base62ToUuid method

Implementation

String base62ToUuid() {
  // Define the Base62 character set.
  final chars =
      '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz';

  // First of all, convert this [String] into a [BigInt].
  BigInt decoded = BigInt.zero;

  for (int i = 0; i < length; i++) {
    // Find the numeric value of the character in the Base62 character set.
    final int value = chars.indexOf(this[i]);

    if (value == -1) {
      throw FormatException('Invalid Base62 character: ${this[i]}');
    }

    decoded = decoded * BigInt.from(62) + BigInt.from(value);
  }

  // Create a list of 16 bytes (128 bits) to store the UUID.
  final bytes = Uint8List(16);

  for (int i = 15; i >= 0; i--) {
    bytes[i] = (decoded & BigInt.from(0xff)).toInt();
    decoded = decoded >> 8;
  }

  // Returns the hexadecimal string of the provided part from [bytes].
  String toHex(int start, int end) => bytes
      .sublist(start, end)
      .map((b) => b.toRadixString(16).padLeft(2, '0'))
      .join();

  return '${toHex(0, 4)}-${toHex(4, 6)}-${toHex(6, 8)}-${toHex(8, 10)}-${toHex(10, 16)}';
}