/*

* Written by Josh Bloch of Google Inc. and released to the public domain,

* as explained at http://creativecommons.org/publicdomain/zero/1.0/.

*

* Adapted from https://android.googlesource.com/platform/libcore/+

* android-4.2.2_r1/luni/src/main/java/java/util/ArrayDeque.java

*/

package dagger.internal;

import java.lang.reflect.Array;

import java.util.AbstractCollection;

import java.util.Collection;

import java.util.ConcurrentModificationException;

import java.util.Iterator;

import java.util.LinkedList;

import java.util.List;

import java.util.NoSuchElementException;

import java.util.Queue;

/**

* Resizable-array implementation of the {@link Queue} interface. Array

* queues have no capacity restrictions; they grow as necessary to support

* usage. They are not thread-safe; in the absence of external

* synchronization, they do not support concurrent access by multiple threads.

* Null elements are prohibited. This class is likely to be faster than

* {@link LinkedList} when used as a queue.

*

* <p>Most <tt>ArrayBackedQueue</tt> operations run in amortized constant time.

* Exceptions include {@link #remove(Object) remove}, {@link

* #removeFirstOccurrence removeFirstOccurrence}, {@link #contains contains},

* {@link #iterator iterator.remove()}, and the bulk operations, all of which

* run in linear time.

*

* <p>The iterators returned by this class's <tt>iterator</tt> method are

* <i>fail-fast</i>: If the queue is modified at any time after the iterator

* is created, in any way except through the iterator's own <tt>remove</tt>

* method, the iterator will generally throw a {@link

* ConcurrentModificationException}. Thus, in the face of concurrent

* modification, the iterator fails quickly and cleanly, rather than risking

* arbitrary, non-deterministic behavior at an undetermined time in the

* future.

*

* <p>Note that the fail-fast behavior of an iterator cannot be guaranteed

* as it is, generally speaking, impossible to make any hard guarantees in the

* presence of unsynchronized concurrent modification. Fail-fast iterators

* throw <tt>ConcurrentModificationException</tt> on a best-effort basis.

* Therefore, it would be wrong to write a program that depended on this

* exception for its correctness: <i>the fail-fast behavior of iterators

* should be used only to detect bugs.</i>

*

* <p>This class and its iterator implement all of the

* <em>optional</em> methods of the {@link Collection} and {@link

* Iterator} interfaces.

*

* @author Josh Bloch and Doug Lea

* @param <E> the type of elements held in this collection

*/

public class ArrayQueue<E> extends AbstractCollection<E>

implements Queue<E>, Cloneable, java.io.Serializable {

/**

* The array in which the elements of the queue are stored.

* The capacity of the queue is the length of this array, which is

* always a power of two. The array is never allowed to become

* full, except transiently within an addX method where it is

* resized (see doubleCapacity) immediately upon becoming full,

* thus avoiding head and tail wrapping around to equal each

* other. We also guarantee that all array cells not holding

* queue elements are always null.

*/

private transient Object[] elements;

/**

* The index of the element at the head of the queue (which is the

* element that would be removed by remove() or pop()); or an

* arbitrary number equal to tail if the queue is empty.

*/

private transient int head;

/**

* The index at which the next element would be added to the tail

* of the queue (via addLast(E), add(E), or push(E)).

*/

private transient int tail;

/**

* The minimum capacity that we'll use for a newly created queue.

* Must be a power of 2.

*/

private static final int MIN_INITIAL_CAPACITY = 8;

// ****** Array allocation and resizing utilities ******

/**

* Allocate empty array to hold the given number of elements.

*

* @param numElements the number of elements to hold

*/

private void allocateElements(int numElements) {

int initialCapacity = MIN_INITIAL_CAPACITY;

// Find the best power of two to hold elements.

// Tests "<=" because arrays aren't kept full.

if (numElements >= initialCapacity) {

initialCapacity = numElements;

initialCapacity |= (initialCapacity >>> 1);

initialCapacity |= (initialCapacity >>> 2);

initialCapacity |= (initialCapacity >>> 4);

initialCapacity |= (initialCapacity >>> 8);

initialCapacity |= (initialCapacity >>> 16);

initialCapacity++;

if (initialCapacity < 0) // Too many elements, must back off

initialCapacity >>>= 1; // Good luck allocating 2 ^ 30 elements

}

elements = new Object[initialCapacity];

}

/**

* Double the capacity of this queue. Call only when full, i.e.,

* when head and tail have wrapped around to become equal.

