namespace AcDream.App.Rendering.Walk;

/// <summary>
/// Campaign FW1 — the frame walk's observable event stream. These events
/// mirror the FW0 oracle-trace vocabulary one-to-one
/// (docs/research/2026-08-30-fw-walk-oracle/README.md): the conformance
/// contract is that <c>RetailFrameWalk</c>, fed the same world state and
/// camera pose as a capture, emits the identical sequence. Richer draw
/// commands (mesh/state/stage tuples for the FW2 ordered stream) layer on
/// later; this vocabulary stays the conformance surface.
/// </summary>
public enum WalkEventKind
{
    /// <summary><c>LScape::draw</c> @0x00506330 ran (outdoor root, or drawn
    /// through an interior frame's exit views).</summary>
    Landscape,

    /// <summary><c>RenderDeviceD3D::DrawBuilding</c> @0x0059f2a0 entered for
    /// one building (identified by its position cell id).</summary>
    Building,

    /// <summary><c>PView::DrawInside</c> @0x005a5860 entered — the frame is
    /// rooted at this interior cell.</summary>
    DrawInside,

    /// <summary><c>PView::DrawCells</c> @0x005a4840 entered with the flood's
    /// cell list (far-to-near iteration happens inside; the event carries the
    /// list in storage order, matching the oracle dump).</summary>
    DrawCells,
}

public readonly record struct WalkEvent(
    WalkEventKind Kind,
    uint CellId,
    int OutsideViewCount,
    IReadOnlyList<uint> Cells)
{
    /// <summary>FW4 slice 1: the landscape turn carries the ACTIVE view
    /// set's <c>ViewCount</c> (retail <c>LScape::draw</c> iterates the
    /// views the walk itself installed — 1 for the outdoor root's
    /// full-screen default view, the interior root's own surviving
    /// exit-view count otherwise). The driver fans exactly this many
    /// terrain slices; the old clip apparatus no longer supplies the
    /// count. Reuses the record's existing <see cref="WalkEvent.OutsideViewCount"/>
    /// field; the conformance trace mapping compares the kind only
    /// (<c>LS</c>), so oracle fixtures are unaffected.</summary>
    public static WalkEvent Landscape(int activeViewCount)
        => new(WalkEventKind.Landscape, 0, activeViewCount, Array.Empty<uint>());

    public static WalkEvent Building(uint positionCellId)
        => new(WalkEventKind.Building, positionCellId, 0, Array.Empty<uint>());

    public static WalkEvent DrawInside(uint cellId)
        => new(WalkEventKind.DrawInside, cellId, 0, Array.Empty<uint>());

    public static WalkEvent DrawCells(int outsideViewCount, IReadOnlyList<uint> cells)
        => new(WalkEventKind.DrawCells, 0, outsideViewCount, cells);
}

/// <summary>
/// The sink a walk emits into. FW1 conformance tests collect events; FW2's
/// production sink will additionally receive the ordered draw stream.
///
/// <para>Campaign FW3.2b-1 additive seam: <see cref="RetailFrameWalk"/> also
/// calls the five richer, default-no-op members below at turns the
/// vocabulary-only <see cref="WalkEvent"/> stream cannot express (a visited
/// landscape cell with no building emits no <see cref="WalkEvent"/> at all;
/// <see cref="WalkEventKind.Building"/> carries only a cell id, not the
/// <see cref="WalkBuilding"/> reference a driver needs to look up shell
/// content, degrade state, or world transform; and punches are not part of
/// the FW1 conformance vocabulary at all — the oracle traces do not log
/// them). Every FW1/FW2 sink that only implements <see cref="Emit"/>
/// continues to compile and behave identically — these are C# default
/// interface members, never called by any pre-FW3.2b-1 code path.</para>
/// </summary>
public interface IWalkEventSink
{
    void Emit(in WalkEvent walkEvent);

    /// <summary>
    /// Fires once per visited landscape cell, AFTER that cell's building
    /// turn (if any) — <c>RenderDeviceD3D::DrawSortCell</c> @0x0059f140
    /// calls <c>DrawBuilding(building)</c> first, then
    /// <c>DrawObjCell(cell)</c> UNCONDITIONALLY (decomp-confirmed
    /// 2026-08-30). <paramref name="cellId"/> follows retail's outdoor cell
    /// encoding — <c>(landblockId &amp; 0xFFFF0000) | (cellIndex + 1)</c> —
    /// the same convention <see cref="WalkLandscapeAssembler.BuildSlot"/>
    /// and <see cref="WalkProductionFrameContext.SetViewer"/> +
    /// <see cref="WalkLandscapeAssembler.SetViewer"/> already use. Default
    /// no-op.
    /// </summary>
    void OnLandscapeCellTurn(uint cellId) { }

