WordPress: Block plugin activation if PHP or WordPress version is too low

index.php

<?php

register_activation_hook(__FILE__, function () {
  $php_version = phpversion();
  $wp_version = $GLOBALS["wp_version"];
  $is_56 = version_compare($php_version, 5.6, ">=");
  $is_70 = version_compare($php_version, 7.0, ">=");
  $php_ok = $is_56 || $is_70;
  $wp_ok = version_compare($wp_version, 4.7, ">=");
  $message = "";
  
  if (!$php_ok) {
    $message .= "Minimum PHP version required is 5.6. Yours is {$php_version}. ";
  } elseif (!$wp_ok) {
    $message .= "Minimum WP version required is 4.7. Yours is {$wp_version}. ";
  }
  
  if (!empty($message)) {
    deactivate_plugins(basename(__FILE__));
    wp_die($message);
  }
});