using System.ComponentModel;
using System.Windows.Data;
using System.Windows.Media;
using CommunityToolkit.Mvvm.ComponentModel;
using CursorLang.Models;
using CursorLang.Services;

namespace CursorLang.ViewModels;

/// <summary>
/// An option in a list. The caption changes together with the language, while the
/// object itself lives for as long as the window does: recreating the list items
/// makes the ComboBox drop the selected value.
/// </summary>
public sealed class EnumOption<T> : ObservableObject where T : struct, Enum
{
    private string _display;

    public EnumOption(T value, string display)
    {
        Value = value;
        _display = display;
    }

    public T Value { get; }

    public string Display
    {
        get => _display;
        set => SetProperty(ref _display, value);
    }

    // Accessibility tools take the name of the list item from here
    public override string ToString() => Display;
}

/// <summary>
/// The settings window. The values are edited right in <see cref="AppSettings"/>,
/// so the popup picks them up at once, without an "Apply" button.
/// </summary>
public sealed partial class SettingsViewModel : ObservableObject, IDisposable
{
    private static readonly Color[] Palette =
    [
        Color.FromRgb(0x20, 0x20, 0x20),
        Color.FromRgb(0x00, 0x00, 0x00),
        Color.FromRgb(0x1E, 0x3A, 0x8A),
        Color.FromRgb(0x0F, 0x76, 0x6E),
        Color.FromRgb(0x7C, 0x2D, 0x12),
        Color.FromRgb(0x86, 0x19, 0x8F),
        Color.FromRgb(0xB9, 0x1C, 0x1C),
        Color.FromRgb(0xF5, 0xF5, 0xF5),
    ];

    private static readonly Color[] ForegroundPalette =
    [
        Color.FromRgb(0xFF, 0xFF, 0xFF),
        Color.FromRgb(0xD4, 0xD4, 0xD4),
        Color.FromRgb(0x00, 0x00, 0x00),
        Color.FromRgb(0xFA, 0xCC, 0x15),
        Color.FromRgb(0x4A, 0xDE, 0x80),
        Color.FromRgb(0x60, 0xA5, 0xFA),
        Color.FromRgb(0xF9, 0x73, 0x16),
        Color.FromRgb(0xF8, 0x71, 0x71),
    ];

    private readonly IStartupService _startup;

    private StartupState _startupState = StartupState.Unavailable;

    public SettingsViewModel(
        AppSettings settings,
        ILocalizationService localization,
        IStartupService startup,
        UpdateViewModel updates)
    {
        Settings = settings;
        Localization = localization;
        Updates = updates;
        _startup = startup;

        // The interface language is a setting like any other and is stored in the same place
        Localization.CurrentLanguage = settings.Language;
        Settings.PropertyChanged += OnSettingsChanged;
        Localization.PropertyChanged += OnLocalizationChanged;

        Themes = CreateOptions<AppTheme>();
        PlacementModes = CreateOptions<PopupPlacementMode>();
        AnchorSides = CreateOptions<AnchorSide>();
        ScreenPositions = CreateOptions<ScreenPosition>();
    }

    public AppSettings Settings { get; }

    public ILocalizationService Localization { get; }

    /// <summary>The updates section: it has a state and commands of its own.</summary>
    public UpdateViewModel Updates { get; }

    public IReadOnlyList<Color> BackgroundPalette { get; } = Palette;

    public IReadOnlyList<Color> TextPalette { get; } = ForegroundPalette;

    public IReadOnlyList<EnumOption<AppTheme>> Themes { get; }

    public IReadOnlyList<EnumOption<PopupPlacementMode>> PlacementModes { get; }

    public IReadOnlyList<EnumOption<AnchorSide>> AnchorSides { get; }

    public IReadOnlyList<EnumOption<ScreenPosition>> ScreenPositions { get; }

    /// <summary>Whether to show the startup setting.</summary>
    public bool IsStartupAvailable => _startupState != StartupState.Unavailable;

    /// <summary>Startup is up to the application rather than to Windows.</summary>
    public bool CanChangeStartup => _startupState is StartupState.Enabled or StartupState.Disabled;

    /// <summary>It has to be explained why the setting does not give in.</summary>
    public bool IsStartupLocked => IsStartupAvailable && !CanChangeStartup;

    /// <summary>
    /// Start the application together with Windows.
    /// </summary>
    /// <remarks>
    /// The value is not stored in the application settings: Windows knows it, and it
    /// may be changed behind our back — in the "Startup apps" section. So the property
    /// answers from the last known state of the task every time.
    /// </remarks>
    public bool RunAtStartup
    {
        get => _startupState is StartupState.Enabled or StartupState.EnabledByPolicy;
        set
        {
            if (value == RunAtStartup)
            {
                return;
            }

            _ = ApplyStartupAsync(value);
        }
    }

    /// <summary>
    /// Asks Windows about the state of startup. Called after the window is shown: the
    /// answer has to be waited for, while the settings must open right away.
    /// </summary>
    public async Task InitializeAsync() => UpdateStartupState(await _startup.GetStateAsync());

    public void Dispose()
    {
        Settings.PropertyChanged -= OnSettingsChanged;
        Localization.PropertyChanged -= OnLocalizationChanged;
    }

    private async Task ApplyStartupAsync(bool enabled) =>
        UpdateStartupState(await _startup.SetEnabledAsync(enabled));

    private void UpdateStartupState(StartupState state)
    {
        _startupState = state;

        // The change is reported even when the state is the same: the checkbox has
        // already been toggled, and only a re-read value can put it back
        OnPropertyChanged(nameof(RunAtStartup));
        OnPropertyChanged(nameof(IsStartupAvailable));
        OnPropertyChanged(nameof(CanChangeStartup));
        OnPropertyChanged(nameof(IsStartupLocked));
    }

    private void OnSettingsChanged(object? sender, PropertyChangedEventArgs e)
    {
        if (e.PropertyName == nameof(AppSettings.Language))
        {
            Localization.CurrentLanguage = Settings.Language;
        }
    }

    // The option captions come from the resources, so on a language change we update
    // only the text — the list items themselves stay the same
    private void OnLocalizationChanged(object? sender, PropertyChangedEventArgs e)
    {
        if (e.PropertyName != Binding.IndexerName)
        {
            return;
        }

        Translate(Themes);
        Translate(PlacementModes);
        Translate(AnchorSides);
        Translate(ScreenPositions);
    }

    private EnumOption<T>[] CreateOptions<T>() where T : struct, Enum =>
        [.. Enum.GetValues<T>().Select(value => new EnumOption<T>(value, GetDisplayName(value)))];

    private void Translate<T>(IReadOnlyList<EnumOption<T>> options) where T : struct, Enum
    {
        foreach (EnumOption<T> option in options)
        {
            option.Display = GetDisplayName(option.Value);
        }
    }

    // The resource key is built from the type name and the value: PopupPlacementMode_AtCursor
    private string GetDisplayName<T>(T value) where T : struct, Enum =>
        Localization[$"{typeof(T).Name}_{value}"];
}