using System;
using System.IO;
using System.Linq;
using FluentAssertions;
using GameCult.Caching;
using GameCult.Caching.MessagePack;
using MessagePack;
using NUnit.Framework;

#nullable enable

namespace GameCult.Mesh.Tests;

// C2a: a single-file document written or read through CultMesh is judged as a cache judges it: ids minted, a list that
// cannot hold ids refused, the header decided by what the file holds.
public sealed class CultMeshSingleFileElementIdTests
{
    private const string HexA = "aaaaaaaaaaaa";
    private static readonly CultRecordKey Key = new("publication");

    private string _root = null!;

    [SetUp]
    public void SetUp()
    {
        _root = Path.Combine(Path.GetTempPath(), "cultmesh-single-file-ids", Guid.NewGuid().ToString("N"));
        Directory.CreateDirectory(_root);
    }

    [TearDown]
    public void TearDown()
    {
        if (Directory.Exists(_root)) Directory.Delete(_root, true);
    }

    private static CultMeshBodyPublicationDocument Publication(params CultMeshBodyDescriptor[] representations) => new()
    {
        BodyId = "aetheria:entities",
        ProducerId = "aetheria",
        SchemaId = "eve.entity_soa.v1",
        Representations = representations
    };

    private static string HeaderOf(string path) =>
        CultDocumentMessagePackSerialization.DeserializeSnapshot(File.ReadAllBytes(path)).FormatVersion;

    private static CultMeshBodyDescriptor Descriptor(string id = "") => new() { Id = id, BodyId = "body" };

    private string Path_(string name) => Path.Combine(_root, name);

    [Test]
    public void TypedWriteMintsTheElementIdsAndMarksTheFileThatHoldsThem()
    {
        var path = Path_("ids.cc");
        var publication = Publication(Descriptor(), Descriptor());

        CultMesh.WriteSingleFileDocument(path, Key, publication);

        publication.Representations.Select(entry => entry.Id).Should().OnlyContain(id => id.Length == 12).And.OnlyHaveUniqueItems();
        HeaderOf(path).Should().Be("cultcache.store.v3");
        CultMesh.ReadSingleFileDocument<CultMeshBodyPublicationDocument>(path, Key).Representations.Select(entry => entry.Id)
            .Should().Equal(publication.Representations.Select(entry => entry.Id));
    }

    // A typed write replaces the whole file with a document it can see, so the ids that document holds decide the header.
    [Test]
    public void TypedWriteDecidesTheHeaderByTheDocumentItWritesEvenOverAMarkedFile()
    {
        var path = Path_("none.cc");
        CultMesh.WriteSingleFileDocument(path, Key, Publication());
        HeaderOf(path).Should().Be("cultcache.store.v1");

        CultMesh.WriteSingleFileDocument(path, Key, Publication(Descriptor()));
        HeaderOf(path).Should().Be("cultcache.store.v3");
        CultMesh.WriteSingleFileDocument(path, Key, Publication());
        HeaderOf(path).Should().Be("cultcache.store.v1", "the whole file is replaced by a document that holds no id");
    }

    // A raw payload is opaque: the writer cannot see what it holds, so a marked file stays marked.
    [Test]
    public void RawPayloadWriteOverAMarkedFileKeepsItMarkedAndOverAnUnmarkedOneStaysV1()
    {
        var path = Path_("raw.cc");
        var schema = new CultMeshSingleFileDocumentSchema("raw:schema", "RawSchema", "1");
        var payload = new byte[] { 0x90 };

        CultMesh.WriteSingleFileDocumentPayload(path, Key, schema, null, payload);
        HeaderOf(path).Should().Be("cultcache.store.v1");

        CultMesh.WriteSingleFileDocument(path, Key, Publication(Descriptor()));
        HeaderOf(path).Should().Be("cultcache.store.v3");
        CultMesh.WriteSingleFileDocumentPayload(path, Key, schema, null, payload);
        HeaderOf(path).Should().Be("cultcache.store.v3", "the payload's ids are not the writer's to see");
    }

    // A raw write does not read the store's records, but it does not overwrite a file it cannot read either: the runtimes agree.
    [Test]
    public void RawPayloadWriteRefusesAFileItCannotReadAndLeavesItUntouched()
    {
        var schema = new CultMeshSingleFileDocumentSchema("raw:schema", "RawSchema", "1");
        var marked = Path_("marked.cc");
        CultMesh.WriteSingleFileDocument(marked, Key, Publication(Descriptor()));
        var whole = File.ReadAllBytes(marked);

        var truncated = Path_("truncated.cc");
        File.WriteAllBytes(truncated, whole[..^1]);
        var unknown = Path_("v9.cc");
        File.WriteAllBytes(unknown, MessagePackSerializer.Serialize(new object[] { "cultcache.store.v9", Array.Empty<object>(), Array.Empty<object>() }));
        // A file is a store only when it is exactly one MessagePack array whose first slot, if a string, is a store header.
        var trailing = Path_("trailing.cc");
        File.WriteAllBytes(trailing, whole.Concat(new byte[] { 1, 2, 3 }).ToArray());
        var scalar = Path_("scalar.cc");
        File.WriteAllBytes(scalar, new byte[] { 0x01 });
        var map = Path_("map.cc");
        File.WriteAllBytes(map, new byte[] { 0x80 });
        var stringFirst = Path_("string-first.cc");
        File.WriteAllBytes(stringFirst, MessagePackSerializer.Serialize(new object[] { "hello", 1 }));

