ProppitIdCypher.java

package resem.util.url;

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

public class ProppitIdCypher {
    List<Integer> blockOrder = Arrays.asList(1, 3, 0, 4, 2);

    public String cypher(String id) {
        try {
            List<String> cypheredId = Arrays.stream(id.split("-"))
                    .map(x -> Long.parseLong(x, 16))
                    .map(x -> x + 42)
                    .map(Long::toHexString)
                    .collect(Collectors.toList());

            return blockOrder.stream().map(cypheredId::get).collect(Collectors.joining("-"));
        } catch (NumberFormatException e) {
            throw new ProppitIdMalformedException(e);
        }
    }

    public String decypher(String id) {
        try {
            Long[] decypheredId = Arrays.stream(id.split("-"))
                    .map(x -> Long.parseLong(x, 16))
                    .map(x -> x - 42)
                    .toArray(Long[]::new);
            List<Integer> blockReverseOrder = (IntStream.range(0, blockOrder.size())
                    .map(x -> blockOrder.indexOf(x))).boxed().collect(Collectors.toList());
            return String.format("%08x-%04x-%04x-%04x-%012x", blockReverseOrder.stream()
                    .map(position -> decypheredId[position]).toArray(Long[]::new));
        } catch (NumberFormatException e) {
            throw new ProppitIdMalformedException(e);
        }
    }
}