Preg replace in content

hi, I tried to fix a little bug in a custom plugin:

this snippet is for search if pattern exist, then if exist make a replace and add css code in header.

seems to work but load css in all page instead of in the page where pattern exist.

any help?

i used gist_embed_add_styles() instead oh enqueue style because this work also in plugin settings page (backend).

thanks in advance.

<?php
// Deny access if called directly
defined("ABSPATH") || die("Access denied.");

// Apply customization to the content for GitHub Gist embeds.
add_filter("the_content", "gist_embed_apply_customization");
function gist_embed_apply_customization($content)
{
    // Check if the content is a singular post or page and contains HTML or Shortcode block
    if ((is_singular("post") || is_singular("page")) && (has_block("core/html") || has_block("core/shortcode"))) {
        // Patterns to match GitHub Gist URLs in HTML and Shortcode blocks
        $patterns = [
            '/\[https:\/\/gist\.github\.com\/([a-zA-Z0-9]+)\/([a-zA-Z0-9]+)(\?file=([a-zA-Z0-9.]+))?]/i', // Pattern for shortcode without .js
            '/<script src="https:\/\/gist\.github\.com\/([a-zA-Z0-9]+)\/([a-zA-Z0-9]+)\.js(\?file=([a-zA-Z0-9.]+))?"><\/script>/i', // Pattern for HTML with .js
        ];

        // Check if the content has any script tags with matching URLs
        $has_matches = false;
        foreach ($patterns as $pattern) {
            if (preg_match_all($pattern, $content, $matches, PREG_SET_ORDER)) {
                $has_matches = true;
                foreach ($matches as $match) {
                    // Append the button HTML after the script tag
                    $fileparam = !empty($match[3]) ? $match[3] : ''; //suppor ?file=filename
                    $gist_url = "https://gist.github.com/" . $match[1] . "/" . $match[2] . "";
                    $add_scriptag_and_htmlbutton = "
                        <script src='" . $gist_url .".js" . $fileparam . "' data-no-optimize='1'></script>
                        <div class='gist-download-button'>
                        	<a href='" . $gist_url ."/' title='View Gist' class='print-yes' style='display:none'>GoTo: " . $gist_url ."</a>
                            <a href='" . $gist_url ."/download' class='print-no'>Download Gist ❤️</a>
                        </div>
                        <!--<br style='clear:both' />-->\n";

                    // Replace the original shortcode or script tag with the modified content
                    $content = preg_replace("/" . preg_quote($match[0], '/') . "/", $add_scriptag_and_htmlbutton, $content, 1);
                }
            }
        }

        // Add custom styles to the wp_head if there are one or more Gist embeds
        if ($has_matches) { add_action("wp_head", "gist_embed_add_styles"); }
    }

    // Return updated content
    return $content;
}

or this simplified release

<?php
// Deny access if called directly
defined('ABSPATH') || exit;

// Apply customization to the content for GitHub Gist embeds.
add_filter("the_content", "gist_embed_apply_customization");

function gist_embed_apply_customization($content) {
    // Patterns to match GitHub Gist URLs in HTML and Shortcode blocks
    $patterns = [
        '/\[https:\/\/gist\.github\.com\/([a-zA-Z0-9]+)\/([a-zA-Z0-9]+)(\?file=([a-zA-Z0-9.]+))?]/i', // Pattern for shortcode without .js
        '/<script src="https:\/\/gist\.github\.com\/([a-zA-Z0-9]+)\/([a-zA-Z0-9]+)\.js(\?file=([a-zA-Z0-9.]+))?"><\/script>/i', // Pattern for HTML with .js
    ];

    $gist_found = false;

    // Check if any pattern matches
    foreach ($patterns as $pattern) {
        if (preg_match($pattern, $content)) {
            $gist_found = true;
            break; // Stop checking patterns once a match is found
        }
    }

    // If no GitHub Gist patterns were found, return content as is
    if (!$gist_found) {
        return $content;
    }

    // Start output buffering
    

    // Replace GitHub Gist embeds with custom HTML
    $content = preg_replace_callback($patterns, 'replace_gist_embed', $content);

    // Get the buffer content and clean the buffer
    

    // Add styles to wp_head if GitHub Gist was found
    if ($gist_found) {
        add_action("wp_head", "gist_embed_add_styles");
    }

    // Return the modified content
    return $content;
}

function replace_gist_embed($matches) {
    $fileparam = !empty($matches[3]) ? $matches[3] : ''; // support ?file=filename
    $gist_url = "https://gist.github.com/" . $matches[1] . "/" . $matches[2];
    return "
        <script src='" . $gist_url . ".js" . $fileparam . "' data-no-optimize='1'></script>
        <div class='gist-download-button'>
            <a href='" . $gist_url . "/' title='View Gist' class='print-yes' style='display:none'>GoTo: " . $gist_url . "</a>
            <a href='" . $gist_url . "/download' class='print-no'>Download Gist ❤️</a>
        </div>\n";
}

// Function to add styles for Gist Embed.
function gist_embed_add_styles()
{
    // Output selected CSS file
    $selected_css_file = get_option('gist_embed_selected_css');
    if (!empty($selected_css_file)) {
        echo "\n<!-- Gist Embed Theme Start -->\n<link rel='stylesheet' href='" . GIST_PLUGIN_URL . "Assets/CSS/StyleSheets/" . $selected_css_file . "' data-no-optimize='1' />\n<!-- Gist Embed Theme End -->";
    }

    // Output custom CSS with Cache burst to ensure the latest version is loaded
    echo "\n<!-- Gist Embed CustomCSS Start -->\n<link rel='stylesheet' href='" . GIST_PLUGIN_URL . "Assets/CSS/GistCustom.css?" . filemtime(GIST_DIR_PATH . "Assets/CSS/GistCustom.css") . "' data-no-optimize='1' />\n<!-- Gist Embed CustomCSS End -->\n";
}