*/

private void doubleCapacity() {

// assert head == tail;

int p = head;

int n = elements.length;

int r = n - p; // number of elements to the right of p

int newCapacity = n << 1;

if (newCapacity < 0)

throw new IllegalStateException("Sorry, queue too big");

Object[] a = new Object[newCapacity];

System.arraycopy(elements, p, a, 0, r);

System.arraycopy(elements, 0, a, r, p);

elements = a;

head = 0;

tail = n;

}

/**

* Constructs an empty array queue with an initial capacity

* sufficient to hold 16 elements.

*/

public ArrayQueue() {

elements = new Object[16];

}

/**

* Constructs an empty array queue with an initial capacity

* sufficient to hold the specified number of elements.

*

* @param numElements lower bound on initial capacity of the queue

*/

public ArrayQueue(int numElements) {

allocateElements(numElements);

}

/**

* Constructs a queue containing the elements of the specified

* collection, in the order they are returned by the collection's

* iterator. (The first element returned by the collection's

* iterator becomes the first element, or <i>front</i> of the

* queue.)

*

* @param c the collection whose elements are to be placed into the queue

* @throws NullPointerException if the specified collection is null

*/

public ArrayQueue(Collection<? extends E> c) {

allocateElements(c.size());

addAll(c);

}

/**

* Inserts the specified element at the end of this queue.

*

* <p>This method is equivalent to {@link #offer}.

*

* @param e the element to add

* @return <tt>true</tt> (as specified by {@link Collection#add})

* @throws NullPointerException if the specified element is null

*/

@Override

public boolean add(E e) {

if (e == null)

throw new NullPointerException("e == null");

elements[tail] = e;

if ((tail = (tail + 1) & (elements.length - 1)) == head)

doubleCapacity();

return true;

}

/**

* Inserts the specified element at the end of this queue.

*

* @param e the element to add

* @return <tt>true</tt> (as specified by {@link Queue#offer})

* @throws NullPointerException if the specified element is null

*/

@Override

public boolean offer(E e) {

return add(e);

}

/**

* Retrieves and removes the head of the queue represented by this queue.

*

* This method differs from {@link #poll poll} only in that it throws an

* exception if this queue is empty.

*

* @return the head of the queue represented by this queue

* @throws NoSuchElementException {@inheritDoc}

*/

@Override

public E remove() {

E x = poll();

if (x == null)

throw new NoSuchElementException();

return x;

}

/**

* Retrieves and removes the head of the queue represented by this queue

* (in other words, the first element of this queue), or returns

* <tt>null</tt> if this queue is empty.

*

* @return the head of the queue represented by this queue, or

* <tt>null</tt> if this queue is empty

*/

@Override

public E poll() {

int h = head;

@SuppressWarnings("unchecked") E result = (E) elements[h];

// Element is null if queue empty

if (result == null)

return null;

elements[h] = null; // Must null out slot

head = (h + 1) & (elements.length - 1);

return result;

}

/**

* Retrieves, but does not remove, the head of the queue represented by

* this queue. This method differs from {@link #peek peek} only in

* that it throws an exception if this queue is empty.

*

* @return the head of the queue represented by this queue

* @throws NoSuchElementException {@inheritDoc}

*/

@Override

public E element() {

@SuppressWarnings("unchecked") E result = (E) elements[head];

if (result == null)

throw new NoSuchElementException();

return result;

}

/**

* Retrieves, but does not remove, the head of the queue represented by

* this queue, or returns <tt>null</tt> if this queue is empty.

*

* @return the head of the queue represented by this queue, or

* <tt>null</tt> if this queue is empty

*/

@Override

public E peek() {

@SuppressWarnings("unchecked") E result = (E) elements[head];

// elements[head] is null if queue empty

return result;

}

/**

* Removes the element at the specified position in the elements array,

* adjusting head and tail as necessary. This can result in motion of

* elements backwards or forwards in the array.

*

* <p>This method is called delete rather than remove to emphasize

* that its semantics differ from those of {@link List#remove(int)}.

