MeWeb/src/MeWeb.App/Services/Localizer.cs

using System.ComponentModel;
using System.Globalization;
using System.Text.Json;

using Avalonia.Data;
using Avalonia.Markup.Xaml;
using Avalonia.Markup.Xaml.MarkupExtensions;

namespace MeWeb.App.Services;

public sealed class Localizer : INotifyPropertyChanged
{
  readonly Dictionary<string, string> english = Load(Languages.Fallback.Code);
  Dictionary<string, string> current;

  public Localizer() => current = english;

  public static Localizer Instance { get; } = new();

  public event PropertyChangedEventHandler PropertyChanged;

  public Language Language { get; private set; } = Languages.Fallback;

  public CultureInfo Culture { get; private set; } = CultureInfo.GetCultureInfo(Languages.Fallback.Code);

  public bool IsRightToLeft => Language.Rtl;

  public string this[string key] => current.GetValueOrDefault(key) ?? english.GetValueOrDefault(key) ?? key;

  public string Format(string key, params object[] args) => string.Format(Culture, this[key], args);

  public void SetLanguage(Language language)
  {
    Language = language ?? Languages.Fallback;
    current = Language.Code == Languages.Fallback.Code ? english : Load(Language.Code);
    Culture = CultureFor(Language.Code);
    CultureInfo.DefaultThreadCurrentCulture = CultureInfo.DefaultThreadCurrentUICulture = Culture;
    CultureInfo.CurrentCulture = CultureInfo.CurrentUICulture = Culture;
    PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("Item[]"));
    PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(string.Empty));
  }

  public static bool Has(string code) => typeof(Localizer).Assembly.GetManifestResourceInfo(ResourceName(code)) is not null;

  static string ResourceName(string code) => $"strings.{code}.json";

  static Dictionary<string, string> Load(string code)
  {
    using var stream = typeof(Localizer).Assembly.GetManifestResourceStream(ResourceName(code));
    if (stream is null) return [];
    return JsonSerializer.Deserialize(stream, AppJsonContext.Default.DictionaryStringString) ?? [];
  }

  static CultureInfo CultureFor(string code)
  {
    try
    {
      return CultureInfo.GetCultureInfo(code);
    }
    catch (CultureNotFoundException)
    {
      return CultureInfo.InvariantCulture;
    }
  }
}

public sealed class TrExtension : MarkupExtension
{
  public TrExtension()
  {
  }

  public TrExtension(string key) => Key = key;

  public string Key { get; set; }

  public override object ProvideValue(IServiceProvider serviceProvider) =>
      new ReflectionBindingExtension($"[{Key}]") { Mode = BindingMode.OneWay, Source = Localizer.Instance }.ProvideValue(serviceProvider);
}