replaced with the page number, so 'Page %' generates "Page 1", "Page 2", etc.
 *                                          Defaults to '%', just the page number.
 *     @type int|bool     $echo             Whether to echo or not. Accepts 1|true or 0|false. Default 1|true.
 * }
 * @return string Formatted output in HTML.
 */
function wp_link_pages( $args = '' ) {
	global $page, $numpages, $multipage, $more;

	$defaults = array(
		'before'           => '<p class="post-nav-links">' . __( 'Pages:' ),
		'after'            => '</p>',
		'link_before'      => '',
		'link_after'       => '',
		'aria_current'     => 'page',
		'next_or_number'   => 'number',
		'separator'        => ' ',
		'nextpagelink'     => __( 'Next page' ),
		'previouspagelink' => __( 'Previous page' ),
		'pagelink'         => '%',
		'echo'             => 1,
	);

	$parsed_args = wp_parse_args( $args, $defaults );

	/**
	 * Filters the arguments used in retrieving page links for paginated posts.
	 *
	 * @since 3.0.0
	 *
	 * @param array $parsed_args An array of page link arguments. See wp_link_pages()
	 *                           for information on accepted arguments.
	 */
	$parsed_args = apply_filters( 'wp_link_pages_args', $parsed_args );

	$output = '';
	if ( $multipage ) {
		if ( 'number' === $parsed_args['next_or_number'] ) {
			$output .= $parsed_args['before'];
			for ( $i = 1; $i <= $numpages; $i++ ) {
				$link = $parsed_args['link_before'] . str_replace( '%', $i, $parsed_args['pagelink'] ) . $parsed_args['link_after'];
				if ( $i != $page || ! $more && 1 == $page ) {
					$link = _wp_link_page( $i ) . $link . '</a>';
				} elseif ( $i === $page ) {
					$link = '<span class="post-page-numbers current" aria-current="' . esc_attr( $parsed_args['aria_current'] ) . '">' . $link . '</span>';
				}
				/**
				 * Filters the HTML output of individual page number links.
				 *
				 * @since 3.6.0
				 *
				 * @param string $link The page number HTML output.
				 * @param int    $i    Page number for paginated posts' page links.
				 */
				$link = apply_filters( 'wp_link_pages_link', $link, $i );

				// Use the custom links separator beginning with the second link.
				$output .= ( 1 === $i ) ? ' ' : $parsed_args['separator'];
				$output .= $link;
			}
			$output .= $parsed_args['after'];
		} elseif ( $more ) {
			$output .= $parsed_args['before'];
			$prev    = $page - 1;
			if ( $prev > 0 ) {
				$link = _wp_link_page( $prev ) . $parsed_args['link_before'] . $parsed_args['previouspagelink'] . $parsed_args['link_after'] . '</a>';

				/** This filter is documented in wp-includes/post-template.php */
				$output .= apply_filters( 'wp_link_pages_link', $link, $prev );
			}
			$next = $page + 1;
			if ( $next <= $numpages ) {
				if ( $prev ) {
					$output .= $parsed_args['separator'];
				}
				$link = _wp_link_page( $next ) . $parsed_args['link_before'] . $parsed_args['nextpagelink'] . $parsed_args['link_after'] . '</a>';

				/** This filter is documented in wp-includes/post-template.php */
				$output .= apply_filters( 'wp_link_pages_link', $link, $next );
			}
			$output .= $parsed_args['after'];
		}
	}

	/**
	 * Filters the HTML output of page links for paginated posts.
	 *
	 * @since 3.6.0
	 *
	 * @param string       $output HTML output of paginated posts' page links.
	 * @param array|string $args   An array or query string of arguments. See wp_link_pages()
	 *                             for information on accepted arguments.
	 */
	$html = apply_filters( 'wp_link_pages', $output, $args );

	if ( $parsed_args['echo'] ) {
		echo $html;
	}
	return $html;
}

/**
 * Helper function for wp_link_pages().
 *
 * @since 3.1.0
 * @access private
 *
 * @global WP_Rewrite $wp_rewrite WordPress rewrite component.
 *
 * @param int $i Page number.
 * @return string Link.
 */
function _wp_link_page( $i ) {
	global $wp_rewrite;
	$post       = get_post();
	$query_args = array();

	if ( 1 == $i ) {
		$url = get_permalink();
	} else {
		if ( ! get_option( 'permalink_structure' ) || in_array( $post->post_status, array( 'draft', 'pending' ), true ) ) {
			$url = add_query_arg( 'page', $i, get_permalink() );
		} elseif ( 'page' === get_option( 'show_on_front' ) && get_option( 'page_on_front' ) == $post->ID ) {
			$url = trailingslashit( get_permalink() ) . user_trailingslashit( "$wp_rewrite->pagination_base/" . $i, 'single_paged' );
		} else {
			$url = trailingslashit( get_permalink() ) . user_trailingslashit( $i, 'single_paged' );
		}
	}

	if ( is_preview() ) {

		if ( ( 'draft' !== $post->post_status ) && isset( $_GET['preview_id'], $_GET['preview_nonce'] ) ) {
			$query_args['preview_id']    = wp_unslash( $_GET['preview_id'] );
			$query_args['preview_nonce'] = wp_unslash( $_GET['preview_nonce'] );
		}

