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/**
 * This file is part of the ramsey/collection library
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 *
 * @copyright Copyright (c) Ben Ramsey &lt;ben@benramsey.com&gt;
 * @license http://opensource.org/licenses/MIT MIT
 */

declare(strict_types=1);

namespace Ramsey\Collection;

use Ramsey\Collection\Exception\NoSuchElementException;
use RuntimeException;

/**
 * A linear collection that supports element insertion and removal at both ends.
 *
 * Most `DoubleEndedQueueInterface` implementations place no fixed limits on the
 * number of elements they may contain, but this interface supports
 * capacity-restricted double-ended queues as well as those with no fixed size
 * limit.
 *
 * This interface defines methods to access the elements at both ends of the
 * double-ended queue. Methods are provided to insert, remove, and examine the
 * element. Each of these methods exists in two forms: one throws an exception
 * if the operation fails, the other returns a special value (either `null` or
 * `false`, depending on the operation). The latter form of the insert operation
 * is designed specifically for use with capacity-restricted implementations; in
 * most implementations, insert operations cannot fail.
 *
 * The twelve methods described above are summarized in the following table:
 *
 * &lt;table&gt;
 * &lt;caption&gt;Summary of DoubleEndedQueueInterface methods&lt;/caption&gt;
 * &lt;thead&gt;
 * &lt;tr&gt;
 * &lt;th&gt;&lt;/th&gt;
 * &lt;th colspan=2&gt;First Element (Head)&lt;/th&gt;
 * &lt;th colspan=2&gt;Last Element (Tail)&lt;/th&gt;
 * &lt;/tr&gt;
 * &lt;tr&gt;
 * &lt;td&gt;&lt;/td&gt;
 * &lt;td&gt;&lt;em&gt;Throws exception&lt;/em&gt;&lt;/td&gt;
 * &lt;td&gt;&lt;em&gt;Special value&lt;/em&gt;&lt;/td&gt;
 * &lt;td&gt;&lt;em&gt;Throws exception&lt;/em&gt;&lt;/td&gt;
 * &lt;td&gt;&lt;em&gt;Special value&lt;/em&gt;&lt;/td&gt;
 * &lt;/tr&gt;
 * &lt;/thead&gt;
 * &lt;tbody&gt;
 * &lt;tr&gt;
 * &lt;th&gt;Insert&lt;/th&gt;
 * &lt;td&gt;&lt;code&gt;addFirst()&lt;/code&gt;&lt;/td&gt;
 * &lt;td&gt;&lt;code&gt;offerFirst()&lt;/code&gt;&lt;/td&gt;
 * &lt;td&gt;&lt;code&gt;addLast()&lt;/code&gt;&lt;/td&gt;
 * &lt;td&gt;&lt;code&gt;offerLast()&lt;/code&gt;&lt;/td&gt;
 * &lt;/tr&gt;
 * &lt;tr&gt;
 * &lt;th&gt;Remove&lt;/th&gt;
 * &lt;td&gt;&lt;code&gt;removeFirst()&lt;/code&gt;&lt;/td&gt;
 * &lt;td&gt;&lt;code&gt;pollFirst()&lt;/code&gt;&lt;/td&gt;
 * &lt;td&gt;&lt;code&gt;removeLast()&lt;/code&gt;&lt;/td&gt;
 * &lt;td&gt;&lt;code&gt;pollLast()&lt;/code&gt;&lt;/td&gt;
 * &lt;/tr&gt;
 * &lt;tr&gt;
 * &lt;th&gt;Examine&lt;/th&gt;
 * &lt;td&gt;&lt;code&gt;firstElement()&lt;/code&gt;&lt;/td&gt;
 * &lt;td&gt;&lt;code&gt;peekFirst()&lt;/code&gt;&lt;/td&gt;
 * &lt;td&gt;&lt;code&gt;lastElement()&lt;/code&gt;&lt;/td&gt;
 * &lt;td&gt;&lt;code&gt;peekLast()&lt;/code&gt;&lt;/td&gt;
 * &lt;/tr&gt;
 * &lt;/tbody&gt;
 * &lt;/table&gt;
 *
 * This interface extends the `QueueInterface`. When a double-ended queue is
 * used as a queue, FIFO (first-in-first-out) behavior results. Elements are
 * added at the end of the double-ended queue and removed from the beginning.
 * The methods inherited from the `QueueInterface` are precisely equivalent to
 * `DoubleEndedQueueInterface` methods as indicated in the following table:
 *
 * &lt;table&gt;
 * &lt;caption&gt;Comparison of QueueInterface and DoubleEndedQueueInterface methods&lt;/caption&gt;
 * &lt;thead&gt;
 * &lt;tr&gt;
 * &lt;th&gt;QueueInterface Method&lt;/th&gt;
 * &lt;th&gt;DoubleEndedQueueInterface Method&lt;/th&gt;
 * &lt;/tr&gt;
 * &lt;/thead&gt;
 * &lt;tbody&gt;
 * &lt;tr&gt;