*

* @return true if elements moved backwards

*/

private boolean delete(int i) {

//checkInvariants();

final Object[] elements = this.elements;

final int mask = elements.length - 1;

final int h = head;

final int t = tail;

final int front = (i - h) & mask;

final int back = (t - i) & mask;

// Invariant: head <= i < tail mod circularity

if (front >= ((t - h) & mask))

throw new ConcurrentModificationException();

// Optimize for least element motion

if (front < back) {

if (h <= i) {

System.arraycopy(elements, h, elements, h + 1, front);

} else { // Wrap around

System.arraycopy(elements, 0, elements, 1, i);

elements[0] = elements[mask];

System.arraycopy(elements, h, elements, h + 1, mask - h);

}

elements[h] = null;

head = (h + 1) & mask;

return false;

} else {

if (i < t) { // Copy the null tail as well

System.arraycopy(elements, i + 1, elements, i, back);

tail = t - 1;

} else { // Wrap around

System.arraycopy(elements, i + 1, elements, i, mask - i);

elements[mask] = elements[0];

System.arraycopy(elements, 1, elements, 0, t);

tail = (t - 1) & mask;

}

return true;

}

}

// *** Collection Methods ***

/**

* Returns the number of elements in this queue.

*

* @return the number of elements in this queue

*/

@Override

public int size() {

return (tail - head) & (elements.length - 1);

}

/**

* Returns <tt>true</tt> if this queue contains no elements.

*

* @return <tt>true</tt> if this queue contains no elements

*/

@Override

public boolean isEmpty() {

return head == tail;

}

/**

* Returns an iterator over the elements in this queue. The elements

* will be ordered from first (head) to last (tail). This is the same

* order that elements would be queueued (via successive calls to

* {@link #remove} or popped (via successive calls to {@link #pop}).

*

* @return an iterator over the elements in this queue

*/

@Override

public Iterator<E> iterator() {

return new QueueIterator();

}

private class QueueIterator implements Iterator<E> {

/**

* Index of element to be returned by subsequent call to next.

*/

private int cursor = head;

/**

* Tail recorded at construction (also in remove), to stop

* iterator and also to check for comodification.

*/

private int fence = tail;

/**

* Index of element returned by most recent call to next.

* Reset to -1 if element is deleted by a call to remove.

*/

private int lastRet = -1;

@Override

public boolean hasNext() {

return cursor != fence;

}

@Override

public E next() {

if (cursor == fence)

throw new NoSuchElementException();

@SuppressWarnings("unchecked") E result = (E) elements[cursor];

// This check doesn't catch all possible comodifications,

// but does catch the ones that corrupt traversal

if (tail != fence || result == null)

throw new ConcurrentModificationException();

lastRet = cursor;

cursor = (cursor + 1) & (elements.length - 1);

return result;

}

@Override

public void remove() {

if (lastRet < 0)

throw new IllegalStateException();

if (delete(lastRet)) { // if left-shifted, undo increment in next()

cursor = (cursor - 1) & (elements.length - 1);

fence = tail;

}

lastRet = -1;

}

}

/**

* Returns <tt>true</tt> if this queue contains the specified element.

* More formally, returns <tt>true</tt> if and only if this queue contains

* at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>.

*

* @param o object to be checked for containment in this queue

* @return <tt>true</tt> if this queue contains the specified element

*/

@Override

public boolean contains(Object o) {

if (o == null)

return false;

int mask = elements.length - 1;

int i = head;

Object x;

while ((x = elements[i]) != null) {

if (o.equals(x))

return true;

i = (i + 1) & mask;

}

return false;

}

/**

* Removes a single instance of the specified element from this queue.

* If the queue does not contain the element, it is unchanged.

* More formally, removes the first element <tt>e</tt> such that

* <tt>o.equals(e)</tt> (if such an element exists).

* Returns <tt>true</tt> if this queue contained the specified element

* (or equivalently, if this queue changed as a result of the call).

*

* @param o element to be removed from this queue, if present

* @return <tt>true</tt> if this queue contained the specified element

*/

@Override

public boolean remove(Object o) {

if (o == null)

return false;

int mask = elements.length - 1;

int i = head;

Object x;

while ((x = elements[i]) != null) {

if (o.equals(x)) {

delete(i);

return true;

}

i = (i + 1) & mask;

}

return false;

}

/**

* Removes all of the elements from this queue.

