using System.Numerics;
using AcDream.App.World;
using Xunit;

namespace AcDream.App.Tests.World;

/// <summary>
/// AP-48 cull (holtburger liveness.rs port): visible = 3×3 landblock neighborhood OR ≤384 m;
/// evict only after 25 s continuously out-of-visibility (arm-on-leave / clear-on-return).
/// </summary>
public sealed class EntityVisibilityCullerTests
{
    private static readonly EntityCullInfo Player =
        new(0x50000001u, new Vector3(0, 0, 0), 169, 180, true);

    // ---- IsVisible ----

    [Fact]
    public void Within384m_isVisible_byDistance_evenInAFarLandblock()
        => Assert.True(EntityVisibilityCuller.IsVisible(
            new Vector3(50, 0, 0), 100, 100, true, new Vector3(0, 0, 0), 169, 180));

    [Fact]
    public void AdjacentLandblock_isVisible_evenWhenFarByPosition()
        => Assert.True(EntityVisibilityCuller.IsVisible(
            new Vector3(5000, 0, 0), 169, 181, true, new Vector3(0, 0, 0), 169, 180));

    [Fact]
    public void FarAndNotAdjacent_isNotVisible()
        => Assert.False(EntityVisibilityCuller.IsVisible(
            new Vector3(5000, 0, 0), 100, 100, true, new Vector3(0, 0, 0), 169, 180));

    // ---- Step lifecycle ----

    [Fact]
    public void Step_visible_clearsDeadlineAndKeeps()
    {
        var (dl, evict) = EntityVisibilityCuller.Step(visible: true, deadline: 123.0, now: 200.0);
        Assert.Null(dl);
        Assert.False(evict);
    }

    [Fact]
    public void Step_notVisible_unarmed_arms()
    {
        var (dl, evict) = EntityVisibilityCuller.Step(visible: false, deadline: null, now: 100.0);
        Assert.Equal(100.0 + EntityVisibilityCuller.DestructionTimeoutSec, dl);
        Assert.False(evict);
    }

    [Fact]
    public void Step_notVisible_armedNotExpired_keeps()
    {
        var (dl, evict) = EntityVisibilityCuller.Step(visible: false, deadline: 125.0, now: 110.0);
        Assert.Equal(125.0, dl);
        Assert.False(evict);
    }

    [Fact]
    public void Step_notVisible_armedExpired_evicts()
    {
        var (dl, evict) = EntityVisibilityCuller.Step(visible: false, deadline: 125.0, now: 125.0);
        Assert.Null(dl);
        Assert.True(evict);
    }

    // ---- Tick integration ----

    [Fact]
    public void Tick_neverEvictsTheLocalPlayer()
    {
        var c = new EntityVisibilityCuller();
        var ents = new[] { Player };
        c.Tick(ents, Player, now: 0);
        c.Tick(ents, Player, now: 1000);
        Assert.Empty(c.Tick(ents, Player, now: 1_000_000));
        Assert.Equal(0, c.ArmedCount);
    }

    [Fact]
    public void Tick_armsThenEvicts_aFarStaleEntity_afterTimeout()
    {
        var c = new EntityVisibilityCuller();
        var far = new EntityCullInfo(0xABCDu, new Vector3(5000, 0, 0), 10, 10, true);
        var ents = new[] { far };

        Assert.Empty(c.Tick(ents, Player, now: 0));    // arm at 0 + 25
        Assert.Equal(1, c.ArmedCount);
        Assert.Empty(c.Tick(ents, Player, now: 24));   // not expired
        var evicted = c.Tick(ents, Player, now: 25);   // expired → evict
        Assert.Equal(new[] { 0xABCDu }, evicted);
        Assert.Equal(0, c.ArmedCount);                  // deadline cleared on evict
    }

    [Fact]
    public void Tick_clearsDeadline_whenEntityReturnsToVisibility_beforeTimeout()
    {
        var c = new EntityVisibilityCuller();
        var far = new EntityCullInfo(0xABCDu, new Vector3(5000, 0, 0), 10, 10, true);
        var near = far with { Pos = new Vector3(50, 0, 0) };   // within 384 m → visible

        Assert.Empty(c.Tick(new[] { far }, Player, now: 0));    // arm
        Assert.Equal(1, c.ArmedCount);
        Assert.Empty(c.Tick(new[] { near }, Player, now: 10));  // returned → clear
        Assert.Equal(0, c.ArmedCount);
        Assert.Empty(c.Tick(new[] { near }, Player, now: 100)); // never evicted
    }
}