WP_Customize_Manager::save PHP Method

    public function save()
    {
        if (!is_user_logged_in()) {
            wp_send_json_error('unauthenticated');
        }
        if (!$this->is_preview()) {
            wp_send_json_error('not_preview');
        }
        $action = 'save-customize_' . $this->get_stylesheet();
        if (!check_ajax_referer($action, 'nonce', false)) {
            wp_send_json_error('invalid_nonce');
        }
        $changeset_post_id = $this->changeset_post_id();
        if ($changeset_post_id && in_array(get_post_status($changeset_post_id), array('publish', 'trash'))) {
            wp_send_json_error('changeset_already_published');
        }
        if (empty($changeset_post_id)) {
            if (!current_user_can(get_post_type_object('customize_changeset')->cap->create_posts)) {
                wp_send_json_error('cannot_create_changeset_post');
            }
        } else {
            if (!current_user_can(get_post_type_object('customize_changeset')->cap->edit_post, $changeset_post_id)) {
                wp_send_json_error('cannot_edit_changeset_post');
            }
        }
        if (!empty($_POST['customize_changeset_data'])) {
            $input_changeset_data = json_decode(wp_unslash($_POST['customize_changeset_data']), true);
            if (!is_array($input_changeset_data)) {
                wp_send_json_error('invalid_customize_changeset_data');
            }
        } else {
            $input_changeset_data = array();
        }
        // Validate title.
        $changeset_title = null;
        if (isset($_POST['customize_changeset_title'])) {
            $changeset_title = sanitize_text_field(wp_unslash($_POST['customize_changeset_title']));
        }
        // Validate changeset status param.
        $is_publish = null;
        $changeset_status = null;
        if (isset($_POST['customize_changeset_status'])) {
            $changeset_status = wp_unslash($_POST['customize_changeset_status']);
            if (!get_post_status_object($changeset_status) || !in_array($changeset_status, array('draft', 'pending', 'publish', 'future'), true)) {
                wp_send_json_error('bad_customize_changeset_status', 400);
            }
            $is_publish = 'publish' === $changeset_status || 'future' === $changeset_status;
            if ($is_publish) {
                if (!current_user_can(get_post_type_object('customize_changeset')->cap->publish_posts)) {
                    wp_send_json_error('changeset_publish_unauthorized', 403);
                }
                if (false === has_action('transition_post_status', '_wp_customize_publish_changeset')) {
                    wp_send_json_error('missing_publish_callback', 500);
                }
            }
        }
        /*
         * Validate changeset date param. Date is assumed to be in local time for
         * the WP if in MySQL format (YYYY-MM-DD HH:MM:SS). Otherwise, the date
         * is parsed with strtotime() so that ISO date format may be supplied
         * or a string like "+10 minutes".
         */
        $changeset_date_gmt = null;
        if (isset($_POST['customize_changeset_date'])) {
            $changeset_date = wp_unslash($_POST['customize_changeset_date']);
            if (preg_match('/^\\d\\d\\d\\d-\\d\\d-\\d\\d \\d\\d:\\d\\d:\\d\\d$/', $changeset_date)) {
                $mm = substr($changeset_date, 5, 2);
                $jj = substr($changeset_date, 8, 2);
                $aa = substr($changeset_date, 0, 4);
                $valid_date = wp_checkdate($mm, $jj, $aa, $changeset_date);
                if (!$valid_date) {
                    wp_send_json_error('bad_customize_changeset_date', 400);
                }
                $changeset_date_gmt = get_gmt_from_date($changeset_date);
            } else {
                $timestamp = strtotime($changeset_date);
                if (!$timestamp) {
                    wp_send_json_error('bad_customize_changeset_date', 400);
                }
                $changeset_date_gmt = gmdate('Y-m-d H:i:s', $timestamp);
            }
            $now = gmdate('Y-m-d H:i:59');
            $is_future_dated = mysql2date('U', $changeset_date_gmt, false) > mysql2date('U', $now, false);
            if (!$is_future_dated) {
                wp_send_json_error('not_future_date', 400);
                // Only future dates are allowed.
            }
            if (!$this->is_theme_active() && ('future' === $changeset_status || $is_future_dated)) {
                wp_send_json_error('cannot_schedule_theme_switches', 400);
                // This should be allowed in the future, when theme is a regular setting.
            }
            $will_remain_auto_draft = !$changeset_status && (!$changeset_post_id || 'auto-draft' === get_post_status($changeset_post_id));
            if ($changeset_date && $will_remain_auto_draft) {
                wp_send_json_error('cannot_supply_date_for_auto_draft_changeset', 400);
            }
        }
        $r = $this->save_changeset_post(array('status' => $changeset_status, 'title' => $changeset_title, 'date_gmt' => $changeset_date_gmt, 'data' => $input_changeset_data));
        if (is_wp_error($r)) {
            $response = $r->get_error_data();
        } else {
            $response = $r;
            // Note that if the changeset status was publish, then it will get set to trash if revisions are not supported.
            $response['changeset_status'] = get_post_status($this->changeset_post_id());
            if ($is_publish && 'trash' === $response['changeset_status']) {
                $response['changeset_status'] = 'publish';
            }
            if ('publish' === $response['changeset_status']) {
                $response['next_changeset_uuid'] = wp_generate_uuid4();
            }
        }
        if (isset($response['setting_validities'])) {
            $response['setting_validities'] = array_map(array($this, 'prepare_setting_validity_for_js'), $response['setting_validities']);
        }
        /**
         * Filters response data for a successful customize_save Ajax request.
         *
         * This filter does not apply if there was a nonce or authentication failure.
         *
         * @since 4.2.0
         *
         * @param array                $response Additional information passed back to the 'saved'
         *                                       event on `wp.customize`.
         * @param WP_Customize_Manager $this     WP_Customize_Manager instance.
         */
        $response = apply_filters('customize_save_response', $response, $this);
        if (is_wp_error($r)) {
            wp_send_json_error($response);
        } else {
            wp_send_json_success($response);
        }
    }