 * &lt;td&gt;&lt;code&gt;add()&lt;/code&gt;&lt;/td&gt;
 * &lt;td&gt;&lt;code&gt;addLast()&lt;/code&gt;&lt;/td&gt;
 * &lt;/tr&gt;
 * &lt;tr&gt;
 * &lt;td&gt;&lt;code&gt;offer()&lt;/code&gt;&lt;/td&gt;
 * &lt;td&gt;&lt;code&gt;offerLast()&lt;/code&gt;&lt;/td&gt;
 * &lt;/tr&gt;
 * &lt;tr&gt;
 * &lt;td&gt;&lt;code&gt;remove()&lt;/code&gt;&lt;/td&gt;
 * &lt;td&gt;&lt;code&gt;removeFirst()&lt;/code&gt;&lt;/td&gt;
 * &lt;/tr&gt;
 * &lt;tr&gt;
 * &lt;td&gt;&lt;code&gt;poll()&lt;/code&gt;&lt;/td&gt;
 * &lt;td&gt;&lt;code&gt;pollFirst()&lt;/code&gt;&lt;/td&gt;
 * &lt;/tr&gt;
 * &lt;tr&gt;
 * &lt;td&gt;&lt;code&gt;element()&lt;/code&gt;&lt;/td&gt;
 * &lt;td&gt;&lt;code&gt;firstElement()&lt;/code&gt;&lt;/td&gt;
 * &lt;/tr&gt;
 * &lt;tr&gt;
 * &lt;td&gt;&lt;code&gt;peek()&lt;/code&gt;&lt;/td&gt;
 * &lt;td&gt;&lt;code&gt;peekFirst()&lt;/code&gt;&lt;/td&gt;
 * &lt;/tr&gt;
 * &lt;/tbody&gt;
 * &lt;/table&gt;
 *
 * Double-ended queues can also be used as LIFO (last-in-first-out) stacks. When
 * a double-ended queue is used as a stack, elements are pushed and popped from
 * the beginning of the double-ended queue. Stack concepts are precisely
 * equivalent to `DoubleEndedQueueInterface` methods as indicated in the table
 * below:
 *
 * &lt;table&gt;
 * &lt;caption&gt;Comparison of stack concepts and DoubleEndedQueueInterface methods&lt;/caption&gt;
 * &lt;thead&gt;
 * &lt;tr&gt;
 * &lt;th&gt;Stack concept&lt;/th&gt;
 * &lt;th&gt;DoubleEndedQueueInterface Method&lt;/th&gt;
 * &lt;/tr&gt;
 * &lt;/thead&gt;
 * &lt;tbody&gt;
 * &lt;tr&gt;
 * &lt;td&gt;&lt;em&gt;push&lt;/em&gt;&lt;/td&gt;
 * &lt;td&gt;&lt;code&gt;addFirst()&lt;/code&gt;&lt;/td&gt;
 * &lt;/tr&gt;
 * &lt;tr&gt;
 * &lt;td&gt;&lt;em&gt;pop&lt;/em&gt;&lt;/td&gt;
 * &lt;td&gt;&lt;code&gt;removeFirst()&lt;/code&gt;&lt;/td&gt;
 * &lt;/tr&gt;
 * &lt;tr&gt;
 * &lt;td&gt;&lt;em&gt;peek&lt;/em&gt;&lt;/td&gt;
 * &lt;td&gt;&lt;code&gt;peekFirst()&lt;/code&gt;&lt;/td&gt;
 * &lt;/tr&gt;
 * &lt;/tbody&gt;
 * &lt;/table&gt;
 *
 * Note that the `peek()` method works equally well when a double-ended queue is
 * used as a queue or a stack; in either case, elements are drawn from the
 * beginning of the double-ended queue.
 *
 * While `DoubleEndedQueueInterface` implementations are not strictly required
 * to prohibit the insertion of `null` elements, they are strongly encouraged to
 * do so. Users of any `DoubleEndedQueueInterface` implementations that do allow
 * `null` elements are strongly encouraged *not* to take advantage of the
 * ability to insert nulls. This is so because `null` is used as a special
 * return value by various methods to indicated that the double-ended queue is
 * empty.
 *
 * @template T
 * @extends QueueInterface&lt;T&gt;
 */
interface DoubleEndedQueueInterface extends QueueInterface
{
    /**
     * Inserts the specified element at the front of this queue if it is
     * possible to do so immediately without violating capacity restrictions.
     *
     * When using a capacity-restricted double-ended queue, it is generally
     * preferable to use the `offerFirst()` method.
     *
     * @param T $element The element to add to the front of this queue.
     *
     * @return bool `true` if this queue changed as a result of the call.
     *
     * @throws RuntimeException if a queue refuses to add a particular element
     *     for any reason other than that it already contains the element.
     *     Implementations should use a more-specific exception that extends
     *     `\RuntimeException`.
     */
    // phpcs:ignore SlevomatCodingStandard.TypeHints.ParameterTypeHint.MissingNativeTypeHint
    public function addFirst($element): bool;