		$url = get_preview_post_link( $post, $query_args, $url );
	}

	return '<a href="' . esc_url( $url ) . '" class="post-page-numbers">';
}

//
// Post-meta: Custom per-post fields.
//

/**
 * Retrieves post custom meta data field.
 *
 * @since 1.5.0
 *
 * @param string $key Meta data key name.
 * @return array|string|false Array of values, or single value if only one element exists.
 *                            False if the key does not exist.
 */
function post_custom( $key = '' ) {
	$custom = get_post_custom();

	if ( ! isset( $custom[ $key ] ) ) {
		return false;
	} elseif ( 1 === count( $custom[ $key ] ) ) {
		return $custom[ $key ][0];
	} else {
		return $custom[ $key ];
	}
}

/**
 * Displays a list of post custom fields.
 *
 * @since 1.2.0
 *
 * @deprecated 6.0.2 Use get_post_meta() to retrieve post meta and render manually.
 */
function the_meta() {
	_deprecated_function( __FUNCTION__, '6.0.2', 'get_post_meta()' );
	$keys = get_post_custom_keys();
	if ( $keys ) {
		$li_html = '';
		foreach ( (array) $keys as $key ) {
			$keyt = trim( $key );
			if ( is_protected_meta( $keyt, 'post' ) ) {
				continue;
			}

			$values = array_map( 'trim', get_post_custom_values( $key ) );
			$value  = implode( ', ', $values );

			$html = sprintf(
				"<li><span class='post-meta-key'>%s</span> %s</li>\n",
				/* translators: %s: Post custom field name. */
				esc_html( sprintf( _x( '%s:', 'Post custom field name' ), $key ) ),
				esc_html( $value )
			);

			/**
			 * Filters the HTML output of the li element in the post custom fields list.
			 *
			 * @since 2.2.0
			 *
			 * @param string $html  The HTML output for the li element.
			 * @param string $key   Meta key.
			 * @param string $value Meta value.
			 */
			$li_html .= apply_filters( 'the_meta_key', $html, $key, $value );
		}

		if ( $li_html ) {
			echo "<ul class='post-meta'>\n{$li_html}</ul>\n";
		}
	}
}

//
// Pages.
//

/**
 * Retrieves or displays a list of pages as a dropdown (select list).
 *
 * @since 2.1.0
 * @since 4.2.0 The `$value_field` argument was added.
 * @since 4.3.0 The `$class` argument was added.
 *
 * @see get_pages()
 *
 * @param array|string $args {
 *     Optional. Array or string of arguments to generate a page dropdown. See get_pages() for additional arguments.
 *
 *     @type int          $depth                 Maximum depth. Default 0.
 *     @type int          $child_of              Page ID to retrieve child pages of. Default 0.
 *     @type int|string   $selected              Value of the option that should be selected. Default 0.
 *     @type bool|int     $echo                  Whether to echo or return the generated markup. Accepts 0, 1,
 *                                               or their bool equivalents. Default 1.
 *     @type string       $name                  Value for the 'name' attribute of the select element.
 *                                               Default 'page_id'.
 *     @type string       $id                    Value for the 'id' attribute of the select element.
 *     @type string       $class                 Value for the 'class' attribute of the select element. Default: none.
 *                                               Defaults to the value of `$name`.
 *     @type string       $show_option_none      Text to display for showing no pages. Default empty (does not display).
 *     @type string       $show_option_no_change Text to display for "no change" option. Default empty (does not display).
 *     @type string       $option_none_value     Value to use when no page is selected. Default empty.
 *     @type string       $value_field           Post field used to populate the 'value' attribute of the option
 *                                               elements. Accepts any valid post field. Default 'ID'.
 * }
 * @return string HTML dropdown list of pages.
 */
function wp_dropdown_pages( $args = '' ) {
	$defaults = array(
		'depth'                 => 0,
		'child_of'              => 0,
		'selected'              => 0,
		'echo'                  => 1,
		'name'                  => 'page_id',
		'id'                    => '',
		'class'                 => '',
		'show_option_none'      => '',
		'show_option_no_change' => '',
		'option_none_value'     => '',
		'value_field'           => 'ID',
	);

	$parsed_args = wp_parse_args( $args, $defaults );

	$pages  = get_pages( $parsed_args );
	$output = '';
	// Back-compat with old system where both id and name were based on $name argument.
	if ( empty( $parsed_args['id'] ) ) {
		$parsed_args['id'] = $parsed_args['name'];
	}

	if ( ! empty( $pages ) ) {
		$class = '';
		if ( ! empty( $parsed_args['class'] ) ) {
			$class = " class='" . esc_attr( $parsed_args['class'] ) . "'";
		}

