package com.buralotech.oss.identifier.uuid;
   
   import com.fasterxml.uuid.Generators;
   import com.fasterxml.uuid.NoArgGenerator;
   import com.fasterxml.uuid.UUIDType;
   import com.fasterxml.uuid.impl.UUIDUtil;
   
   import java.nio.ByteBuffer;
   import java.nio.ByteOrder;
  import java.time.Instant;
  import java.util.regex.Pattern;
  
  /**
   * Encapsulates the logic that is specific to the standard type 6 UUID format.
   */
  public class UUIDVersion6Delegate implements UUIDVersionDelegate {
  
      /**
       * The regular expression pattern used to validate identifiers.
       */
      private static final Pattern PATTERN = Pattern.compile("[0-9a-zA-Z_-]{8}[NOPQ][0-9a-zA-Z_-][159DHLPTXaeimquy][0-9a-zA-Z_-]{10}[FVk-]");
  
      /**
       * Used to generate time based UUIDs.
       */
      private final NoArgGenerator generator = Generators.timeBasedReorderedGenerator();
  
      /**
       * Generate an identifier using an underlying UUID generator.
       *
       * @return The generated identifier as a byte array.
       */
      @Override
      public byte[] generate() {
          final var uuid = generator.generate();
          return UUIDUtil.asByteArray(uuid);
      }
  
      /**
       * Check that the binary representation is valid. The service has already checked that it is non-null and a valid length.
       *
       * @param binary The binary representation.
       * @return {@code true} if the binary representation is valid. Otherwise, {@code false}.
       */
      @Override
      public boolean isValidBinary(final byte[] binary) {
          return ((binary[6] & 0xf0) >> 4 == 6) && ((binary[8] & 0xc0) >> 6 == 2);
      }
  
      /**
       * Check that the text representation is valid. The service has already checked that it is non-null and a valid length.
       *
       * @param text The binary representation.
       * @return {@code true} if the text representation is valid. Otherwise, {@code false}.
       */
      @Override
      public boolean isValidText(final String text) {
          return PATTERN.matcher(text).matches();
      }
  
      /**
       * Extract the timestamp from the UUID.
       *
       * @param binary The binary representation of the UUID.
       * @return The timestamp as an Instant.
       */
      @Override
      public Instant toInstant(final byte[] binary) {
          return Instant.ofEpochMilli(UUIDUtil.extractTimestamp(UUIDUtil.constructUUID(UUIDType.TIME_BASED_REORDERED, binary)));
      }
  
      /**
       * Create a UUID as a byte array from a timestamp.
       *
       * @param ticks  The timestamp in 100 nanoseconds.
       * @param suffix The second portion of the UUID.
       * @return The UUID as a byte array.
       */
      @Override
      public byte[] fromTicks(final long ticks, final long suffix) {
          final var bytes = new byte[16];
          final var buffer = ByteBuffer.wrap(bytes);
          buffer.order(ByteOrder.BIG_ENDIAN);
          buffer.putLong(((ticks & 0xFFFFFFFFFFFFF000L) << 4) | 0x06000L | (ticks & 0x0FFFL));
          buffer.putLong(suffix);
          return bytes;
      }
  }