_On_The_Request_Culture()
    {
        // UseRequestLocalization honours Accept-Language, so CurrentCulture is caller-controlled. Under tr-TR
        // the old `q.ToLower()` turned "I" into "\u0131" and the default linguistic StartsWith(string) compounded
        // it, so the same library answered differently per caller. The contract is ordinal: "I" matches
        // "Istanbul" and does NOT match "\u0131pek", in every culture.
        await using (TvContext context = _db.CreateContext())
        {
            context.SongMetadata.Add(Song("One", ["Istanbul Orkestrasi", "\u0131pek"]));
            context.ArtistMetadata.Add(Artist("Idil Biret"));
            await context.SaveChangesAsync();
        }

        var handler = new GetSearchFieldValuesHandler(_db.Factory);
        var expected = new List<string> { "Idil Biret", "Istanbul Orkestrasi" };

        CultureInfo original = CultureInfo.CurrentCulture;
        try
        {
            foreach (string culture in new[] { "en-US", "tr-TR", "az-AZ", "lt-LT" })
            {
                CultureInfo.CurrentCulture = new CultureInfo(culture);

                Option<SearchFieldValuesResponseModel> result = await handler.Handle(
                    new GetSearchFieldValues("artist", "I", 50),
                    CancellationToken.None);

                result.IsSome.ShouldBeTrue();
                result.IfSome(r => r.Values.ShouldBe(expected, $"culture {culture} changed the result"));
            }
        }
        finally
        {
            CultureInfo.CurrentCulture = original;
        }
    }

    [Test]
    public async Task Ordering_Is_Ordinal_And_Culture_Independent()
    {
        // The merge sorts ordinally rather than by culture, so the response order does not depend on the caller
        // either. Ordinal puts all ASCII uppercase before ASCII lowercase, and non-ASCII last.
        await using (TvContext context = _db.CreateContext())
        {
            context.SongMetadata.Add(Song("One", ["Zulu", "apple", "\u00C9clair", "Apple"]));
            await context.SaveChangesAsync();
        }

        var handler = new GetSearchFieldValuesHandler(_db.Factory);
        var expected = new List<string> { "Apple", "Zulu", "apple", "\u00C9clair" };

        CultureInfo original = CultureInfo.CurrentCulture;
        try
        {
            foreach (string culture in new[] { "en-US", "sv-SE" })
            {
                CultureInfo.CurrentCulture = new CultureInfo(culture);

                Option<SearchFieldValuesResponseModel> result = await handler.Handle(
                    new GetSearchFieldValues("artist", string.Empty, 50),
                    CancellationToken.None);

                result.IfSome(r => r.Values.ShouldBe(expected, $"culture {culture} changed the order"));
            }
        }
        finally
        {
            CultureInfo.CurrentCulture = original;
        }
    }

    [Test]
    public async Task Ordering_Is_Best_Effort_When_A_Source_Truncates()
    {
        // Documents the acknowledged imprecision rather than claiming exactness the code does not have. The EF
        // source truncates by the DATABASE collation, which is NOT the ordinal ordering the merge then applies —
        // so a value the database ranked outside its first `limit` never reaches the merge, even if the merge
        // would have ranked it first.
        //
        // "Zulu" vs "apple" is the pair that actually diverges: ordinal puts every ASCII uppercase letter before
        // every lowercase one, so ordinal ranks "Zulu" first, while a case-insensitive database ordering ranks
        // "apple" first. (An earlier version used "Zulu"/"Éclair", where BOTH orderings pick "Zulu" — it could
        // not have told the two apart, and the divergence it claimed to show did not exist.)
        await using (TvContext context = _db.CreateContext())
        {
            context.ArtistMetadata.Add(Artist("Zulu"));
            context.ArtistMetadata.Add(Artist("apple"));
            await context.SaveChangesAsync();
        }

        var handler = new GetSearchFieldValuesHandler(_db.Factory);

        // with room for both, the ordinal merge ranks "Zulu" first
        (await handler.Handle(new GetSearchFieldValues("artist", string.Empty, 50), CancellationToken.None))
            .IfSome(r => r.Values.ShouldBe(new List<string> { "Zulu", "apple" }));

