Lets you add custom fields to a WordPress post or page via shortcodes. This allows you to use the WordPress mobile app to update custom fields. Currently working on this for a product release and wanted to share.

gistfile1.txt

<?php
/*
Plugin Name: Custom Field Shortcodes
Version: 0.0.1
Plugin URI: https://gist.github.com/joshcanhelp/87e1bb70f97475bccc9eb123e3fe2f1c
Description: Lets you add custom fields to a WordPress post or page via shortcodes.
Author: Josh Can Help
Author URI: http://www.joshcanhelp.com/
License: GPL v3
*/

class CustomFieldShortcodes {

	public $shortcode = '';
	public $post_types = array();

	/**
	 * WpdShortcodeFields constructor.
	 *
	 * @param string $shortcode - Shortcode used, like [sc_fields]
	 * @param array $post_types- What post types should it operate on?
	 */

	public function __construct( $shortcode, $post_types ) {

		// Set the class shortcode to look for

		$this->shortcode = $shortcode;

		// Add the shortcode with the constructor param

		add_shortcode( $shortcode, array( $this, 'shortcode' ) );

		// Set the post types to use

		$this->post_types = $post_types;

		// Add the save_post processing

		add_action( 'save_post', array( $this, 'save_post' ), 100, 2 );
	}


	/**
	 * Declaring the shortcode so it's not inadvertently shown
	 *
	 * @return string
	 */

	public function shortcode() {
		return '';
	}

	/**
	 * Process shortcodes to save WPD fields from the mobile app
	 * Formatted like: [shortcode url=http://www.joshcanhelp.com featured=yes]
	 *
	 * @param int     $post_id
	 * @param WP_Post $post
	 */

	public function save_post( $post_id, $post ) {


		// Not needed for revisions

		if ( wp_is_post_revision( $post_id ) ) {
			return;
		}

		// Not a post type we're working with

		if ( ! in_array( $post->post_type, $this->post_types ) ) {
			return;
		}

		$matches = array();
		preg_match_all( '/' . get_shortcode_regex() . '/s', $post->post_content, $matches );

		// No fields to process, exit ...

		if ( empty( $matches[2] ) || ! in_array( $this->shortcode, $matches[2] ) ) {
			return;
		}

		// Look for the first shortcode

		$sc_index = NULL;

		$shortcode_start = '[' . $this->shortcode . ' ';
		foreach ( $matches[0] as $index => $poss_match ) {

			if ( $shortcode_start === substr( $poss_match, 0, strlen( $shortcode_start ) ) ) {
				$sc_index = $index;
			}
		}

		// Got nothing, exit ...

		if ( is_null( $sc_index ) ) {
			return;
		}

		$new_content = $post->post_content;

		/*
		 * Looking for attributes and storing as needed
		 */

		if ( ! empty( $matches[3][ $sc_index ] ) ) {
			$sc_attrs = explode( ' ', $matches[3][ $sc_index ] );

			foreach ( $sc_attrs as $sc_attr ) {
				
				if ( substr( $sc_attr, 0, strlen( 'url=' ) ) === 'url=' ) {

					// Takes a "url" attribute and stores it as a custom field
					
					$outbound_link = substr( $sc_attr, strlen( 'url=' ) );
					$outbound_link = str_replace( '"', '', $outbound_link );
					$outbound_link = esc_url( $outbound_link );

					update_post_meta( $post_id, 'link', $outbound_link );

				} else if ( substr( $sc_attr, 0, strlen( 'featured=' ) ) === 'featured=' ) {
						
					// Takes a "featured" attribute and stores it as a true/false
					
					$is_featured = substr( $sc_attr, strlen( 'featured=' ) );
					$is_featured = str_replace( '"', '', $is_featured );

					if ( 1 == $is_featured || 'yes' === $is_featured ) {
						update_post_meta( $post_id, 'featured', 'yes' );
					} elseif ( 0 == $is_featured || 'no' === $is_featured ) {
						delete_post_meta( $post_id, 'featured' );
					}
				}
				
				/*
				 * Add new attribute checks here 
				 */
			}
		}

		// Shortcode content

		if ( ! empty( $matches[5][ $sc_index ] ) ) {
			$blurb = $matches[5][ $sc_index ];
			update_post_meta( $post_id, 'blurb', wp_kses( $blurb, wp_kses_allowed_html() ) );
		}

		// Remove all the shortcodes found

		foreach ( $matches[0] as $index => $match ) {
			if ( $this->shortcode === $matches[2][ $index ] ) {
				$new_content = str_replace( $match, '', $new_content );
			}
		}

		// Avoid infinite loops with this hook

		remove_action( 'save_post', array( $this, 'save_post' ), 100 );

		// Skip default WP-Drudge processing

		remove_action( 'save_post', 'wpd_save_metas', 10 );

		// Update cleaned content

		wp_update_post(
			array(
				'ID' => $post_id,
				'post_content' => trim( $new_content ),
			)
		);

		add_action( 'save_post', array( $this, 'save_post' ), 100, 2 );
		add_action( 'save_post', 'wpd_save_metas', 10 );

	}
}

new CustomFieldShortcodes( 'wpdrudge', array( 'post' ) );