using System.Collections.Generic;
using System.Numerics;
using DatReaderWriter.Enums;

namespace AcDream.Core.Physics;

/// <summary>
/// Indoor walking Phase 2 (2026-05-19). Cached building portal data
/// for outdoor→indoor cell entry. One per outdoor landcell that contains
/// a building stab. Mirrors retail's <c>BuildingObj.Portals</c> array
/// (per the pseudocode doc §"LandCell.find_transit_cells").
/// </summary>
public sealed class BuildingPhysics
{
    public required Matrix4x4 WorldTransform { get; init; }
    public required Matrix4x4 InverseWorldTransform { get; init; }
    public required IReadOnlyList<BldPortalInfo> Portals { get; init; }

    /// <summary>
    /// BR-7 / A6.P4 (2026-06-11): the building's shell part-0 GfxObj id.
    /// 0x01 BuildingInfo.ModelId values are stored verbatim; 0x02 Setup
    /// models are resolved to their FIRST part at cache time (the
    /// CacheBuilding call site reads the dat). Drives the retail building
    /// collision channel (<c>CBuildingObj::find_building_collisions</c>,
    /// Ghidra 0x006b5300: one BSP test on <c>part_array-&gt;parts[0]</c>).
    /// 0 = unknown (legacy cache entries / tests) — the channel is inert.
    /// </summary>
    public uint ModelId { get; init; }
}

/// <summary>
/// One building portal: the connection from a SortCell's BuildingObj to
/// an interior EnvCell. ExactMatch is decoded from <see cref="Flags"/>
/// bit 0 (<c>PortalFlags.ExactMatch = 0x0001</c>).
/// </summary>
public readonly struct BldPortalInfo
{
    public BldPortalInfo(uint otherCellId, short otherPortalId, ushort flags)
    {
        OtherCellId   = otherCellId;
        OtherPortalId = otherPortalId;
        Flags         = flags;
    }

    /// <summary>Full id of the interior EnvCell this portal connects to.</summary>
    public uint   OtherCellId   { get; }
    /// <summary>
    /// The portal id within the destination EnvCell — SIGNED, like retail's
    /// <c>CBldPortal.other_portal_id</c> (<c>int</c>, acclient.h:32098,
    /// sign-extended from the dat's 16-bit field). <c>-1</c> (wire
    /// <c>0xFFFF</c>) means "no reciprocal portal"; retail's
    /// <c>CEnvCell::check_building_transit</c> (Ghidra 0x0052c5d0) rejects
    /// the whole transit when this is negative — the <c>arg2 &gt;= 0</c>
    /// gate is the first instruction. BN's pseudo-C renders the comparison
    /// unsigned (wrong); the sign-extension is Ghidra-proven
    /// (wf1-interior-collision.md, BR-7 verified corrections).
    /// DatReaderWriter parses the field as <c>ushort</c>; construction
    /// sites reinterpret via <c>unchecked((short)value)</c>.
    /// </summary>
    public short  OtherPortalId { get; }
    public ushort Flags         { get; }

    /// <summary>
    /// Bit 0 of <see cref="Flags"/> (<c>DatReaderWriter.Enums.PortalFlags.ExactMatch</c>).
    ///
    /// <para>
    /// Reserved per retail's <c>CBldPortal::exact_match</c>. NOT currently
    /// consumed by <see cref="CellTransit.CheckBuildingTransit"/> — every
    /// portal overlap is treated as a valid entry trigger. If a future
    /// regression surfaces (e.g., a building entered by overlapping a
    /// non-exact-match portal), wire this into the entry test.
    /// </para>
    /// </summary>
    public bool ExactMatch => (Flags & (ushort)PortalFlags.ExactMatch) != 0;
}