<?php
    //Enqueue CSS and Javascript
    function enqueue_scripts() {
        //LoadCSS - Use the 'loadCSS_parser()' function to implement loadCSS to CSS scripts below
        //LoadCSS v2.1.0 - See https://github.com/filamentgroup/loadCSS/
        wp_enqueue_script( 'loadCSS', get_template_directory_uri() . '/libs/loadCSS/cssrelpreload.js', false, null, false );
        
        //Google Fonts
        wp_enqueue_style( 'google-fonts', 'https://fonts.googleapis.com/css?family=Poppins:400,700', false );   //Disable if you're not using this
        
        //Critical CSS Inline styling - To prevent a flashof unstyled HTML when using LoadCSS, disable if you're not using this
        //Use https://jonassebastianohlsson.com/criticalpathcssgenerator/ or the 'grunt-criticalcss' wrapper with Grunt
        wp_register_style( 'site-critical', false );
        wp_enqueue_style( 'site-critical' );
        wp_add_inline_style( 'site-critical', file_get_contents(get_stylesheet_directory() . '/critical.min.css'), array( 'google-fonts' ) );   //Depends on 'google-fonts'

        //CSS - Remove any references to this file from your theme. i.e. in header.php, as it will be loaded here instead
        //E.g. bloginfo('stylesheet_url');
        wp_enqueue_style( 'site', get_template_directory_uri() . 'style.css', array( 'site-critical' ) );   //Your website's CSS, depends on 'site-critical'
    }
    add_action( 'wp_enqueue_scripts', 'enqueue_scripts', 15 );   //Prirority: 1 (High)



    //Convert CSS scripts for use with loadCSS library - https://github.com/filamentgroup/loadCSS
    if (!is_admin()) {
        function loadCSS_parser( $tag ){
            //If not a stylesheet, do not edit
            if ( FALSE === strpos( $tag, "rel='stylesheet'" ) ) return $tag;

            //Of if tag includes any of these file names do not load via LoadCSS:
            //if ( strpos( $tag, "specificfilename.min.css" ) ) return $tag;


            //** Excluded files
                    //Some file which cannot be loaded asynchronously 
                    if ( strpos( $tag, "filename.min.css" ) ) return $tag;
            
            
            //Set a variable which will hold the default script for a '<noscript>' tag
            $noscript = '<noscript>' . $tag . '</noscript>';
            
            //Change 'rel' value from 'stylesheet' to 'preload'
            $tag = preg_replace("/='stylesheet'/", '="preload"', $tag);
            
            //Add 'as' and 'onload' attributes
            $tag = preg_replace("/type='text\/css'/", 'as="style" onload="this.onload=null;this.rel=\'stylesheet\'"', $tag);
            
            //Remove media attribute
            $tag = preg_replace("/media='.*'/", '', $tag);
            
            
            return $tag . $noscript;    //Return
        }
        add_filter( 'style_loader_tag', 'loadCSS_parser' );
    }



    //Pass Defer or Async to JavaScript files
    if (!is_admin()) {
        function async_defer_js ( $url ) {
            //If file is not a .js file, do not alter
            if ( FALSE === strpos( $url, '.js' ) ) return $url;
            
            
            //** Excluded files
                //jQuery
                if ( strpos( $url, 'jquery.js' ) ) return $url;         //Replace this with your jQuery file
            
            
            //** If Async - Files for Async
                //loadCSS
                if ( strpos( $url, 'cssrelpreload.js' ) ) return "$url' async='true";
            
            
            //** If Defer
                //By default add defer tag to all JS files unless specified as async/excluded above
                return "$url' defer='true";
        }
        add_filter( 'clean_url', 'async_defer_js', 11, 1 );
    }
?>