* The queue will be empty after this call returns.

*/

@Override

public void clear() {

int h = head;

int t = tail;

if (h != t) { // clear all cells

head = tail = 0;

int i = h;

int mask = elements.length - 1;

do {

elements[i] = null;

i = (i + 1) & mask;

} while (i != t);

}

}

/**

* Returns an array containing all of the elements in this queue

* in proper sequence (from first to last element).

*

* <p>The returned array will be "safe" in that no references to it are

* maintained by this queue. (In other words, this method must allocate

* a new array). The caller is thus free to modify the returned array.

*

* <p>This method acts as bridge between array-based and collection-based

* APIs.

*

* @return an array containing all of the elements in this queue

*/

@Override

public Object[] toArray() {

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

}

/**

* Returns an array containing all of the elements in this queue in

* proper sequence (from first to last element); the runtime type of the

* returned array is that of the specified array. If the queue fits in

* the specified array, it is returned therein. Otherwise, a new array

* is allocated with the runtime type of the specified array and the

* size of this queue.

*

* <p>If this queue fits in the specified array with room to spare

* (i.e., the array has more elements than this queue), the element in

* the array immediately following the end of the queue is set to

* <tt>null</tt>.

*

* <p>Like the {@link #toArray()} method, this method acts as bridge between

* array-based and collection-based APIs. Further, this method allows

* precise control over the runtime type of the output array, and may,

* under certain circumstances, be used to save allocation costs.

*

* <p>Suppose <tt>x</tt> is a queue known to contain only strings.

* The following code can be used to dump the queue into a newly

* allocated array of <tt>String</tt>:

*

* <pre> {@code String[] y = x.toArray(new String[0]);}</pre>

*

* Note that <tt>toArray(new Object[0])</tt> is identical in function to

* <tt>toArray()</tt>.

*

* @param a the array into which the elements of the queue are to

* be stored, if it is big enough; otherwise, a new array of the

* same runtime type is allocated for this purpose

* @return an array containing all of the elements in this queue

* @throws ArrayStoreException if the runtime type of the specified array

* is not a supertype of the runtime type of every element in

* this queue

* @throws NullPointerException if the specified array is null

*/

@Override

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

int size = size();

if (a.length < size)

a = (T[]) java.lang.reflect.Array.newInstance(

a.getClass().getComponentType(), size);

if (head < tail) {

System.arraycopy(elements, head, a, 0, size());

} else if (head > tail) {

int headPortionLen = elements.length - head;

System.arraycopy(elements, head, a, 0, headPortionLen);

System.arraycopy(elements, 0, a, headPortionLen, tail);

}

if (a.length > size)

a[size] = null;

return a;

}

// *** Object methods ***

/**

* Returns a copy of this queue.

*

* @return a copy of this queue

*/

@Override

public ArrayQueue<E> clone() {

try {

ArrayQueue<E> result = (ArrayQueue<E>) super.clone();

E[] newElements = (E[]) Array.newInstance(elements.getClass().getComponentType(),

elements.length);

System.arraycopy(elements, 0, newElements, 0, elements.length);

result.elements = newElements;

return result;

} catch (CloneNotSupportedException e) {

throw new AssertionError();

}

}

/**

* Appease the serialization gods.

*/

private static final long serialVersionUID = 2340985798034038923L;

/**

* Serialize this queue.

*

* @serialData The current size (<tt>int</tt>) of the queue,

* followed by all of its elements (each an object reference) in

* first-to-last order.

*/

private void writeObject(java.io.ObjectOutputStream s)

throws java.io.IOException {

s.defaultWriteObject();

// Write out size

s.writeInt(size());

// Write out elements in order.

int mask = elements.length - 1;

for (int i = head; i != tail; i = (i + 1) & mask)

s.writeObject(elements[i]);

}

/**

* Deserialize this queue.

*/

private void readObject(java.io.ObjectInputStream s)

throws java.io.IOException, ClassNotFoundException {

s.defaultReadObject();

// Read in size and allocate array

int size = s.readInt();

allocateElements(size);

head = 0;

tail = size;

// Read in all elements in the proper order.

for (int i = 0; i < size; i++)

elements[i] = s.readObject();

}

}