Register custom post status and display it in the post status list

custom-post-status.php

<?php

// Register post status
add_action( 'init', function() {

    register_post_status( 'mysite-accepted', array(
        'label'       => _x( 'Accepted', 'post status label', 'mysite' ),
        'label_count' => _n_noop( 'Accepted <span class="count">(%s)</span>', 'Accepted <span class="count">(%s)</span>', 'mysite' ),
    ) );

    register_post_status( 'mysite-rejected', array(
        'label'       => _x( 'Rejected', 'post status label', 'mysite' ),
        'label_count' => _n_noop( 'Rejected <span class="count">(%s)</span>', 'Rejected <span class="count">(%s)</span>', 'mysite' ),
    ) );

} );

// List of registered post status
function mysite_get_post_statuses() {
    return array(
        'mysite-accepted' => __( 'Accepted', 'mysite' ),
        'mysite-rejected' => __( 'Rejected', 'mysite' ),
    );
}

// Default post status
function mysite_get_default_post_status() {
    return 'mysite-accepted';
}

// Append registered post status in the dropdown in post editor page
add_action( 'post_submitbox_misc_actions', function() {

    global $post;

    if ( $post->post_type !== 'custom_post_type' ) {
        return;
    }

    $statuses = mysite_get_post_statuses();
    $post_status = $post->post_status;

    if ( !in_array( $post_status, array_keys( $statuses ) ) ) {
        $post_status = mysite_get_default_post_status();
    }

    $display = null;
    $append  = array();

    // Display the status for the post
    $display = "
        $( '#post-status-display' ).text( '" . esc_js( $statuses[ $post_status ] ) . "' );
        $( 'select[name=\"post_status\"]' ).val( '" . esc_js( $post_status ) . "' );
        $( 'input[name=\"hidden_post_status\"]' ).val( '" . esc_js( $post_status ) . "' );
    ";

    // Append registered status
    foreach ( $statuses as $key => $label ) {
        $selected = null;
        if ( $key === $post_status ) {
            $selected = ' selected';
        }

        $append[] = '<option value=\"' . esc_js( $key ) . '\"' . $selected . '>' . esc_js( $label ) . '</option>';
    }

    echo "
        <script type=\"text/javascript\">
            jQuery( document ).ready( function( $ ) {
                " . $display . "
                $( 'select[name=\"post_status\"]' ).html( '" . implode( '', $append ) . "' );

                $( '#publishing-action input[type=\"submit\"]' ).attr( { 'name': 'save', id: 'save' } ).val( 'Save' );
            } );
        </script>
    ";

} );

// Append registered post status in the dropdown in quick edit
add_action( 'admin_footer-edit.php', function() {

    global $post;

    if ( $post->post_type !== 'custom_post_type' ) {
        return;
    }

    $statuses = mysite_get_post_statuses();
    $append = array();

    // Append registered status
    foreach ( $statuses as $key => $label ) {
        $selected = null;
        if ( $key === $post->post_status ) {
            $selected = ' selected';
        }

        $append[] = '<option value=\"' . esc_js( $key ) . '\"' . $selected . '>' . esc_js( $label ) . '</option>';
    }

    echo "
        <script type=\"text/javascript\">
            jQuery( document ).ready( function( $ ) {
                $( 'select[name=\"_status\"]' ).html( '" . implode( '', $append ) . "' );
            } );
        </script>
    ";

} );