using System.Reflection;
using System.Text;
using Elastic.Clients.Elasticsearch;
using Elastic.Transport;
using ErsatzTV.Core.Domain;
using ErsatzTV.Core.Interfaces.Metadata;
using ErsatzTV.Core.Interfaces.Repositories;
using ErsatzTV.Core.Search;
using ErsatzTV.Infrastructure.Data;
using ErsatzTV.Infrastructure.Extensions;
using ErsatzTV.Infrastructure.Search;
using ErsatzTV.Tests.Support;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Logging;
using NSubstitute;
using NUnit.Framework;
using Shouldly;

namespace ErsatzTV.Tests.Integration;

/// <summary>
///     ersatztv#824 — the gap ersatztv#701 named rather than papered over.
///     <para>
///         <c>ElasticSearchIndex.UpdateSong</c> holds an INDEPENDENT copy of the logic
///         <see cref="SongIndexerMetadataMutationTests" /> pins on <c>LuceneSearchIndex</c>. #701 removed
///         <c>metadata.AlbumArtists ??= []; metadata.Artists ??= [];</c> from both, but only Lucene gained
///         a regression test — so reintroducing the mutation in the Elastic copy ALONE left the whole
///         suite green. This fixture closes that: the assertions are the same three, driven through the
///         real <c>ElasticSearchIndex</c> against a real <see cref="TvContext" />.
///     </para>
///     <para>
///         <b>Why a stubbed transport rather than a live server.</b> #824 listed "inject a non-network
///         <c>ElasticsearchClient</c> transport" as option 1 and it is what shipped:
///         <c>Elastic.Transport.InMemoryRequestInvoker</c> is public in the pinned Elastic.Transport, and
///         <c>ElasticsearchClientSettings(NodePool, IRequestInvoker)</c> accepts it. No server, no socket,
///         no new package.
///     </para>
///     <para>
///         <b>The canned response body is load-bearing, not decoration.</b> A bare
///         <c>InMemoryRequestInvoker()</c> answers with an EMPTY body, which the client cannot deserialize
///         into an <c>IndexResponse</c>. That throw lands in <c>UpdateSong</c>'s catch, which logs a
///         warning and assigns <c>metadata.Song = null</c> — so the fixture would measure the ERROR path
///         while every "did not mutate" assertion below still passed, vacuously. The
///         <see cref="ThrowOnWarningLogger{T}" /> is the belt to that brace: it fails the test if the
///         catch ran at all.
///     </para>
///     <para>
///         The client is injected into the private <c>_client</c> field rather than obtained normally,
///         because <c>CreateClient</c> reads the process-wide static <c>ElasticSearchIndex.Uri</c> and
///         would open a real socket. <c>UpdateItems</c> — unlike <c>IndexExists</c> and
///         <c>Initialize</c> — never runs <c>_client ??= CreateClient()</c>, so the injected instance is
///         the one used and an uninjected one would simply be null.
///     </para>
/// </summary>
[TestFixture]
[NonParallelizable]
public class ElasticSongIndexerMetadataMutationTests
{
    private const string TestIndexName = "etv-824-test";

    private string? _originalIndexName;

    /// <summary>
    ///     <c>ElasticSearchIndex.IndexName</c> is a process-wide static. Only <c>Startup</c> reads it today,
    ///     so leaving it set leaks nothing that currently runs — but a static this fixture writes and never
    ///     restores is a cross-test hazard waiting for the first test that does read it.
    /// </summary>
    [SetUp]
    public void SetUp() => _originalIndexName = ElasticSearchIndex.IndexName;

    [TearDown]
    public void TearDown() => ElasticSearchIndex.IndexName = _originalIndexName;

    /// <summary>
    ///     A well-formed <c>IndexResponse</c>. See the fixture docstring: an empty body diverts the run
    ///     into <c>UpdateSong</c>'s catch and makes every assertion below vacuous.
    /// </summary>
    private const string IndexResponseBody =
        """
        {"_index":"etv-824-test","_id":"1","_version":1,"result":"created",
         "_shards":{"total":1,"successful":1,"failed":0},"_seq_no":0,"_primary_term":1}
        """;

