/*
 * @(#)ElementFilter.java	1.6 06/08/02
 *
 * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package javax.lang.model.util;

import java.lang.Iterable;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.Set;
import java.util.EnumSet;
import java.util.ArrayList;
import java.util.LinkedHashSet;
import java.util.NoSuchElementException;

import javax.lang.model.element.*;
import javax.lang.model.type.*;


/**
 * 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
 * @version 1.6 06/08/02
 * @since 1.6
 */
public class ElementFilter {
    private ElementFilter() {} // Do not instantiate.

    private static Set<ElementKind> CONSTRUCTOR_KIND = 
	Collections.unmodifiableSet(EnumSet.of(ElementKind.CONSTRUCTOR));

    private static Set<ElementKind> FIELD_KINDS = 
	Collections.unmodifiableSet(EnumSet.of(ElementKind.FIELD,
					       ElementKind.ENUM_CONSTANT));
    private static Set<ElementKind> METHOD_KIND = 
	Collections.unmodifiableSet(EnumSet.of(ElementKind.METHOD));

    private static Set<ElementKind> PACKAGE_KIND = 
	Collections.unmodifiableSet(EnumSet.of(ElementKind.PACKAGE));

    private static 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) {
	List<E> list = new ArrayList<E>();
	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<E>();
	for (Element e : elements) {
	    if (targetKinds.contains(e.getKind()))
		set.add(clazz.cast(e));
	}
	return set;
    }
}