    /**
     * Inserts the specified element at the end of this queue if it is possible
     * to do so immediately without violating capacity restrictions.
     *
     * When using a capacity-restricted double-ended queue, it is generally
     * preferable to use the `offerLast()` method.
     *
     * This method is equivalent to `add()`.
     *
     * @param T $element The element to add to the end of this queue.
     *
     * @return bool `true` if this queue changed as a result of the call.
     *
     * @throws RuntimeException if a queue refuses to add a particular element
     *     for any reason other than that it already contains the element.
     *     Implementations should use a more-specific exception that extends
     *     `\RuntimeException`.
     */
    // phpcs:ignore SlevomatCodingStandard.TypeHints.ParameterTypeHint.MissingNativeTypeHint
    public function addLast($element): bool;

    /**
     * Inserts the specified element at the front of this queue if it is
     * possible to do so immediately without violating capacity restrictions.
     *
     * When using a capacity-restricted queue, this method is generally
     * preferable to `addFirst()`, which can fail to insert an element only by
     * throwing an exception.
     *
     * @param T $element The element to add to the front of this queue.
     *
     * @return bool `true` if the element was added to this queue, else `false`.
     */
    // phpcs:ignore SlevomatCodingStandard.TypeHints.ParameterTypeHint.MissingNativeTypeHint
    public function offerFirst($element): bool;

    /**
     * Inserts the specified element at the end of this queue if it is possible
     * to do so immediately without violating capacity restrictions.
     *
     * When using a capacity-restricted queue, this method is generally
     * preferable to `addLast()` which can fail to insert an element only by
     * throwing an exception.
     *
     * @param T $element The element to add to the end of this queue.
     *
     * @return bool `true` if the element was added to this queue, else `false`.
     */
    // phpcs:ignore SlevomatCodingStandard.TypeHints.ParameterTypeHint.MissingNativeTypeHint
    public function offerLast($element): bool;

    /**
     * Retrieves and removes the head of this queue.
     *
     * This method differs from `pollFirst()` only in that it throws an
     * exception if this queue is empty.
     *
     * @return T the first element in this queue.
     *
     * @throws NoSuchElementException if this queue is empty.
     */
    public function removeFirst();

    /**
     * Retrieves and removes the tail of this queue.
     *
     * This method differs from `pollLast()` only in that it throws an exception
     * if this queue is empty.
     *
     * @return T the last element in this queue.
     *
     * @throws NoSuchElementException if this queue is empty.
     */
    public function removeLast();

    /**
     * Retrieves and removes the head of this queue, or returns `null` if this
     * queue is empty.
     *
     * @return T|null the head of this queue, or `null` if this queue is empty.
     */
    public function pollFirst();

    /**
     * Retrieves and removes the tail of this queue, or returns `null` if this
     * queue is empty.
     *
     * @return T|null the tail of this queue, or `null` if this queue is empty.
     */
    public function pollLast();

    /**
     * Retrieves, but does not remove, the head of this queue.
     *
     * This method differs from `peekFirst()` only in that it throws an
     * exception if this queue is empty.
     *
     * @return T the head of this queue.
     *
     * @throws NoSuchElementException if this queue is empty.
     */
    public function firstElement();

    /**
     * Retrieves, but does not remove, the tail of this queue.
     *
     * This method differs from `peekLast()` only in that it throws an exception
     * if this queue is empty.
     *
     * @return T the tail of this queue.
     *
     * @throws NoSuchElementException if this queue is empty.
     */
    public function lastElement();

    /**
     * Retrieves, but does not remove, the head of this queue, or returns `null`
     * if this queue is empty.
     *
     * @return T|null the head of this queue, or `null` if this queue is empty.
     */
    public function peekFirst();

    /**
     * Retrieves, but does not remove, the tail of this queue, or returns `null`
     * if this queue is empty.
     *
     * @return T|null the tail of this queue, or `null` if this queue is empty.
     */
    public function peekLast();
}
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