    [Test]
    public async Task UpdateSong_Must_Not_Mutate_Nullable_Artists_On_A_Tracked_Entity()
    {
        await using var harness = await InMemoryTvContext.CreateAsync();

        int metadataId;
        int songId;
        await using (TvContext context = harness.CreateContext())
        {
            var library = new LocalLibrary { Name = "Music", MediaKind = LibraryMediaKind.Songs };
            context.Add(library);
            await context.SaveChangesAsync();

            var libraryPath = new LibraryPath { Path = "/music", LibraryId = library.Id };
            context.Add(libraryPath);
            await context.SaveChangesAsync();

            var song = new Song
            {
                LibraryPathId = libraryPath.Id,
                MediaVersions = [],
                SongMetadata =
                [
                    new SongMetadata
                    {
                        MetadataKind = MetadataKind.Fallback,
                        Title = "Untagged Track",
                        SortTitle = "untagged track",
                        DateAdded = new DateTime(2026, 1, 1, 0, 0, 0, DateTimeKind.Utc),

                        // The shape FallbackMetadataProvider.GetSongMetadata leaves behind: it never
                        // assigns either primitive collection, so both columns persist as NULL.
                        Artists = null!,
                        AlbumArtists = null!,

                        Genres = [],
                        Tags = [],
                        Studios = [],
                        Actors = [],
                        Artwork = [],
                        Guids = []
                    }
                ]
            };

            context.Add(song);
            await context.SaveChangesAsync();
            metadataId = song.SongMetadata[0].Id;
            songId = song.Id;
        }

        // The seed must actually have produced NULL columns, or every assertion below is vacuous.
        (await ReadRawArtists(harness, metadataId)).ShouldBeNull();

        await using (TvContext context = harness.CreateContext())
        {
            // Deliberately TRACKED -- the indexer's own contract is what is being pinned, not the
            // AsNoTracking() habit of today's two callers. See SongIndexerMetadataMutationTests.
            Song tracked = await context.Songs
                .IncludeForSearch()
                .AsSplitQuery()
                .SingleAsync();

            SongMetadata metadata = tracked.SongMetadata[0];
            metadata.Artists.ShouldBeNull("EF must materialize the NULL column as null, not as an empty list");

            var logger = new ThrowOnWarningLogger<ElasticSearchIndex>();
            var index = new ElasticSearchIndex(
                new SearchQueryParser(
                    Substitute.For<ISmartCollectionCache>(),
                    Substitute.For<ILogger<SearchQueryParser>>()),
                logger);

            var invoker = new CapturingRequestInvoker(
                new InMemoryRequestInvoker(
                    Encoding.UTF8.GetBytes(IndexResponseBody),
                    200,
                    exception: null,
                    contentType: "application/json",
                    // The X-Elastic-Product header is REQUIRED, not cosmetic. The client runs a product
                    // check on its first response and throws UnsupportedProductException ("the server is
                    // not a supported distribution of Elasticsearch") without it -- which lands in
                    // UpdateSong's catch and makes the fixture measure the error path. Measured: this is
                    // exactly how this fixture first failed.
                    headers: ProductCheckHeaders()));

            var settings = new ElasticsearchClientSettings(
                    new SingleNodePool(new Uri("http://localhost:9200")),
                    invoker)
                .DefaultIndex(TestIndexName);

            ElasticSearchIndex.IndexName = TestIndexName;

            typeof(ElasticSearchIndex)
                .GetField("_client", BindingFlags.NonPublic | BindingFlags.Instance)!
                .SetValue(index, new ElasticsearchClient(settings));

            // A bare substitute returns null from GetAllLanguageCodes, which NPEs inside AddLanguages and
            // would divert the run into UpdateSong's catch.
            var languageCodeService = Substitute.For<ILanguageCodeService>();
            languageCodeService.GetAllLanguageCodes(Arg.Any<List<string>>()).Returns([]);
            languageCodeService.GetAllLanguageCodes(Arg.Any<string>()).Returns([]);

            await index.UpdateItems(
                Substitute.For<ISearchRepository>(),
                Substitute.For<IFallbackMetadataProvider>(),
                languageCodeService,
                [tracked]);

            // Surfacing the exception rather than asserting ShouldBeNull: the catch is the fixture's
            // most likely failure mode (see the canned-response note above), and "expected null but was
            // <Exception>" without the message sends the next reader hunting for a cause the fixture
            // already had in its hand.
            if (logger.Failure is not null)
            {
                Assert.Fail("UpdateSong threw and its catch ran, so this probe measured the error path "
                    + $"rather than the indexing path: {logger.Failure}");
            }

