using AcDream.App.UI;
using Xunit;

namespace AcDream.App.Tests.UI;

/// <summary>
/// Pure unit tests for <see cref="UiScrollbar.ThumbRect"/> — no GL dependency.
/// </summary>
public class UiScrollbarTests
{
    // Model: content=400, view=100, trackLen=200.
    // ThumbRatio = 100/400 = 0.25  →  thumbH = max(8, 200*0.25) = 50.
    // Travel = 200 - 50 = 150.

    [Fact]
    public void ThumbRect_AtStart_HasCorrectSizeAndZeroOffset()
    {
        var m = new UiScrollable { ContentHeight = 400, ViewHeight = 100 };
        // PositionRatio = 0 (start).
        var (y, h) = UiScrollbar.ThumbRect(m, trackTop: 0f, trackLen: 200f);
        Assert.Equal(50f, h, 3f);
        Assert.Equal(0f, y, 3f);
    }

    [Fact]
    public void ThumbRect_AtEnd_PinsToBottomOfTrack()
    {
        var m = new UiScrollable { ContentHeight = 400, ViewHeight = 100 };
        m.ScrollToEnd(); // PositionRatio = 1.
        float trackTop = 16f, trackLen = 200f;
        var (y, h) = UiScrollbar.ThumbRect(m, trackTop, trackLen);
        Assert.Equal(50f, h, 3f);
        // y = trackTop + travel * 1 = 16 + 150 = 166.
        Assert.Equal(166f, y, 3f);
    }

    [Fact]
    public void ThumbRect_WithButtonH_CorrectlyOffsetsFromTrackTop()
    {
        // Matches task spec: content=400, view=100, trackLen=200, PositionRatio=1.
        // thumbH=50; travel=150; y = trackTop + 150 = trackTop + 150.
        var m = new UiScrollable { ContentHeight = 400, ViewHeight = 100 };
        m.ScrollToEnd();
        var (y, h) = UiScrollbar.ThumbRect(m, trackTop: 16f, trackLen: 200f);
        Assert.Equal(50f, h, 3f);
        Assert.Equal(166f, y, 3f); // 16 + 150
    }

    [Fact]
    public void ThumbRect_MidScroll_InterpolatesPosition()
    {
        // content=400 view=100 → MaxScroll=300; ScrollY=150 → PositionRatio=0.5.
        var m = new UiScrollable { ContentHeight = 400, ViewHeight = 100 };
        m.SetScrollY(150);
        Assert.Equal(0.5f, m.PositionRatio, 3);

        var (y, h) = UiScrollbar.ThumbRect(m, trackTop: 0f, trackLen: 200f);
        Assert.Equal(50f, h, 3f);
        // y = 0 + 150 * 0.5 = 75.
        Assert.Equal(75f, y, 3f);
    }

    [Fact]
    public void ThumbRect_SmallContent_EnforcesMinThumb()
    {
        // content=1000, view=10, trackLen=200 → ThumbRatio=0.01 → raw=2 < 8 → clamp to 8.
        var m = new UiScrollable { ContentHeight = 1000, ViewHeight = 10 };
        var (_, h) = UiScrollbar.ThumbRect(m, trackTop: 0f, trackLen: 200f);
        Assert.Equal(8f, h, 3f);
    }

    [Fact]
    public void ThumbRect_NoOverflow_ThumbFillsTrack()
    {
        // content <= view → ThumbRatio = 1 → thumbH = trackLen.
        var m = new UiScrollable { ContentHeight = 50, ViewHeight = 100 };
        var (y, h) = UiScrollbar.ThumbRect(m, trackTop: 16f, trackLen: 100f);
        Assert.Equal(100f, h, 3f);
        Assert.Equal(16f, y, 3f); // travel = 0 → y = trackTop
    }
}