		$output = "<select name='" . esc_attr( $parsed_args['name'] ) . "'" . $class . " id='" . esc_attr( $parsed_args['id'] ) . "'>\n";
		if ( $parsed_args['show_option_no_change'] ) {
			$output .= "\t<option value=\"-1\">" . $parsed_args['show_option_no_change'] . "</option>\n";
		}
		if ( $parsed_args['show_option_none'] ) {
			$output .= "\t<option value=\"" . esc_attr( $parsed_args['option_none_value'] ) . '">' . $parsed_args['show_option_none'] . "</option>\n";
		}
		$output .= walk_page_dropdown_tree( $pages, $parsed_args['depth'], $parsed_args );
		$output .= "</select>\n";
	}

	/**
	 * Filters the HTML output of a list of pages as a dropdown.
	 *
	 * @since 2.1.0
	 * @since 4.4.0 `$parsed_args` and `$pages` added as arguments.
	 *
	 * @param string    $output      HTML output for dropdown list of pages.
	 * @param array     $parsed_args The parsed arguments array. See wp_dropdown_pages()
	 *                               for information on accepted arguments.
	 * @param WP_Post[] $pages       Array of the page objects.
	 */
	$html = apply_filters( 'wp_dropdown_pages', $output, $parsed_args, $pages );

	if ( $parsed_args['echo'] ) {
		echo $html;
	}

	return $html;
}

/**
 * Retrieves or displays a list of pages (or hierarchical post type items) in list (li) format.
 *
 * @since 1.5.0
 * @since 4.7.0 Added the `item_spacing` argument.
 *
 * @see get_pages()
 *
 * @global WP_Query $wp_query WordPress Query object.
 *
 * @param array|string $args {
 *     Optional. Array or string of arguments to generate a list of pages. See get_pages() for additional arguments.
 *
 *     @type int          $child_of     Display only the sub-pages of a single page by ID. Default 0 (all pages).
 *     @type string       $authors      Comma-separated list of author IDs. Default empty (all authors).
 *     @type string       $date_format  PHP date format to use for the listed pages. Relies on the 'show_date' parameter.
 *                                      Default is the value of 'date_format' option.
 *     @type int          $depth        Number of levels in the hierarchy of pages to include in the generated list.
 *                                      Accepts -1 (any depth), 0 (all pages), 1 (top-level pages only), and n (pages to
 *                                      the given n depth). Default 0.
 *     @type bool         $echo         Whether or not to echo the list of pages. Default true.
 *     @type string       $exclude      Comma-separated list of page IDs to exclude. Default empty.
 *     @type array        $include      Comma-separated list of page IDs to include. Default empty.
 *     @type string       $link_after   Text or HTML to follow the page link label. Default null.
 *     @type string       $link_before  Text or HTML to precede the page link label. Default null.
 *     @type string       $post_type    Post type to query for. Default 'page'.
 *     @type string|array $post_status  Comma-separated list or array of post statuses to include. Default 'publish'.
 *     @type string       $show_date    Whether to display the page publish or modified date for each page. Accepts
 *                                      'modified' or any other value. An empty value hides the date. Default empty.
 *     @type string       $sort_column  Comma-separated list of column names to sort the pages by. Accepts 'post_author',
 *                                      'post_date', 'post_title', 'post_name', 'post_modified', 'post_modified_gmt',
 *                                      'menu_order', 'post_parent', 'ID', 'rand', or 'comment_count'. Default 'post_title'.
 *     @type string       $title_li     List heading. Passing a null or empty value will result in no heading, and the list
 *                                      will not be wrapped with unordered list `<ul>` tags. Default 'Pages'.
 *     @type string       $item_spacing Whether to preserve whitespace within the menu's HTML. Accepts 'preserve' or 'discard'.
 *                                      Default 'preserve'.
 *     @type Walker       $walker       Walker instance to use for listing pages. Default empty which results in a
 *                                      Walker_Page instance being used.
 * }
 * @return void|string Void if 'echo' argument is true, HTML list of pages if 'echo' is false.
 */
function wp_list_pages( $args = '' ) {
	$defaults = array(
		'depth'        => 0,
		'show_date'    => '',
		'date_format'  => get_option( 'date_format' ),
		'child_of'     => 0,
		'exclude'      => '',
		'title_li'     => __( 'Pages' ),
		'echo'         => 1,
		'authors'      => '',
		'sort_column'  => 'menu_order, post_title',
		'link_before'  => '',
		'link_after'   => '',
		'item_spacing' => 'preserve',
		'walker'       => '',
	);

	$parsed_args = wp_parse_args( $args, $defaults );

	if ( ! in_array( $parsed_args['item_spacing'], array( 'preserve', 'discard' ), true ) ) {
		// Invalid value, fall back to default.
		$parsed_args['item_spacing'] = $defaults['item_spacing'];
	}

	$output       = '';
	$current_page = 0;

	// Sanitize, mostly to keep spaces out.
	$parsed_args['exclude'] = preg_replace( '/[^0-9,]/', '', $parsed_args['exclude'] );

