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

using ErsatzTV.Application.Search.Queries;
using ErsatzTV.Infrastructure;
using ErsatzTV.Infrastructure.Data;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Logging.Abstractions;
using NUnit.Framework;
using Shouldly;

namespace ErsatzTV.Tests.Application.Search;

/// <summary>
///     Provider-shape guards for the <c>artist</c> / <c>album_artist</c> facet-value sources (#578).
///     <para>
///         <see cref="GetSearchFieldValuesHandlerTests" /> runs against in-memory SQLite, so it structurally
///         cannot see a MySQL translation or collation difference. These tests build the same LINQ against the
///         Pomelo MySQL provider and assert the generated SQL — <c>ToQueryString</c> compiles the query without
///         touching a server, so no MySQL instance is needed.
///     </para>
/// </summary>
[TestFixture]
[NonParallelizable]
public class SearchFieldValuesQueryShapeTests
{
    private bool _wasSqlite;

    [SetUp]
    public void SetUp() => _wasSqlite = TvContext.IsSqlite;

    [TearDown]
    public void TearDown() => TvContext.IsSqlite = _wasSqlite;

    [Test]
    public void Artist_Entity_Union_Translates_On_Both_Providers_With_Lower_And_A_Row_Limit()
    {
        foreach ((string provider, Func<TvContext> create) in Providers())
        {
            using TvContext context = create();

            // calls the handler's own source builder (internal, via InternalsVisibleTo) rather than rebuilding
            // the LINQ here — a copy would keep passing after the handler's query changed underneath it
            string sql = GetSearchFieldValuesHandler.GetSource(context, "artist")
                .Where(v => v != null && v.ToLower().StartsWith("a"))
                .Distinct()
                .OrderBy(v => v)
                .Take(50)
                .ToQueryString();

            // case-insensitivity comes from LOWER() on the column, not from the provider's LIKE collation
            sql.ShouldContain("LOWER(", Case.Insensitive, $"{provider}: {sql}");
            sql.ShouldContain("LIKE", Case.Insensitive, $"{provider}: {sql}");
            sql.ShouldContain("MusicVideoArtist", Case.Insensitive, $"{provider}: {sql}");
            // the whole thing is one bounded server-side query, never a client-side scan
            sql.ShouldContain("LIMIT", Case.Insensitive, $"{provider}: {sql}");
        }
    }

    [Test]
    public void Regression_Pin_Song_List_Columns_Cannot_Be_Projected_Server_Side_On_Either_Provider()
    {
        // REGRESSION PIN, not coverage of #578: this asserts pre-existing EF/provider behaviour and passes
        // against the code before this change.
        //
        // Documents WHY the handler drops to raw SQL for SongMetadata.Artists / .AlbumArtists rather than
        // SelectMany-ing them: EF maps them as JSON primitive collections and neither provider can translate
        // the projection (SQLite needs APPLY; Pomelo has no primitive-collection support). If a provider
        // upgrade ever makes this translate, this test fails and the raw-SQL path can be retired.
        foreach ((string provider, Func<TvContext> create) in Providers())
        {
            using TvContext context = create();

            Should.Throw<InvalidOperationException>(
                () => context.SongMetadata.SelectMany(m => m.Artists).Distinct().Take(50).ToQueryString(),
                $"{provider} unexpectedly translated a primitive-collection projection");

            Should.Throw<InvalidOperationException>(
                () => context.SongMetadata.SelectMany(m => m.AlbumArtists).Distinct().Take(50).ToQueryString(),
                $"{provider} unexpectedly translated a primitive-collection projection");
        }
    }

    [Test]
    public void List_Valued_Page_Query_Has_No_Predicate_Beyond_The_Keyset_Cursor()
    {
        // This is the whole basis of the row bound, so it is asserted rather than assumed. LIMIT truncates what
        // survives a RESIDUAL predicate — one that discards rows the engine already produced — so with such a
        // predicate present it bounds the output rather than the row count, and the engine may produce and
        // discard arbitrarily many rows first. That is how four successive revisions scanned past their own
        // bound. The cursor `Id > @AfterId` is NOT such a predicate: it is a seek on the ordering key, which
        // positions the scan without discarding anything, so LIMIT n yields n logical rows.
        //
        // What this test can and cannot do: it pins the SQL STRING. It cannot pin an execution plan, MVCC
        // visibility work or payload I/O -- physical work is NOT bounded (see the record: MySQL traverses
        // deleted-but-unpurged index records, and TEXT payloads spill to overflow pages).
        string sql = GetSearchFieldValuesHandler.ListValuedSql("Artists");

        sql.ShouldBe(
            "SELECT Id, Artists AS Payload FROM SongMetadata WHERE Id > @AfterId ORDER BY Id LIMIT @Batch");

        // named explicitly so a future "optimization" that reintroduces server-side selectivity fails here
        sql.ShouldNotContain("LIKE");
        sql.ShouldNotContain("LOWER");
        sql.ShouldNotContain("IS NOT NULL");
    }

    private static IEnumerable<(string Provider, Func<TvContext> Create)> Providers() =>
    [
        ("sqlite", Sqlite),
        ("mysql", MySql)
    ];

    private static TvContext Sqlite()
    {
        TvContext.IsSqlite = true;
        var builder = new DbContextOptionsBuilder<TvContext>();
        builder.UseSqlite("Data Source=:memory:");
        return Create(builder.Options);
    }

    private static TvContext MySql()
    {
        TvContext.IsSqlite = false;
        var builder = new DbContextOptionsBuilder<TvContext>();
        builder.UseMySql(
            "Server=localhost;Database=ersatztv_query_shape;User=root;Password=ersatztv;",
            new MySqlServerVersion(new Version(8, 0, 36)));
        return Create(builder.Options);
    }

    private static TvContext Create(DbContextOptions<TvContext> options) =>
        new(
            options,
            NullLoggerFactory.Instance,
            new SlowQueryInterceptor(NullLogger<SlowQueryInterceptor>.Instance));
}