[backend/federation] Add LDLocalizedString

Iceshrimp.Backend/Core/Federation/ActivityStreams/Types/LDValueObject.cs

@@ -1,3 +1,4 @@
+using System.Globalization;
 using Iceshrimp.Backend.Core.Configuration;
 using Iceshrimp.Backend.Core.Extensions;
 using Newtonsoft.Json;
@@ -6,10 +7,113 @@ using J = Newtonsoft.Json.JsonPropertyAttribute;
 
 namespace Iceshrimp.Backend.Core.Federation.ActivityStreams.Types;
 
+public class LDLocalizedString
+{
+	/// <summary>
+	/// 	key: BCP 47 language code, with empty string meaning "unknown"
+	/// 	value: content, in that language
+	/// </summary>
+	public Dictionary<string, string?> Values { get; set; }
+
+	public LDLocalizedString()
+	{
+		Values = [];
+	}
+
+	public LDLocalizedString(string? language, string? value)
+	{
+		Values = [];
+
+		// this is required to create a non-Map field for non-JsonLD remotes.
+		Values.Add("", value);
+
+		if (language != null)
+		{
+			language = NormalizeLanguageCode(language);
+
+			if (language != null && language != "")
+				Values.Add(language, value);
+		}
+	}
+
+	/// <summary>
+	/// 	If the remote sends different content to multiple languages, try and guess which one they prefer "by default".
+	/// 	
+	/// 	This idea was taken from Sharkey's implementation.
+	/// 	https://activitypub.software/TransFem-org/Sharkey/-/merge_requests/401#note_1174
+	/// </summary>
+	/// <param name="language">The guessed language</param>
+	/// <returns>The value, in the guessed language</returns>
+	public string? GuessPreferredValue(out string? language)
+	{
+		if (Values.Count > 1)
+		{
+			var unknownValue = GetUnknownValue();
+			if (unknownValue != null)
+			{
+				var preferred = Values.FirstOrDefault(i => !IsUnknownLanguage(i.Key) && i.Value == unknownValue);
+				if (preferred.Value != null)
+				{
+					language = NormalizeLanguageCode(preferred.Key);
+					return preferred.Value;
+				}
+			}
+		}
+		else if (Values.Count == 0)
+		{
+			language = null;
+			return null;
+		}
+
+		var first = Values.FirstOrDefault(i => !IsUnknownLanguage(i.Key));
+		if (first.Value == null)
+		{
+			first = Values.FirstOrDefault();
+			if (first.Value == null)
+			{
+				language = null;
+				return null;
+			}
+		}
+
+		language = IsUnknownLanguage(first.Key) ? null : NormalizeLanguageCode(first.Key);
+		return first.Value;
+	}
+
+	public static string? NormalizeLanguageCode(string lang)
+	{
+		try
+		{
+			return CultureInfo.GetCultureInfo(lang).ToString();
+		}
+		catch (CultureNotFoundException)
+		{
+			// invalid language code
+			return null;
+		}
+	}
+
+	// Akkoma forces all non-localized text to be in the "und" language by adding { "@language":"und" } to it's context
+	public static bool IsUnknownLanguage(string? lang) => lang == null || lang == "" || lang == "und";
+	public string? GetUnknownValue()
+	{
+		string? value;
+
+		if (Values.TryGetValue("", out value))
+			return value;
+
+		if (Values.TryGetValue("und", out value))
+			return value;
+
+		return null;
+	}
+}
+
 public class LDValueObject<T>
 {
-	[J("@type")]  public          string? Type  { get; set; }
-	[J("@value")] public required T       Value { get; set; }
+	[J("@type")]      public          string? Type  { get; set; }
+	[J("@value")]     public required T       Value { get; set; }
+	[J("@language")]  public          string? Language { get; set; }
 }
 
 public class ValueObjectConverter : JsonConverter
@@ -158,3 +262,52 @@ public sealed class XsdString(string? str)
 
 	public override string? ToString() => str;
 }
+
+public class LocalizedValueObjectConverter : JsonConverter<LDLocalizedString>
+{
+    public override LDLocalizedString? ReadJson(JsonReader reader, Type objectType, LDLocalizedString? existingValue, bool hasExistingValue, JsonSerializer serializer)
+    {
+		var obj  = JArray.Load(reader);
+		var list = obj.ToObject<List<LDValueObject<string?>>>();
+		if (list == null || list.Count == 0)
+			return null;
+
+		var localized = new LDLocalizedString();
+
+		foreach (var item in list)
+		{
+			localized.Values.Add(item.Language ?? "", item.Value);
+		}
+
+		return localized;
+    }
+
+    public override void WriteJson(JsonWriter writer, LDLocalizedString? value, JsonSerializer serializer)
+    {
+		if (value == null)
+		{
+			writer.WriteNull();
+			return;
+		}
+
+		writer.WriteStartArray();
+
+		foreach (var item in value.Values)
+		{
+			writer.WriteStartObject();
+
+			if (!LDLocalizedString.IsUnknownLanguage(item.Key))
+			{
+				writer.WritePropertyName("@language");
+				writer.WriteValue(item.Key);
+			}
+
+			writer.WritePropertyName("@value");
+			writer.WriteValue(item.Value);
+
+			writer.WriteEndObject();
+		}
+
+		writer.WriteEndArray();
+    }
+}