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   * Copyright (c) 2005, 2020, 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 jdkx.lang.model.util;
  
  import java.util.Collections;
  import java.util.List;
  import java.util.Set;
  import java.util.EnumSet;
  import java.util.ArrayList;
  import java.util.LinkedHashSet;
  
  import jdkx.lang.model.element.*;
  import jdkx.lang.model.element.ModuleElement.Directive;
  import jdkx.lang.model.element.ModuleElement.DirectiveKind;
  import jdkx.lang.model.element.ModuleElement.ExportsDirective;
  import jdkx.lang.model.element.ModuleElement.OpensDirective;
  import jdkx.lang.model.element.ModuleElement.ProvidesDirective;
  import jdkx.lang.model.element.ModuleElement.RequiresDirective;
  import jdkx.lang.model.element.ModuleElement.UsesDirective;
  
  
  /**
   * Filters for selecting just the elements of interest from a
   * collection of elements.  The returned sets and lists are new
   * collections and do use the argument as a backing store.  The
   * methods in this class do not make any attempts to guard against
   * concurrent modifications of the arguments.  The returned sets and
   * lists are mutable but unsafe for concurrent access.  A returned set
   * has the same iteration order as the argument set to a method.
   *
   * <p>If iterables and sets containing {@code null} are passed as
   * arguments to methods in this class, a {@code NullPointerException}
   * will be thrown.
   *
   * @author Joseph D. Darcy
   * @author Scott Seligman
   * @author Peter von der Ah&eacute;
   * @author Martin Buchholz
   * @since 1.6
   */
  public class ElementFilter {
      private ElementFilter() {} // Do not instantiate.
  
      private static final Set<ElementKind> CONSTRUCTOR_KIND =
          Collections.unmodifiableSet(EnumSet.of(ElementKind.CONSTRUCTOR));
  
      private static final Set<ElementKind> FIELD_KINDS =
          Collections.unmodifiableSet(EnumSet.of(ElementKind.FIELD,
                                                 ElementKind.ENUM_CONSTANT));
      private static final Set<ElementKind> METHOD_KIND =
          Collections.unmodifiableSet(EnumSet.of(ElementKind.METHOD));
  
      private static final Set<ElementKind> PACKAGE_KIND =
          Collections.unmodifiableSet(EnumSet.of(ElementKind.PACKAGE));
  
      private static final Set<ElementKind> MODULE_KIND =
          Collections.unmodifiableSet(EnumSet.of(ElementKind.MODULE));
  
      @SuppressWarnings("preview")
      private static final Set<ElementKind> TYPE_KINDS =
          Collections.unmodifiableSet(EnumSet.of(ElementKind.CLASS,
                                                 ElementKind.ENUM,
                                                 ElementKind.INTERFACE,
                                                 ElementKind.RECORD,
                                                 ElementKind.ANNOTATION_TYPE));
  
      @SuppressWarnings("preview")
      private static final Set<ElementKind> RECORD_COMPONENT_KIND =
          Collections.unmodifiableSet(EnumSet.of(ElementKind.RECORD_COMPONENT));
  
      /**
       * {@return a list of fields in {@code elements}}
       * @param elements the elements to filter
       */
      public static List<VariableElement>
              fieldsIn(Iterable<? extends Element> elements) {
          return listFilter(elements, FIELD_KINDS, VariableElement.class);
      }
  
      /**
       * {@return a set of fields in {@code elements}}
       * @param elements the elements to filter
       */
      public static Set<VariableElement>
              fieldsIn(Set<? extends Element> elements) {
          return setFilter(elements, FIELD_KINDS, VariableElement.class);
      }
  
      /**
       * {@return a list of record components in {@code elements}}
       * @param elements the elements to filter
       * @since 16
       */
      public static List<RecordComponentElement>
          recordComponentsIn(Iterable<? extends Element> elements) {
          return listFilter(elements, RECORD_COMPONENT_KIND, RecordComponentElement.class);
      }
  
      /**
       * {@return a set of record components in {@code elements}}
       * @param elements the elements to filter
       * @since 16
       */
      public static Set<RecordComponentElement>
      recordComponentsIn(Set<? extends Element> elements) {
          return setFilter(elements, RECORD_COMPONENT_KIND, RecordComponentElement.class);
      }
  
      /**
       * {@return a list of constructors in {@code elements}}
       * @param elements the elements to filter
       */
      public static List<ExecutableElement>
              constructorsIn(Iterable<? extends Element> elements) {
          return listFilter(elements, CONSTRUCTOR_KIND, ExecutableElement.class);
      }
  
      /**
       * {@return a set of constructors in {@code elements}}
       * @param elements the elements to filter
       */
      public static Set<ExecutableElement>
              constructorsIn(Set<? extends Element> elements) {
          return setFilter(elements, CONSTRUCTOR_KIND, ExecutableElement.class);
      }
  
      /**
       * {@return a list of methods in {@code elements}}
       * @param elements the elements to filter
       */
      public static List<ExecutableElement>
              methodsIn(Iterable<? extends Element> elements) {
          return listFilter(elements, METHOD_KIND, ExecutableElement.class);
      }
  
