<?php
/**
 * Whether this site looks like it caches its pages.
 *
 * @package Adminkeep
 */

namespace Adminkeep\Service;

defined( 'ABSPATH' ) || exit;

/**
 * A cheap, local guess at whether a page cache is active, for the contact form's WordPress
 * Nonce warning: a cached page keeps a nonce that expires within a day, and every message sent
 * from it after that is refused.
 *
 * Two signs, neither needing a request: the WP_CACHE constant, which the caching plugins set in
 * wp-config.php, and a known page-cache plugin being active. A cache run by the host (Kinsta,
 * WP Engine, SiteGround's own, Cloudflare APO) leaves no sign that can be trusted, so none is
 * claimed; the note under the WordPress Nonce choice covers those.
 *
 * It is a guess in the other direction too: a caching plugin can be active with page caching
 * switched off, or with the contact page left out. The filter is the way to say so.
 */
class PageCacheDetector {

	/**
	 * Filter for the verdict. Return false to silence a false positive (a cache that leaves the
	 * contact page out), true to have the warning on a site whose cache cannot be seen from here.
	 */
	const FILTER = 'adminkeep_contact_form_page_cache_detected';

	/**
	 * Known page-cache plugins, plugin file => name. A paid edition is listed beside its free one
	 * where it installs under another folder.
	 */
	const PLUGINS = array(
		'wp-rocket/wp-rocket.php'                    => 'WP Rocket',
		'w3-total-cache/w3-total-cache.php'          => 'W3 Total Cache',
		'wp-super-cache/wp-cache.php'                => 'WP Super Cache',
		'litespeed-cache/litespeed-cache.php'        => 'LiteSpeed Cache',
		'wp-fastest-cache/wpFastestCache.php'        => 'WP Fastest Cache',
		'cache-enabler/cache-enabler.php'            => 'Cache Enabler',
		'sg-cachepress/sg-cachepress.php'            => 'SiteGround Speed Optimizer',
		'breeze/breeze.php'                          => 'Breeze',
		'hummingbird-performance/wp-hummingbird.php' => 'Hummingbird',
		'wp-hummingbird/wp-hummingbird.php'          => 'Hummingbird',
		'comet-cache/comet-cache.php'                => 'Comet Cache',
		'comet-cache-pro/comet-cache-pro.php'        => 'Comet Cache',
		'swift-performance-lite/performance.php'     => 'Swift Performance',
		'swift-performance/performance.php'          => 'Swift Performance',
	);

	/**
	 * The page cache that looks active.
	 *
	 * @return string|null The plugin's name, '' for a cache that cannot be named, or null when
	 *                     none looks active.
	 */
	public function detected() {
		$name     = $this->plugin_name();
		$detected = '' !== $name || $this->wp_cache();

		/**
		 * Filters whether a page cache counts as detected for the contact form's warning.
		 *
		 * @param bool   $detected Whether a page cache looks active.
		 * @param string $name     The caching plugin found, or '' when none was recognised.
		 */
		// The name is written out, not read from self::FILTER, so a code checker can see its prefix.
		$detected = (bool) apply_filters( 'adminkeep_contact_form_page_cache_detected', $detected, $name );

		return $detected ? $name : null;
	}

	/**
	 * The first known page-cache plugin that is active, or ''.
	 *
	 * @return string
	 */
	private function plugin_name() {
		$active = $this->active_plugins();

		foreach ( self::PLUGINS as $file => $name ) {
			if ( in_array( $file, $active, true ) ) {
				return $name;
			}
		}

		return '';
	}

	/**
	 * Whether WP_CACHE is on. Its own method so a test can say so: PHP would never let a test
	 * undefine the real constant.
	 *
	 * @return bool
	 */
	protected function wp_cache() {
		return defined( 'WP_CACHE' ) && WP_CACHE;
	}

	/**
	 * The active plugins' files, network-active ones included. Read from the options rather than
	 * is_plugin_active(), which exists only in the admin: the settings panel's state is also read
	 * over REST and by WP-CLI.
	 *
	 * @return string[]
	 */
	protected function active_plugins() {
		$active = (array) get_option( 'active_plugins', array() );

		if ( is_multisite() ) {
			$active = array_merge( $active, array_keys( (array) get_site_option( 'active_sitewide_plugins', array() ) ) );
		}

		return array_map( 'strval', $active );
	}
}