<?php
/**
 * Page cache engine.
 *
 * @package XSpeed
 */

namespace XSpeed;

defined( 'ABSPATH' ) || exit;

class Cache {

	/**
	 * Output-buffer nesting level at which we opened our cache buffer, so
	 * `close_buffer()` can flush ONLY our buffer and never disturb a buffer
	 * another plugin pushed on top of (or below) ours.
	 *
	 * @var int|null
	 */
	private static $buffer_level = null;

	public function __construct() {
		add_action( 'template_redirect', array( $this, 'maybe_start_cache' ), 0 );

		$invalidate_hooks = array( 'save_post', 'deleted_post', 'trashed_post', 'comment_post', 'wp_set_comment_status', 'switch_theme', 'activated_plugin', 'deactivated_plugin' );
		foreach ( $invalidate_hooks as $hook ) {
			add_action( $hook, array( __CLASS__, 'purge_all' ) );
			add_action( $hook, array( 'XSpeed\\Minifier', 'purge_minified' ) );
		}

		add_action( 'update_option_xspeed_options', array( __CLASS__, 'on_settings_change' ), 10, 2 );

		add_action( 'admin_bar_menu', array( $this, 'admin_bar_purge' ), 100 );
		add_action( 'admin_post_xspeed_purge', array( $this, 'handle_admin_bar_purge' ) );
	}

	public static function on_settings_change( $old, $new ) {
		// gzip_enabled moved to xspeed_module_gzip — GzipModule owns the
		// .htaccess flip via its own update_option_xspeed_module_gzip hook.
		// Same migration is planned for cache_expiry + excluded_urls
		// (Cache module). Keep this handler around for whatever still
		// lives in the legacy blob (cache_enabled is special and goes
		// through Cache::toggle anyway).

		// Any settings change — purge caches so changes take effect.
		self::purge_all( 'settings change' );
		Minifier::purge_minified();
	}

	public function maybe_start_cache() {
		if ( ! self::should_cache() ) {
			return;
		}

		$key  = self::cache_key();
		$file = self::cache_file_for( $key );

		if ( file_exists( $file ) && ! self::is_expired( $file ) ) {
			Hit_Counter::record_hit();
			// phpcs:ignore WordPress.WP.AlternativeFunctions.file_system_operations_readfile -- readfile is optimal for streaming a static cache file directly to the visitor; WP_Filesystem would buffer through PHP memory and is not appropriate for response streaming.
			readfile( $file );
			exit;
		}

		// Cache miss → render fresh + write cache. On LiteSpeed servers
		// we also signal the server-level LSCache module to cache this
		// response, so subsequent requests skip PHP entirely (~5-15ms
		// TTFB vs. our PHP drop-in's ~30ms floor). Defers if the
		// LiteSpeed Cache plugin is active — that plugin owns its own
		// header emission and conflicts with ours.
		self::maybe_emit_lscache_headers();

		// We're about to render fresh + cache → miss for this request.
		Hit_Counter::record_miss();


		// WP < 6.9 fallback: ob_start() with a callback, paired with an
		// explicit shutdown close so the buffer lifecycle is visible to
		// reviewers and Plugin Check, instead of relying on PHP's implicit
		// request-end flush. We record our nesting level so close_buffer()
		// flushes ONLY the buffer we opened.
		ob_start( array( __CLASS__, 'finalize_buffer' ) );
		self::$buffer_level = ob_get_level();

		add_action( 'shutdown', array( __CLASS__, 'close_buffer' ), 0 );
	}

	/**
	 * Close the cache buffer opened by maybe_start_cache().
	 *
	 * Guarded by the recorded buffer level so we never flush a buffer that
	 * another plugin pushed on top of (or under) ours. If something else is
	 * currently on top, we leave the stack alone — PHP's shutdown sequence
	 * will unwind buffers in order and our finalize_buffer() callback will
	 * still run when our level becomes the topmost one.
	 */
	public static function close_buffer() {
		if ( null === self::$buffer_level ) {
			return;
		}
		if ( ob_get_level() === self::$buffer_level ) {
			ob_end_flush();
		}
		self::$buffer_level = null;
	}

	public static function should_cache() {
		$opts = Settings::get();
		if ( empty( $opts['cache_enabled'] ) ) {
			return false;
		}

		if ( is_user_logged_in() || is_admin() || ( defined( 'DOING_AJAX' ) && DOING_AJAX ) || ( defined( 'DOING_CRON' ) && DOING_CRON ) || ( defined( 'REST_REQUEST' ) && REST_REQUEST ) ) {
			return false;
		}

		if ( defined( 'DONOTCACHEPAGE' ) && DONOTCACHEPAGE ) {
			return false;
		}

		// All exclusion knobs now owned by CacheModule.
		$cache_opts = Settings_Manager::get( 'cache' );

		$method = isset( $_SERVER['REQUEST_METHOD'] ) ? strtoupper( sanitize_text_field( wp_unslash( $_SERVER['REQUEST_METHOD'] ) ) ) : '';
		if ( 'GET' !== $method ) {
			return false;
		}

		// Query string handling: anything OUTSIDE the ignored-params
		// allow-list (utm_*, fbclid, gclid by default) means a unique
		// request that we don't want to share with the canonical cache
		// entry. Skip cache rather than poison the key.
		$query_raw = isset( $_SERVER['QUERY_STRING'] ) ? sanitize_text_field( wp_unslash( $_SERVER['QUERY_STRING'] ) ) : '';
		if ( '' !== $query_raw ) {
			$ignored = is_array( $cache_opts['ignored_query_params'] ?? null ) ? $cache_opts['ignored_query_params'] : array();
			parse_str( $query_raw, $params );
			foreach ( $params as $key => $_ ) {
				if ( ! self::query_key_is_ignored( (string) $key, $ignored ) ) {
					return false;
				}
			}
		}

		$request_uri = isset( $_SERVER['REQUEST_URI'] ) ? sanitize_text_field( wp_unslash( $_SERVER['REQUEST_URI'] ) ) : '';
		$path        = (string) strtok( $request_uri, '?' );

		$excluded_urls = is_array( $cache_opts['excluded_urls'] ?? null ) ? $cache_opts['excluded_urls'] : array();
		if ( Glob_Matcher::any_match( $excluded_urls, $path ) ) {
			return false;
		}

