Update encoders

IOUtils/Data/Encoder.cs

@@ -0,0 +1,59 @@
+using System.Numerics;
+using System.Text;
+
+namespace IOUtils.Data;
+
+public class Encoder {
+    public static readonly Encoder Base2 = new("01");
+    public static readonly Encoder Base10 = new("0123456789");
+    public static readonly Encoder Base16 = new("0123456789ABCDEF");
+    public static readonly Encoder Base36 = new("0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ");
+    public static readonly Encoder Base62 = new("0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz");
+    public static readonly Encoder Base64 = new("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/");
+    public static readonly Encoder Base64UriSafe = new("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_");
+
+    public char[] Characters { get; }
+
+    public Encoder(char[] characters) {
+        if (characters.Length < 2)
+            throw new ArgumentException("The encoder must have at least two characters", nameof(characters));
+
+        if (characters.Length != characters.Distinct().Count())
+            throw new ArgumentException("The encoder must not have duplicate characters", nameof(characters));
+
+        Characters = characters;
+    }
+
+    public Encoder(string characters) : this(characters.ToCharArray()) { }
+
+    public string Encode(byte[] bytes, bool isBigEndian = true) {
+        BigInteger dividend = new(bytes, true, isBigEndian);
+
+        StringBuilder encodedStringBuilder = new();
+
+        while (!dividend.IsZero) {
+            dividend = BigInteger.DivRem(dividend, Characters.Length, out BigInteger remainder);
+
+            char encodedChar = Characters[(int)remainder];
+            encodedStringBuilder.Insert(0, encodedChar);
+        }
+
+        return encodedStringBuilder.ToString();
+    }
+
+    public byte[] Decode(string encoded, bool isBigEndian = true) {
+        BigInteger decodedValue = BigInteger.Zero;
+
+        foreach (int charIndex in encoded.Select(encodedChar => Array.IndexOf(Characters, encodedChar))) {
+            if (charIndex is -1) {
+                throw new ArgumentException("The encoding contains unknown characters", nameof(encoded));
+            }
+
+            decodedValue = BigInteger.Add(BigInteger.Multiply(decodedValue, Characters.Length), charIndex);
+        }
+
+        return decodedValue.IsZero
+            ? Array.Empty<byte>()
+            : decodedValue.ToByteArray(true, isBigEndian);
+    }
+}