        // with limit=1 the database picks the survivor by ITS ordering, and the merge only ever sees that one
        (await handler.Handle(new GetSearchFieldValues("artist", string.Empty, 1), CancellationToken.None))
            .IfSome(r => r.Values.ShouldBe(new List<string> { "apple" }));
    }

    [Test]
    public async Task A_Match_Behind_Many_NonMatching_Rows_Is_Still_Found()
    {
        // Fails a883e5f0, which capped rows at a fixed 1000 AFTER a deliberately over-matching SQL pre-filter:
        // the 1001st row -- the only exact match -- was discarded before the in-memory filter ever saw it and
        // the endpoint returned []. The pre-filter is gone, and the property it broke now holds for any match
        // within the read ceiling: preceding non-matching rows do not hide it. Past the ceiling it is still
        // lost by design -- see List_Valued_Walk_Reads_At_Most_20000_Rows, which pins that boundary.
        await using (TvContext context = _db.CreateContext())
        {
            for (var i = 0; i < 1000; i++)
            {
                context.SongMetadata.Add(Song($"Filler {i}", ["zzz-filler"], ["zzz-filler-album"]));
            }

            context.SongMetadata.Add(Song("Needle", ["\u00E9clair"], ["\u00E9clair"]));
            await context.SaveChangesAsync();
        }

        var handler = new GetSearchFieldValuesHandler(_db.Factory);

        Option<SearchFieldValuesResponseModel> albumArtist = await handler.Handle(
            new GetSearchFieldValues("album_artist", "\u00E9", 50),
            CancellationToken.None);

        albumArtist.IsSome.ShouldBeTrue();
        albumArtist.IfSome(r => r.Values.ShouldBe(new List<string> { "\u00E9clair" }));

        // same starvation shape on the merged `artist` field
        Option<SearchFieldValuesResponseModel> artist = await handler.Handle(
            new GetSearchFieldValues("artist", "\u00E9", 50),
            CancellationToken.None);

        artist.IsSome.ShouldBeTrue();
        artist.IfSome(r => r.Values.ShouldBe(new List<string> { "\u00E9clair" }));

        // ... and for a prefix beginning with a character that JSON escapes on disk. That used to collapse the
        // SQL pattern to the bare anchor; there is no prefix predicate at all now, so it is simply an ordinary
        // prefix -- kept because it is the input shape that broke the old scheme.
        await using (TvContext context = _db.CreateContext())
        {
            context.SongMetadata.Add(Song("Ampersand", ["&Me"]));
            await context.SaveChangesAsync();
        }

        Option<SearchFieldValuesResponseModel> escapedPrefix = await handler.Handle(
            new GetSearchFieldValues("artist", "&M", 50),
            CancellationToken.None);

        escapedPrefix.IsSome.ShouldBeTrue();
        escapedPrefix.IfSome(r => r.Values.ShouldBe(new List<string> { "&Me" }));
    }

    private static ArtistMetadata Artist(string title) => new()
    {
        MetadataKind = MetadataKind.External,
        DateAdded = DateTime.UtcNow,
        DateUpdated = DateTime.UtcNow,
        Title = title
    };

    private static MusicVideoMetadata MusicVideo(string title, params string[] artists) => new()
    {
        MetadataKind = MetadataKind.External,
        DateAdded = DateTime.UtcNow,
        DateUpdated = DateTime.UtcNow,
        Title = title,
        Artists = artists.Map(a => new MusicVideoArtist { Name = a }).ToList()
    };

    private static SongMetadata Song(string title, IList<string> artists, IList<string> albumArtists = null) => new()
    {
        MetadataKind = MetadataKind.External,
        DateAdded = DateTime.UtcNow,
        DateUpdated = DateTime.UtcNow,
        Title = title,
        Artists = artists,
        AlbumArtists = albumArtists
    };