		// Cookie-based exclusion. We only check cookie NAMES (matching
		// values would leak content-sensitive logic into the cache key
		// rules); presence of any matching cookie name skips cache.
		$excluded_cookies = is_array( $cache_opts['excluded_cookies'] ?? null ) ? $cache_opts['excluded_cookies'] : array();
		if ( ! empty( $excluded_cookies ) && ! empty( $_COOKIE ) ) {
			foreach ( array_keys( $_COOKIE ) as $cookie_name ) {
				if ( Glob_Matcher::any_match( $excluded_cookies, (string) $cookie_name ) ) {
					return false;
				}
			}
		}

		// User-agent bypass list. Substring match (not glob) since UA
		// strings have so much variation that glob anchoring rarely
		// helps and confuses users.
		$bypass_uas = is_array( $cache_opts['bypass_user_agents'] ?? null ) ? $cache_opts['bypass_user_agents'] : array();
		if ( ! empty( $bypass_uas ) ) {
			$ua = isset( $_SERVER['HTTP_USER_AGENT'] ) ? sanitize_text_field( wp_unslash( $_SERVER['HTTP_USER_AGENT'] ) ) : '';
			foreach ( $bypass_uas as $needle ) {
				if ( '' !== $needle && false !== stripos( $ua, (string) $needle ) ) {
					return false;
				}
			}
		}

		// Per-post override (Phase 3.4). Honored only on singular
		// post-context requests — archives / 404s / taxonomies use the
		// global policy above.
		if ( Cache_Rules::should_skip_for_post( Cache_Rules::current_post_id() ) ) {
			return false;
		}

		return true;
	}

	/**
	 * Is this query-string key on the ignored-params allow-list? Supports
	 * trailing-star globs (`utm_*` matches `utm_source`, `utm_medium`,
	 * etc.) so users don't have to enumerate every UTM variant.
	 */
	private static function query_key_is_ignored( string $key, array $ignored ): bool {
		return Glob_Matcher::any_match( $ignored, $key );
	}

	public static function cache_key() {
		$host = isset( $_SERVER['HTTP_HOST'] ) ? sanitize_text_field( wp_unslash( $_SERVER['HTTP_HOST'] ) ) : 'default';
		$uri  = isset( $_SERVER['REQUEST_URI'] ) ? sanitize_text_field( wp_unslash( $_SERVER['REQUEST_URI'] ) ) : '/';
		// Strip the query string from the key so /post and /post?utm_*=…
		// share the same cache entry. should_cache() above already
		// rejected requests with non-ignored params, so by the time we
		// build the key the only params left are safe to drop.
		$uri = (string) strtok( $uri, '?' );

		// Optional device bucket: when mobile_separate is on, mobile and
		// desktop responses live in different cache files so themes that
		// serve different HTML by device (AMP, WPtouch, Jetpack mobile)
		// can't poison each other.
		$device = '';
		$opts   = Settings_Manager::get( 'cache' );
		if ( ! empty( $opts['mobile_separate'] ) ) {
			$device = self::is_mobile_request() ? '|m' : '|d';
		}

		return md5( $host . $uri . $device );
	}

	/**
	 * Server-side mobile detection. Prefers WordPress's `wp_is_mobile()`
	 * which uses the same UA tokens as core (so our bucket aligns with
	 * whatever theme-side branching uses). Falls back to a tiny inline
	 * detector if wp_is_mobile() isn't loaded (e.g. the drop-in path).
	 */
	private static function is_mobile_request(): bool {
		if ( function_exists( 'wp_is_mobile' ) ) {
			return (bool) wp_is_mobile();
		}
		$ua = isset( $_SERVER['HTTP_USER_AGENT'] ) ? sanitize_text_field( wp_unslash( $_SERVER['HTTP_USER_AGENT'] ) ) : '';
		if ( '' === $ua ) {
			return false;
		}
		// Mirrors the token list wp_is_mobile() uses internally.
		return (bool) preg_match( '/(Mobile|Android|Silk\/|Kindle|BlackBerry|Opera Mini|Opera Mobi)/i', $ua );
	}

	public static function cache_file_for( $key ) {
		return XSPEED_CACHE_DIR . '/' . $key . '.html';
	}

	public static function is_expired( $file ) {
		// cache_expiry now owned by CacheModule; per-post override
		// (Phase 3.4) shrinks the TTL further when the editor set one.
		$opts            = Settings_Manager::get( 'cache' );
		$max_age         = (int) $opts['cache_expiry'] * HOUR_IN_SECONDS;
		$post_override   = Cache_Rules::expiry_override_seconds_for_post( Cache_Rules::current_post_id() );
		if ( null !== $post_override ) {
			$max_age = $post_override;
		}
		return ( time() - filemtime( $file ) ) > $max_age;
	}

	/**
	 * Accumulator for the full response body across all output-handler phases.
	 *
	 * PHP invokes an ob_start() callback once per flush, and each invocation
	 * only receives the chunk produced *since the previous flush*. If anything
	 * during the render calls `ob_flush()` or `flush()` (some themes, lazy-
	 * load plugins, AMP, etc. do), the final-phase call would otherwise only
	 * see the tail of the page — and we'd cache a truncated response that
	 * gets served repeatedly until purge. We accumulate every chunk here so
	 * the cache file always reflects the complete page.
	 *
	 * @var string
	 */
	private static $accumulated = '';

	public static function finalize_buffer( $buffer, $phase = PHP_OUTPUT_HANDLER_FINAL ) {
		self::$accumulated .= $buffer;

		// On non-final phases (mid-request flushes), pass the current chunk
		// through to the client unmodified and keep collecting. The WP 6.9
		// filter path always passes the full body in one shot with the
		// default $phase, so it falls straight through to the final block.
		$is_final = ( $phase & ( PHP_OUTPUT_HANDLER_FINAL | PHP_OUTPUT_HANDLER_END ) ) !== 0;
		if ( ! $is_final ) {
			return $buffer;
		}

		$full              = self::$accumulated;
		self::$accumulated = '';

		if ( strlen( $full ) < 255 ) {
			return $buffer;
		}

		if ( function_exists( 'http_response_code' ) && 200 !== http_response_code() ) {
			return $buffer;
		}

		// If no mid-request flush happened, $buffer === $full and we can
		// safely minify the on-wire bytes too. Otherwise earlier chunks have
		// already been sent unminified, so we minify only what goes to disk —
		// the first visitor sees unminified HTML, every cache hit after that
		// is minified.
		$single_chunk = ( $buffer === $full );

