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.extensions.sql.meta.provider.datacatalog;
  
  import static java.util.stream.Collectors.joining;
  import static org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions.checkNotNull;
  
  import java.util.List;
  import java.util.regex.Pattern;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.ImmutableMap;
  
  /** Utils to work with ZetaSQL-compatible IDs. */
  class ZetaSqlIdUtils {
  
    /**
     * Some special characters we explicitly handle.
     *
     * <p>Everything else is ignored, e.g. tabs, newlines, etc.
     */
    private static final Pattern SPECIAL_CHARS_ESCAPE =
        Pattern.compile(
            "(?<SpecialChar>["
                + "\\\\" // slash
                + "`" //    backtick
                + "'" //    single quote
                + "\"" //   double quote
                + "?" //    question mark
                + "])");
  
    private static final ImmutableMap<String, String> WHITESPACES =
        ImmutableMap.of(
            "\n", "\\\\n",
            "\t", "\\\\t",
            "\r", "\\\\r",
            "\f", "\\\\f");
  
    private static final Pattern SIMPLE_ID = Pattern.compile("[A-Za-z_][A-Za-z_0-9]*");
  
    /**
     * Joins parts into a single compound ZetaSQL identifier.
     *
     * <p>Escapes backticks, slashes, double and single quotes, doesn't handle other special
     * characters for now.
     */
    static String escapeAndJoin(List<String> parts) {
      return parts.stream()
          .map(ZetaSqlIdUtils::escapeSpecialChars)
          .map(ZetaSqlIdUtils::replaceWhitespaces)
          .map(ZetaSqlIdUtils::backtickIfNeeded)
          .collect(joining("."));
    }
  
    private static String escapeSpecialChars(String str) {
      return SPECIAL_CHARS_ESCAPE.matcher(str).replaceAll("\\\\${SpecialChar}");
    }
  
    private static String replaceWhitespaces(String s) {
      return WHITESPACES.keySet().stream()
          .reduce(
              s,
              (str, whitespace) ->
                  str.replaceAll(whitespace, checkNotNull(WHITESPACES.get(whitespace))));
    }
  
    private static String backtickIfNeeded(String s) {
      return SIMPLE_ID.matcher(s).matches() ? s : ("`" + s + "`");
    }
  }
  