	// Allow plugins to filter an array of excluded pages (but don't put a nullstring into the array).
	$exclude_array = ( $parsed_args['exclude'] ) ? explode( ',', $parsed_args['exclude'] ) : array();

	/**
	 * Filters the array of pages to exclude from the pages list.
	 *
	 * @since 2.1.0
	 *
	 * @param string[] $exclude_array An array of page IDs to exclude.
	 */
	$parsed_args['exclude'] = implode( ',', apply_filters( 'wp_list_pages_excludes', $exclude_array ) );

	$parsed_args['hierarchical'] = 0;

	// Query pages.
	$pages = get_pages( $parsed_args );

	if ( ! empty( $pages ) ) {
		if ( $parsed_args['title_li'] ) {
			$output .= '<li class="pagenav">' . $parsed_args['title_li'] . '<ul>';
		}
		global $wp_query;
		if ( is_page() || is_attachment() || $wp_query->is_posts_page ) {
			$current_page = get_queried_object_id();
		} elseif ( is_singular() ) {
			$queried_object = get_queried_object();
			if ( is_post_type_hierarchical( $queried_object->post_type ) ) {
				$current_page = $queried_object->ID;
			}
		}

		$output .= walk_page_tree( $pages, $parsed_args['depth'], $current_page, $parsed_args );

		if ( $parsed_args['title_li'] ) {
			$output .= '</ul></li>';
		}
	}

	/**
	 * Filters the HTML output of the pages to list.
	 *
	 * @since 1.5.1
	 * @since 4.4.0 `$pages` added as arguments.
	 *
	 * @see wp_list_pages()
	 *
	 * @param string    $output      HTML output of the pages list.
	 * @param array     $parsed_args An array of page-listing arguments. See wp_list_pages()
	 *                               for information on accepted arguments.
	 * @param WP_Post[] $pages       Array of the page objects.
	 */
	$html = apply_filters( 'wp_list_pages', $output, $parsed_args, $pages );

	if ( $parsed_args['echo'] ) {
		echo $html;
	} else {
		return $html;
	}
}

/**
 * Displays or retrieves a list of pages with an optional home link.
 *
 * The arguments are listed below and part of the arguments are for wp_list_pages() function.
 * Check that function for more info on those arguments.
 *
 * @since 2.7.0
 * @since 4.4.0 Added `menu_id`, `container`, `before`, `after`, and `walker` arguments.
 * @since 4.7.0 Added the `item_spacing` argument.
 *
 * @param array|string $args {
 *     Optional. Array or string of arguments to generate a page menu. See wp_list_pages() for additional arguments.
 *
 *     @type string          $sort_column  How to sort the list of pages. Accepts post column names.
 *                                         Default 'menu_order, post_title'.
 *     @type string          $menu_id      ID for the div containing the page list. Default is empty string.
 *     @type string          $menu_class   Class to use for the element containing the page list. Default 'menu'.
 *     @type string          $container    Element to use for the element containing the page list. Default 'div'.
 *     @type bool            $echo         Whether to echo the list or return it. Accepts true (echo) or false (return).
 *                                         Default true.
 *     @type int|bool|string $show_home    Whether to display the link to the home page. Can just enter the text
 *                                         you'd like shown for the home link. 1|true defaults to 'Home'.
 *     @type string          $link_before  The HTML or text to prepend to $show_home text. Default empty.
 *     @type string          $link_after   The HTML or text to append to $show_home text. Default empty.
 *     @type string          $before       The HTML or text to prepend to the menu. Default is '<ul>'.
 *     @type string          $after        The HTML or text to append to the menu. Default is '</ul>'.
 *     @type string          $item_spacing Whether to preserve whitespace within the menu's HTML. Accepts 'preserve'
 *                                         or 'discard'. Default 'discard'.
 *     @type Walker          $walker       Walker instance to use for listing pages. Default empty which results in a
 *                                         Walker_Page instance being used.
 * }
 * @return void|string Void if 'echo' argument is true, HTML menu if 'echo' is false.
 */
function wp_page_menu( $args = array() ) {
	$defaults = array(
		'sort_column'  => 'menu_order, post_title',
		'menu_id'      => '',
		'menu_class'   => 'menu',
		'container'    => 'div',
		'echo'         => true,
		'link_before'  => '',
		'link_after'   => '',
		'before'       => '<ul>',
		'after'        => '</ul>',
		'item_spacing' => 'discard',
		'walker'       => '',
	);
	$args     = wp_parse_args( $args, $defaults );

	if ( ! in_array( $args['item_spacing'], array( 'preserve', 'discard' ), true ) ) {
		// Invalid value, fall back to default.
		$args['item_spacing'] = $defaults['item_spacing'];
	}

	if ( 'preserve' === $args['item_spacing'] ) {
		$t = "\t";
		$n = "\n";
	} else {
		$t = '';
		$n = '';
	}

