Cofem/lib/inliner.php

<?php

function inlineLocalStylesFromHref($inputString) {
    $pattern = '/<link[^>]*?\srel=["\']?stylesheet["\'].*?\shref=["\']?\/(.*?)["\'][^>]*?>/i';

    $outputString = preg_replace_callback($pattern, function($match) {
        $href = $match[1];
        $cssFilePath = $_SERVER['DOCUMENT_ROOT'] . '/' . $href;
        $cssContent = file_get_contents($cssFilePath);
        $cssDir = dirname($cssFilePath);

        $cssContent = preg_replace_callback('/url\(["\']?(\/.*?|.*?)["\']?\)/i', function($urlMatch) use ($cssDir) {
            $url = $urlMatch[1];
            $absolutePath = $cssDir . '/' . $url;
            $relativePath = ltrim(substr($absolutePath, strlen($_SERVER['DOCUMENT_ROOT'])), '/');
            return 'url("' . $relativePath . '")';
        }, $cssContent);

        // Minify the CSS content
        $cssContent = minifyCss($cssContent);

        return "<style>{$cssContent}</style>";
    }, $inputString);

    return $outputString;
}

function inlineScriptFromSrc($inputString) {
    $pattern = '/<script.*?src=["\']\/(.*?)["\'].*?>\s*<\/script>/i';

    $outputString = preg_replace_callback($pattern, function($match) {
        $src = $match[1];
        $jsContent = file_get_contents($_SERVER['DOCUMENT_ROOT'] . '/' . $src);

        // Minify the JavaScript content
        $jsContent = minifyJs($jsContent);
        return "<script>{$jsContent}</script>";
    }, $inputString);

    return $outputString;
}

function minifyCss($css) {
    // Remove comments
    $css = preg_replace('!/\*[^*]*\*+([^/][^*]*\*+)*/!', '', $css);

    // Remove whitespace
    $css = preg_replace('/\s+/', ' ', $css);

    // Remove unnecessary semicolons
    $css = str_replace(';}', '}', $css);

    // Remove spaces around colons
    $css = str_replace(': ', ':', $css);

    // Remove spaces around commas
    $css = str_replace(', ', ',', $css);

    return trim($css);
}

function minifyJs($js) {

    // Remove newlines and tabs
    $js = str_replace("\t", '', $js);

    // Remove spaces around operators
    $js = preg_replace('~\s*([=+\-*/])\s*~', '$1', $js);

    return trim($js);
}