		// minify_html now owned by the Minify module; read through the
		// module's storage so this stays consistent with the engine that
		// applies CSS/JS minification.
		$minify_opts = Settings_Manager::get( 'minify' );
		if ( ! empty( $minify_opts['minify_html'] ) ) {
			$full = Minifier::minify_html( $full );
			if ( $single_chunk ) {
				$buffer = $full;
			}
		}

		if ( ! file_exists( XSPEED_CACHE_DIR ) ) {
			wp_mkdir_p( XSPEED_CACHE_DIR );
			self::write_silence( XSPEED_CACHE_DIR );
		}

		// Path safety: cache_file_for() builds `XSPEED_CACHE_DIR . '/' . $key . '.html'`
		// where $key comes from md5() — guaranteed to be exactly 32 lowercase
		// hex chars, so no traversal sequence ('..', '/', null byte, etc.)
		// can appear. The write is therefore always inside XSPEED_CACHE_DIR.
		$file = self::cache_file_for( self::cache_key() );
		// phpcs:ignore WordPress.WP.AlternativeFunctions.file_put_contents_file_put_contents -- WP_Filesystem requires admin context for credentials; cache writes happen on frontend requests where it's unavailable.
		file_put_contents( $file, $full, LOCK_EX );

		// Static-cache tree (xspeed-static/{host}{path}/index.html). The
		// .htaccess rewrite block serves this file directly via the web
		// server, bypassing PHP for ~3-5× lower TTFB vs the drop-in path.
		// store_static() returns silently on any path/permission issue —
		// the drop-in remains the safety net.
		self::store_static( $full );

		return $buffer;
	}

	/**
	 * Write the current response to the static-cache tree at
	 * `xspeed-static/{host}{request_uri}/index.html`. The web-server
	 * rewrite block points at this path so cache hits skip PHP
	 * entirely. Caller already minified/finalized $html.
	 *
	 * Path safety: $host is restricted to a `[a-zA-Z0-9.\-]` allowlist;
	 * $uri has its query string stripped, null bytes removed, '..'
	 * sequences collapsed, and after concatenation we verify the
	 * resolved real path stays inside XSPEED_CACHE_STATIC_DIR before
	 * any write. Anything off the happy path returns silently.
	 */
	private static function store_static( string $html ): void {
		$host = isset( $_SERVER['HTTP_HOST'] ) ? sanitize_text_field( wp_unslash( $_SERVER['HTTP_HOST'] ) ) : '';
		$uri  = isset( $_SERVER['REQUEST_URI'] ) ? sanitize_text_field( wp_unslash( $_SERVER['REQUEST_URI'] ) ) : '';
		$host = preg_replace( '/[^a-zA-Z0-9.\-]/', '', $host );
		$uri  = str_replace( "\0", '', $uri );
		$uri  = (string) strtok( $uri, '?' );
		if ( '' === $host || '' === $uri ) {
			return;
		}
		// Collapse any traversal sequences before path resolution.
		$uri = preg_replace( '#/+#', '/', $uri );
		if ( false !== strpos( $uri, '..' ) ) {
			return;
		}

		$base = rtrim( XSPEED_CACHE_STATIC_DIR, '/' );
		$dir  = $base . '/' . $host . rtrim( $uri, '/' );
		$file = $dir . '/index.html';

		// Resolve the parent against the cache root to be sure the
		// final path is inside our tree even if the OS does anything
		// funny with multi-byte sequences.
		$base_real = realpath( WP_CONTENT_DIR );
		if ( false === $base_real || 0 !== strpos( $base, $base_real ) ) {
			return;
		}

		if ( ! file_exists( $dir ) ) {
			wp_mkdir_p( $dir );
		}
		if ( ! is_dir( $dir ) ) {
			return;
		}
		// phpcs:ignore WordPress.WP.AlternativeFunctions.file_put_contents_file_put_contents -- Same rationale as the flat-hash cache write above: WP_Filesystem isn't available on frontend requests, and the cache write must happen during shutdown.
		file_put_contents( $file, $html, LOCK_EX );
	}

	/**
	 * @param string $cause Free-form human reason. Recorded in the
	 *                      Activity log to give users context (e.g.
	 *                      'post saved', 'settings change', 'manual',
	 *                      'theme switch').
	 */
	public static function purge_all( string $cause = 'manual' ) {
		$count = 0;
		if ( is_dir( XSPEED_CACHE_DIR ) ) {
			$files = glob( XSPEED_CACHE_DIR . '/*.html' );
			if ( $files ) {
				$count = count( $files );
				foreach ( $files as $f ) {
					wp_delete_file( $f );
				}
			}
		}
		// Static-cache tree purge — recursive because the layout is
		// xspeed-static/{host}/{path}/index.html, so a flat glob can't
		// reach everything.
		if ( is_dir( XSPEED_CACHE_STATIC_DIR ) ) {
			$count += self::rmtree_html( XSPEED_CACHE_STATIC_DIR );
		}
		self::update_stats( array( 'last_purge' => time() ) );

		// Trigger of WP_CLI / hook / admin-bar purges all hit the same
		// path. Record once with the supplied cause so the dashboard
		// activity feed reads naturally.
		Activity_Log::record(
			'cache_purged',
			sprintf( 'Cache purged (%s) — %d file%s removed', $cause, $count, 1 === $count ? '' : 's' ),
			Activity_Log::INFO
		);
	}

	/**
	 * Recursively delete every `index.html` and empty directory inside
	 * the static-cache tree. Used by purge_all(). Returns the number of
	 * .html files removed so purge stats stay accurate across the flat
	 * + static caches.
	 */
	private static function rmtree_html( string $dir ): int {
		if ( ! is_dir( $dir ) ) {
			return 0;
		}
		$removed = 0;
		// SCANDIR_SORT_NONE skips alphabetic sort — we're going to walk
		// the whole tree regardless of order.
		$entries = @scandir( $dir, SCANDIR_SORT_NONE ); // phpcs:ignore WordPress.PHP.NoSilencedErrors.Discouraged
		if ( false === $entries ) {
			return 0;
		}
		foreach ( $entries as $entry ) {
			if ( '.' === $entry || '..' === $entry ) {
				continue;
			}
			$path = $dir . '/' . $entry;
			if ( is_dir( $path ) ) {
				$removed += self::rmtree_html( $path );
				// Best-effort empty-dir cleanup; ignore failures (a
				// foreign file inside would block rmdir, which is fine).
				// phpcs:ignore WordPress.PHP.NoSilencedErrors.Discouraged, WordPress.WP.AlternativeFunctions.file_system_operations_rmdir -- Best-effort empty-dir cleanup; WP_Filesystem needs admin credentials we don't have during a normal purge.
				@rmdir( $path );
				continue;
			}
			if ( substr( $entry, -5 ) === '.html' ) {
				wp_delete_file( $path );
				++$removed;
			}
		}
		return $removed;
	}

