Combined Guids media path scheme

src/Umbraco.Core/GuidUtils.cs

@@ -40,5 +40,72 @@ namespace Umbraco.Core
 
             public DecomposedGuid(Guid value) : this() => this.Value = value;
         }
+
+        private static readonly char[] Base32Table =
+        {
+            'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p',
+            'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5'
+        };
+
+        /// <summary>
+        /// Converts a Guid into a base-32 string.
+        /// </summary>
+        /// <param name="guid">A Guid.</param>
+        /// <param name="length">The string length.</param>
+        /// <returns>A base-32 encoded string.</returns>
+        /// <remarks>
+        /// <para>A base-32 string representation of a Guid is the shortest, efficient, representation
+        /// that is case insensitive (base-64 is case sensitive).</para>
+        /// <para>Length must be 1-26, anything else becomes 26.</para>
+        /// </remarks>
+        public static string ToBase32String(Guid guid, int length = 26)
+        {
+            if (length <= 0 || length > 26)
+                length = 26;
+
+            var bytes = guid.ToByteArray(); // a Guid is 128 bits ie 16 bytes
+
+            // this could be optimized by making it unsafe,
+            // and fixing the table + bytes + chars (see Convert.ToBase64CharArray)
+
+            // each block of 5 bytes = 5*8 = 40 bits
+            // becomes 40 bits = 8*5 = 8 byte-32 chars
+            // a Guid is 3 blocks + 8 bits
+
+            // so it turns into a 3*8+2 = 26 chars string
+            var chars = new char[length];
+
+            var i = 0;
+            var j = 0;
+
+            while (i < 15)
+            {
+                if (j == length) break;
+                chars[j++] = Base32Table[(bytes[i] & 0b1111_1000) >> 3];
+                if (j == length) break;
+                chars[j++] = Base32Table[((bytes[i] & 0b0000_0111) << 2) | ((bytes[i + 1] & 0b1100_0000) >> 6)];
+                if (j == length) break;
+                chars[j++] = Base32Table[(bytes[i + 1] & 0b0011_1110) >> 1];
+                if (j == length) break;
+                chars[j++] = Base32Table[(bytes[i + 1] & 0b0000_0001) | ((bytes[i + 2] & 0b1111_0000) >> 4)];
+                if (j == length) break;
+                chars[j++] = Base32Table[((bytes[i + 2] & 0b0000_1111) << 1) | ((bytes[i + 3] & 0b1000_0000) >> 7)];
+                if (j == length) break;
+                chars[j++] = Base32Table[(bytes[i + 3] & 0b0111_1100) >> 2];
+                if (j == length) break;
+                chars[j++] = Base32Table[((bytes[i + 3] & 0b0000_0011) << 3) | ((bytes[i + 4] & 0b1110_0000) >> 5)];
+                if (j == length) break;
+                chars[j++] = Base32Table[bytes[i + 4] & 0b0001_1111];
+
+                i += 5;
+            }
+
+            if (j < length)
+                chars[j++] = Base32Table[(bytes[i] & 0b1111_1000) >> 3];
+            if (j < length)
+                chars[j] = Base32Table[(bytes[i] & 0b0000_0111) << 2];
+
+            return new string(chars);
+        }
     }
 }