using System.Globalization;
using System.Resources;
using CommunityToolkit.Mvvm.ComponentModel;

namespace CursorLang.Core.Services;

/// <summary>
/// Takes the strings from the resources and, when the language changes, asks WPF to
/// re-read every binding.
/// </summary>
/// <remarks>
/// Both processes use it: the settings window for its whole interface, the agent for
/// the three captions of the tray menu. The theme no longer reaches that menu — Windows
/// draws it — but the language still does.
/// </remarks>
public sealed class LocalizationService : ObservableObject, ILocalizationService
{
    /// <summary>
    /// The name WPF reports when an indexer changes. Spelt out rather than taken from
    /// <c>Binding.IndexerName</c>: that constant lives in PresentationFramework, and
    /// Core is read by the agent, which does not load WPF.
    /// </summary>
    public const string IndexerName = "Item[]";

    private static readonly ResourceManager Resources =
        new("CursorLang.Core.Resources.Strings", typeof(LocalizationService).Assembly);

    private CultureInfo _culture = CultureInfo.GetCultureInfo("en");

    public string this[string key] => Resources.GetString(key, _culture) ?? key;

    public IReadOnlyList<LanguageOption> AvailableLanguages { get; } =
    [
        new LanguageOption("en", "English"),
        new LanguageOption("ru", "Русский"),
    ];

    public string CurrentLanguage
    {
        get => _culture.TwoLetterISOLanguageName;
        set
        {
            if (string.IsNullOrWhiteSpace(value) || value == CurrentLanguage)
            {
                return;
            }

            _culture = CultureInfo.GetCultureInfo(value);
            CultureInfo.CurrentUICulture = _culture;

            OnPropertyChanged(nameof(CurrentLanguage));

            // We report a change of the indexer: that is how every binding of the
            // {Binding Localization[Key]} kind updates, that is, all the interface text
            OnPropertyChanged(IndexerName);
        }
    }
}