using System.Numerics;
using AcDream.Core.Physics;

namespace AcDream.Core.Tests.Physics;

/// <summary>
/// C3c-F5: moved from tests/AcDream.App.Tests/Physics/
/// RemoteSpawnPlacementSettlerTests.cs when the #270 settler moved to Core
/// (App -> <see cref="SpawnPlacementSettler"/>) so the local player's
/// Runtime first-entry activation can share it. Test bodies unchanged.
/// </summary>
public sealed class SpawnPlacementSettlerTests
{
    private const uint Landblock = 0xA9B40000u;
    private const uint Cell = Landblock | 0x0001u;
    private const float Radius = 0.48f;
    private const float Height = 1.835f;

    [Fact]
    public void FloorWithinFirstGravityFrame_CommitsGroundContactOnce()
    {
        PhysicsEngine engine = BuildFlatEngine();
        PhysicsBody body = AirborneBody(new Vector3(12f, 12f, 0.25f));
        int hitGround = 0;
        int leaveGround = 0;

        bool settled = SpawnPlacementSettler.TrySettle(
            engine,
            body,
            body.Position,
            Cell,
            Radius,
            Height,
            ObjectInfoState.EdgeSlide,
            movingEntityId: 0x70000001u,
            () => hitGround++,
            () => leaveGround++);

        Assert.True(settled);
        Assert.True(body.InContact);
        Assert.True(body.OnWalkable);
        Assert.Equal(1, hitGround);
        Assert.Equal(0, leaveGround);
    }

    [Fact]
    public void MissingCell_CanRetryAfterHydrationWithoutReconstructingBody()
    {
        var engine = new PhysicsEngine { DataCache = new PhysicsDataCache() };
        PhysicsBody body = AirborneBody(new Vector3(12f, 12f, 0.25f));
        Vector3 originalPosition = body.Position;

        Assert.False(TrySettle(engine, body));
        Assert.False(body.InContact);
        Assert.Equal(originalPosition, body.Position);

        AddFlatLandblock(engine);

        Assert.True(TrySettle(engine, body));
        Assert.True(body.InContact);
        Assert.True(body.OnWalkable);
    }

    [Fact]
    public void FloorOutsideSettleDistance_LeavesGenuinelyAirborneBodyUnchanged()
    {
        PhysicsEngine engine = BuildFlatEngine();
        PhysicsBody body = AirborneBody(new Vector3(12f, 12f, 1.25f));
        Vector3 originalPosition = body.Position;

        Assert.False(TrySettle(engine, body));

        Assert.False(body.InContact);
        Assert.False(body.OnWalkable);
        Assert.Equal(originalPosition, body.Position);
    }

    /// <summary>
    /// #276: the settle must adopt the transition's RESOLVED cell, not only
    /// its position. Retail's
    /// <c>CPhysicsObj::SetPositionInternal(CTransition const*)</c>
    /// (<c>0x00515330</c>) commits both <c>curr_pos.objcell_id</c> and the
    /// frame.
    ///
    /// <para>
    /// The body is seeded with an ENVCELL id over plain outdoor terrain,
    /// which is what makes this discriminating. A bare
    /// <c>body.Position = settle.Position</c> mirrors the world delta into
    /// the local frame and lets <c>AdjustToOutside</c> recompute the cell —
    /// but only for outdoor ids; the mirror deliberately PRESERVES an
    /// EnvCell id, because one cannot be derived from a position. So the old
    /// code leaves the stale EnvCell in place and only the resolved-cell
    /// adoption reaches the outdoor cell the body physically settled in.
    /// This is the "outdoor/EnvCell seam" half of #276, in the outward
    /// direction.
    /// </para>
    /// </summary>
    [Fact]
    public void SettleLeavingAnEnvCell_AdoptsTheTransitionsResolvedOutdoorCell()
    {
        const uint StaleEnvCell = Landblock | 0x0100u;
        PhysicsEngine engine = BuildFlatEngine();
        PhysicsBody body = AirborneBody(new Vector3(12f, 12f, 0.25f));
        body.StageDormantCellFrame(
            StaleEnvCell,
            body.Position,
            body.Position);
        Assert.Equal(StaleEnvCell, body.CellPosition.ObjCellId);

        bool settled = SpawnPlacementSettler.TrySettle(
            engine,
            body,
            body.Position,
            Cell,
            Radius,
            Height,
            ObjectInfoState.EdgeSlide,
            movingEntityId: 0x70000001u,
            static () => { },
            static () => { });

        Assert.True(settled);
        Assert.True(body.InContact);

        // The discriminating assertion: the body no longer claims the EnvCell
        // it never physically occupied, and its cell is an OUTDOOR landcell
        // (low word 1..0x40) of the same landblock it settled in.
        Assert.NotEqual(StaleEnvCell, body.CellPosition.ObjCellId);
        Assert.Equal(Landblock, body.CellPosition.ObjCellId & 0xFFFF0000u);
        Assert.InRange(body.CellPosition.ObjCellId & 0xFFFFu, 1u, 0x40u);
    }

    private static bool TrySettle(PhysicsEngine engine, PhysicsBody body) =>
        SpawnPlacementSettler.TrySettle(
            engine,
            body,
            body.Position,
            Cell,
            Radius,
            Height,
            ObjectInfoState.EdgeSlide,
            movingEntityId: 0x70000001u,
            static () => { },
            static () => { });

    private static PhysicsBody AirborneBody(Vector3 position) => new()
    {
        Position = position,
        Orientation = Quaternion.Identity,
        State = PhysicsStateFlags.Gravity | PhysicsStateFlags.ReportCollisions,
        TransientState = TransientStateFlags.None,
    };

    private static PhysicsEngine BuildFlatEngine()
    {
        var engine = new PhysicsEngine { DataCache = new PhysicsDataCache() };
        AddFlatLandblock(engine);
        return engine;
    }

    private static void AddFlatLandblock(PhysicsEngine engine) =>
        engine.AddLandblock(
            Landblock,
            new TerrainSurface(new byte[81], new float[256]),
            Array.Empty<CellSurface>(),
            Array.Empty<PortalPlane>(),
            worldOffsetX: 0f,
            worldOffsetY: 0f);
}