using System.Numerics;

namespace AcDream.App.Rendering.Wb;

/// <summary>
/// Per-(entity, partIdx, batchIdx) classification result, stored flat inside
/// <see cref="EntityCacheEntry.Batches"/>. For Setup multi-part MeshRefs each
/// subPart contributes its own <see cref="CachedBatch"/> entries, with
/// <see cref="RestPose"/> already containing the
/// <c>subPart.PartTransform * meshRef.PartTransform</c> product.
/// <see cref="LocalSortCenter"/> preserves the authored GfxObj key used by
/// retail's delayed-alpha viewer-distance ordering on cache hits.
/// <see cref="Group"/> is a registration-checked fast handle into the
/// dispatcher's bounded group table; a retired or synthetic entry falls back
/// to key lookup and refreshes this array entry.
///
/// Accessibility: <c>internal</c> because <see cref="GroupKey"/> is
/// <c>internal</c> and shows up in this struct's constructor / <c>Deconstruct</c>
/// signature. The cache itself is dispatcher-internal coordination state;
/// <see cref="InternalsVisibleTo"/> on <c>AcDream.App</c> exposes the type to
/// <c>AcDream.Core.Tests</c>.
/// </summary>
internal readonly record struct CachedBatch(
    GroupKey Key,
    ulong BindlessTextureHandle,
    Matrix4x4 RestPose,
    Vector3 LocalSortCenter = default,
    WbDrawDispatcher.InstanceGroup? Group = null,
    long GroupRegistration = 0);

/// <summary>
/// Immutable retail-picking descriptor for one static entity part. The cache
/// stores only authored identity and rest pose; the current entity transform
/// and the selection system's live frustum/geometry verdict remain per-frame.
/// </summary>
internal readonly record struct CachedSelectionPart(
    int PartIndex,
    uint GfxObjId,
    Matrix4x4 RestPose);

/// <summary>
/// One entity's cached classification. <see cref="Batches"/> is flat across
/// (partIdx, batchIdx) and ordered as <c>WbDrawDispatcher.ClassifyBatches</c>
/// produced them. <see cref="LandblockHint"/> lets
/// <see cref="EntityClassificationCache.InvalidateLandblock"/> sweep entries
/// efficiently when a landblock demotes or unloads.
///
/// Accessibility: <c>internal</c> for the same reason as <see cref="CachedBatch"/>
/// — its <see cref="Batches"/> property is <c>CachedBatch[]</c>, which
/// transitively involves <see cref="GroupKey"/>.
/// </summary>
internal sealed class EntityCacheEntry
{
    public required uint EntityId { get; init; }
    public required uint LandblockHint { get; init; }
    public required CachedBatch[] Batches { get; init; }
    public CachedSelectionPart[] SelectionParts { get; init; } = [];
}