using System.Numerics;

namespace AcDream.Core.World;

public sealed class WorldEntity
{
    public required uint Id { get; init; }
    /// <summary>
    /// Server-assigned GUID (from CreateObject). Zero for dat-hydrated
    /// scenery/static entities that don't come from the server.
    /// Used by GpuWorldState for persistent-entity rescue on landblock unload.
    /// </summary>
    public uint ServerGuid { get; init; }
    public required uint SourceGfxObjOrSetupId { get; init; }
    /// <summary>
    /// World-space position. Settable so Phase 6.7 position-update events
    /// can reseat an existing entity without rebuilding its meshes.
    /// </summary>
    public required Vector3 Position { get; set; }
    /// <summary>Settable for the same reason as <see cref="Position"/>.</summary>
    public required Quaternion Rotation { get; set; }
    /// <summary>
    /// Per-part mesh references with their root-relative transforms.
    /// Mutable so the animation tick can replace it each frame for
    /// entities that play a cycle (Phase 6.4); static entities set it
    /// once at hydration and never touch it again.
    /// </summary>
    public required IReadOnlyList<MeshRef> MeshRefs { get; set; }

    /// <summary>
    /// Optional per-entity palette override (server-specified base +
    /// subpalette overlays). When non-null, applies to every palette-
    /// indexed texture on this entity. Used for character skin/hair
    /// colors, creature recolors (e.g. stone-colored drudge statue),
    /// and team colors. Non-palette-indexed textures ignore this field.
    /// </summary>
    public PaletteOverride? PaletteOverride { get; init; }

    /// <summary>
    /// EnvCell or outdoor cell ID that owns this entity (room geometry, static
    /// object, or live object inside/outside a cell).
    /// the cell). Used by portal visibility to filter interior entities — only
    /// entities whose ParentCellId appears in the visible set are rendered.
    /// Null for outdoor dat scenery/building stabs or unresolved live entities.
    /// </summary>
    public uint? ParentCellId { get; set; }

    /// <summary>
    /// True when this entity originates from <c>LandBlockInfo.Buildings[]</c>
    /// (the dat array that carries building shells: cottage walls, smithy walls,
    /// inn walls — every solid building enclosure). False for entities from
    /// <c>LandBlockInfo.Objects[]</c> (rocks, fences, lampposts, tree clusters —
    /// outdoor scenery placeholders). The two arrays are conflated through
    /// hydration today but the dat itself carries the distinction; retail
    /// (<c>CLandBlock::init_buildings</c>) and WorldBuilder
    /// (<c>SceneryInstance.IsBuilding</c>) both preserve it.
    ///
    /// <para>
    /// Read at draw time by <c>WbDrawDispatcher</c>'s <c>IndoorPass</c>
    /// partition so building shells can render when the camera is inside their
    /// own building (they ARE the indoor walls), not stencil-gated as outdoor
    /// scenery would be.
    /// </para>
    /// </summary>
    public bool IsBuildingShell { get; init; }

    /// <summary>
    /// Dat-derived EnvCell anchor for a building shell. Building shells are
    /// top-level landblock stabs, so they do not have a real ParentCellId, but
    /// the LandBlockInfo.Buildings[] portal list names cells owned by the same
    /// building. The indoor renderer uses this anchor only for draw scoping:
    /// a shell renders in IndoorPass when its anchor belongs to the camera
    /// building's EnvCell set. Collision still treats the shell as an outdoor
    /// stab unless ParentCellId is explicitly set.
    /// </summary>
    public uint? BuildingShellAnchorCellId { get; init; }

    /// <summary>
    /// Uniform scale applied to this entity's mesh by the scenery pipeline.
    /// For scenery objects this is spawn.Scale (typically 0.8–1.3). For stabs
    /// and interior static objects this is 1.0 (no scaling).
    ///
    /// Used by the collision registration path to scale CylSphere / Sphere /
    /// Setup.Radius shapes so they match the visually-scaled mesh. Without
    /// this, scaled scenery has a collision cylinder that's smaller than the
    /// visible trunk, producing "partial passthrough" bugs.
    /// </summary>
    public float Scale { get; init; } = 1.0f;

    /// <summary>
    /// Server-sent part-swap overrides from <c>AnimPartChange</c>. Each entry
    /// replaces a Setup part's GfxObj with an alternate model (clothing, weapons,
    /// helmets). Carried on the entity so <c>EntitySpawnAdapter</c> can populate
    /// <c>AnimatedEntityState</c>'s override map at spawn time. Empty for atlas-
    /// tier entities.
    /// </summary>
    public IReadOnlyList<PartOverride> PartOverrides { get; init; } = Array.Empty<PartOverride>();

    /// <summary>
    /// Bitmask of hidden Setup parts. Bit <c>i</c> set hides part <c>i</c> at
    /// draw time. Sourced from the server's <c>CreateObject</c> record when
    /// present. Zero (no parts hidden) is the default.
    /// </summary>
    public ulong HiddenPartsMask { get; init; }

