/*

 * Copyright (c) 1999, 2013, 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

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package com.sun.tools.javac.util;

import java.util.AbstractQueue;

import java.util.Collection;

import java.util.Iterator;

import java.util.NoSuchElementException;

/** A class for constructing lists by appending elements. Modelled after

 *  java.lang.StringBuffer.

 *

 *  <p><b>This is NOT part of any supported API.

 *  If you write code that depends on this, you do so at your own risk.

 *  This code and its internal interfaces are subject to change or

 *  deletion without notice.</b>

 */

public class ListBuffer<A> extends AbstractQueue<A> {

    public static <T> ListBuffer<T> of(T x) {

        ListBuffer<T> lb = new ListBuffer<>();

        lb.add(x);

        return lb;

    }

    /** The list of elements of this buffer.

     */

    private List<A> elems;

    /** A pointer pointing to the last element of 'elems' containing data,

     *  or null if the list is empty.

     */

    private List<A> last;

    /** The number of element in this buffer.

     */

    private int count;

    /** Has a list been created from this buffer yet?

     */

    private boolean shared;

    /** Create a new initially empty list buffer.

     */

    public ListBuffer() {

        clear();

    }

    public final void clear() {

        this.elems = List.nil();

        this.last = null;

        count = 0;

        shared = false;

    }

    /** Return the number of elements in this buffer.

     */

    public int length() {

        return count;

    }

    public int size() {

        return count;

    }

    /** Is buffer empty?

     */

    public boolean isEmpty() {

        return count == 0;

    }

    /** Is buffer not empty?

     */

    public boolean nonEmpty() {

        return count != 0;

    }

    /** Copy list and sets last.

     */

    private void copy() {

        if (elems.nonEmpty()) {

            List<A> orig = elems;

            while ((orig = orig.tail).nonEmpty()) {

                last = last.tail;

            }

        }

    }

    /** Prepend an element to buffer.

     */

    public ListBuffer<A> prepend(A x) {

        elems = elems.prepend(x);

        if (last == null) last = elems;

        count++;

        return this;

    }

    /** Append an element to buffer.

     */

    public ListBuffer<A> append(A x) {

        Assert.checkNonNull(x);

        if (shared) copy();

        if (last != null) {

            last.tail = newLast;

            last = newLast;

        } else {

            elems = last = newLast;

        }

        count++;

        return this;

    }

    /** Append all elements in a list to buffer.

     */

    public ListBuffer<A> appendList(List<A> xs) {

        while (xs.nonEmpty()) {

            append(xs.head);

            xs = xs.tail;

        }

        return this;

    }

    /** Append all elements in a list to buffer.

     */

    public ListBuffer<A> appendList(ListBuffer<A> xs) {

        return appendList(xs.toList());

    }

    /** Append all elements in an array to buffer.

     */

    public ListBuffer<A> appendArray(A[] xs) {

        for (A x : xs) {

            append(x);

        }

        return this;

    }

    /** Convert buffer to a list of all its elements.

     */

    public List<A> toList() {

        shared = true;

        return elems;

    }

    /** Does the list contain the specified element?

     */

    public boolean contains(Object x) {

        return elems.contains(x);

    }

    /** Convert buffer to an array

     */

    public <T> T[] toArray(T[] vec) {

        return elems.toArray(vec);

    }

    public Object[] toArray() {

        return toArray(new Object[size()]);

    }

    /** The first element in this buffer.

     */

    public A first() {

        return elems.head;

    }

    /** Return first element in this buffer and remove

     */

    public A next() {

        A x = elems.head;

        if (!elems.isEmpty()) {

            elems = elems.tail;

            if (elems.isEmpty()) last = null;

            count--;

        }

        return x;

    }

    /** An enumeration of all elements in this buffer.

     */

    public Iterator<A> iterator() {

        return new Iterator<A>() {

            List<A> elems = ListBuffer.this.elems;

            public boolean hasNext() {

                return !elems.isEmpty();

            }

            public A next() {

                if (elems.isEmpty())

                    throw new NoSuchElementException();

                A elem = elems.head;

                elems = elems.tail;

                return elem;

            }

            public void remove() {

                throw new UnsupportedOperationException();

            }

        };

    }

    public boolean add(A a) {

        append(a);

        return true;

    }

    public boolean remove(Object o) {

        throw new UnsupportedOperationException();

    }

    public boolean containsAll(Collection<?> c) {

        for (Object x: c) {

            if (!contains(x))

                return false;

        }

        return true;

    }

    public boolean addAll(Collection<? extends A> c) {

        for (A a: c)

            append(a);

        return true;

    }

    public boolean removeAll(Collection<?> c) {

        throw new UnsupportedOperationException();

    }

    public boolean retainAll(Collection<?> c) {

        throw new UnsupportedOperationException();

    }

    public boolean offer(A a) {

        append(a);

        return true;

    }

    public A poll() {

        return next();

    }

    public A peek() {

        return first();

    }

    public A last() {

        return last != null ? last.head : null;

    }

}