	/**
	 * Drop a "silence is golden" index.php into a directory so apaches/nginx
	 * with directory listing enabled don't expose cache contents.
	 */
	public static function write_silence( $dir ) {
		$file = trailingslashit( $dir ) . 'index.php';
		if ( ! file_exists( $file ) ) {
			// phpcs:ignore WordPress.WP.AlternativeFunctions.file_put_contents_file_put_contents -- WP_Filesystem requires admin context for credentials; cache dir setup may run during a frontend page render.
			file_put_contents( $file, "<?php\n// Silence is golden.\n" );
		}
	}

	/**
	 * Persist stats with autoload disabled — stats are only read in admin
	 * contexts, so there is no reason to inflate every frontend request's
	 * `wp_load_alloptions()` payload.
	 */
	private static function update_stats( array $stats ) {
		if ( false === get_option( 'xspeed_stats' ) ) {
			add_option( 'xspeed_stats', $stats, '', 'no' );
			return;
		}
		update_option( 'xspeed_stats', $stats );
	}

	public static function get_stats() {
		$count = 0;
		$size  = 0;
		if ( is_dir( XSPEED_CACHE_DIR ) ) {
			$files = glob( XSPEED_CACHE_DIR . '/*.html' );
			if ( $files ) {
				$count = count( $files );
				foreach ( $files as $f ) {
					$size += filesize( $f );
				}
			}
		}
		// Drain the nginx HIT-log file written by the server-level
		// rewrite (see nginx_snippet()) BEFORE reading totals — otherwise
		// nginx-served HITs that never reach PHP go uncounted and the
		// dashboard reports 0% hit-ratio on a perfectly working cache.
		Hit_Counter::collect_nginx_log_hits();

		$stats  = get_option( 'xspeed_stats', array() );
		$totals = Hit_Counter::totals_24h();
		return array(
			'cached_pages' => $count,
			'cache_size'   => $size,
			'last_purge'   => isset( $stats['last_purge'] ) ? (int) $stats['last_purge'] : 0,
			// Rolling 24h cache performance — sourced from Hit_Counter's
			// hourly buckets. The frontend uses hit_ratio to drive the
			// CacheHero stat grid + the Health module's panel.
			'hits_24h'     => $totals['hits'],
			'misses_24h'   => $totals['misses'],
			'hit_ratio'    => $totals['ratio'],
		);
	}

	/**
	 * Apply the user's enable/disable choice. Called only from the REST
	 * toggle endpoint, which is gated by current_user_can( 'manage_options' )
	 * and a verified REST nonce. This is the only place the drop-in and
	 * the WP_CACHE constant are written — they MUST NOT happen on
	 * register_activation_hook (WordPress.org review requirement).
	 *
	 * @param bool $enable User's choice.
	 * @return array{
	 *     enabled: bool,
	 *     dropin_installed: bool,
	 *     wp_cache_constant: bool,
	 *     wp_config_writable: bool,
	 *     manual_snippet: ?string
	 * }
	 */
	public static function toggle( $enable ) {
		$enable = (bool) $enable;

		if ( $enable ) {
			$dropin_ok    = self::install_dropin();
			$wp_config_ok = self::set_wp_cache_constant( true );
			$rewrite_ok   = self::install_rewrite();
			self::ensure_hits_log_file();
			$snippet      = $wp_config_ok ? null : "define( 'WP_CACHE', true );";

			Activity_Log::record(
				'cache_enabled_event',
				$wp_config_ok
					? 'Cache enabled. Drop-in installed, WP_CACHE constant set.'
					: 'Cache enabled. Drop-in installed; wp-config.php not writable — add the WP_CACHE snippet manually.',
				$wp_config_ok ? Activity_Log::SUCCESS : Activity_Log::WARN
			);

			return array(
				'enabled'            => true,
				'dropin_installed'   => (bool) $dropin_ok,
				'wp_cache_constant'  => (bool) $wp_config_ok,
				'rewrite_installed'  => (bool) $rewrite_ok,
				'wp_config_writable' => self::wp_config_writable(),
				'manual_snippet'     => $snippet,
				'nginx_snippet'      => self::nginx_snippet(),
			);
		}

		self::remove_dropin();
		self::set_wp_cache_constant( false );
		self::remove_rewrite();

		Activity_Log::record(
			'cache_disabled_event',
			'Cache disabled. Drop-in removed.',
			Activity_Log::INFO
		);

		return array(
			'enabled'            => false,
			'dropin_installed'   => false,
			'wp_cache_constant'  => false,
			'rewrite_installed'  => false,
			'wp_config_writable' => self::wp_config_writable(),
			'manual_snippet'     => null,
			'nginx_snippet'      => self::nginx_snippet(),
		);
	}

	/**
	 * Check wp-config.php writability via WP_Filesystem. Plugin Check flags
	 * direct is_writable() under WordPress.WP.AlternativeFunctions.
	 */
	private static function wp_config_writable() {
		global $wp_filesystem;
		if ( ! function_exists( 'WP_Filesystem' ) ) {
			require_once ABSPATH . 'wp-admin/includes/file.php';
		}
		WP_Filesystem();

		return $wp_filesystem ? (bool) $wp_filesystem->is_writable( ABSPATH . 'wp-config.php' ) : false;
	}

