using System.Globalization;

namespace MeterVault.App.Localization;

/// <summary>
/// UI-language plumbing around <see cref="Strings"/>, the strongly-typed accessor MSBuild generates
/// from <c>Strings.resx</c> (see the <c>EmbeddedResource</c> block in the project file).
/// </summary>
/// <remarks>
/// <para>
/// The neutral resource is English and every other language ships as a satellite assembly, so an
/// <c>Accept-Language</c> we don't translate degrades to English rather than to raw resource keys.
/// Strings are referenced as compiled properties (<c>S.Common_Save</c>), not string lookups, so a
/// key that no longer exists is a build error instead of a mystery label at runtime.
/// </para>
/// <para>
/// Number and date <em>formatting</em> follows <see cref="CultureInfo.CurrentCulture"/> and the UI
/// language follows <see cref="CultureInfo.CurrentUICulture"/>; the request-localization middleware
/// sets both from the same choice, so the two never disagree.
/// </para>
/// </remarks>
public static class Loc
{
    /// <summary>Cultures the UI ships translations for. The first entry is the neutral fallback.</summary>
    public static IReadOnlyList<string> SupportedCultures { get; } = ["en", "de"];

    /// <summary>Formats a resource carrying <c>{0}</c>-style placeholders in the request's culture.</summary>
    public static string F(string format, params object?[] args) =>
        string.Format(CultureInfo.CurrentCulture, format, args);

    /// <summary>
    /// Maps a requested language onto one we actually ship, matching on the two-letter tag so
    /// <c>de-AT</c> and <c>de-CH</c> get German instead of falling through to English.
    /// </summary>
    /// <returns><c>true</c> when the request named a language we translate.</returns>
    public static bool TryResolve(string? requested, out string resolved)
    {
        resolved = SupportedCultures[0];

        if (string.IsNullOrWhiteSpace(requested))
        {
            return false;
        }

        var trimmed = requested.Trim();
        var separator = trimmed.IndexOfAny(['-', '_']);
        var language = separator < 0 ? trimmed : trimmed[..separator];

        foreach (var supported in SupportedCultures)
        {
            if (string.Equals(supported, language, StringComparison.OrdinalIgnoreCase))
            {
                resolved = supported;
                return true;
            }
        }

        return false;
    }

    /// <summary>The display name of a supported culture, written in that language ("Deutsch", "English").</summary>
    public static string DisplayName(string culture) =>
        CultureInfo.GetCultureInfo(culture).NativeName;
}