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+2 = 4.
        // 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 x=48 is at distance |48-51| = 3, which is within
        // the radius+2 threshold, so it stays loaded (hysteresis keeps radius+2).
        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);
        // Visible is strictly the 5×5 window around (51, 50).
        Assert.Equal(25, region.Visible.Count);
        // Resident includes the hysteresis-retained x=48 column (5 entries)
        // plus the full new window, for 30 total.
        Assert.Equal(30, region.Resident.Count);
    }

    [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, > radius+2 = 4 → unload. x=49 is 4 away, not > 4 → keep. x=50 is 3 away, not > 4 → 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);
    }

    [Fact]
    public void Constructor_NearXEdgeOnly_ClampsOnlyXAxis()
    {
        // cx=0, cy=50, radius=2:
        // X is clamped to [0..2] (3 entries)
        // Y is unclamped [48..52] (5 entries)
        // Total = 3 × 5 = 15 landblocks.
        var region = new StreamingRegion(cx: 0, cy: 50, radius: 2);

        Assert.Equal(15, region.Visible.Count);
    }

    [Fact]
    public void Constructor_SmallRadius_IDsMatchEncodingRule()
    {
        // Verify EncodeLandblockId emits the LandBlock terminator (0xFFFF),
        // not the LandBlockInfo terminator (0xFFFE). The earlier version of
        // this test pinned 0xFFFE and codified the bug that produced "ball
        // of spikes" terrain in Phase A.1's first live run — LandblockLoader
        // was being asked to read the LandBlockInfo file as a LandBlock,
        // which corrupted the dat reader's buffer position and returned a
        // half-populated heightmap. radius=0 at (0x12, 0x34) → exactly one
        // entry, id = 0x1234FFFF.
        var region = new StreamingRegion(cx: 0x12, cy: 0x34, radius: 0);

        Assert.Single(region.Visible);
        Assert.Contains(0x1234FFFFu, region.Visible);
    }
}