/*
    * 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.eclipse.aether.internal.impl.transport.http;
  
  import javax.inject.Named;
  import javax.inject.Singleton;
  
  import java.util.Arrays;
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  import java.util.function.Function;
  
  import org.eclipse.aether.internal.impl.checksum.Md5ChecksumAlgorithmFactory;
  import org.eclipse.aether.internal.impl.checksum.Sha1ChecksumAlgorithmFactory;
  import org.eclipse.aether.spi.connector.transport.http.ChecksumExtractorStrategy;
  
  /**
   * Generic checksum extractor that goes for "X-" headers.
   */
  @Singleton
  @Named(XChecksumExtractor.NAME)
  public final class XChecksumExtractor extends ChecksumExtractorStrategy {
      public static final String NAME = "xChecksum";
  
      /**
       * Header name prefixes, to be suffixed by lower case algorithm name. Tried in order, first prefix that yields
       * any checksum wins.
       */
      private static final List<String> HEADER_PREFIXES = Arrays.asList(
              // Central style: x-checksum-sha1: c74edb60ca2a0b57ef88d9a7da28f591e3d4ce7b
              "x-checksum-",
              // Google style: x-goog-meta-checksum-sha1: c74edb60ca2a0b57ef88d9a7da28f591e3d4ce7b
              "x-goog-meta-checksum-",
              // AWS S3 style: x-amz-meta-checksum-sha1: c74edb60ca2a0b57ef88d9a7da28f591e3d4ce7b
              "x-amz-meta-checksum-");
  
      @Override
      public Map<String, String> extractChecksums(Function<String, String> headerGetter) {
          for (String headerPrefix : HEADER_PREFIXES) {
              Map<String, String> result = extractChecksums(headerGetter, headerPrefix);
              if (!result.isEmpty()) {
                  return result;
              }
          }
          return null;
      }
  
      private static Map<String, String> extractChecksums(Function<String, String> headerGetter, String headerPrefix) {
          HashMap<String, String> result = new HashMap<>();
          String value = headerGetter.apply(headerPrefix + "sha1");
          if (value != null) {
              result.put(Sha1ChecksumAlgorithmFactory.NAME, value);
          }
          value = headerGetter.apply(headerPrefix + "md5");
          if (value != null) {
              result.put(Md5ChecksumAlgorithmFactory.NAME, value);
          }
          return result;
      }
  }