/*
    * Copyright 2016 The Netty Project
    *
    * The Netty Project licenses this file to you under the Apache License,
    * version 2.0 (the "License"); you may not use this file except in compliance
    * with the License. You may obtain a copy of the License at:
    *
    *   https://www.apache.org/licenses/LICENSE-2.0
    *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
   * License for the specific language governing permissions and limitations
   * under the License.
   */
  package io.netty.handler.codec.smtp;
  
  import java.util.Arrays;
  import java.util.Collections;
  import java.util.List;
  
  final class SmtpUtils {
  
      static List<CharSequence> toUnmodifiableList(CharSequence... sequences) {
          if (sequences == null || sequences.length == 0) {
              return Collections.emptyList();
          }
          return Collections.unmodifiableList(Arrays.asList(sequences));
      }
  
      /**
       * Validates SMTP parameters to prevent SMTP command injection.
       * Throws IllegalArgumentException if any parameter contains CRLF sequences.
       */
      static void validateSMTPParameters(CharSequence... parameters) {
          if (parameters != null) {
              for (CharSequence parameter : parameters) {
                  if (parameter != null) {
                      validateSMTPParameter(parameter);
                  }
              }
          }
      }
  
      /**
       * Validates SMTP parameters to prevent SMTP command injection.
       * Throws IllegalArgumentException if any parameter contains CRLF sequences.
       */
      static void validateSMTPParameters(List<CharSequence> parameters) {
          if (parameters != null) {
              for (CharSequence parameter : parameters) {
                  if (parameter != null) {
                      validateSMTPParameter(parameter);
                  }
              }
          }
      }
  
      private static void validateSMTPParameter(CharSequence parameter) {
          if (parameter instanceof String) {
              String paramStr = (String) parameter;
              if (paramStr.indexOf('\r') != -1 || paramStr.indexOf('\n') != -1) {
                  throw new IllegalArgumentException("SMTP parameter contains CRLF characters: " + parameter);
              }
          } else {
              for (int i = 0; i < parameter.length(); i++) {
                  char c = parameter.charAt(i);
                  if (c == '\r' || c == '\n') {
                      throw new IllegalArgumentException("SMTP parameter contains CRLF characters: " + parameter);
                  }
              }
          }
      }
  
      private SmtpUtils() { }
  }