/**
 * Add a "deck" (aka subhead) meta box to post page(s) and position it
 * under the title.
 *
 * @todo Move to class.
 * @see http://codex.wordpress.org/Function_Reference/add_meta_box
 * @see http://wordpress.org/extend/ideas/topic/add-meta-box-to-multiple-post-types
 * @see https://github.com/Horttcore/WordPress-Subtitle
 * @see http://codex.wordpress.org/Function_Reference/wp_nonce_field
 */

# Adds a box to the main column on the Post and Page edit screens:
function foo_deck($post_type) {

    # Allowed post types to show meta box:
    $post_types = array('post', 'page');

    if (in_array($post_type, $post_types)) {

        # Add a meta box to the administrative interface:
        add_meta_box(
            'foo-deck-meta-box', // HTML 'id' attribute of the edit screen section.
            'Deck',              // Title of the edit screen section, visible to user.
            'foo_deck_meta_box', // Function that prints out the HTML for the edit screen section.
            $post_type,          // The type of Write screen on which to show the edit screen section.
            'advanced',          // The part of the page where the edit screen section should be shown.
            'high'               // The priority within the context where the boxes should show.
        );

    }

}

# Callback that prints the box content:
function foo_deck_meta_box($post) {

    # Use `get_post_meta()` to retrieve an existing value from the database and use the value for the form:
    $deck = get_post_meta($post->ID, '_deck', true);

    # Form field to display:
    ?>

        <label class="screen-reader-text" for="foo_deck">Deck</label>
        <input id="foo_deck" type="text" autocomplete="off" value="<?=esc_attr($deck)?>" name="foo_deck" placeholder="Deck">

    <?php

    # Display the nonce hidden form field:
    wp_nonce_field(
        plugin_basename(__FILE__), // Action name.
        'foo_deck_meta_box'        // Nonce name.
    );

}

/**
 * @see http://wordpress.stackexchange.com/a/16267/32387
 */

# Save our custom data when the post is saved:
function foo_deck_save_postdata($post_id) {

    # Is the current user is authorised to do this action?
    if ((($_POST['post_type'] === 'page') && current_user_can('edit_page', $post_id) || current_user_can('edit_post', $post_id))) { // If it's a page, OR, if it's a post, can the user edit it?

        # Stop WP from clearing custom fields on autosave:
        if ((( ! defined('DOING_AUTOSAVE')) || ( ! DOING_AUTOSAVE)) && (( ! defined('DOING_AJAX')) || ( ! DOING_AJAX))) {

            # Nonce verification:
            if (wp_verify_nonce($_POST['foo_deck_meta_box'], plugin_basename(__FILE__))) {

                # Get the posted deck:
                $deck = sanitize_text_field($_POST['foo_deck']);

                # Add, update or delete?
                if ($deck !== '') {

                    # Deck exists, so add OR update it:
                    add_post_meta($post_id, '_deck', $deck, true) OR update_post_meta($post_id, '_deck', $deck);

                } else {

                    # Deck empty or removed:
                    delete_post_meta($post_id, '_deck');

                }

            }

        }

    }

}

# Get the deck:
function foo_get_deck($post_id = FALSE) {

    $post_id = ($post_id) ? $post_id : get_the_ID();

    return apply_filters('foo_the_deck', get_post_meta($post_id, '_deck', TRUE));

}

# Display deck (this will feel better when OOP):
function foo_the_deck() {

    echo foo_get_deck(get_the_ID());

}

# Conditional checker:
function foo_has_subtitle($post_id = FALSE) {

    if (foo_get_deck($post_id)) return TRUE;

}

# Define the custom box:
add_action('add_meta_boxes', 'foo_deck');
# Do something with the data entered:
add_action('save_post', 'foo_deck_save_postdata');

/**
 * @see http://wordpress.stackexchange.com/questions/36600
 * @see http://wordpress.stackexchange.com/questions/94530/
 */

# Now move advanced meta boxes after the title:
function foo_move_deck() {

    # Get the globals:
    global $post, $wp_meta_boxes;

    # Output the "advanced" meta boxes:
    do_meta_boxes(get_current_screen(), 'advanced', $post);

    # Remove the initial "advanced" meta boxes:
    unset($wp_meta_boxes['post']['advanced']);

}

add_action('edit_form_after_title', 'foo_move_deck');

function foo_deck( $post_type ) {
        if ( in_array( $post_type, array( 'post', 'page' ) ) ) {
            add_meta_box(
                'contact_details_meta',
                'Contact Details',
                'contact_details_meta',
                $post_type,
                'test', // change to something other then normal, advanced or side
                'high'
            );
}

add_action('add_meta_boxes', 'foo_deck');

function foo_move_deck() {
        # Get the globals:
        global $post, $wp_meta_boxes;

        # Output the "advanced" meta boxes:
        do_meta_boxes( get_current_screen(), 'test', $post );

        # Remove the initial "advanced" meta boxes:
        unset($wp_meta_boxes['post']['test']);
    }

add_action('edit_form_after_title', 'foo_move_deck');