    /// <summary>
    /// Fires at <see cref="RetailFrameWalk.DrawBuilding"/> once retail's own
    /// gate has passed — <c>RenderDeviceD3D::DrawBuilding</c> @0x0059f2a0
    /// wraps its ENTIRE body (the alpha barrier, the portal pass, the shell
    /// draw) in <c>if (part-&gt;gfxobj[part-&gt;deg_level] != 0)</c>
    /// @0x0059f2d3 — a degraded-out slot draws NOTHING beyond the
    /// unconditional <see cref="WalkEventKind.Building"/> <see cref="Emit"/>
    /// call. <see cref="WalkBuilding.HasGeometry"/> and a non-null
    /// <see cref="WalkBuilding.SelectDrawingBsp"/> result together model that
    /// one gate, so this hook fires only after both have passed. This is the
    /// ALPHA BARRIER turn (<c>D3DPolyRender::FlushAlphaList(0f)</c>
    /// @0x0059f30b) — retail's own order runs it BEFORE the portal pass
    /// (<c>CPhysicsPart::Draw(parts, 1)</c>), which in turn runs BEFORE the
    /// shell draw (<c>CPhysicsPart::Draw(parts, 0)</c> — see
    /// <see cref="OnBuildingShellTurn"/>, fired separately, after the portal
    /// pass completes). Default no-op.
    /// </summary>
    void OnBuildingTurn(WalkBuilding building) { }

    /// <summary>
    /// Fires at the END of <see cref="RetailFrameWalk.DrawBuilding"/>, after
    /// its two-pass portal walk (punches + look-ins, across every active
    /// view) has fully completed — <c>CPhysicsPart::Draw(parts, 0)</c>
    /// @0x0059f331, retail's plain-mesh draw of the building's own shell,
    /// which runs strictly AFTER <c>CPhysicsPart::Draw(parts, 1)</c> (the
    /// portal flavor) per the decomp sequence at @0x0059f30b–0x0059f345. Only
    /// fires when <see cref="OnBuildingTurn"/> also fired (same gate; see its
    /// doc comment) — a degraded-out slot reaches neither. Default no-op.
    /// </summary>
    void OnBuildingShellTurn(WalkBuilding building) { }

    /// <summary>
    /// Fires when the two-pass portal machinery
    /// (<see cref="WalkBuildingPortals"/>) would draw a far-Z punch fan
    /// (<c>DrawPortalPolyInternal</c> @0x0059bc90, pass 1) — carries the
    /// owning building and the polygon in BUILDING-LOCAL space (as stored on
    /// the emitted <see cref="WalkPortalRef"/>) so a driver can resolve the
    /// world transform itself. The FW1 oracle traces never log punches
    /// (<see cref="RetailFrameWalk"/>'s internal <c>PortalPassSink.OnPunch</c>
    /// stayed a no-op through FW1/FW2 for exactly that reason). Default
    /// no-op.
    /// </summary>
    /// <param name="building">The building whose portal walk emitted the
    /// punch.</param>
    /// <param name="polygon">The portal polygon, building-local.</param>
    /// <param name="activeViewIndex">The active-view index the two-pass walk
    /// is pinned to (retail <c>building_view</c> @0x0059f3bf) — the punch
    /// fan clips against THIS view's slice planes in production.</param>
    void OnPunchGeometry(
        WalkBuilding building, WalkPolygon polygon, int activeViewIndex)
    { }

    /// <summary>
    /// Fires once per interior root, at the point <c>PView::DrawCells</c>
    /// @0x005a4840 actually DRAWS the root flood's own cells — NOT where the
    /// <see cref="WalkEventKind.DrawCells"/> <see cref="Emit"/> call for the
    /// SAME flood fires (that one sits at breakpoint-ENTRY order, matching
    /// the FW0 oracle traces; it only RECORDS the flood list). Retail's own
    /// order inside <c>DrawCells</c> is: <c>LScape::draw</c> FIRST
    /// (pc:432719, only when exit views survived — see
    /// <see cref="RetailFrameWalk.DrawLandscape"/> and
    /// <see cref="WalkEventKind.Landscape"/>), then a full depth clear
    /// (pc:432731-432732), then the exit-portal seals (pc:432785-432786) —
    /// BOTH unconditional for an interior root's
    /// own flood, whether or not a landscape turn just ran — and ONLY THEN
    /// the flood's cells far-to-near (shell then contents per cell, same
    /// discipline as <see cref="OnLandscapeCellTurn"/>'s per-cell contents
    /// and a building's look-in). This hook fires at that later point, so
    /// this is where a driver should actually draw <paramref name="cells"/>.
    /// Building look-in floods are UNAFFECTED — retail calls
    /// <c>DrawCells</c> re-entrantly there with <c>ov==0</c> and no
    /// landscape/clear/seal step, so their <see cref="WalkEventKind.DrawCells"/>
    /// <see cref="Emit"/> call still fires at the actual draw point (a
    /// driver may keep drawing those immediately, as before). Default no-op.
    /// </summary>
    void OnInteriorFloodDrawTurn(IReadOnlyList<uint> cells) { }
}