using AcDream.App.Rendering.Gpu;
using AcDream.Core.Meshing;
using DatReaderWriter.Enums;

namespace AcDream.App.Rendering.Wb;

/// <summary>
/// Bucket identity for <see cref="WbDrawDispatcher"/>'s per-frame group dictionary.
/// Two (entity, batch) pairs that share the same <see cref="GroupKey"/> render
/// in a single <c>glMultiDrawElementsIndirect</c> draw command. Promoted to
/// <c>internal</c> at file scope (was a private nested type) so
/// <see cref="EntityClassificationCache"/> can store it inside <see cref="CachedBatch"/>
/// without depending on dispatcher internals.
///
/// <para>Campaign V slice V4t replaced the raw 64-bit
/// <c>ARB_bindless_texture</c> handle with <see cref="GpuTextureSlot"/>. The
/// substitution is a bijection — the device interns one slot per resident
/// handle — so exactly the same (entity, batch) pairs bucket together as
/// before, which is the property that keeps submission order identical. This
/// key's VALUE never orders anything: groups are enumerated in the dictionary's
/// insertion order and sorted by cull mode then camera distance
/// (<c>CompareOpaqueSubmissionOrder</c> / <c>CompareTransparentSubmissionOrder</c>),
/// and the delayed-alpha path sorts by viewer distance then submission ordinal.
/// The key reaches only equality, hashing, and the scene-digest fingerprints.</para>
///
/// <para>Campaign VM VM6 review fix round: <see cref="FoliageFlags"/> joined
/// the key so a mesh subset reachable from BOTH a procedural-scenery entity
/// and a non-scenery entity (same index range/texture/translucency/cull
/// mode) buckets into two DIFFERENT groups instead of coalescing into one
/// group whose <c>InstanceGroup.FoliageFlags</c> was last-writer-wins between
/// the two classifications — which flickered the shared group's flags
/// between frames and let the caster (keyed correctly from the start) and
/// the receiver (previously keyed without this field) disagree about the
/// same subset.</para>
///
/// <para>Campaign VM VM6 review fix round 3 (N2b): <see cref="FoliageFlags"/>
/// is REQUIRED (no default) and declared before <see cref="CullMode"/> (which
/// keeps its default) so that a <c>new GroupKey(...)</c> omitting it is a
/// compile error, not a silent fall-back to 0. The round-2 packed-classifier
/// blocker (F1) was exactly a silently-defaulted FoliageFlags reaching
/// production; a caller can no longer forget this field the way that one
/// could.</para>
/// </summary>
internal readonly record struct GroupKey(
    uint FirstIndex,
    int BaseVertex,
    int IndexCount,
    GpuTextureSlot TextureSlot,
    uint TextureLayer,
    TranslucencyKind Translucency,
    uint FoliageFlags,
    CullMode CullMode = CullMode.CounterClockwise);