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package io.github.mmm.crypto.hash;

import java.security.MessageDigest;

import io.github.mmm.crypto.AbstractGetIterationCount;
import io.github.mmm.crypto.provider.SecurityProvider;

/**
 * This is an implementation of {@link HashCreator} that {@link #hash(boolean) calculates hashes} in multiple
 * rounds. Therefore, the actual {@link #update(byte[]) data} is hashed once and then for the number of rounds given at
 * construction time the initial hash is hashed again with the same hash algorithm.
 *
 * @author Joerg Hohwiller (hohwille at users.sourceforge.net)
 * @since 1.0.0
 */
public class HashCreatorImplMultipleRounds extends HashCreatorImplDigest {

  private final MessageDigest roundDigest;

  private final int iterationCount;

  /**
   * The constructor.
   *
   * @param hashAlgorithm the name of the hash algorithm to use (e.g. "SHA-256").
   * @param iterationCount {@link AbstractGetIterationCount}. Has to be greater than {@code 1}.
   * @param provider the {@link SecurityProvider} to use.
   */
  public HashCreatorImplMultipleRounds(String hashAlgorithm, SecurityProvider provider, int iterationCount) {

    super(hashAlgorithm, provider);
    if (iterationCount <= 1) {
      throw new IllegalArgumentException("Iteration count (" + iterationCount + ") has to be greater than 1!");
    }
    this.roundDigest = getProvider().createDigest(hashAlgorithm);
    this.iterationCount = iterationCount;
  }

  @Override
  public byte[] hash(boolean reset) {

    byte[] hash = super.hash(reset);
    for (int i = 1; i < this.iterationCount; i++) {
      hash = this.roundDigest.digest(hash);
    }
    return hash;
  }

}