1 files changed, 97 insertions, 0 deletions
diff --git a/src/Agent.Core/Localization/LocaleCatalog.cs b/src/Agent.Core/Localization/LocaleCatalog.cs
new file mode 100644
index 0000000..3c49283
--- /dev/null
+++ b/src/Agent.Core/Localization/LocaleCatalog.cs
@@ -0,0 +1,97 @@
+using System.Text.Json;
+using System.Text.RegularExpressions;
+
+namespace Agent.Core.Localization;
+
+public sealed partial class LocaleCatalog
+{
+    private readonly IReadOnlyDictionary<string, IReadOnlyDictionary<string, string>> _locales;
+    private readonly IReadOnlyDictionary<string, string> _fallback;
+
+    private LocaleCatalog(string selectedLocale, IReadOnlyDictionary<string, IReadOnlyDictionary<string, string>> locales, IReadOnlyDictionary<string, string> fallback)
+    {
+        SelectedLocale = selectedLocale;
+        _locales = locales;
+        _fallback = fallback;
+    }
+
+    public string SelectedLocale { get; }
+    public IReadOnlyCollection<string> Keys => _fallback.Keys.ToArray();
+
+    public static LocaleCatalog Load(string directory, string selectedLocale, string fallbackLocale = "en")
+    {
+        if (!Directory.Exists(directory)) throw new LocaleException($"Locale directory does not exist: {directory}");
+
+        var locales = new Dictionary<string, IReadOnlyDictionary<string, string>>(StringComparer.OrdinalIgnoreCase);
+        foreach (string file in Directory.EnumerateFiles(directory, "*.json", SearchOption.TopDirectoryOnly))
+        {
+            string locale = Path.GetFileNameWithoutExtension(file);
+            locales.Add(locale, ReadFlatObject(file));
+        }
+
+        if (!locales.TryGetValue(fallbackLocale, out IReadOnlyDictionary<string, string>? fallback))
+            throw new LocaleException($"Fallback locale '{fallbackLocale}' is missing.");
+
+        HashSet<string> baselineKeys = fallback.Keys.ToHashSet(StringComparer.Ordinal);
+        Dictionary<string, HashSet<string>> baselinePlaceholders = fallback.ToDictionary(static p => p.Key, static p => Placeholders(p.Value), StringComparer.Ordinal);
+        foreach ((string locale, IReadOnlyDictionary<string, string> values) in locales)
+        {
+            string? unknown = values.Keys.FirstOrDefault(key => !baselineKeys.Contains(key));
+            if (unknown is not null) throw new LocaleException($"Locale '{locale}' contains unknown key '{unknown}'.");
+            foreach ((string key, string message) in values)
+            {
+                if (!baselinePlaceholders[key].SetEquals(Placeholders(message)))
+                    throw new LocaleException($"Locale '{locale}' has mismatched placeholders for key '{key}'.");
+            }
+        }
+
+        if (!locales.ContainsKey(selectedLocale)) throw new LocaleException($"Selected locale '{selectedLocale}' is missing.");
+        return new LocaleCatalog(selectedLocale, locales, fallback);
+    }
+
+    public string Get(string key)
+    {
+        if (_locales[SelectedLocale].TryGetValue(key, out string? selected)) return selected;
+        return _fallback.TryGetValue(key, out string? fallback) ? fallback : key;
+    }
+
+    public string Format(string key, IReadOnlyDictionary<string, object?> values)
+    {
+        string template = Get(key);
+        return PlaceholderRegex().Replace(template, match =>
+        {
+            string name = match.Groups[1].Value;
+            if (!values.TryGetValue(name, out object? value)) throw new LocaleException($"Missing placeholder value '{name}' for key '{key}'.");
+            return Convert.ToString(value, System.Globalization.CultureInfo.InvariantCulture) ?? string.Empty;
+        });
+    }
+
+    private static Dictionary<string, string> ReadFlatObject(string file)
+    {
+        try
+        {
+            using JsonDocument document = JsonDocument.Parse(File.ReadAllText(file));
+            if (document.RootElement.ValueKind != JsonValueKind.Object) throw new LocaleException($"Locale file must contain a JSON object: {file}");
+            var result = new Dictionary<string, string>(StringComparer.Ordinal);
+            foreach (JsonProperty property in document.RootElement.EnumerateObject())
+            {
+                if (property.Value.ValueKind != JsonValueKind.String) throw new LocaleException($"Locale value '{property.Name}' must be a string.");
+                if (!result.TryAdd(property.Name, property.Value.GetString()!)) throw new LocaleException($"Duplicate locale key '{property.Name}'.");
+            }
+            return result;
+        }
+        catch (LocaleException)
+        {
+            throw;
+        }
+        catch (Exception ex) when (ex is JsonException or IOException or UnauthorizedAccessException)
+        {
+            throw new LocaleException($"Could not load locale file '{file}': {ex.Message}", ex);
+        }
+    }
+
+    private static HashSet<string> Placeholders(string text) => PlaceholderRegex().Matches(text).Select(static m => m.Groups[1].Value).ToHashSet(StringComparer.Ordinal);
+
+    [GeneratedRegex("\\{([A-Za-z][A-Za-z0-9_]*)\\}", RegexOptions.CultureInvariant)]
+    private static partial Regex PlaceholderRegex();
+}