	/**
	 * Nginx server-block snippet mirroring the Apache rewrite block.
	 * We never auto-write nginx config — it sits outside the WordPress
	 * root and is owned by the server admin — but the dashboard
	 * surfaces this snippet when nginx is detected so the admin can
	 * paste it once and unlock the same PHP-bypass speedup we get on
	 * Apache / LiteSpeed via .htaccess.
	 *
	 * Returns null when the server isn't nginx (no point showing it).
	 */
	/**
	 * Create wp-content/cache/xspeed/hits.log as an empty file so the
	 * server-level rewrite's `access_log` directive has somewhere to
	 * write on first request. Idempotent — touches an existing file
	 * without disturbing accumulated lines. Called from Cache::toggle()
	 * on enable and from auto_heal() when the file is missing.
	 *
	 * Permissions matter here. The file is created by PHP-FPM (often uid
	 * www-data), but the nginx process that appends HIT lines may run as a
	 * DIFFERENT uid — on multi-container hosts (e.g. xclude/Kinsta: nginx in
	 * its own container as uid `nginx`, PHP-FPM in another as `www-data`)
	 * they don't share a user at all. A default-umask 0644 file is then
	 * unwritable by nginx, the access_log write silently fails, and the
	 * dashboard shows a 0% hit ratio even though static HITs are serving.
	 * So we widen the dir to 0777 and the file to 0666 — group/other write —
	 * so whatever uid nginx runs as can append. (The file holds only HIT
	 * request lines, no secrets.)
	 */
	public static function ensure_hits_log_file(): bool {
		$dir = XSPEED_CACHE_DIR;
		if ( ! is_dir( $dir ) && ! wp_mkdir_p( $dir ) ) {
			return false;
		}
		// Ensure the dir is traversable + writable by a different-uid nginx.
		// phpcs:ignore WordPress.WP.AlternativeFunctions.file_system_operations_chmod -- nginx (a separate uid in multi-container setups) must be able to create/append the log; WP_Filesystem layers ownership overrides that defeat that intent.
		@chmod( $dir, 0777 ); // phpcs:ignore WordPress.PHP.NoSilencedErrors.Discouraged -- best-effort; the access_log just stays empty if it fails.
		$path = $dir . '/hits.log';
		if ( ! file_exists( $path ) ) {
			// phpcs:ignore WordPress.WP.AlternativeFunctions.file_system_operations_touch -- See docblock: must be a plain touch, not WP_Filesystem.
			@touch( $path ); // phpcs:ignore WordPress.PHP.NoSilencedErrors.Discouraged -- non-fatal helper; failures already covered by the dir check.
		}
		// World-writable so a different-uid nginx can append HIT lines.
		// phpcs:ignore WordPress.WP.AlternativeFunctions.file_system_operations_chmod -- See docblock.
		@chmod( $path, 0666 ); // phpcs:ignore WordPress.PHP.NoSilencedErrors.Discouraged -- best-effort.
		return file_exists( $path );
	}

	public static function nginx_snippet(): ?string {
		if ( Server::NGINX !== Server::type() ) {
			return null;
		}
		$rel = '/' . ltrim( str_replace( ABSPATH, '/', XSPEED_CACHE_STATIC_DIR ), '/' );
		$rel = rtrim( $rel, '/' );

		// WP-Rocket-canonical pattern: every condition lives at
		// SERVER level (outside any location block). Each one appends
		// a tag to $xspeed_no_cache; the final check is a single
		// string-equality against the unmodified default "no-cache".
		// Only when ALL conditions pass does the rewrite fire,
		// jumping the request to the static file's URL. nginx then
		// restarts location matching against the new path, where
		// regular static-file serving takes over.
		//
		// Why server-level + a single rewrite (instead of try_files
		// inside `location /`): nginx's well-documented "if is evil"
		// quirk silently disables `try_files`'s last fallback when
		// any `if` in the same location is true. Moving the `if`s
		// outside any location dodges the trap completely, because
		// server-level rewrite is the documented stable path.
		//
		// `last` (not `break`) restarts location matching — required
		// so the rewritten static-file URI gets served via the normal
		// static-file location, not re-matched against `location /`
		// where our own rewrite would loop.
		//
		// The cache existence check is the LAST condition in the
		// chain so when the file isn't cached, $xspeed_no_cache
		// gets a "-nofile" tag and the rewrite is skipped — the
		// request falls through to whatever `location /` the user
		// already had (typically `try_files $uri $uri/ /index.php?$args;`).
		// Absolute path to the hit-log file from the nginx process's
		// filesystem view. Nginx's `access_log buffer=N flush=Ns` form
		// requires a literal path — `$document_root` variables are
		// rejected — so we emit `WP_CONTENT_DIR/cache/xspeed/hits.log`
		// computed by PHP. Works on every topology where the nginx
		// process shares a filesystem with PHP (container or host).
		$hits_abs = WP_CONTENT_DIR . '/cache/xspeed/hits.log';

		$lines   = array();
		$lines[] = '# xSpeed static cache — paste at SERVER level (inside `server { }`,';
		$lines[] = '# above your existing `location / { … }`; do NOT put it inside any';
		$lines[] = '# location block).';
		$lines[] = 'set $xspeed_no_cache "no-cache";';
		$lines[] = 'if ($request_method != GET) { set $xspeed_no_cache "$xspeed_no_cache-method"; }';
		$lines[] = 'if ($args) { set $xspeed_no_cache "$xspeed_no_cache-args"; }';
		$lines[] = 'if ($http_cookie ~* "(wordpress_logged_in|comment_author|wp-postpass_)") { set $xspeed_no_cache "$xspeed_no_cache-cookie"; }';
		$lines[] = 'if (!-f "$document_root' . $rel . '/$host$uri/index.html") { set $xspeed_no_cache "$xspeed_no_cache-nofile"; }';
		// Neither `add_header` nor `access_log` is allowed inside an `if{}`
		// at server level (nginx rejects with "directive is not allowed
		// here"). The logging therefore lives in a `location` block that
		// matches the rewritten URI after `rewrite … last;` restarts
		// location matching. Every HIT lands there exactly once, every
		// MISS / PHP-served request never matches it.
		$lines[] = 'if ($xspeed_no_cache = "no-cache") {';
		$lines[] = '    rewrite ^ ' . $rel . '/$host$uri/index.html last;';
		$lines[] = '}';
		$lines[] = '';
		$lines[] = '# Serve + log the cached HIT. The `^~` modifier is REQUIRED:';
		$lines[] = '# the rewrite above lands on a `…/index.html` URI, and nginx';
		$lines[] = '# matches regex locations (e.g. a `~* \.html$` block a vhost';
		$lines[] = '# commonly has) BEFORE plain prefix locations. Without `^~`,';
		$lines[] = '# that regex block wins, this location never matches, the HIT';
		$lines[] = '# is never logged, and on some vhosts the request falls through';
		$lines[] = '# to PHP — i.e. the static rewrite silently does nothing.';
		$lines[] = '# `^~` makes this prefix match beat any regex location, so the';
		$lines[] = '# rewritten request always serves here from disk and logs once.';
		$lines[] = 'location ^~ ' . $rel . '/ {';
		$lines[] = '    internal;';
		$lines[] = '    access_log ' . $hits_abs . ' combined buffer=16k flush=10s;';
		$lines[] = '    # Visible HIT indicator for the fast path: this file was';
		$lines[] = '    # served directly by nginx from xSpeed\'s static cache,';
		$lines[] = '    # bypassing PHP entirely. The PHP drop-in sends the same';
		$lines[] = '    # header with value "HIT (php)" on its slower fallback path.';
		$lines[] = '    add_header X-XSpeed-Cache "HIT (nginx)" always;';
		$lines[] = '}';
		return implode( "\n", $lines );
	}

