cursor-lang/CursorLang.Tests/Models/AppSettingsTests.cs

using System.ComponentModel;
using System.Reflection;
using System.Text.Json;
using System.Windows.Media;
using CursorLang.Models;

namespace CursorLang.Tests.Models;

public sealed class AppSettingsTests
{
    [Fact]
    public void Default_values_describe_a_tooltip_at_the_cursor()
    {
        var settings = new AppSettings();

        Assert.Equal("en", settings.Language);
        Assert.Equal(AppTheme.System, settings.Theme);
        Assert.Equal(PopupPlacementMode.AtCursor, settings.PlacementMode);
        Assert.Equal(AnchorSide.BottomRight, settings.CursorSide);
        Assert.Equal(16, settings.CursorOffset);
        Assert.Equal(AnchorSide.BottomRight, settings.CaretSide);
        Assert.Equal(16, settings.CaretOffset);
        Assert.Equal(ScreenPosition.BottomRight, settings.ScreenPosition);
        Assert.Equal(24, settings.ScreenMargin);
        Assert.Equal(20, settings.FontSize);
        Assert.Equal(0.9, settings.Opacity);
        Assert.Equal(500, settings.DurationMilliseconds);
        Assert.Equal(300, settings.CapsLockHoldMilliseconds);
        Assert.Equal(Color.FromRgb(0x20, 0x20, 0x20), settings.BackgroundColor);
        Assert.Equal(Color.FromRgb(0xFF, 0xFF, 0xFF), settings.ForegroundColor);
    }

    // The app must not change how the system behaves until it is asked to
    [Fact]
    public void Caps_Lock_interception_is_off_by_default()
    {
        Assert.False(new AppSettings().UseCapsLockHotkey);
    }

    [Fact]
    public void The_time_on_screen_is_derived_from_milliseconds()
    {
        var settings = new AppSettings { DurationMilliseconds = 1250 };

        Assert.Equal(TimeSpan.FromMilliseconds(1250), settings.Duration);
    }

    [Fact]
    public void The_hold_threshold_is_derived_from_milliseconds()
    {
        var settings = new AppSettings { CapsLockHoldMilliseconds = 400 };

        Assert.Equal(TimeSpan.FromMilliseconds(400), settings.CapsLockHoldDelay);
    }

    [Theory]
    [MemberData(nameof(WritableProperties))]
    public void A_changed_setting_is_announced_to_subscribers(string propertyName)
    {
        var settings = new AppSettings();
        List<string?> changed = [];
        settings.PropertyChanged += (_, e) => changed.Add(e.PropertyName);

        SetDifferentValue(settings, propertyName);

        Assert.Contains(propertyName, changed);
    }

    [Theory]
    [MemberData(nameof(WritableProperties))]
    public void Writing_the_same_value_leaves_subscribers_alone(string propertyName)
    {
        var settings = new AppSettings();
        PropertyInfo property = typeof(AppSettings).GetProperty(propertyName)!;
        object? value = property.GetValue(settings);

        List<string?> changed = [];
        settings.PropertyChanged += (_, e) => changed.Add(e.PropertyName);

        property.SetValue(settings, value);

        Assert.Empty(changed);
    }

    // Duration and CapsLockHoldDelay are derived from other settings and have
    // no business being in the file
    [Fact]
    public void Derived_values_stay_out_of_the_file()
    {
        using JsonDocument document = JsonSerializer.SerializeToDocument(new AppSettings());

        List<string> names = [.. document.RootElement.EnumerateObject().Select(property => property.Name)];

        Assert.DoesNotContain(nameof(AppSettings.Duration), names);
        Assert.DoesNotContain(nameof(AppSettings.CapsLockHoldDelay), names);

        // What they are derived from, on the other hand, has to be stored
        Assert.Contains(nameof(AppSettings.DurationMilliseconds), names);
        Assert.Contains(nameof(AppSettings.CapsLockHoldMilliseconds), names);
    }

    [Fact]
    public void Settings_report_changes_as_INotifyPropertyChanged()
    {
        Assert.IsAssignableFrom<INotifyPropertyChanged>(new AppSettings());
    }

    public static TheoryData<string> WritableProperties()
    {
        var data = new TheoryData<string>();

        foreach (string name in WritablePropertyNames())
        {
            data.Add(name);
        }

        return data;
    }

    /// <summary>Names of the settings the user is able to change.</summary>
    internal static IEnumerable<string> WritablePropertyNames() =>
        typeof(AppSettings).GetProperties()
            .Where(property => property.CanWrite)
            .Select(property => property.Name);

    // A value guaranteed to differ from the current one: each kind of setting
    // has its own way of differing
    private static void SetDifferentValue(AppSettings settings, string propertyName)
    {
        PropertyInfo property = typeof(AppSettings).GetProperty(propertyName)!;
        object? current = property.GetValue(settings);

        object next = current switch
        {
            string text => text + "-other",
            double number => number + 1,
            bool flag => !flag,
            Color color => Color.FromRgb((byte)(color.R + 1), color.G, color.B),
            Enum value => NextEnumValue(value),
            DateTimeOffset moment => moment.AddDays(1),

            // A setting never set yet: the app has not checked for updates once
            null when property.PropertyType == typeof(DateTimeOffset?) => DateTimeOffset.UnixEpoch,

            _ => throw new NotSupportedException($"Unknown kind of setting: {property.PropertyType}"),
        };

        property.SetValue(settings, next);
    }

    private static object NextEnumValue(Enum current)
    {
        Array values = Enum.GetValues(current.GetType());

        foreach (object? value in values)
        {
            if (!Equals(value, current))
            {
                return value!;
            }
        }

        throw new NotSupportedException($"{current.GetType()} has a single value");
    }
}