using AcDream.App.Streaming;
using Xunit;

namespace AcDream.Core.Tests.Streaming;

public class StreamingRegionTests
{
    [Fact]
    public void Constructor_Radius2_Produces25Landblocks()
    {
        var region = new StreamingRegion(cx: 50, cy: 50, radius: 2);

        Assert.Equal(25, region.Visible.Count);
    }

    [Fact]
    public void Constructor_NearOrigin_ClampsToWorldEdge()
    {
        // Center at (0, 0) with radius 2: only the +X / +Y quadrant is
        // in-bounds. That's a 3×3 subset of the 5×5 window = 9 landblocks.
        var region = new StreamingRegion(cx: 0, cy: 0, radius: 2);

        Assert.Equal(9, region.Visible.Count);
    }

    [Fact]
    public void Constructor_NearFarEdge_ClampsToWorldEdge()
    {
        var region = new StreamingRegion(cx: 0xFF, cy: 0xFF, radius: 2);

        Assert.Equal(9, region.Visible.Count);
    }

    [Fact]
    public void RecenterTo_SamePosition_EmptyDiff()
    {
        var region = new StreamingRegion(cx: 50, cy: 50, radius: 2);

        var diff = region.RecenterTo(50, 50);

        Assert.Empty(diff.ToLoad);
        Assert.Empty(diff.ToUnload);
    }

    [Fact]
    public void RecenterTo_SingleStepEast_LoadsColumn_NoUnloadsDueToHysteresis()
    {
        // Radius 2 → unload threshold is radius+1 = 3.
        // Starting center (50,50) covers X in [48..52]. Step to (51,50):
        // new coverage X in [49..53]. New column is x=53 (5 entries).
        // Departing column would be x=48, but |48-51| = 3 which equals the
        // threshold, so it stays loaded (hysteresis keeps radius+1).
        var region = new StreamingRegion(cx: 50, cy: 50, radius: 2);

        var diff = region.RecenterTo(51, 50);

        Assert.Equal(5, diff.ToLoad.Count);
        Assert.Empty(diff.ToUnload);
    }

    [Fact]
    public void RecenterTo_ThreeStepEast_LoadsAndUnloadsColumns()
    {
        // Starting (50,50) covers X in [48..52]. Step to (53,50):
        // new coverage X in [51..55]. New columns: x=53,54,55 (15 entries).
        // x=48 is now 5 away → unload. x=49,50 still within radius+1 → keep.
        var region = new StreamingRegion(cx: 50, cy: 50, radius: 2);

        var diff = region.RecenterTo(53, 50);

        Assert.Equal(15, diff.ToLoad.Count);
        Assert.Equal(5, diff.ToUnload.Count);
    }

    [Fact]
    public void RecenterTo_LongTeleport_UnloadsEverythingLoadsEverything()
    {
        var region = new StreamingRegion(cx: 50, cy: 50, radius: 2);

        var diff = region.RecenterTo(200, 200);

        Assert.Equal(25, diff.ToLoad.Count);
        Assert.Equal(25, diff.ToUnload.Count);
    }
}