	/**
	 * Filters the arguments used to generate a page-based menu.
	 *
	 * @since 2.7.0
	 *
	 * @see wp_page_menu()
	 *
	 * @param array $args An array of page menu arguments. See wp_page_menu()
	 *                    for information on accepted arguments.
	 */
	$args = apply_filters( 'wp_page_menu_args', $args );

	$menu = '';

	$list_args = $args;

	// Show Home in the menu.
	if ( ! empty( $args['show_home'] ) ) {
		if ( true === $args['show_home'] || '1' === $args['show_home'] || 1 === $args['show_home'] ) {
			$text = __( 'Home' );
		} else {
			$text = $args['show_home'];
		}
		$class = '';
		if ( is_front_page() && ! is_paged() ) {
			$class = 'class="current_page_item"';
		}
		$menu .= '<li ' . $class . '><a href="' . esc_url( home_url( '/' ) ) . '">' . $args['link_before'] . $text . $args['link_after'] . '</a></li>';
		// If the front page is a page, add it to the exclude list.
		if ( 'page' === get_option( 'show_on_front' ) ) {
			if ( ! empty( $list_args['exclude'] ) ) {
				$list_args['exclude'] .= ',';
			} else {
				$list_args['exclude'] = '';
			}
			$list_args['exclude'] .= get_option( 'page_on_front' );
		}
	}

	$list_args['echo']     = false;
	$list_args['title_li'] = '';
	$menu                 .= wp_list_pages( $list_args );

	$container = sanitize_text_field( $args['container'] );

	// Fallback in case `wp_nav_menu()` was called without a container.
	if ( empty( $container ) ) {
		$container = 'div';
	}

	if ( $menu ) {

		// wp_nav_menu() doesn't set before and after.
		if ( isset( $args['fallback_cb'] ) &&
			'wp_page_menu' === $args['fallback_cb'] &&
			'ul' !== $container ) {
			$args['before'] = "<ul>{$n}";
			$args['after']  = '</ul>';
		}

		$menu = $args['before'] . $menu . $args['after'];
	}

	$attrs = '';
	if ( ! empty( $args['menu_id'] ) ) {
		$attrs .= ' id="' . esc_attr( $args['menu_id'] ) . '"';
	}

	if ( ! empty( $args['menu_class'] ) ) {
		$attrs .= ' class="' . esc_attr( $args['menu_class'] ) . '"';
	}

	$menu = "<{$container}{$attrs}>" . $menu . "</{$container}>{$n}";

	/**
	 * Filters the HTML output of a page-based menu.
	 *
	 * @since 2.7.0
	 *
	 * @see wp_page_menu()
	 *
	 * @param string $menu The HTML output.
	 * @param array  $args An array of arguments. See wp_page_menu()
	 *                     for information on accepted arguments.
	 */
	$menu = apply_filters( 'wp_page_menu', $menu, $args );

	if ( $args['echo'] ) {
		echo $menu;
	} else {
		return $menu;
	}
}

//
// Page helpers.
//

/**
 * Retrieves HTML list content for page list.
 *
 * @uses Walker_Page to create HTML list content.
 * @since 2.1.0
 *
 * @param array $pages
 * @param int   $depth
 * @param int   $current_page
 * @param array $args
 * @return string
 */
function walk_page_tree( $pages, $depth, $current_page, $args ) {
	if ( empty( $args['walker'] ) ) {
		$walker = new Walker_Page();
	} else {
		/**
		 * @var Walker $walker
		 */
		$walker = $args['walker'];
	}

	foreach ( (array) $pages as $page ) {
		if ( $page->post_parent ) {
			$args['pages_with_children'][ $page->post_parent ] = true;
		}
	}

	return $walker->walk( $pages, $depth, $args, $current_page );
}

/**
 * Retrieves HTML dropdown (select) content for page list.
 *
 * @since 2.1.0
 * @since 5.3.0 Formalized the existing `...$args` parameter by adding it
 *              to the function signature.
 *
 * @uses Walker_PageDropdown to create HTML dropdown content.
 * @see Walker_PageDropdown::walk() for parameters and return description.
 *
 * @param mixed ...$args Elements array, maximum hierarchical depth and optional additional arguments.
 * @return string
 */
function walk_page_dropdown_tree( ...$args ) {
	if ( empty( $args[2]['walker'] ) ) { // The user's options are the third parameter.
		$walker = new Walker_PageDropdown();
	} else {
		/**
		 * @var Walker $walker
		 */
		$walker = $args[2]['walker'];
	}

	return $walker->walk( ...$args );
}

//
// Attachments.
//

/**
 * Displays an attachment page link using an image or icon.
 *
 * @since 2.0.0
 *
 * @param int|WP_Post $post       Optional. Post ID or post object.
 * @param bool        $fullsize   Optional. Whether to use full size. Default false.
 * @param bool        $deprecated Deprecated. Not used.
 * @param bool        $permalink Optional. Whether to include permalink. Default false.
 */
function the_attachment_link( $post = 0, $fullsize = false, $deprecated = false, $permalink = false ) {
	if ( ! empty( $deprecated ) ) {
		_deprecated_argument( __FUNCTION__, '2.5.0' );
	}

	if ( $fullsize ) {
		echo wp_get_attachment_link( $post, 'full', $permalink );
	} else {
		echo wp_get_attachment_link( $post, 'thumbnail', $permalink );
	}
}

