using System.Numerics;

namespace AcDream.App.Rendering.Walk;

/// <summary>A cell-local portal polygon with its plane (retail
/// <c>CPolygon</c>: vertices + <c>plane</c> @+0x20).</summary>
public sealed class WalkPolygon
{
    public Vector3[] Vertices = [];
    public WalkPlane Plane;
}

/// <summary>Retail <c>CCellPortal</c> (stride 0x18). The exit-to-landscape
/// sentinel is <c>OtherCellId == 0xFFFFFFFF</c>; <c>OtherPortalId == -1</c>
/// means "no reciprocal".</summary>
public struct WalkCellPortal
{
    public uint OtherCellId;
    public int PolygonIndex;
    public int PortalSide;
    public int OtherPortalId;
    public bool ExactMatch;
}

/// <summary>
/// The flood's cell model (retail <c>CEnvCell</c> as the walk sees it).
/// Retail stores the walk state ON the cell (num_view / portal_view stack /
/// cached neighbor pointers); this port keeps the same placement so the
/// transcription stays line-by-line — production adapters construct these
/// from the committed cell registry (FW3 wiring).
/// </summary>
public sealed class WalkCell
{
    public uint CellId;
    public WalkCellPortal[] Portals = [];
    public WalkPolygon[] PortalPolygons = [];
    public uint[] StabList = [];

    /// <summary>Cell-local → landblock-local (retail <c>CEnvCell.pos</c>;
    /// the frame the flood's plane tests and projections run in).</summary>
    public Matrix4x4 WorldTransform = Matrix4x4.Identity;
    public Matrix4x4 InverseWorldTransform = Matrix4x4.Identity;

    // ---- walk state (retail: fields on CEnvCell) ----
    public int NumView;
    public readonly List<WalkPortalView> PortalViews = new();
    public WalkCell?[] CachedNeighbors = [];

    public WalkPortalView TopView => PortalViews[NumView - 1];

    /// <summary><c>CEnvCell::curr_view_push</c> @0x005a5090: push one
    /// view-recursion level (lazy slot, exactly three counters reset).</summary>
    public void PushView()
    {
        while (PortalViews.Count <= NumView)
            PortalViews.Add(new WalkPortalView());
        PortalViews[NumView].ResetForPush();
        NumView++;
        if (CachedNeighbors.Length < Portals.Length)
            CachedNeighbors = new WalkCell?[Portals.Length];
    }

    public void PopView() => NumView--;
}

/// <summary>
/// The per-frame context retail keeps in globals (<c>Render::FrameCurrent</c>
/// after <c>positionPush(3, cell.pos)</c>, the projection state, the visible
/// cell registry, and the <c>cliplandscape</c> toggle — .data default 1).
/// </summary>
public interface IWalkFrameContext
{
    /// <summary>The eye position in the cell's local frame (retail: the
    /// pushed frame's <c>viewer.viewpoint</c>).</summary>
    Vector3 ViewpointIn(WalkCell cell);

    /// <summary>Object(cell-local)→clip matrix for projecting the cell's
    /// portal polygons (retail: the pushed frame composed with
    /// WorldToView·ViewToClip).</summary>
    Matrix4x4 ObjectToClip(WalkCell cell);

    /// <summary><c>CEnvCell::GetVisible</c>: the committed/visible cell
    /// registry. Returning null skips the portal silently (retail behavior —
    /// but implementations should count the miss for the fail-loud rule).</summary>
    WalkCell? GetVisible(uint cellId);

    IWalkRayCaster Rays { get; }
    Vector3 WorldViewpoint { get; }
    float ViewportWidth { get; }
    float ViewportHeight { get; }

    /// <summary>Retail global <c>cliplandscape</c> (.data @0x00820f4c = 1).</summary>
    bool ClipLandscape => true;
}