class TimestampToString {

  @Udf(description = "Converts a BIGINT millisecond timestamp value into the"
      + " string representation of the timestamp in the given format. Single quotes in the"
      + " timestamp format can be escaped with '', for example: 'yyyy-MM-dd''T''HH:mm:ssX'"
      + " The system default time zone is used when no time zone is explicitly provided."
      + " The format pattern should be in the format expected"
      + " by java.time.format.DateTimeFormatter")
  public String timestampToString(
      @UdfParameter(
          description = "Milliseconds since"
              + " January 1, 1970, 00:00:00 GMT.") final long epochMilli,
      @UdfParameter(
          description = "The format pattern should be in the format expected by"
              + " java.time.format.DateTimeFormatter.") final String formatPattern) {
    try {
      final Timestamp timestamp = new Timestamp(epochMilli);
      final DateTimeFormatter formatter = formatters.get(formatPattern);
      return timestamp.toInstant()
          .atZone(ZoneId.systemDefault())
          .format(formatter);
    } catch (final ExecutionException | RuntimeException e) {
      throw new KsqlFunctionException("Failed to format timestamp " + epochMilli
          + " with formatter '" + formatPattern
          + "': " + e.getMessage(), e);
    }

  }

}