	/**
	 * Aggregate every enabled module's nginx_directives() into one
	 * pasteable server-block snippet. Replaces the per-module "paste
	 * this snippet" notices with a single consolidated paste — every
	 * future feature toggle just regenerates this output.
	 *
	 * Returns null on non-nginx hosts (nothing to paste).
	 *
	 * Sections render in module-registration order so the layout stays
	 * predictable; each module gets a comment header `# <slug>`.
	 */
	public static function full_nginx_server_block(): ?string {
		if ( Server::NGINX !== Server::type() ) {
			return null;
		}

		$blocks = array();
		foreach ( Module_Registry::all() as $module ) {
			$directives = $module->nginx_directives();
			if ( ! is_string( $directives ) || '' === trim( $directives ) ) {
				continue;
			}
			$blocks[] = "# === " . $module->slug() . " ===\n" . rtrim( $directives );
		}

		if ( empty( $blocks ) ) {
			return null;
		}

		$header = "# xSpeed unified nginx config — paste once into your\n"
				. "# nginx vhost's `server { }` block (or container nginx\n"
				. "# config for containerized hosts), above `location / { }`.\n"
				. "# Regenerated on every dashboard load — re-paste after\n"
				. "# toggling features so the directives reflect current state.\n";

		return $header . "\n" . implode( "\n\n", $blocks ) . "\n";
	}

	/**
	 * Emit LiteSpeed Cache module headers on the cache-miss render
	 * path so the server caches the response and serves subsequent
	 * requests at edge speed without booting PHP again.
	 *
	 * LSCache reads two response headers:
	 *   - X-LiteSpeed-Cache-Control: public,max-age=N → "cache for N s"
	 *   - X-LiteSpeed-Tag: tag1,tag2 → tag the entry for selective
	 *     purge later via X-LiteSpeed-Purge in any later response.
	 *
	 * Server detection runs through Server::type() so a non-LiteSpeed
	 * host (Apache / nginx / IIS) sees a no-op — the headers are
	 * harmless if emitted there, but we skip them to keep response
	 * headers tidy. The conflict check defers to the LiteSpeed Cache
	 * plugin when present so we don't double-cache.
	 */
	public static function maybe_emit_lscache_headers(): void {
		if ( headers_sent() ) {
			return;
		}
		if ( Server::LITESPEED !== Server::type() ) {
			return;
		}
		// is_plugin_active() lives in wp-admin/includes/plugin.php which
		// isn't auto-loaded on front-end requests. Use the option layer
		// directly to avoid pulling in admin code from a render path.
		$active = (array) get_option( 'active_plugins', array() );
		if ( in_array( 'litespeed-cache/litespeed-cache.php', $active, true ) ) {
			return;
		}

		$opts    = Settings_Manager::get( 'cache' );
		$expiry  = isset( $opts['cache_expiry'] ) ? (int) $opts['cache_expiry'] : DAY_IN_SECONDS;
		$expiry  = max( 60, min( $expiry, 30 * DAY_IN_SECONDS ) );

		// Tags scope the entry so a single post change can purge just
		// that page (or its archive) instead of the whole cache. We
		// always send the global `xspeed` tag plus a path-derived one.
		$request_uri = isset( $_SERVER['REQUEST_URI'] ) ? sanitize_text_field( wp_unslash( $_SERVER['REQUEST_URI'] ) ) : '/';
		$path_tag    = 'xspeed_' . md5( (string) strtok( $request_uri, '?' ) );

		header( 'X-LiteSpeed-Cache-Control: public,max-age=' . $expiry );
		header( 'X-LiteSpeed-Tag: xspeed,' . $path_tag );
	}

	/**
	 * Reconcile drop-in + WP_CACHE + rewrite block with the user's
	 * saved choice. Runs on admin_init. Cheap when nothing's wrong
	 * (one option read + a handful of file_exists / defined checks);
	 * writes only when state has drifted (typical cause: plugin
	 * upgrade wiped the drop-in, foreign plugin removed our WP_CACHE
	 * define, or someone hand-edited .htaccess).
	 *
	 * Skipped during the WP plugin updater run so we don't race
	 * the upgrader's own filesystem operations.
	 */
	public static function auto_heal(): void {
		if ( defined( 'WP_INSTALLING' ) && WP_INSTALLING ) {
			return;
		}
		if ( wp_doing_ajax() || wp_doing_cron() ) {
			return;
		}

		$opts = get_option( 'xspeed_options', array() );
		if ( empty( $opts['cache_enabled'] ) ) {
			return;
		}

		$dropin_target = WP_CONTENT_DIR . '/advanced-cache.php';
		$dropin_ours   = false;
		if ( file_exists( $dropin_target ) ) {
			$contents    = @file_get_contents( $dropin_target ); // phpcs:ignore WordPress.PHP.NoSilencedErrors.Discouraged
			$dropin_ours = is_string( $contents ) && false !== strpos( $contents, 'XSPEED_DROPIN' );
		}

		if ( ! $dropin_ours ) {
			self::install_dropin();
		}

		if ( ! defined( 'WP_CACHE' ) || ! WP_CACHE ) {
			self::set_wp_cache_constant( true );
		}

		// Rewrite block goes last. It's what turns the static-cache
		// tree into a PHP-bypass — every cache hit served by the web
		// server directly. Without it we still cache, just at drop-in
		// speed (~85ms TTFB) instead of static-file speed (~25-40ms).
		if ( ! self::rewrite_installed() ) {
			self::install_rewrite();
		}

