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   * Copyright (c) 2016, Oracle and/or its affiliates. All rights reserved.
   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.  Oracle designates this
   * particular file as subject to the "Classpath" exception as provided
   * by Oracle in the LICENSE file that accompanied this code.
   *
   * This code is distributed in the hope that it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   * version 2 for more details (a copy is included in the LICENSE file that
   * accompanied this code).
   *
   * You should have received a copy of the GNU General Public License version
   * 2 along with this work; if not, write to the Free Software Foundation,
   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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   */
  
  package openjdk.tools.jdeps;
  
  import java.io.PrintWriter;
  import java.lang.module.ModuleDescriptor;
  import java.util.Deque;
  import java.util.HashSet;
  import java.util.LinkedList;
  import java.util.Map;
  import java.util.Optional;
  import java.util.Set;
  import java.util.stream.Stream;
  
  import static java.lang.module.ModuleDescriptor.Requires.Modifier.*;
  import static openjdk.tools.jdeps.Module.*;
  
  /**
   * A builder to create a Graph<Module>
   */
  public class ModuleGraphBuilder extends Graph.Builder<Module> {
      final JdepsConfiguration config;
  
      ModuleGraphBuilder(JdepsConfiguration config) {
          this.config = config;
      }
  
      /**
       * Adds a module to the graph.
       */
      ModuleGraphBuilder addModule(Module module) {
          addNode(module);
          return this;
      }
  
      /**
       * Apply transitive reduction on the resulting graph
       */
      public Graph<Module> reduced() {
          Graph<Module> graph = build();
          // transitive reduction
          Graph<Module> newGraph = buildGraph(graph.edges()).reduce();
  
          if (DEBUG) {
              PrintWriter log = new PrintWriter(System.err);
              System.err.println("before transitive reduction: ");
              graph.printGraph(log);
              System.err.println("after transitive reduction: ");
              newGraph.printGraph(log);
          }
  
          return newGraph;
      }
  
      public Graph<Module> buildGraph() {
          Graph<Module> graph = build();
          return buildGraph(graph.edges());
      }
  
      /**
       * Build a graph of module from the given dependences.
       *
       * It transitively includes all implied read edges.
       */
      private Graph<Module> buildGraph(Map<Module, Set<Module>> edges) {
          Graph.Builder<Module> builder = new Graph.Builder<>();
          Set<Module> visited = new HashSet<>();
          Deque<Module> deque = new LinkedList<>();
          edges.entrySet().stream().forEach(e -> {
              Module m = e.getKey();
              deque.add(m);
              e.getValue().stream().forEach(v -> {
                  deque.add(v);
                  builder.addEdge(m, v);
              });
          });
  
          // read requires transitive from ModuleDescriptor
          Module source;
          while ((source = deque.poll()) != null) {
              if (visited.contains(source))
                  continue;
  
              visited.add(source);
              builder.addNode(source);
              Module from = source;
              requiresTransitive(from).forEach(m -> {
                  deque.add(m);
                  builder.addEdge(from, m);
              });
          }
          return builder.build();
      }
  
      /*
       * Returns a stream of modules upon which the given module `requires transitive`
       */
      public Stream<Module> requiresTransitive(Module m) {
          // find requires transitive
          return m.descriptor()
                  .requires().stream()
                  .filter(req -> req.modifiers().contains(TRANSITIVE))
                  .map(ModuleDescriptor.Requires::name)
                  .map(config::findModule)
                  .flatMap(Optional::stream);
      }
  }
  