    [Test]
    public async Task Dedupes_Repeated_Values()
    {
        await using (TvContext context = _db.CreateContext())
        {
            context.Set<Genre>().AddRange(
                new Genre { Name = "Action" },
                new Genre { Name = "Action" });
            await context.SaveChangesAsync();
        }

        var handler = new GetSearchFieldValuesHandler(_db.Factory);

        Option<SearchFieldValuesResponseModel> result = await handler.Handle(
            new GetSearchFieldValues("genre", string.Empty, 50),
            CancellationToken.None);

        result.IsSome.ShouldBeTrue();
        result.IfSome(r => r.Values.ShouldBe(new List<string> { "Action" }));
    }

    /// <summary>
    ///     ersatztv#668. The EF-sourced fields prefix-match through SQL <c>LOWER()</c>, which on SQLite folds
    ///     ASCII only: <c>lower('Édith')</c> returns <c>'Édith'</c> unchanged, so a stored value whose
    ///     prefix carries an uppercase non-ASCII character is unreachable from any query long enough to reach it.
    ///     The stored-LOWERCASE case already worked (the handler lowercases the query before it reaches SQL, so
    ///     both casings of the query fold to the same pattern) and is pinned alongside it, because the fix must
    ///     SUPPLEMENT that path rather than replace it.
    /// </summary>
    [TestCase("genre", "é")]
    [TestCase("genre", "É")]
    public async Task Ef_Sourced_Stored_Uppercase_Accent_Is_Reachable(string field, string query)
    {
        await using (TvContext context = _db.CreateContext())
        {
            context.Set<Genre>().AddRange(
                new Genre { Name = "Édith" },
                new Genre { Name = "Zulu" });
            await context.SaveChangesAsync();
        }

        var handler = new GetSearchFieldValuesHandler(_db.Factory);

        Option<SearchFieldValuesResponseModel> result = await handler.Handle(
            new GetSearchFieldValues(field, query, 50),
            CancellationToken.None);

        result.IsSome.ShouldBeTrue();
        result.IfSome(r => r.Values.ShouldBe(new List<string> { "Édith" }));
    }

    /// <inheritdoc cref="Ef_Sourced_Stored_Uppercase_Accent_Is_Reachable" />
    [TestCase("genre", "é")]
    [TestCase("genre", "É")]
    public async Task Ef_Sourced_Stored_Lowercase_Accent_Stays_Reachable(string field, string query)
    {
        await using (TvContext context = _db.CreateContext())
        {
            context.Set<Genre>().AddRange(
                new Genre { Name = "édith" },
                new Genre { Name = "Zulu" });
            await context.SaveChangesAsync();
        }

        var handler = new GetSearchFieldValuesHandler(_db.Factory);

        Option<SearchFieldValuesResponseModel> result = await handler.Handle(
            new GetSearchFieldValues(field, query, 50),
            CancellationToken.None);

        result.IsSome.ShouldBeTrue();
        result.IfSome(r => r.Values.ShouldBe(new List<string> { "édith" }));
    }

