content: /*
   * Licensed to the Apache Software Foundation (ASF) under one
   * or more contributor license agreements.  See the NOTICE file
   * distributed with this work for additional information
   * regarding copyright ownership.  The ASF 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
   *
   *     http://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 org.apache.beam.sdk.io;
  
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.annotations.VisibleForTesting;
  
  public class FileSystemUtils {
  
    /**
     * Expands glob expressions to regular expressions.
     *
     * <p>This method is intended for internal usage and does not guarantee backwards compatibility.
     *
     * @param globExp the glob expression to expand
     * @return a string with the regular expression this glob expands to
     */
    @VisibleForTesting
    public static String wildcardToRegexp(String globExp) {
      StringBuilder dst = new StringBuilder();
      char[] src = globExp.replace("**/*", "**").toCharArray();
      int i = 0;
      while (i < src.length) {
        char c = src[i++];
        switch (c) {
          case '*':
            // One char lookahead for **
            if (i < src.length && src[i] == '*') {
              dst.append(".*");
              ++i;
            } else {
              dst.append("[^/]*");
            }
            break;
          case '?':
            dst.append("[^/]");
            break;
          case '.':
          case '+':
          case '{':
          case '}':
          case '(':
          case ')':
          case '|':
          case '^':
          case '$':
            // These need to be escaped in regular expressions
            dst.append('\\').append(c);
            break;
          case '\\':
            i = doubleSlashes(dst, src, i);
            break;
          default:
            dst.append(c);
            break;
        }
      }
      return dst.toString();
    }
  
    private static int doubleSlashes(StringBuilder dst, char[] src, int i) {
      // Emit the next character without special interpretation
      dst.append('\\');
      if ((i + 1) < src.length) {
        dst.append('\\');
        dst.append(src[i]);
        i++;
      } else {
        // A backslash at the very end is treated like an escaped backslash
        dst.append('\\');
      }
      return i;
    }
  }
  