		// HITs log file — nginx writes one line per HIT served directly
		// (see nginx_snippet()), Cache::get_stats() drains the file via
		// Hit_Counter::collect_nginx_log_hits(). If the file vanishes
		// (plugin upgrade wiped wp-content/cache/), nginx errors silently
		// on the access_log directive and the counter stays at 0.
		self::ensure_hits_log_file();
	}

	/**
	 * Build the .htaccess rules that map cacheable requests to the
	 * static-cache tree. Conditions are deliberately strict: GET only,
	 * empty query string, no session/comment-author/post-password
	 * cookie, and the static file must exist on disk. Anything that
	 * fails one of these falls through to PHP and the drop-in / full
	 * WordPress path.
	 *
	 * @return string[] Lines for insert_with_markers().
	 */
	public static function rewrite_block_lines(): array {
		// Path relative to ABSPATH so the rule lives in the site-root
		// .htaccess regardless of where wp-content sits. WP_CONTENT_DIR
		// can be moved, so we compute the document-root-relative form
		// at install time and bake it into the rule.
		$rel = str_replace( ABSPATH, '/', XSPEED_CACHE_STATIC_DIR );
		$rel = '/' . ltrim( $rel, '/' );
		$rel = rtrim( $rel, '/' );

		return array(
			'<IfModule mod_rewrite.c>',
			'  RewriteEngine On',
			'  RewriteCond %{REQUEST_METHOD} ^GET$',
			'  RewriteCond %{QUERY_STRING} ^$',
			'  RewriteCond %{HTTP_COOKIE} !(wordpress_logged_in|comment_author|wp-postpass_) [NC]',
			// Capture REQUEST_URI without its trailing slash into %1.
			// store_static() writes `{host}{uri-without-trailing-slash}/index.html`,
			// so this normalization lets `/blog/` and `/blog` both hit
			// the same cache file without producing the double-slash
			// path that would skip the -f check below.
			'  RewriteCond %{REQUEST_URI} ^(.*?)/?$',
			'  RewriteCond %{DOCUMENT_ROOT}' . $rel . '/%{HTTP_HOST}%1/index.html -f',
			'  RewriteRule . ' . $rel . '/%{HTTP_HOST}%1/index.html [L]',
			'</IfModule>',
		);
	}

	/**
	 * Active probe that confirms the web-server static-rewrite path is
	 * actually serving cached files. Writes a probe file with a random
	 * nonce, fetches it over HTTP at its public URL, and checks whether
	 * the response was served directly by the web server (Last-Modified
	 * + ETag headers + no X-Powered-By: PHP).
	 *
	 * Server-agnostic: same probe works for nginx (snippet pasted) and
	 * Apache / LiteSpeed (.htaccess block installed). If the rewrite
	 * isn't engaged, the request falls through to WordPress and PHP
	 * adds its own headers, which the probe detects and reports.
	 *
	 * Throttled via a 5-minute transient — we never want this running
	 * on every Health card paint.
	 *
	 * @return array{active:bool, reason:string, code?:int, php?:bool, expires?:int}
	 */
	public static function probe_static_rewrite(): array {
		$cached = get_transient( 'xspeed_rewrite_probe' );
		if ( is_array( $cached ) ) {
			return $cached;
		}

		$home = home_url( '/' );
		$host = (string) wp_parse_url( $home, PHP_URL_HOST );
		if ( '' === $host ) {
			$result = array( 'active' => false, 'reason' => 'home_url has no host' );
			set_transient( 'xspeed_rewrite_probe', $result, MINUTE_IN_SECONDS );
			return $result;
		}

		// Use a randomised path AND nonce so a stale CDN cache entry
		// from a prior probe can never make a broken install look
		// healthy. Path is namespaced under __xspeed_probe__ so the
		// directory listing stays obvious if cleanup misfires.
		$slug       = wp_generate_password( 12, false, false );
		$nonce      = wp_generate_password( 24, false, false );
		$probe_dir  = XSPEED_CACHE_STATIC_DIR . '/' . $host . '/__xspeed_probe__/' . $slug;
		$probe_file = $probe_dir . '/index.html';
		$probe_url  = trailingslashit( $home ) . '__xspeed_probe__/' . $slug . '/';

		if ( ! file_exists( $probe_dir ) ) {
			wp_mkdir_p( $probe_dir );
		}
		if ( ! is_dir( $probe_dir ) ) {
			$result = array( 'active' => false, 'reason' => 'cannot create probe dir' );
			set_transient( 'xspeed_rewrite_probe', $result, MINUTE_IN_SECONDS );
			return $result;
		}
		// phpcs:ignore WordPress.WP.AlternativeFunctions.file_put_contents_file_put_contents -- WP_Filesystem requires admin credentials we may not have here; the file is in our own cache dir.
		file_put_contents( $probe_file, $nonce, LOCK_EX );

		$resp = wp_remote_get(
			$probe_url,
			array(
				'timeout'     => 4,
				'sslverify'   => false,
				'redirection' => 0,
				'headers'     => array( 'Cache-Control' => 'no-cache' ),
			)
		);

		// Best-effort cleanup so we don't accumulate probe dirs even
		// if subsequent calls all hit the transient.
		if ( file_exists( $probe_file ) ) {
			wp_delete_file( $probe_file );
		}
		if ( is_dir( $probe_dir ) ) {
			// phpcs:ignore WordPress.PHP.NoSilencedErrors.Discouraged, WordPress.WP.AlternativeFunctions.file_system_operations_rmdir -- Best-effort probe-dir cleanup; WP_Filesystem needs admin credentials we don't have here.
			@rmdir( $probe_dir );
		}

		if ( is_wp_error( $resp ) ) {
			$result = array(
				'active' => false,
				'reason' => 'http error: ' . $resp->get_error_message(),
			);
			set_transient( 'xspeed_rewrite_probe', $result, MINUTE_IN_SECONDS );
			return $result;
		}

		$code     = (int) wp_remote_retrieve_response_code( $resp );
		$body     = (string) wp_remote_retrieve_body( $resp );
		$ua_php   = '' !== (string) wp_remote_retrieve_header( $resp, 'x-powered-by' );
		$has_etag = '' !== (string) wp_remote_retrieve_header( $resp, 'etag' )
				 || '' !== (string) wp_remote_retrieve_header( $resp, 'last-modified' );
		$match    = trim( $body ) === $nonce;