    /// <summary>
    ///     ersatztv#668. The Unicode fold added for the non-ASCII branch may OVER-match — the in-memory
    ///     <see cref="StringComparison.OrdinalIgnoreCase" /> filter runs afterwards and drops the extras —
    ///     but it must never UNDER-match. Each case pins the endpoint's answer against what that filter
    ///     alone would say, so a fold that starts dropping rows fails here. It does NOT catch removal of the
    ///     in-memory filter — every case here is either a positive that SQL alone returns, or an ASCII-query
    ///     negative that SQL alone rejects. That direction is
    ///     <see cref="Unicode_Fold_Over_Match_Is_Discarded_By_The_Ordinal_Filter" />'s job.
    ///     <para>
    ///         The negative cases here have ASCII queries, so they exercise the FAST PATH (the fold is
    ///         skipped entirely) and pin that it is exact: <c>"ſweet".StartsWith("S", OrdinalIgnoreCase)</c>
    ///         is false even though <c>char.ToUpperInvariant('ſ')</c> IS <c>'S'</c>. The over-match the fold
    ///         itself produces is a different path and is covered by
    ///         <see cref="Unicode_Fold_Over_Match_Is_Discarded_By_The_Ordinal_Filter" />.
    ///     </para>
    /// </summary>
    [TestCase("Édith", "é", true, TestName = "Fold_UppercaseAccent_LowercaseQuery")]
    [TestCase("Édith", "É", true, TestName = "Fold_UppercaseAccent_UppercaseQuery")]
    [TestCase("Özdemir", "ö", true, TestName = "Fold_Umlaut")]
    [TestCase("Sigur Rós", "sigur", true, TestName = "Fold_AsciiPrefix_NonAsciiLater")]
    [TestCase("Straße", "stra", true, TestName = "Fold_Eszett_AsciiQuery")]
    // explicit escapes: these three are visually indistinguishable from their ASCII lookalikes in a diff,
    // and an ASCII 'K' here would silently turn the KELVIN SIGN case into a trivially-true one
    [TestCase("\u017Fweet", "S", false, TestName = "Fold_LongS_IsNotOrdinalEqualToS")]
    [TestCase("\u212Aelvin", "k", false, TestName = "Fold_KelvinSign_IsNotOrdinalEqualToK")]
    [TestCase("\u0130stanbul", "i", false, TestName = "Fold_DottedCapitalI_IsNotOrdinalEqualToI")]
    public async Task Unicode_Fold_Agrees_With_The_Ordinal_Filter(string stored, string query, bool expected)
    {
        await using (TvContext context = _db.CreateContext())
        {
            context.Set<Genre>().Add(new Genre { Name = stored });
            await context.SaveChangesAsync();
        }

        // the oracle: what the endpoint's own final filter says, computed independently of the database
        stored.StartsWith(query, StringComparison.OrdinalIgnoreCase).ShouldBe(expected);

        var handler = new GetSearchFieldValuesHandler(_db.Factory);

        Option<SearchFieldValuesResponseModel> result = await handler.Handle(
            new GetSearchFieldValues("genre", query, 50),
            CancellationToken.None);

        result.IsSome.ShouldBeTrue();
        result.IfSome(r => r.Values.ShouldBe(expected ? new List<string> { stored } : []));
    }

    /// <summary>
    ///     ersatztv#668. Drives a row THROUGH the fold that the ordinal filter must then discard — the
    ///     harmless over-match direction the whole design rests on, which the ASCII-query negative cases
    ///     above cannot reach. q="ſ" is non-ASCII so the fold runs; <c>ToUpperInvariant('ſ')</c> is 'S', so
    ///     the SQL pattern is <c>S%</c> and SQLite genuinely returns "Sword" — and the response must still
    ///     be empty, because <c>"Sword".StartsWith("ſ", OrdinalIgnoreCase)</c> is false.
    /// </summary>
    [Test]
    public async Task Unicode_Fold_Over_Match_Is_Discarded_By_The_Ordinal_Filter()
    {
        await using (TvContext context = _db.CreateContext())
        {
            context.Set<Genre>().Add(new Genre { Name = "Sword" });
            await context.SaveChangesAsync();
        }

        // Premises, asserted because the expectation is an EMPTY list and would otherwise pass for the
        // wrong reason -- e.g. if the branch stopped running, or a hand-rolled fold stopped mapping ſ to S,
        // SQL would return nothing and this test would still be green.
        GetSearchFieldValuesHandler.ContainsNonAscii("\u017F").ShouldBeTrue();
        char.ToUpperInvariant('\u017F').ShouldBe('S');
        "Sword".StartsWith("\u017F", StringComparison.OrdinalIgnoreCase).ShouldBeFalse();

        var handler = new GetSearchFieldValuesHandler(_db.Factory);

        Option<SearchFieldValuesResponseModel> result = await handler.Handle(
            new GetSearchFieldValues("genre", "\u017F", 50),
            CancellationToken.None);

        result.IsSome.ShouldBeTrue();
        result.IfSome(r => r.Values.ShouldBeEmpty());
    }

