cursor-lang/CursorLang.Core/Models/AppSettings.cs

using System.ComponentModel;
using System.Text.Json.Serialization;
using CommunityToolkit.Mvvm.ComponentModel;

namespace CursorLang.Core.Models;

/// <summary>
/// The application settings, as the settings window writes them to settings.json.
/// </summary>
/// <remarks>
/// Everything about the popup — the side, the offset, the font size, the opacity and
/// both colours — belongs to a placement mode rather than to the application, and is
/// kept in a <see cref="PopupModeSettings"/> of its own for each of them. So the
/// settings of a mode are still there after a trip through the other two.
///
/// Both processes hold an instance of this, but only the settings window writes: the
/// agent re-reads the file and pours the fresh values into the instance it already has,
/// so everything subscribed to it stays subscribed. See <see cref="CopyFrom"/>.
/// </remarks>
public sealed partial class AppSettings : ObservableObject
{
    /// <summary>The interface language as a culture code: "ru", "en".</summary>
    [ObservableProperty]
    private string _language = "en";

    /// <summary>The look of the settings window.</summary>
    [ObservableProperty]
    private AppTheme _theme = AppTheme.System;

    /// <summary>Where the popup is shown: at the cursor, at the caret or at a fixed point.</summary>
    [ObservableProperty]
    private PopupPlacementMode _placementMode = PopupPlacementMode.AtCursor;

    /// <summary>How long the popup stays on screen, in milliseconds.</summary>
    [ObservableProperty]
    private double _durationMilliseconds = 500;

    /// <summary>
    /// Intercept Caps Lock and switch the layout with it instead of changing the case.
    /// Off by default: the application must not change the behaviour of the system
    /// until it is asked to.
    /// </summary>
    [ObservableProperty]
    private bool _useCapsLockHotkey;

    /// <summary>
    /// After how long a Caps Lock hold cancels the switch, in milliseconds.
    /// </summary>
    [ObservableProperty]
    private double _capsLockHoldMilliseconds = 300;

    public AppSettings()
    {
        AtCursor.PropertyChanged += OnModeChanged;
        AtCaret.PropertyChanged += OnModeChanged;
        FixedPoint.PropertyChanged += OnModeChanged;
    }

    /// <summary>The <see cref="PopupPlacementMode.AtCursor"/> mode.</summary>
    /// <remarks>
    /// The modes are handed out rather than replaced — the instance is the same for the
    /// life of the settings, so a binding and a subscription to it hold. That is what
    /// the creation handling is for: without it the deserializer would want a setter,
    /// and reading the file would swap the object everything is bound to.
    /// </remarks>
    [JsonObjectCreationHandling(JsonObjectCreationHandling.Populate)]
    public CursorModeSettings AtCursor { get; } = new();

    /// <summary>The <see cref="PopupPlacementMode.AtCaret"/> mode.</summary>
    [JsonObjectCreationHandling(JsonObjectCreationHandling.Populate)]
    public CaretModeSettings AtCaret { get; } = new();

    /// <summary>The <see cref="PopupPlacementMode.FixedPoint"/> mode.</summary>
    [JsonObjectCreationHandling(JsonObjectCreationHandling.Populate)]
    public FixedPointModeSettings FixedPoint { get; } = new();

    /// <summary>The settings of the mode currently chosen.</summary>
    /// <remarks>
    /// The settings window binds the look through here, and the popup asks for it here
    /// too: what is on screen is always the settings of the mode in force. A change of
    /// <see cref="PlacementMode"/> announces this as changed, so the bindings follow.
    /// </remarks>
    [JsonIgnore]
    public PopupModeSettings Current => PlacementMode switch
    {
        PopupPlacementMode.AtCaret => AtCaret,
        PopupPlacementMode.FixedPoint => FixedPoint,
        _ => AtCursor,
    };

    /// <summary><see cref="DurationMilliseconds"/> as a <see cref="TimeSpan"/>.</summary>
    [JsonIgnore]
    public TimeSpan Duration => TimeSpan.FromMilliseconds(DurationMilliseconds);

    /// <summary><see cref="CapsLockHoldMilliseconds"/> as a <see cref="TimeSpan"/>.</summary>
    [JsonIgnore]
    public TimeSpan CapsLockHoldDelay => TimeSpan.FromMilliseconds(CapsLockHoldMilliseconds);

    /// <summary>
    /// Takes the values of another instance over, raising a change notification for
    /// every property that has actually moved.
    /// </summary>
    /// <remarks>
    /// This is how the agent learns about an edit: the settings window is a separate
    /// process, so the fresh values arrive as a freshly parsed instance and are poured
    /// into the one everything is already bound to, rather than replacing it. The modes
    /// are filled the same way, and for the same reason.
    /// </remarks>
    public void CopyFrom(AppSettings other)
    {
        Language = other.Language;
        Theme = other.Theme;
        PlacementMode = other.PlacementMode;
        DurationMilliseconds = other.DurationMilliseconds;
        UseCapsLockHotkey = other.UseCapsLockHotkey;
        CapsLockHoldMilliseconds = other.CapsLockHoldMilliseconds;

        AtCursor.CopyFrom(other.AtCursor);
        AtCaret.CopyFrom(other.AtCaret);
        FixedPoint.CopyFrom(other.FixedPoint);
    }

    // The mode in force decides what the look means, so a switch of the mode is a
    // change of everything bound through Current
    partial void OnPlacementModeChanged(PopupPlacementMode value) => OnPropertyChanged(nameof(Current));

    /// <summary>
    /// Passes a change made inside a mode on as a change of the settings.
    /// </summary>
    /// <remarks>
    /// A mode is an object of its own, so an edit in it is not an edit of this one as
    /// far as <see cref="INotifyPropertyChanged"/> goes. The settings window binds
    /// through the path and hears the mode itself, but the service that writes the file
    /// listens to the settings alone — and without this a font size dragged in the
    /// window would never reach the disk. The name says where the change happened:
    /// "AtCaret.FontSize".
    /// </remarks>
    private void OnModeChanged(object? sender, PropertyChangedEventArgs e) =>
        OnPropertyChanged($"{NameOfMode(sender)}.{e.PropertyName}");

    private string NameOfMode(object? mode) =>
        ReferenceEquals(mode, AtCaret) ? nameof(AtCaret)
            : ReferenceEquals(mode, FixedPoint) ? nameof(FixedPoint)
            : nameof(AtCursor);
}