/**
 * Retrieves an attachment page link using an image or icon, if possible.
 *
 * @since 2.5.0
 * @since 4.4.0 The `$post` parameter can now accept either a post ID or `WP_Post` object.
 *
 * @param int|WP_Post  $post      Optional. Post ID or post object.
 * @param string|int[] $size      Optional. Image size. Accepts any registered image size name, or an array
 *                                of width and height values in pixels (in that order). Default 'thumbnail'.
 * @param bool         $permalink Optional. Whether to add permalink to image. Default false.
 * @param bool         $icon      Optional. Whether the attachment is an icon. Default false.
 * @param string|false $text      Optional. Link text to use. Activated by passing a string, false otherwise.
 *                                Default false.
 * @param array|string $attr      Optional. Array or string of attributes. Default empty.
 * @return string HTML content.
 */
function wp_get_attachment_link( $post = 0, $size = 'thumbnail', $permalink = false, $icon = false, $text = false, $attr = '' ) {
	$_post = get_post( $post );

	if ( empty( $_post ) || ( 'attachment' !== $_post->post_type ) || ! wp_get_attachment_url( $_post->ID ) ) {
		return __( 'Missing Attachment' );
	}

	$url = wp_get_attachment_url( $_post->ID );

	if ( $permalink ) {
		$url = get_attachment_link( $_post->ID );
	}

	if ( $text ) {
		$link_text = $text;
	} elseif ( $size && 'none' !== $size ) {
		$link_text = wp_get_attachment_image( $_post->ID, $size, $icon, $attr );
	} else {
		$link_text = '';
	}

	if ( '' === trim( $link_text ) ) {
		$link_text = $_post->post_title;
	}

	if ( '' === trim( $link_text ) ) {
		$link_text = esc_html( pathinfo( get_attached_file( $_post->ID ), PATHINFO_FILENAME ) );
	}

	/**
	 * Filters the list of attachment link attributes.
	 *
	 * @since 6.2.0
	 *
	 * @param array $attributes An array of attributes for the link markup,
	 *                          keyed on the attribute name.
	 * @param int   $id         Post ID.
	 */
	$attributes = apply_filters( 'wp_get_attachment_link_attributes', array( 'href' => $url ), $_post->ID );

	$link_attributes = '';
	foreach ( $attributes as $name => $value ) {
		$value            = 'href' === $name ? esc_url( $value ) : esc_attr( $value );
		$link_attributes .= ' ' . esc_attr( $name ) . "='" . $value . "'";
	}

	$link_html = "<a$link_attributes>$link_text</a>";

	/**
	 * Filters a retrieved attachment page link.
	 *
	 * @since 2.7.0
	 * @since 5.1.0 Added the `$attr` parameter.
	 *
	 * @param string       $link_html The page link HTML output.
	 * @param int|WP_Post  $post      Post ID or object. Can be 0 for the current global post.
	 * @param string|int[] $size      Requested image size. Can be any registered image size name, or
	 *                                an array of width and height values in pixels (in that order).
	 * @param bool         $permalink Whether to add permalink to image. Default false.
	 * @param bool         $icon      Whether to include an icon.
	 * @param string|false $text      If string, will be link text.
	 * @param array|string $attr      Array or string of attributes.
	 */
	return apply_filters( 'wp_get_attachment_link', $link_html, $post, $size, $permalink, $icon, $text, $attr );
}

/**
 * Wraps attachment in paragraph tag before content.
 *
 * @since 2.0.0
 *
 * @param string $content
 * @return string
 */
function prepend_attachment( $content ) {
	$post = get_post();

	if ( empty( $post->post_type ) || 'attachment' !== $post->post_type ) {
		return $content;
	}

	if ( wp_attachment_is( 'video', $post ) ) {
		$meta = wp_get_attachment_metadata( get_the_ID() );
		$atts = array( 'src' => wp_get_attachment_url() );
		if ( ! empty( $meta['width'] ) && ! empty( $meta['height'] ) ) {
			$atts['width']  = (int) $meta['width'];
			$atts['height'] = (int) $meta['height'];
		}
		if ( has_post_thumbnail() ) {
			$atts['poster'] = wp_get_attachment_url( get_post_thumbnail_id() );
		}
		$p = wp_video_shortcode( $atts );
	} elseif ( wp_attachment_is( 'audio', $post ) ) {
		$p = wp_audio_shortcode( array( 'src' => wp_get_attachment_url() ) );
	} else {
		$p = '<p class="attachment">';
		// Show the medium sized image representation of the attachment if available, and link to the raw file.
		$p .= wp_get_attachment_link( 0, 'medium', false );
		$p .= '</p>';
	}