    /// <summary>
    ///     ersatztv#668. The escaping's load-bearing role is NOT filtering — the in-memory ordinal filter
    ///     already drops an over-match, which is why a plain count assertion stays green even with the
    ///     escaping removed. It is preventing LIMIT CROWDING: an unescaped <c>_</c> also matches the space,
    ///     binary ORDER BY ranks "100 Édith" first, LIMIT 1 returns only that, the filter discards it, and
    ///     the genuine "100_Édith" is never returned at all. This case fails if the escaping is removed.
    /// </summary>
    [Test]
    public async Task Unicode_Fold_Escaping_Prevents_Limit_Crowding()
    {
        await using (TvContext context = _db.CreateContext())
        {
            context.Set<Genre>().AddRange(
                new Genre { Name = "100 \u00C9dith" },
                new Genre { Name = "100_\u00C9dith" });
            await context.SaveChangesAsync();
        }

        var handler = new GetSearchFieldValuesHandler(_db.Factory);

        Option<SearchFieldValuesResponseModel> result = await handler.Handle(
            new GetSearchFieldValues("genre", "100_\u00C9", 1),
            CancellationToken.None);

        result.IsSome.ShouldBeTrue();
        result.IfSome(r => r.Values.ShouldBe(new List<string> { "100_\u00C9dith" }));
    }

    /// <summary>
    ///     ersatztv#668. The non-ASCII branch is raw SQL, so it gets none of the LIKE-wildcard escaping EF
    ///     does for <c>StartsWith</c>. An unescaped <c>%</c> or <c>_</c> in the query would match anything.
    /// </summary>
    [TestCase("100%É", 1, TestName = "Escapes_Percent")]
    [TestCase("100_É", 0, TestName = "Escapes_Underscore")]
    public async Task Unicode_Fold_Escapes_Like_Wildcards(string query, int expectedCount)
    {
        await using (TvContext context = _db.CreateContext())
        {
            context.Set<Genre>().AddRange(
                new Genre { Name = "100%Édith" },
                new Genre { Name = "100XÉdith" });
            await context.SaveChangesAsync();
        }

        var handler = new GetSearchFieldValuesHandler(_db.Factory);

        Option<SearchFieldValuesResponseModel> result = await handler.Handle(
            new GetSearchFieldValues("genre", query, 50),
            CancellationToken.None);

        result.IsSome.ShouldBeTrue();
        result.IfSome(r => r.Values.Count.ShouldBe(expectedCount));
    }

    /// <summary>
    ///     ersatztv#668. The non-ASCII branch duplicates each field's discriminator predicate in raw SQL, so
    ///     it must reproduce EF's NULL semantics: EF compiles <c>ExternalTypeId != NfoCountryTypeId</c> with
    ///     null semantics, which INCLUDES a NULL-typed row. Plain SQL <c>&lt;&gt;</c> would silently drop it.
    /// </summary>
    [Test]
    public async Task Unicode_Fold_Tag_Discriminator_Matches_Ef_Null_Semantics()
    {
        await using (TvContext context = _db.CreateContext())
        {
            context.Set<Tag>().AddRange(
                new Tag { Name = "Édith", ExternalTypeId = null },
                new Tag { Name = "Éclair", ExternalTypeId = Tag.PlexNetworkTypeId },
                new Tag { Name = "Ézra", ExternalTypeId = Tag.NfoCountryTypeId });
            await context.SaveChangesAsync();
        }

        var handler = new GetSearchFieldValuesHandler(_db.Factory);

        Option<SearchFieldValuesResponseModel> tags = await handler.Handle(
            new GetSearchFieldValues("tag", "é", 50),
            CancellationToken.None);

        // the NULL-typed row is a tag; the network- and country-typed rows are excluded
        tags.IsSome.ShouldBeTrue();
        tags.IfSome(r => r.Values.ShouldBe(new List<string> { "Édith" }));

        Option<SearchFieldValuesResponseModel> networks = await handler.Handle(
            new GetSearchFieldValues("network", "é", 50),
            CancellationToken.None);

        networks.IsSome.ShouldBeTrue();
        networks.IfSome(r => r.Values.ShouldBe(new List<string> { "Éclair" }));
    }
}