Migrate existing code

Integrations/Kea/KeaDhcpLease.cs

@@ -0,0 +1,63 @@
+using System.Buffers;
+using System.Globalization;
+
+using DotNext.Buffers;
+
+using CommunityToolkit.HighPerformance.Buffers;
+
+namespace DotNetDDI.Integrations.Kea;
+
+public static class KeaDhcpLease
+{
+	private static ReadOnlySpan<char> EscapeTag => ['&', '#', 'x'];
+
+	// ref: https://github.com/isc-projects/kea/blob/Kea-2.5.3/src/lib/util/csv_file.cc#L479
+	public static string Unescape(in ReadOnlySpan<char> text)
+	{
+		return text.IndexOf(EscapeTag) switch
+		{
+			-1 => text.ToString(),
+			int i => SlowPath(i, text)
+		};
+
+		static string SlowPath(int esc_pos, in ReadOnlySpan<char> text)
+		{
+			SpanReader<char> reader = new(text);
+			using ArrayPoolBufferWriter<char> writer = new(text.Length);
+			while (reader.RemainingCount > 0)
+			{
+				writer.Write(reader.Read(esc_pos));
+				reader.Advance(EscapeTag.Length);
+
+				bool converted = false;
+				char escapedChar = default;
+				if (reader.RemainingCount >= 2)
+				{
+					if (byte.TryParse(reader.RemainingSpan[..2], NumberStyles.AllowHexSpecifier, null, out var b))
+					{
+						converted = true;
+						escapedChar = (char)b;
+						reader.Advance(2);
+					}
+				}
+
+				if (converted)
+				{
+					writer.Write([escapedChar]);
+				}
+				else
+				{
+					writer.Write(EscapeTag);
+				}
+
+				esc_pos = reader.RemainingSpan.IndexOf(EscapeTag);
+				if (esc_pos == -1)
+				{
+					writer.Write(reader.ReadToEnd());
+				}
+			}
+
+			return writer.WrittenSpan.ToString();
+		}
+	}
+}