    // Per Phase A.5 spec §4.6 Change #2 — cache per-entity AABB so the
    // dispatcher's frustum cull is a memory read, not a per-frame recompute.
    // AabbDirty starts true so the dispatcher calls RefreshAabb on first read
    // (AabbMin/AabbMax are Vector3.Zero until refreshed).
    public Vector3 AabbMin { get; private set; }
    public Vector3 AabbMax { get; private set; }
    public bool AabbDirty { get; private set; } = true;

    /// <summary>
    /// Root-local geometry bounds: the union over MeshRefs of each part's dat
    /// vertex AABB transformed by its part transform (see
    /// <c>Meshing.LocalBoundsAccumulator</c>). Set at hydration from the same
    /// vertex data that gets drawn — the every-case fix for the "#119 bounds
    /// must cover the mesh" class. When absent (HasLocalBounds false), the
    /// part-offset heuristic below is the fallback.
    /// </summary>
    public Vector3 LocalBoundMin { get; private set; }
    public Vector3 LocalBoundMax { get; private set; }
    public bool HasLocalBounds { get; private set; }

    public void SetLocalBounds(Vector3 min, Vector3 max)
    {
        LocalBoundMin = min;
        LocalBoundMax = max;
        HasLocalBounds = true;
        AabbDirty = true;
    }

    private const float DefaultAabbRadius = 5.0f;

    public void RefreshAabb()
    {
        var p = Position;

        // #119 follow-up (2026-06-11): the box must cover the MESH, not just the
        // anchor. BOTH visibility gates derive from this box: the dispatcher's
        // per-entity frustum cull (WbDrawDispatcher.WalkEntitiesInto) and the
        // viewcone sphere (RetailPViewRenderer.EntitySphere = this box's
        // bounding sphere). The original fixed ±5 m anchor box dropped the AAB3
        // tower staircase (parts spiralling 15 m above the anchor) whenever the
        // gaze left the anchor's neighborhood — stairs visible looking down,
        // gone looking up.
        //
        // Preferred path: dat-vertex-derived root-local bounds (SetLocalBounds
        // at hydration), rotated into world axes — re-boxing the 8 rotated
        // corners contains the rotated contents, so this is correct for EVERY
        // shape including a single tall part at identity transform (which the
        // offset heuristic below cannot see). DefaultAabbRadius stays as a
        // margin: it absorbs animated-pose drift (MeshRefs are swapped per
        // frame for animated entities while local bounds are rest-pose) and
        // keeps small objects at their historical box size.
        if (HasLocalBounds)
        {
            Vector3 lo = LocalBoundMin, hi = LocalBoundMax;
            var rot = Rotation;
            Vector3 min = default, max = default;
            for (int c = 0; c < 8; c++)
            {
                var corner = new Vector3(
                    (c & 1) == 0 ? lo.X : hi.X,
                    (c & 2) == 0 ? lo.Y : hi.Y,
                    (c & 4) == 0 ? lo.Z : hi.Z);
                var t = Vector3.Transform(corner, rot);
                if (c == 0) { min = max = t; }
                else { min = Vector3.Min(min, t); max = Vector3.Max(max, t); }
            }
            AabbMin = p + min - new Vector3(DefaultAabbRadius);
            AabbMax = p + max + new Vector3(DefaultAabbRadius);
            AabbDirty = false;
            return;
        }

        // Fallback (no hydration bounds — e.g. tests, minimal fixtures): anchor
        // box expanded by the largest part-translation magnitude. Rotation-
        // invariant; covers multi-part spreads but NOT a single part whose mesh
        // extends >5 m from its own origin — which is why hydrated entities use
        // the vertex-derived path above.
        float radius = DefaultAabbRadius;
        var refs = MeshRefs;
        if (refs is not null)
        {
            float maxOffset = 0f;
            for (int i = 0; i < refs.Count; i++)
            {
                float len = refs[i].PartTransform.Translation.Length();
                if (len > maxOffset) maxOffset = len;
            }
            radius += maxOffset;
        }

        AabbMin = new Vector3(p.X - radius, p.Y - radius, p.Z - radius);
        AabbMax = new Vector3(p.X + radius, p.Y + radius, p.Z + radius);
        AabbDirty = false;
    }

    public void SetPosition(Vector3 pos)
    {
        Position = pos;
        AabbDirty = true;
    }
}

/// <summary>
/// Lightweight value type for a server-sent <c>AnimPartChange</c> (part index
/// → replacement GfxObj id). Decouples <c>WorldEntity</c> (Core) from the
/// network-layer <c>CreateObject.AnimPartChange</c> type.
/// </summary>
public readonly record struct PartOverride(byte PartIndex, uint GfxObjId);