return ordering.compare(function.apply(left), function.apply(right));
  }

  @Override
  public boolean equals(@Nullable Object object) {
    if (object == this) {
      return true;
    }
    if (object instanceof ByFunctionOrdering) {
      ByFunctionOrdering<?, ?> that = (ByFunctionOrdering<?, ?>) object;

    }

    @Override
    public Iterator<String> iterator() {
        return map.keySet().iterator();
    }

    @Override
    public int size() {
        return map.size();
    }

    @Override
    public boolean isEmpty() {
        return map.isEmpty();
    }

    @Override
    public boolean contains(final Object o) {
        return map.containsKey(o);
    }

    @Override

     * - Downloaded artifacts
     */
    PERSISTENT,

    /**
     * Data should be retained for the duration of the current Maven session.
     * Suitable for:
     * - Build-wide configuration
     * - Project model caching
     * - Inter-module metadata
     */
    SESSION_SCOPED,

    /**
     * Data should only be retained for the current build request.
     * Suitable for:
     * - Plugin execution results

            return false;
        }
    }

    static class MockSystemHelper extends SystemHelper {
        @Override
        public long getCurrentTimeAsLong() {
            return System.currentTimeMillis();
        }

        @Override
        public String getSearchRoleByRole(String role) {
            return "search_" + role;
        }
    }

    private Map<String, Object> fields;

    @Override
    public String getId() {
        return asDocMeta().id();
    }

    public void setId(final String id) {
        asDocMeta().id(id);
    }

    @Override
    public Long getVersionNo() {
        return asDocMeta().version();
    }

    public void setVersionNo(final Long version) {
        asDocMeta().version(version);
    }

    @Override
    protected String getNamePrefix() {
        return NAME_PREFIX;
    }

    @Override
    protected String getApiPath() {
        return API_PATH;
    }

    @Override
    protected String getKeyProperty() {
        return KEY_PROPERTY;
    }

    @Override
    protected String getListEndpointSuffix() {
        return LIST_ENDPOINT_SUFFIX;
    }

    @Override

    @Override
    protected String getNamePrefix() {
        return NAME_PREFIX;
    }

    @Override
    protected String getApiPath() {
        return API_PATH;
    }

    @Override
    protected String getKeyProperty() {
        return KEY_PROPERTY;
    }

    @Override
    protected String getListEndpointSuffix() {
        return LIST_ENDPOINT_SUFFIX;
    }

    @Override

  protected final @Nullable T endOfData() {
    state = State.DONE;
    return null;
  }

  @Override
  public final boolean hasNext() {
    checkState(state != State.FAILED);
    switch (state) {
      case DONE:
        return false;
      case READY:
        return true;
      default:
    }
    return tryToComputeNext();
  }

  private boolean tryToComputeNext() {

     *
     * @return the count of bytes written
     */
    public long getCount() {
        return this.count;
    }

    @Override
    protected int writeParameterWordsWireFormat(final byte[] dst, final int dstIndex) {
        return 0;
    }

    @Override
    protected int writeBytesWireFormat(final byte[] dst, final int dstIndex) {
        return 0;
    }

    @Override

        return 0;
    }

    @Override
    protected int readParametersWireFormat(final byte[] buffer, final int bufferIndex, final int len) {
        return 0;
    }

    @Override
    protected int readDataWireFormat(final byte[] buffer, final int bufferIndex, final int len) {
        return 0;
    }

    @Override
    public String toString() {