package com.atlassian.vcache.internal.core;
   
   import com.google.common.hash.Hashing;
   
   import java.nio.charset.Charset;
   import java.nio.charset.StandardCharsets;
   import java.util.Base64;
   
   /**
   * Implementation of {@link ExternalCacheKeyGenerator} that encodes using the <tt>SHA-1</tt> hashing algorithm.
   *
   * @since 1.0.0
   */
  public class Sha1ExternalCacheKeyGenerator extends ExternalCacheKeyGenerator {
      private static final Charset DIGEST_CHARSET = StandardCharsets.UTF_8;
  
      public Sha1ExternalCacheKeyGenerator(String productIdentifier) {
          super(productIdentifier);
      }
  
      @Override
      protected String encode(String plain) {
          /*
           * We are not using MessageDigest#getInstance because under high load this becomes a contention. This is a known issue in Java
           * documented here: https://bugs.java.com/bugdatabase/view_bug.do?bug_id=7092821
           * We are using the Guava implementation instead as they have optimized this bit.
           */
          final byte[] digest = Hashing.sha1().hashString(plain, DIGEST_CHARSET).asBytes();
          return Base64.getEncoder().encodeToString(digest);
      }
  }