Dynamic URL parameters for WP pages

gistfile1.txt

<?php
/**
 * Plugin Name: Dynamic Parameters
 */

$dynamic_page_slugs = [
  'product-detail' => [ // product-detail/12345/awesome_product
    'product_id' => '(\d+)',
    'product_name' => '([a-zA-Z0-9-_]+)',
  ],
];
/*
The above example for /product-details/12345/awesome_product/ would produce...
  Regex: product-detail/(\d+)/([a-zA-Z0-9-_]+)
  Query: index.php?pagename=product-detail&vip_composable_params=product_id:$matches[1]|product_name:$matches[2]
  String: product_id:12345|product_name:awesome_product
  Params array:
    [product_id] => 12345
    [product_name] => awesome_product
*/

add_filter('query_vars', function ($vars) {
  $vars[] = 'vip_composable_params';
  return $vars;
});

add_action('init', function() use ($dynamic_page_slugs) {
  // create a rule for each dynamic page
  foreach ($dynamic_page_slugs as $slug => $params) {
    $regex = $slug . '/'; // Start with the slug
    $query = 'index.php?pagename=' . $slug; // Start building the query string
    $vip_composable_params = [];
    $i = 1; // Start matches from 1
  
    foreach ($params as $param => $pattern) {
      $regex .= $pattern;
      $vip_composable_params[] = $param . ':$matches[' . $i . ']';
      $i++;
      if ($i <= count($params)) {
        $regex .= '/';
      }
    }
    
    if ($regex[-1] === '/') {
      $regex = rtrim($regex, '/');
    }
  
    $query .= '&vip_composable_params=' . implode('|', $vip_composable_params);

    echo "<b>Regex:</b> $regex<br>";
    echo "<b>Query:</b> $query<br>";

    add_rewrite_rule(
      '^' . $regex . '/?$',
      $query,
      'top'
    );
  }

  // Force flush rewrite rules every page load :)
  flush_rewrite_rules();
});

// Flush rewrite rules on plugin activation
// Not a good option because the code could change without the plugin being reactivated.
register_activation_hook(__FILE__, function () {
  flush_rewrite_rules();
});

// Display params
add_action('template_redirect', function() {
  $params_string = get_query_var('vip_composable_params');
  $params = [];
  
  // echo "<b>String:</b> $params_string<br>";

  if (!empty($params_string)) {
    $param_pairs = explode('|', $params_string);
    foreach ($param_pairs as $pair) {
      list($key, $value) = explode(':', $pair);
      $params[$key] = $value;
    }
    echo '<pre>Params ' . print_r($params, true) . '</pre>';
  } else {
    echo 'No parameters provided.';
  }
});