<?php
/**
 * Page cache detection.
 *
 * @package AIBlackout
 */

namespace AIBlackout\Audit;

use AIBlackout\Enforcement\ServerProfile;

defined( 'ABSPATH' ) || exit;

/**
 * Detects whether a page cache stands between visitors and PHP.
 *
 * @since 1.0.0
 */
class PageCache {

	/**
	 * The drop-in that short-circuits WordPress before plugins load.
	 *
	 * @var string
	 */
	const DROP_IN = 'advanced-cache.php';

	/**
	 * Known page-caching plugins, by plugin file, mapped to a display name.
	 *
	 * @var array
	 */
	const KNOWN_PLUGINS = array(
		'litespeed-cache/litespeed-cache.php'        => 'LiteSpeed Cache',
		'wp-super-cache/wp-cache.php'                => 'WP Super Cache',
		'w3-total-cache/w3-total-cache.php'          => 'W3 Total Cache',
		'wp-rocket/wp-rocket.php'                    => 'WP Rocket',
		'wp-fastest-cache/wpFastestCache.php'        => 'WP Fastest Cache',
		'cache-enabler/cache-enabler.php'            => 'Cache Enabler',
		'breeze/breeze.php'                          => 'Breeze',
		'comet-cache/comet-cache.php'                => 'Comet Cache',
		'surge/surge.php'                            => 'Surge',
		'wp-optimize/wp-optimize.php'                => 'WP-Optimize',
		'nitropack/main.php'                         => 'NitroPack',
		'swift-performance-lite/performance.php'     => 'Swift Performance Lite',
		'hummingbird-performance/wp-hummingbird.php' => 'Hummingbird',
	);

	/**
	 * Server profile, used to tell an installed cache from an operating one.
	 *
	 * @var ServerProfile
	 */
	private $server;

	/**
	 * Constructor.
	 *
	 * @param ServerProfile $server Server profile.
	 */
	public function __construct( ServerProfile $server ) {
		$this->server = $server;
	}

	/**
	 * Whether the `advanced-cache.php` drop-in is in place and enabled.
	 *
	 * @return bool True when the drop-in is active.
	 */
	public function has_drop_in(): bool {
		if ( ! function_exists( 'get_dropins' ) ) {
			require_once ABSPATH . 'wp-admin/includes/plugin.php';
		}

		if ( ! array_key_exists( self::DROP_IN, get_dropins() ) ) {
			return false;
		}

		// The drop-in is only loaded when WP_CACHE is true.
		return defined( 'WP_CACHE' ) && WP_CACHE;
	}

	/**
	 * Returns the active caching plugins, as display names.
	 *
	 * @return string[] Display names, empty when none are active.
	 */
	public function get_active_plugins(): array {
		if ( ! function_exists( 'is_plugin_active' ) ) {
			require_once ABSPATH . 'wp-admin/includes/plugin.php';
		}

		$found = array();

		foreach ( self::KNOWN_PLUGINS as $file => $label ) {
			if ( is_plugin_active( $file ) ) {
				$found[ $file ] = $label;
			}
		}

		return $found;
	}

	/**
	 * Whether a page cache is actually operating.
	 *
	 * @return bool True when responses can be served without running our gate.
	 */
	public function is_operating(): bool {
		return $this->has_drop_in();
	}

	/**
	 * Whether a caching plugin is installed but not actually caching.
	 *
	 * @return bool True when a cache plugin is present but inactive in practice.
	 */
	public function is_installed_but_dormant(): bool {
		return ! empty( $this->get_active_plugins() ) && ! $this->has_drop_in();
	}

	/**
	 * Returns the evidence behind the verdict, for display.
	 *
	 * @return array List of human-readable evidence strings.
	 */
	public function get_evidence(): array {
		$evidence = array();

		$plugins = $this->get_active_plugins();

		if ( ! empty( $plugins ) ) {
			$evidence[] = sprintf(
				/* translators: %s: Comma-separated list of plugin names. */
				__( 'Caching plugin active: %s', 'ai-blackout' ),
				implode( ', ', $plugins )
			);
		}

		$evidence[] = $this->has_drop_in()
			? __( 'The advanced-cache.php drop-in is installed and enabled, so pages can be served before plugins load.', 'ai-blackout' )
			: __( 'No advanced-cache.php drop-in is installed, so WordPress is not serving pages from a plugin page cache.', 'ai-blackout' );

		if ( $this->is_installed_but_dormant() ) {
			$evidence[] = $this->describe_dormancy();
		}

		return $evidence;
	}

	/**
	 * Explains why an installed caching plugin is not caching.
	 *
	 * @return string Human-readable explanation.
	 */
	public function describe_dormancy(): string {
		$plugins = $this->get_active_plugins();

		if ( isset( $plugins['litespeed-cache/litespeed-cache.php'] ) && ! $this->is_litespeed_server() ) {
			return __( 'LiteSpeed Cache is active, but its page cache only works on a LiteSpeed server. This site is not on one, so it is not caching pages.', 'ai-blackout' );
		}

		return __( 'A caching plugin is active but has not installed a page cache, so pages are not being served from a cache.', 'ai-blackout' );
	}

	/**
	 * Whether the server is LiteSpeed.
	 *
	 * @return bool True on LiteSpeed.
	 */
	private function is_litespeed_server(): bool {
		return ServerProfile::LITESPEED === $this->server->get_type();
	}
}