            // POSITIVE CONTROL, and it is not optional: every assertion below says something did NOT
            // happen, so all of them hold vacuously if UpdateSong never ran. The Lucene fixture uses
            // `writer.NumDocs == 1` for exactly this; the transport-level equivalent is that the indexer
            // actually issued the index request for THIS song. Like NumDocs, it proves the song-indexing
            // path ran -- it does NOT prove the artist reads specifically ran.
            invoker.Requests.Count.ShouldBe(
                1,
                "UpdateSong did not issue exactly one index request, so the assertions below would pass "
                + $"without exercising the code under test. Captured: [{string.Join(", ", invoker.Requests)}]");

            // The document id is compared as the LAST PATH SEGMENT, not with ShouldContain. A substring
            // test is a false-pass vector here: the index name itself carries digits ("etv-824-test"), so
            // ShouldContain("2") or ShouldContain("4") would be satisfied by the index name alone for a
            // song whose id happened to be 2 or 4, and the assertion would stop discriminating without
            // ever failing.
            string path = invoker.Requests[0].Split(' ')[^1].Split('?')[0];
            path.Split('/')[^1].ShouldBe(
                songId.ToString(),
                $"the index request was not for the seeded song. Captured: {invoker.Requests[0]}");

            // 1. The indexer left the entity alone.
            metadata.Artists.ShouldBeNull();
            metadata.AlbumArtists.ShouldBeNull();

            // 2. ...so EF has nothing to persist. This is the assertion that fails loudly the day the
            //    mutation returns, even if a later refactor stopped the value from being observable above.
            context.Entry(metadata).State.ShouldBe(EntityState.Unchanged);

            // 3. And the save that a real caller would go on to make does not rewrite the column.
            await context.SaveChangesAsync();
        }

        (await ReadRawArtists(harness, metadataId)).ShouldBeNull();
    }

    private static Dictionary<string, IEnumerable<string>> ProductCheckHeaders() =>
        new(StringComparer.OrdinalIgnoreCase) { ["x-elastic-product"] = ["Elasticsearch"] };

    /// <summary>
    ///     Records every request the client actually issues, so the fixture can prove the code under test
    ///     ran. Delegates the answering to a real <see cref="InMemoryRequestInvoker" /> rather than
    ///     hand-building a response.
    /// </summary>
    private sealed class CapturingRequestInvoker(InMemoryRequestInvoker inner) : IRequestInvoker
    {
        public List<string> Requests { get; } = [];

        public ResponseFactory ResponseFactory => inner.ResponseFactory;

        public TResponse Request<TResponse>(
            Endpoint endpoint,
            BoundConfiguration boundConfiguration,
            PostData? postData)
            where TResponse : TransportResponse, new()
        {
            Requests.Add($"{endpoint.Method} {endpoint.PathAndQuery}");
            return inner.Request<TResponse>(endpoint, boundConfiguration, postData);
        }

        public Task<TResponse> RequestAsync<TResponse>(
            Endpoint endpoint,
            BoundConfiguration boundConfiguration,
            PostData? postData,
            CancellationToken cancellationToken)
            where TResponse : TransportResponse, new()
        {
            Requests.Add($"{endpoint.Method} {endpoint.PathAndQuery}");
            return inner.RequestAsync<TResponse>(endpoint, boundConfiguration, postData, cancellationToken);
        }

        // IRequestInvoker extends IDisposable, but InMemoryRequestInvoker holds no disposable state and
        // exposes no Dispose of its own -- there is nothing to forward to.
        public void Dispose()
        {
        }
    }

    private static async Task<object?> ReadRawArtists(InMemoryTvContext harness, int metadataId)
    {
        await using TvContext context = harness.CreateContext();
        await using var command = context.Database.GetDbConnection().CreateCommand();
        command.CommandText = $"SELECT Artists FROM SongMetadata WHERE Id = {metadataId}";
        object? value = await command.ExecuteScalarAsync();

        // ExecuteScalar returns CLR null both for "the column is NULL" and for "there is no such row",
        // and the second is reachable: UpdateSong's catch assigns metadata.Song = null, which severs a
        // required relationship and cascades the row to Deleted, so a SaveChanges on the error path
        // DELETES it and a plain null check would pass for the wrong reason.
        if (value is null)
        {
            Assert.Fail($"SongMetadata row {metadataId} no longer exists, so its Artists column cannot "
                + "be read -- the probe measured a deleted row rather than a preserved NULL.");
        }

        return value is DBNull ? null : value;
    }
}