        foreach (var path in new[] { truncated, unknown, trailing, scalar, map, stringFirst })
        {
            var before = File.ReadAllBytes(path);
            Assert.Throws<NotSupportedException>(() => CultMesh.WriteSingleFileDocumentPayload(path, Key, schema, null, new byte[] { 0x90 }), path);
            File.ReadAllBytes(path).Should().Equal(before, path + " was rewritten");
        }

        // An empty file and a legacy envelope array (first slot not a string, empty included) carry no header and are written.
        foreach (var (name, bytes) in new[] { ("empty.cc", Array.Empty<byte>()), ("empty-array.cc", new byte[] { 0x90 }), ("legacy.cc", new byte[] { 0x91, 0x80 }) })
        {
            var path = Path_(name);
            File.WriteAllBytes(path, bytes);
            CultMesh.WriteSingleFileDocumentPayload(path, Key, schema, null, new byte[] { 0x90 });
            HeaderOf(path).Should().Be("cultcache.store.v1", name);
        }

        CultMesh.WriteSingleFileDocumentPayload(marked, Key, schema, null, new byte[] { 0x90 });
        HeaderOf(marked).Should().Be("cultcache.store.v3", "a whole marked file is still written and stays marked");
    }

    [Test]
    public void TypedWriteRefusesADuplicateIdAndAnElementObjectTwiceAndLeavesTheFileAlone()
    {
        var path = Path_("refused.cc");
        CultMesh.WriteSingleFileDocument(path, Key, Publication(Descriptor()));
        var before = File.ReadAllBytes(path);

        var duplicate = Publication(Descriptor(HexA), Descriptor(HexA));
        var refusal = Assert.Throws<CultElementIdException>(() => CultMesh.WriteSingleFileDocument(path, Key, duplicate))!;
        refusal.ElementId.Should().Be(HexA);

        var once = Descriptor();
        var twice = Publication(once, once);
        Assert.Throws<CultElementIdException>(() => CultMesh.WriteSingleFileDocument(path, Key, twice))!.Message.Should().Contain("twice");
        once.Id.Should().BeEmpty("a refusal mints nothing");

        File.ReadAllBytes(path).Should().Equal(before);
    }

    [Test]
    public void AFailedTypedWriteGivesTheMintedIdsBack()
    {
        var blocked = Path_("blocked.cc");
        Directory.CreateDirectory(blocked);
        var element = Descriptor();

        Assert.That(() => CultMesh.WriteSingleFileDocument(blocked, Key, Publication(element)), Throws.Exception);

        element.Id.Should().BeEmpty("a write that does not land gives its ids back");
    }

    [Test]
    public void TypedReadRefusesWhatALoadRefusesAndMintsWhatALoadMints()
    {
        var path = Path_("disk.cc");
        CultMesh.WriteSingleFileDocument(path, Key, Publication(Descriptor()));
        var snapshot = CultDocumentMessagePackSerialization.DeserializeSnapshot(File.ReadAllBytes(path));

        var duplicate = Publication(Descriptor(HexA), Descriptor(HexA));
        snapshot.Records[0].Payload = MessagePackSerializer.Serialize(duplicate);
        File.WriteAllBytes(path, CultDocumentMessagePackSerialization.SerializeSnapshot(snapshot));
        var refusal = Assert.Throws<CultElementIdException>(() => CultMesh.ReadSingleFileDocument<CultMeshBodyPublicationDocument>(path, Key))!;
        refusal.ElementId.Should().Be(HexA);

        // A payload written before ids: two reads, and a cache load, agree on the ids minted.
        snapshot.Records[0].Payload = MessagePackSerializer.Serialize(Publication(Descriptor(), Descriptor()));
        File.WriteAllBytes(path, CultDocumentMessagePackSerialization.SerializeSnapshot(snapshot));
        var first = CultMesh.ReadSingleFileDocument<CultMeshBodyPublicationDocument>(path, Key).Representations.Select(entry => entry.Id).ToArray();
        first.Should().OnlyContain(id => id.Length == 12);
        CultMesh.ReadSingleFileDocument<CultMeshBodyPublicationDocument>(path, Key).Representations.Select(entry => entry.Id).Should().Equal(first);
        using var cache = CultCacheMessagePack.Create(path, new CultCacheOpenOptions
        {
            Registry = CultDocumentRegistry.ForTypes(new[] { typeof(CultMeshBodyPublicationDocument) }),
            ReadOnly = true
        });
        cache.Get<CultMeshBodyPublicationDocument>(Key)!.Representations.Select(entry => entry.Id).Should().Equal(first);
    }
}