      /**
       * {@return a set of methods in {@code elements}}
       * @param elements the elements to filter
       */
      public static Set<ExecutableElement>
              methodsIn(Set<? extends Element> elements) {
          return setFilter(elements, METHOD_KIND, ExecutableElement.class);
      }
  
      /**
       * {@return a list of classes and interfaces in {@code elements}}
       * @param elements the elements to filter
       */
      public static List<TypeElement>
              typesIn(Iterable<? extends Element> elements) {
          return listFilter(elements, TYPE_KINDS, TypeElement.class);
      }
  
      /**
       * {@return a set of types in {@code elements}}
       * @param elements the elements to filter
       */
      public static Set<TypeElement>
              typesIn(Set<? extends Element> elements) {
          return setFilter(elements, TYPE_KINDS, TypeElement.class);
      }
  
      /**
       * {@return a list of packages in {@code elements}}
       * @param elements the elements to filter
       */
      public static List<PackageElement>
              packagesIn(Iterable<? extends Element> elements) {
          return listFilter(elements, PACKAGE_KIND, PackageElement.class);
      }
  
      /**
       * {@return a set of packages in {@code elements}}
       * @param elements the elements to filter
       */
      public static Set<PackageElement>
              packagesIn(Set<? extends Element> elements) {
          return setFilter(elements, PACKAGE_KIND, PackageElement.class);
      }
  
      /**
       * {@return a list of modules in {@code elements}}
       * @param elements the elements to filter
       * @since 9
       */
      public static List<ModuleElement>
              modulesIn(Iterable<? extends Element> elements) {
          return listFilter(elements, MODULE_KIND, ModuleElement.class);
      }
  
      /**
       * {@return a set of modules in {@code elements}}
       * @param elements the elements to filter
       * @since 9
       */
      public static Set<ModuleElement>
              modulesIn(Set<? extends Element> elements) {
          return setFilter(elements, MODULE_KIND, ModuleElement.class);
      }
  
      // Assumes targetKinds and E are sensible.
      private static <E extends Element> List<E> listFilter(Iterable<? extends Element> elements,
                                                            Set<ElementKind> targetKinds,
                                                            Class<E> clazz) {
          List<E> list = new ArrayList<>();
          for (Element e : elements) {
              if (targetKinds.contains(e.getKind()))
                  list.add(clazz.cast(e));
          }
          return list;
      }
  
      // Assumes targetKinds and E are sensible.
      private static <E extends Element> Set<E> setFilter(Set<? extends Element> elements,
                                                          Set<ElementKind> targetKinds,
                                                          Class<E> clazz) {
          // Return set preserving iteration order of input set.
          Set<E> set = new LinkedHashSet<>();
          for (Element e : elements) {
              if (targetKinds.contains(e.getKind()))
                  set.add(clazz.cast(e));
          }
          return set;
      }
  
      /**
       * {@return a list of {@code exports} directives in {@code directives}}
       * @param directives the directives to filter
       * @since 9
       */
      public static List<ExportsDirective>
              exportsIn(Iterable<? extends Directive> directives) {
          return listFilter(directives, DirectiveKind.EXPORTS, ExportsDirective.class);
      }
  
      /**
       * {@return a list of {@code opens} directives in {@code directives}}
       * @param directives the directives to filter
       * @since 9
       */
      public static List<OpensDirective>
              opensIn(Iterable<? extends Directive> directives) {
          return listFilter(directives, DirectiveKind.OPENS, OpensDirective.class);
      }
  
      /**
       * {@return a list of {@code provides} directives in {@code directives}}
       * @param directives the directives to filter
       * @since 9
       */
      public static List<ProvidesDirective>
              providesIn(Iterable<? extends Directive> directives) {
          return listFilter(directives, DirectiveKind.PROVIDES, ProvidesDirective.class);
      }
  
      /**
       * {@return a list of {@code requires} directives in {@code directives}}
       * @param directives the directives to filter
       * @since 9
       */
      public static List<RequiresDirective>
              requiresIn(Iterable<? extends Directive> directives) {
          return listFilter(directives, DirectiveKind.REQUIRES, RequiresDirective.class);
      }
  
      /**
       * {@return a list of {@code uses} directives in {@code directives}}
       * @param directives the directives to filter
       * @since 9
       */
      public static List<UsesDirective>
              usesIn(Iterable<? extends Directive> directives) {
          return listFilter(directives, DirectiveKind.USES, UsesDirective.class);
      }
  
      // Assumes directiveKind and D are sensible.
      private static <D extends Directive> List<D> listFilter(Iterable<? extends Directive> directives,
                                                            DirectiveKind directiveKind,
                                                            Class<D> clazz) {
          List<D> list = new ArrayList<>();
          for (Directive d : directives) {
              if (d.getKind() == directiveKind)
                  list.add(clazz.cast(d));
          }
          return list;
      }
  }
  