using System.Collections.Generic;
using AcDream.Core.Physics;

namespace AcDream.App.Rendering.Wb;

/// <summary>
/// Per-entity render state for animated entities (characters, creatures,
/// equipped items). Holds AC-specific per-instance customizations the WB
/// atlas cache doesn't carry: <c>AnimPartChange</c> override map +
/// <c>HiddenParts</c> bitmask. Also holds a reference to acdream's existing
/// <see cref="AnimationSequencer"/> — Phase N.4 explicitly does not touch
/// the sequencer; we just route through it at draw time.
///
/// <para>
/// Lifecycle: created by <c>EntitySpawnAdapter.OnCreate</c> (Task 17) when
/// a server <c>CreateObject</c> is processed; destroyed by
/// <c>EntitySpawnAdapter.OnRemove</c> on <c>RemoveObject</c>. The mesh
/// data backing each part is cached in WB's <c>ObjectMeshManager</c>;
/// per-instance customizations don't go through the atlas — they overlay
/// at draw time.
/// </para>
/// </summary>
public sealed class AnimatedEntityState
{
    private readonly Dictionary<int, ulong> _partGfxObjOverrides = new();
    private ulong _hiddenMask = 0;

    /// <summary>Reference to acdream's existing animation sequencer.
    /// Phase N.4 doesn't touch the sequencer; the draw dispatcher consumes
    /// per-part transforms it produces per frame.</summary>
    public AnimationSequencer Sequencer { get; }

    public AnimatedEntityState(AnimationSequencer sequencer)
    {
        System.ArgumentNullException.ThrowIfNull(sequencer);
        Sequencer = sequencer;
    }

    /// <summary>Set the <c>HiddenParts</c> bitmask for this entity. Bit
    /// <c>i</c> set hides part <c>i</c> at draw time.</summary>
    public void HideParts(ulong hiddenMask) => _hiddenMask = hiddenMask;

    /// <summary>True if part <c>partIdx</c> should be skipped at draw
    /// time. Returns false for part indices outside [0, 63].</summary>
    public bool IsPartHidden(int partIdx)
    {
        if (partIdx < 0 || partIdx >= 64) return false;
        return (_hiddenMask & (1ul << partIdx)) != 0;
    }

    /// <summary>Override the GfxObj id for a Setup part. Used for
    /// AnimPartChange — e.g. wielding a weapon swaps the hand-part's
    /// GfxObj.</summary>
    public void SetPartOverride(int partIdx, ulong gfxObjId)
        => _partGfxObjOverrides[partIdx] = gfxObjId;

    /// <summary>Look up the GfxObj override for a part. Returns false if
    /// no override is set (caller should fall back to Setup default).</summary>
    public bool TryGetPartOverride(int partIdx, out ulong gfxObjId)
        => _partGfxObjOverrides.TryGetValue(partIdx, out gfxObjId);

    /// <summary>Resolve the GfxObj id for <paramref name="partIdx"/>:
    /// override if set, else <paramref name="setupDefault"/>. Used by the
    /// draw dispatcher to pick the right cached mesh data per part.</summary>
    public ulong ResolvePartGfxObj(int partIdx, ulong setupDefault)
        => TryGetPartOverride(partIdx, out var ov) ? ov : setupDefault;
}