LlamaCasty/ytLive.Tests/PreviewHistoryTests.cs

using System.Collections.ObjectModel;
using System.Linq;
using Xunit;
using ytLive.Models;

namespace ytLive.Tests;

/// <summary>
/// Preview undo/redo (creator directive 2026-11-01). The contract that matters: one gesture is
/// one undo step, a restored layout is exactly what was there before, and redo survives several
/// undos — because a stack that only works one step deep is worse than none.
/// </summary>
public class PreviewHistoryTests
{
    private static Scene NewScene(params SceneElement[] elements)
    {
        var scene = new Scene { Name = "Live" };
        foreach (var element in elements) scene.Elements.Add(element);
        return scene;
    }

    private static SceneElement NewElement(double x = 0, double y = 0, double w = 100, double h = 100)
        => new Source { Name = "Layer", X = x, Y = y, Width = w, Height = h };

    [Fact]
    public void Undo_restores_geometry_and_redo_reapplies_it()
    {
        var element = NewElement(10, 20);
        var scenes = new ObservableCollection<Scene> { NewScene(element) };
        var history = new PreviewHistory();

        history.Capture(scenes);
        element.X = 300;
        element.Y = 400;

        Assert.True(history.Undo(scenes));
        Assert.Equal(10, element.X);
        Assert.Equal(20, element.Y);

        Assert.True(history.Redo(scenes));
        Assert.Equal(300, element.X);
        Assert.Equal(400, element.Y);
    }

    [Fact]
    public void Undo_removes_a_layer_added_after_the_snapshot_and_redo_brings_it_back()
    {
        var first = NewElement();
        var scene = NewScene(first);
        var scenes = new ObservableCollection<Scene> { scene };
        var history = new PreviewHistory();

        history.Capture(scenes);
        var added = NewElement();
        scene.Elements.Add(added);

        history.Undo(scenes);
        Assert.Single(scene.Elements);
        Assert.DoesNotContain(added, scene.Elements);

        history.Redo(scenes);
        Assert.Equal(2, scene.Elements.Count);
        Assert.Contains(added, scene.Elements);
    }

    [Fact]
    public void Undo_restores_a_removed_layer_in_its_original_position()
    {
        var top = NewElement();
        var middle = NewElement();
        var bottom = NewElement();
        var scene = NewScene(top, middle, bottom);
        var scenes = new ObservableCollection<Scene> { scene };

        var history = new PreviewHistory();
        history.Capture(scenes);
        scene.Elements.Remove(middle);

        history.Undo(scenes);
        Assert.Equal(new SceneElement[] { top, middle, bottom }, scene.Elements.ToArray());
    }

    [Fact]
    public void A_new_edit_after_undo_drops_the_redo_branch()
    {
        var element = NewElement();
        var scenes = new ObservableCollection<Scene> { NewScene(element) };
        var history = new PreviewHistory();

        history.Capture(scenes);
        element.X = 50;
        history.Undo(scenes);

        Assert.True(history.CanRedo);
        history.Capture(scenes);
        Assert.False(history.CanRedo);
    }

    [Fact]
    public void The_stack_is_bounded()
    {
        var scenes = new ObservableCollection<Scene> { NewScene(NewElement()) };
        var history = new PreviewHistory();

        for (var i = 0; i < PreviewHistory.MaxDepth + 20; i++) history.Capture(scenes);

        Assert.Equal(PreviewHistory.MaxDepth, history.UndoDepth);
    }

    [Fact]
    public void Undo_with_nothing_captured_is_a_no_op()
    {
        var element = NewElement(5, 5);
        var scenes = new ObservableCollection<Scene> { NewScene(element) };
        var history = new PreviewHistory();

        Assert.False(history.Undo(scenes));
        Assert.Equal(5, element.X);
    }
}