	/**
	 * Filters the attachment markup to be prepended to the post content.
	 *
	 * @since 2.0.0
	 *
	 * @see prepend_attachment()
	 *
	 * @param string $p The attachment HTML output.
	 */
	$p = apply_filters( 'prepend_attachment', $p );

	return "$p\n$content";
}

//
// Misc.
//

/**
 * Retrieves protected post password form content.
 *
 * @since 1.0.0
 *
 * @param int|WP_Post $post Optional. Post ID or WP_Post object. Default is global $post.
 * @return string HTML content for password form for password protected post.
 */
function get_the_password_form( $post = 0 ) {
	$post   = get_post( $post );
	$label  = 'pwbox-' . ( empty( $post->ID ) ? rand() : $post->ID );
	$output = '<form action="' . esc_url( site_url( 'wp-login.php?action=postpass', 'login_post' ) ) . '" class="post-password-form" method="post">
	<p>' . __( 'This content is password protected. To view it please enter your password below:' ) . '</p>
	<p><label for="' . $label . '">' . __( 'Password:' ) . ' <input name="post_password" id="' . $label . '" type="password" spellcheck="false" size="20" /></label> <input type="submit" name="Submit" value="' . esc_attr_x( 'Enter', 'post password form' ) . '" /></p></form>
	';

	/**
	 * Filters the HTML output for the protected post password form.
	 *
	 * If modifying the password field, please note that the core database schema
	 * limits the password field to 20 characters regardless of the value of the
	 * size attribute in the form input.
	 *
	 * @since 2.7.0
	 * @since 5.8.0 Added the `$post` parameter.
	 *
	 * @param string  $output The password form HTML output.
	 * @param WP_Post $post   Post object.
	 */
	return apply_filters( 'the_password_form', $output, $post );
}

/**
 * Determines whether the current post uses a page template.
 *
 * This template tag allows you to determine if you are in a page template.
 * You can optionally provide a template filename or array of template filenames
 * and then the check will be specific to that template.
 *
 * For more information on this and similar theme functions, check out
 * the {@link https://developer.wordpress.org/themes/basics/conditional-tags/
 * Conditional Tags} article in the Theme Developer Handbook.
 *
 * @since 2.5.0
 * @since 4.2.0 The `$template` parameter was changed to also accept an array of page templates.
 * @since 4.7.0 Now works with any post type, not just pages.
 *
 * @param string|string[] $template The specific template filename or array of templates to match.
 * @return bool True on success, false on failure.
 */
function is_page_template( $template = '' ) {
	if ( ! is_singular() ) {
		return false;
	}

	$page_template = get_page_template_slug( get_queried_object_id() );

	if ( empty( $template ) ) {
		return (bool) $page_template;
	}

	if ( $template == $page_template ) {
		return true;
	}

	if ( is_array( $template ) ) {
		if ( ( in_array( 'default', $template, true ) && ! $page_template )
			|| in_array( $page_template, $template, true )
		) {
			return true;
		}
	}

	return ( 'default' === $template && ! $page_template );
}

/**
 * Gets the specific template filename for a given post.
 *
 * @since 3.4.0
 * @since 4.7.0 Now works with any post type, not just pages.
 *
 * @param int|WP_Post $post Optional. Post ID or WP_Post object. Default is global $post.
 * @return string|false Page template filename. Returns an empty string when the default page template
 *                      is in use. Returns false if the post does not exist.
 */
function get_page_template_slug( $post = null ) {
	$post = get_post( $post );

	if ( ! $post ) {
		return false;
	}

	$template = get_post_meta( $post->ID, '_wp_page_template', true );

	if ( ! $template || 'default' === $template ) {
		return '';
	}

	return $template;
}

/**
 * Retrieves formatted date timestamp of a revision (linked to that revisions's page).
 *
 * @since 2.6.0
 *
 * @param int|object $revision Revision ID or revision object.
 * @param bool       $link     Optional. Whether to link to revision's page. Default true.
 * @return string|false i18n formatted datetimestamp or localized 'Current Revision'.
 */
function wp_post_revision_title( $revision, $link = true ) {
	$revision = get_post( $revision );

	if ( ! $revision ) {
		return $revision;
	}

	if ( ! in_array( $revision->post_type, array( 'post', 'page', 'revision' ), true ) ) {
		return false;
	}

	/* translators: Revision date format, see https://www.php.net/manual/datetime.format.php */
	$datef = _x( 'F j, Y @ H:i:s', 'revision date format' );
	/* translators: %s: Revision date. */
	$autosavef = __( '%s [Autosave]' );
	/* translators: %s: Revision date. */
	$currentf = __( '%s [Current Revision]' );

