_admin_notice_post_locked()

function _admin_notice_post_locked() {
	if ( ! $post = get_post() )
		return;

	$user = null;
	if (  $user_id = wp_check_post_lock( $post->ID ) )
		$user = get_userdata( $user_id );

	if ( $user ) {

		/**
		 * Filters whether to show the post locked dialog.
		 *
		 * Returning a falsey value to the filter will short-circuit displaying the dialog.
		 *
		 * @since WP-3.6.0
		 *
		 * @param bool         $display Whether to display the dialog. Default true.
		 * @param WP_Post      $post    Post object.
		 * @param WP_User|bool $user    WP_User object on success, false otherwise.
		 */
		if ( ! apply_filters( 'show_post_locked_dialog', true, $post, $user ) )
			return;

		$locked = true;
	} else {
		$locked = false;
	}

	if ( $locked && ( $sendback = wp_get_referer() ) &&
		false === strpos( $sendback, 'post.php' ) && false === strpos( $sendback, 'post-new.php' ) ) {

		$sendback_text = __('Go back');
	} else {
		$sendback = admin_url( 'edit.php' );

		if ( 'post' != $post->post_type )
			$sendback = add_query_arg( 'post_type', $post->post_type, $sendback );

		$sendback_text = get_post_type_object( $post->post_type )->labels->all_items;
	}

	$hidden = $locked ? '' : ' hidden';

	?>
	<div id="post-lock-dialog" class="notification-dialog-wrap<?php echo $hidden; ?>">
	<div class="notification-dialog-background"></div>
	<div class="notification-dialog">
	<?php

	if ( $locked ) {
		$query_args = array();
		if ( get_post_type_object( $post->post_type )->public ) {
			if ( 'publish' == $post->post_status || $user->ID != $post->post_author ) {
				// Latest content is in autosave
				$nonce = wp_create_nonce( 'post_preview_' . $post->ID );
				$query_args['preview_id'] = $post->ID;
				$query_args['preview_nonce'] = $nonce;
			}
		}

		$preview_link = get_preview_post_link( $post->ID, $query_args );

		/**
		 * Filters whether to allow the post lock to be overridden.
		 *
		 * Returning a falsey value to the filter will disable the ability
		 * to override the post lock.
		 *
		 * @since WP-3.6.0
		 *
		 * @param bool    $override Whether to allow overriding post locks. Default true.
		 * @param WP_Post $post     Post object.
		 * @param WP_User $user     User object.
		 */
		$override = apply_filters( 'override_post_lock', true, $post, $user );
		$tab_last = $override ? '' : ' wp-tab-last';

		?>
		<div class="post-locked-message">
		<div class="post-locked-avatar"><?php echo get_avatar( $user->ID, 64 ); ?></div>
		<p class="currently-editing wp-tab-first" tabindex="0">
		<?php
			if ( $override ) {
				/* translators: %s: user's display name */
				printf( __( '%s is already editing this post. Do you want to take over?' ), esc_html( $user->display_name ) );
			} else {
				/* translators: %s: user's display name */
				printf( __( '%s is already editing this post.' ), esc_html( $user->display_name ) );
			}
		?>
		</p>
		<?php
		/**
		 * Fires inside the post locked dialog before the buttons are displayed.
		 *
		 * @since WP-3.6.0
		 *
		 * @param WP_Post $post Post object.
		 */
		do_action( 'post_locked_dialog', $post );
		?>
		<p>
		<a class="button" href="<?php echo esc_url( $sendback ); ?>"><?php echo $sendback_text; ?></a>
		<?php if ( $preview_link ) { ?>
		<a class="button<?php echo $tab_last; ?>" href="<?php echo esc_url( $preview_link ); ?>"><?php _e('Preview'); ?></a>
		<?php
		}

		// Allow plugins to prevent some users overriding the post lock
		if ( $override ) {
			?>
			<a class="button button-primary wp-tab-last" href="<?php echo esc_url( add_query_arg( 'get-post-lock', '1', wp_nonce_url( get_edit_post_link( $post->ID, 'url' ), 'lock-post_' . $post->ID ) ) ); ?>"><?php _e('Take over'); ?></a>
			<?php
		}

		?>
		</p>
		</div>
		<?php
	} else {
		?>
		<div class="post-taken-over">
			<div class="post-locked-avatar"></div>
			<p class="wp-tab-first" tabindex="0">
			<span class="currently-editing"></span><br />
			<span class="locked-saving hidden"><img src="<?php echo esc_url( admin_url( 'images/spinner-2x.gif' ) ); ?>" width="16" height="16" alt="" /> <?php _e( 'Saving revision&hellip;' ); ?></span>
			<span class="locked-saved hidden"><?php _e('Your latest changes were saved as a revision.'); ?></span>
			</p>
			<?php
			/**
			 * Fires inside the dialog displayed when a user has lost the post lock.
			 *
			 * @since WP-3.6.0
			 *
			 * @param WP_Post $post Post object.
			 */
			do_action( 'post_lock_lost_dialog', $post );
			?>
			<p><a class="button button-primary wp-tab-last" href="<?php echo esc_url( $sendback ); ?>"><?php echo $sendback_text; ?></a></p>
		</div>
		<?php
	}

	?>
	</div>
	</div>
	<?php
}