Combine+Minify styles of parent theme and add as inline-style in wordpress

include-in-theme-functions.php

function parent_style_cache() {
    global $wp_styles, $wpdb;

    $updateFlag = 0;
    $returnCss = null;

    /**
     * Check if our table exists else create
     */
    require_once ABSPATH . 'wp-admin/includes/upgrade.php';

    $table_name = $wpdb->prefix . "theme_cache";
    $sql = "CREATE TABLE IF NOT EXISTS `$table_name` (
    id mediumint(9) NOT NULL AUTO_INCREMENT,
    time varchar(25) NOT NULL,
    name varchar(25) NOT NULL,
    text LONGTEXT NOT NULL,
    PRIMARY KEY (id)
    );";
    dbDelta($sql);
    
    
    /**
     *  Insert empty row
     */
    $exists = $wpdb->get_row( "SELECT * FROM `$table_name` WHERE name = 'parent_styles' LIMIT 1;" );
    if(!$exists) {
        $wpdb->query("INSERT INTO `$table_name`(`time`,`text`,`name`) VALUES('','','parent_styles');");
    }


    /**
     * Check for latest styles
     */
    $now = date('YmdHis');
    $result = $wpdb->get_row("SELECT `time`,`text` FROM `$table_name` WHERE `name` = 'parent_styles' LIMIT 1;");
    if ($result) {
        $diff = $now - ($result->time);
        if (($now - $result->time) > 86400) {
            $updateFlag = 1;
        } else {
            $returnCss = stripslashes($result->text);
        }
    } 
    
    #DEBUG#$updateFlag = 1;
    

    /**
     * If updateFlag == 1, update the styles in database
     */
    $wp_styles->all_deps($wp_styles->queue);

    $handles = $wp_styles->to_do;
    $deregHandle = [];
    $css_code = '';

    foreach ($handles as $handle) {
        
        $src = strtok($wp_styles->registered[$handle]->src, '?');
        

        if (strpos($src, 'http') !== false) {
            $site_url = site_url();

            if (strpos($src, $site_url) !== false) {
                $css_file_path = str_replace($site_url, '', $src);
            } else {
                $css_file_path = $src;
            }

            $css_file_path = ltrim($css_file_path, '/');
        } else {
            $css_file_path = ltrim($src, '/');
        }

        if( $handle != 'child-style' && strpos($css_file_path, 'fonts.googleapis.com') === false ){
            print "<!-- HANDLE $handle $src -->";  
            
            $deregHandle[] = $handle;

            if ($updateFlag === 1) {
                $css_code .= file_get_contents($css_file_path);
            }
        }

        if ($css_code != "" && $updateFlag == 1) {
            
            // Remove comments
            $css_code = preg_replace('!/\*[^*]*\*+([^/][^*]*\*+)*/!', '', $css_code);
            // Remove space after colons
            $css_code = str_replace(': ', ':', $css_code);
            // Remove whitespace
            $css_code = str_replace(array("\r\n", "\r", "\n", "\t", '  ', '    ', '    '), '', $css_code);
            // 
            
        }
    }

    /**
     * Lets update the database cache
     */
    if ($updateFlag === 1):
        $returnCss  = $css_code;
        $css_code   = addslashes($css_code);
        if ($wpdb->update($table_name, ['text' => $css_code, 'time' => date('YmdHis')], ['name' => 'parent_styles'])) {
            // echo '<!-- STYLE CACHE UPDATED -->';
        }
    endif;

    foreach ($deregHandle as $handle) {
        print "<!-- DEREGISTERING $handle -->";
        wp_deregister_style($handle);
    }
    // print '<!-- RETURN CSS is ' . $returnCss .' -->'."\r\n<br/>";

    wp_add_inline_style('child-style', $returnCss);
    // echo '/* I CAN INSERT HERE, IF YOU INSTRUCT ME TO */';

    // # -- FUTURE UPGRADE
    // wp_enqueue_style('merged-style', get_stylesheet_directory_uri() . '/css/merged-style.css');

}
add_action('wp_print_styles', 'parent_style_cache');