/*

 * Copyright (c) 2005, 2012, 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 javax.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 javax.lang.model.element.*;

/**

 * 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.

 *

 * <p>Note that a <i>static import</i> statement can make the text of

 * calls to the methods in this class more concise; for example:

 *

 * <blockquote><pre>

 *     import static javax.lang.model.util.ElementFilter.*;

 *     ...

 *         {@code List<VariableElement>} fs = fieldsIn(someClass.getEnclosedElements());

 * </pre></blockquote>

 *

 * @author Joseph D. Darcy

 * @author Scott Seligman

 * @author Peter von der Ahé

 * @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> TYPE_KINDS =

        Collections.unmodifiableSet(EnumSet.of(ElementKind.CLASS,

                                               ElementKind.ENUM,

                                               ElementKind.INTERFACE,

                                               ElementKind.ANNOTATION_TYPE));

    /**

     * Returns a list of fields in {@code elements}.

     * @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);

    }

    /**

     * Returns a set of fields in {@code elements}.

     * @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);

    }

    /**

     * Returns a list of constructors in {@code elements}.

     * @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);

    }

    /**

     * Returns a set of constructors in {@code elements}.

     * @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);

    }

    /**

     * Returns a list of methods in {@code elements}.

     * @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);

    }

    /**

     * Returns a set of methods in {@code elements}.

     * @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);

    }

    /**

     * Returns a list of types in {@code elements}.

     * @return a list of types 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);

    }

    /**

     * Returns a set of types in {@code elements}.

     * @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);

    }

    /**

     * Returns a list of packages in {@code elements}.

     * @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);

    }

    /**

     * Returns a set of packages in {@code elements}.

     * @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);

    }

    // Assumes targetKinds and E are sensible.

    private static <E extends Element> List<E> listFilter(Iterable<? extends Element> elements,

                                                          Set<ElementKind> targetKinds,

                                                          Class<E> clazz) {

        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.

        for (Element e : elements) {

            if (targetKinds.contains(e.getKind()))

                set.add(clazz.cast(e));

        }

        return set;

    }

}