code: /**
   * This file is part of Eclipse Steady.
   *
   * Licensed 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.
   *
   * SPDX-License-Identifier: Apache-2.0
   * SPDX-FileCopyrightText: Copyright (c) 2018-2020 SAP SE or an SAP affiliate company and Eclipse Steady contributors
   */
  package org.eclipse.steady.backend.util;
  
  import java.util.HashSet;
  import java.util.List;
  import java.util.ServiceLoader;
  import java.util.Set;
  
  import org.eclipse.steady.backend.model.Library;
  import org.eclipse.steady.backend.model.LibraryId;
  import org.eclipse.steady.shared.enums.DigestAlgorithm;
  import org.eclipse.steady.shared.enums.ProgrammingLanguage;
  import org.eclipse.steady.shared.util.CollectionUtil;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /**
   * Loops over available implementations of {@link DigestVerifier} in order to verify the digest of a given {@link Library}.
   */
  public class DigestVerifierEnumerator implements DigestVerifier {
  
    private static Logger log = LoggerFactory.getLogger(DigestVerifierEnumerator.class);
  
    private String url = null;
  
    /** Release timestamp of the given digest (null if unknown). */
    private java.util.Calendar timestamp;
  
    /** {@inheritDoc} */
    @Override
    public Set<ProgrammingLanguage> getSupportedLanguages() {
      final Set<ProgrammingLanguage> l = new HashSet<ProgrammingLanguage>();
      final ServiceLoader<DigestVerifier> loader = ServiceLoader.load(DigestVerifier.class);
      for (DigestVerifier dv : loader) {
        l.addAll(dv.getSupportedLanguages());
      }
      return l;
    }
  
    /** {@inheritDoc} */
    @Override
    public Set<DigestAlgorithm> getSupportedDigestAlgorithms() {
      final Set<DigestAlgorithm> l = new HashSet<DigestAlgorithm>();
      final ServiceLoader<DigestVerifier> loader = ServiceLoader.load(DigestVerifier.class);
      for (DigestVerifier dv : loader) {
        l.addAll(dv.getSupportedDigestAlgorithms());
      }
      return l;
    }
  
    /** {@inheritDoc} */
    @Override
    public String getVerificationUrl() {
      return url;
    }
  
    /** {@inheritDoc} */
    @Override
    public java.util.Calendar getReleaseTimestamp() {
      return this.timestamp;
    }
  
    /**
     * {@inheritDoc}
     *
     * Loops over available implementations of {@link DigestVerifier} in order to verify the digest of a given {@link Library}.
     */
    public List<LibraryId> verify(Library _lib) throws VerificationException {
      if (_lib == null || _lib.getDigest() == null)
        throw new IllegalArgumentException("No library or digest provided: [" + _lib + "]");
  
      // Will only have a list of LibraryIds or an empty list if either one verifier returns (thus, no
      // exception happened)
      List<LibraryId> verified = null;
      int exception_count = 0;
  
      // Perform the loop
      final ServiceLoader<DigestVerifier> loader = ServiceLoader.load(DigestVerifier.class);
      for (DigestVerifier l : loader) {
        // Check that programming language and digest alg match (in order to avoid a couple of
        // queries)
        final CollectionUtil<ProgrammingLanguage> u = new CollectionUtil<ProgrammingLanguage>();
        final Set<ProgrammingLanguage> developed_in = _lib.getDevelopedIn();
        if ((developed_in.isEmpty() || u.haveIntersection(developed_in, l.getSupportedLanguages()))
            && l.getSupportedDigestAlgorithms().contains(_lib.getDigestAlgorithm())) {
          try {
            verified = l.verify(_lib);
            if (verified != null && verified.size() > 0) {
              this.url = l.getVerificationUrl();
              this.timestamp = l.getReleaseTimestamp();
              break;
            }
          } catch (VerificationException e) {
            exception_count++;
            log.error(e.getMessage());
          }
        }
      }
  
      // Return null if an exception happened, verified otherwise
      return (exception_count == 0 ? verified : null);
    }
  }
  