	$date      = date_i18n( $datef, strtotime( $revision->post_modified ) );
	$edit_link = get_edit_post_link( $revision->ID );
	if ( $link && current_user_can( 'edit_post', $revision->ID ) && $edit_link ) {
		$date = "<a href='$edit_link'>$date</a>";
	}

	if ( ! wp_is_post_revision( $revision ) ) {
		$date = sprintf( $currentf, $date );
	} elseif ( wp_is_post_autosave( $revision ) ) {
		$date = sprintf( $autosavef, $date );
	}

	return $date;
}

/**
 * Retrieves formatted date timestamp of a revision (linked to that revisions's page).
 *
 * @since 3.6.0
 *
 * @param int|object $revision Revision ID or revision object.
 * @param bool       $link     Optional. Whether to link to revision's page. Default true.
 * @return string|false gravatar, user, i18n formatted datetimestamp or localized 'Current Revision'.
 */
function wp_post_revision_title_expanded( $revision, $link = true ) {
	$revision = get_post( $revision );

	if ( ! $revision ) {
		return $revision;
	}

	if ( ! in_array( $revision->post_type, array( 'post', 'page', 'revision' ), true ) ) {
		return false;
	}

	$author = get_the_author_meta( 'display_name', $revision->post_author );
	/* translators: Revision date format, see https://www.php.net/manual/datetime.format.php */
	$datef = _x( 'F j, Y @ H:i:s', 'revision date format' );

	$gravatar = get_avatar( $revision->post_author, 24 );

	$date      = date_i18n( $datef, strtotime( $revision->post_modified ) );
	$edit_link = get_edit_post_link( $revision->ID );
	if ( $link && current_user_can( 'edit_post', $revision->ID ) && $edit_link ) {
		$date = "<a href='$edit_link'>$date</a>";
	}

	$revision_date_author = sprintf(
		/* translators: Post revision title. 1: Author avatar, 2: Author name, 3: Time ago, 4: Date. */
		__( '%1$s %2$s, %3$s ago (%4$s)' ),
		$gravatar,
		$author,
		human_time_diff( strtotime( $revision->post_modified_gmt ) ),
		$date
	);

	/* translators: %s: Revision date with author avatar. */
	$autosavef = __( '%s [Autosave]' );
	/* translators: %s: Revision date with author avatar. */
	$currentf = __( '%s [Current Revision]' );

	if ( ! wp_is_post_revision( $revision ) ) {
		$revision_date_author = sprintf( $currentf, $revision_date_author );
	} elseif ( wp_is_post_autosave( $revision ) ) {
		$revision_date_author = sprintf( $autosavef, $revision_date_author );
	}

	/**
	 * Filters the formatted author and date for a revision.
	 *
	 * @since 4.4.0
	 *
	 * @param string  $revision_date_author The formatted string.
	 * @param WP_Post $revision             The revision object.
	 * @param bool    $link                 Whether to link to the revisions page, as passed into
	 *                                      wp_post_revision_title_expanded().
	 */
	return apply_filters( 'wp_post_revision_title_expanded', $revision_date_author, $revision, $link );
}

/**
 * Displays a list of a post's revisions.
 *
 * Can output either a UL with edit links or a TABLE with diff interface, and
 * restore action links.
 *
 * @since 2.6.0
 *
 * @param int|WP_Post $post Optional. Post ID or WP_Post object. Default is global $post.
 * @param string      $type 'all' (default), 'revision' or 'autosave'
 */
function wp_list_post_revisions( $post = 0, $type = 'all' ) {
	$post = get_post( $post );

	if ( ! $post ) {
		return;
	}

	// $args array with (parent, format, right, left, type) deprecated since 3.6.
	if ( is_array( $type ) ) {
		$type = ! empty( $type['type'] ) ? $type['type'] : $type;
		_deprecated_argument( __FUNCTION__, '3.6.0' );
	}

	$revisions = wp_get_post_revisions( $post->ID );

	if ( ! $revisions ) {
		return;
	}

	$rows = '';
	foreach ( $revisions as $revision ) {
		if ( ! current_user_can( 'read_post', $revision->ID ) ) {
			continue;
		}

		$is_autosave = wp_is_post_autosave( $revision );
		if ( ( 'revision' === $type && $is_autosave ) || ( 'autosave' === $type && ! $is_autosave ) ) {
			continue;
		}

		$rows .= "\t<li>" . wp_post_revision_title_expanded( $revision ) . "</li>\n";
	}

	echo "<div class='hide-if-js'><p>" . __( 'JavaScript must be enabled to use this feature.' ) . "</p></div>\n";

	echo "<ul class='post-revisions hide-if-no-js'>\n";
	echo $rows;
	echo '</ul>';
}

/**
 * Retrieves the parent post object for the given post.
 *
 * @since 5.7.0
 *
 * @param int|WP_Post|null $post Optional. Post ID or WP_Post object. Default is global $post.
 * @return WP_Post|null Parent post object, or null if there isn't one.
 */
function get_post_parent( $post = null ) {
	$wp_post = get_post( $post );
	return ! empty( $wp_post->post_parent ) ? get_post( $wp_post->post_parent ) : null;
}

/**
 * Returns whether the given post has a parent post.
 *
 * @since 5.7.0
 *
 * @param int|WP_Post|null $post Optional. Post ID or WP_Post object. Default is global $post.
 * @return bool Whether the post has a parent post.
 */
function has_post_parent( $post = null ) {
	return (bool) get_post_parent( $post );
}