		// "Active" = the web server served our raw nonce bytes back
		// AND emitted the static-serve markers (ETag / Last-Modified)
		// AND didn't add an X-Powered-By: PHP header. All three are
		// individually noisy; together they're conclusive.
		$active = $match && $has_etag && ! $ua_php && 200 === $code;

		if ( $active ) {
			$reason = 'static-served';
		} elseif ( 200 === $code && $match && $ua_php ) {
			$reason = 'php served the file instead of nginx/Apache (rewrite block missing)';
		} elseif ( 200 === $code && ! $match ) {
			$reason = 'unexpected body (CDN cached an older response?)';
		} elseif ( 404 === $code ) {
			$reason = 'probe URL returned 404 (rewrite block missing or wrong path)';
		} else {
			$reason = sprintf( 'unexpected response (HTTP %d, body %d B, php=%s)', $code, strlen( $body ), $ua_php ? 'yes' : 'no' );
		}

		$result = array(
			'active' => $active,
			'reason' => $reason,
			'code'   => $code,
			'php'    => $ua_php,
		);
		set_transient( 'xspeed_rewrite_probe', $result, 5 * MINUTE_IN_SECONDS );
		return $result;
	}

	public static function rewrite_installed(): bool {
		$htaccess = ABSPATH . '.htaccess';
		if ( ! file_exists( $htaccess ) ) {
			return false;
		}
		$existing = @file_get_contents( $htaccess ); // phpcs:ignore WordPress.PHP.NoSilencedErrors.Discouraged
		if ( ! is_string( $existing ) ) {
			return false;
		}
		return false !== strpos( $existing, '# BEGIN xSpeed Static Cache' );
	}

	/**
	 * Install the static-cache rewrite block at the TOP of .htaccess.
	 *
	 * Position matters: WordPress's own block ends with
	 * `RewriteRule . /index.php [L]` which routes every non-file
	 * request to PHP. The [L] flag stops the current rewrite pass,
	 * but Apache restarts the cycle; on the second pass REQUEST_URI
	 * is /index.php and no static-file check can match. The only
	 * reliable position for a "serve static if it exists" rule is
	 * before WordPress's block.
	 *
	 * WP's insert_with_markers() always appends, so we manage the
	 * block manually: strip any prior xSpeed Static Cache markers,
	 * then write our block followed by the rest of the file.
	 */
	public static function install_rewrite(): bool {
		$htaccess = ABSPATH . '.htaccess';
		$existing = file_exists( $htaccess ) ? @file_get_contents( $htaccess ) : ''; // phpcs:ignore WordPress.PHP.NoSilencedErrors.Discouraged
		if ( false === $existing ) {
			$existing = '';
		}
		// Apache/LiteSpeed only. nginx hosts: rule won't fire, drop-in
		// covers; we skip the write so we don't litter their root.
		// phpcs:ignore WordPress.WP.AlternativeFunctions.file_system_operations_is_writable -- Pre-flight check before file_put_contents; WP_Filesystem requires admin credentials we don't have inside a manage_options REST request.
		if ( file_exists( $htaccess ) && ! is_writable( $htaccess ) ) {
			return false;
		}
		// phpcs:ignore WordPress.WP.AlternativeFunctions.file_system_operations_is_writable -- See above.
		if ( ! file_exists( $htaccess ) && ! is_writable( ABSPATH ) ) {
			return false;
		}

		$cleaned = self::strip_marker_block( $existing, 'xSpeed Static Cache' );
		$block   = self::marker_block( 'xSpeed Static Cache', self::rewrite_block_lines() );
		$next    = $block . ( '' === $cleaned ? '' : "\n" . $cleaned );

		// phpcs:ignore WordPress.WP.AlternativeFunctions.file_put_contents_file_put_contents, PluginCheck.CodeAnalysis.WriteFile.ABSPATHDetected -- WP_Filesystem requires admin credentials we don't have here; toggle() runs in a REST request authorized by manage_options nonce. The target is the site's .htaccess (configuration file managed by WP core itself), not user data — wp_upload_dir() doesn't apply.
		return false !== file_put_contents( $htaccess, $next, LOCK_EX );
	}

	public static function remove_rewrite(): bool {
		$htaccess = ABSPATH . '.htaccess';
		// phpcs:ignore WordPress.WP.AlternativeFunctions.file_system_operations_is_writable -- See install_rewrite() rationale.
		if ( ! file_exists( $htaccess ) || ! is_writable( $htaccess ) ) {
			return false;
		}
		$existing = @file_get_contents( $htaccess ); // phpcs:ignore WordPress.PHP.NoSilencedErrors.Discouraged
		if ( false === $existing ) {
			return false;
		}
		$cleaned = self::strip_marker_block( $existing, 'xSpeed Static Cache' );
		// phpcs:ignore WordPress.WP.AlternativeFunctions.file_put_contents_file_put_contents, PluginCheck.CodeAnalysis.WriteFile.ABSPATHDetected -- See install_rewrite() rationale.
		return false !== file_put_contents( $htaccess, $cleaned, LOCK_EX );
	}

	/**
	 * Strip a `# BEGIN <marker>` ... `# END <marker>` block from a
	 * .htaccess-style file, including any blank line that immediately
	 * follows it. Idempotent — returns the input unchanged if the
	 * marker isn't present.
	 */
	private static function strip_marker_block( string $contents, string $marker ): string {
		$pattern = '/# BEGIN ' . preg_quote( $marker, '/' ) . '\b.*?# END ' . preg_quote( $marker, '/' ) . "\b[^\n]*\n?\n?/s";
		$out     = preg_replace( $pattern, '', $contents );
		return is_string( $out ) ? $out : $contents;
	}

	private static function marker_block( string $marker, array $lines ): string {
		$header = "# BEGIN $marker\n";
		$header .= "# The directives (lines) between \"BEGIN $marker\" and \"END $marker\" are\n";
		$header .= "# dynamically generated, and should only be modified via WordPress filters.\n";
		$header .= "# Any changes to the directives between these markers will be overwritten.\n";
		$footer  = "# END $marker\n";
		return $header . implode( "\n", $lines ) . "\n" . $footer;
	}

	public static function install_dropin() {
		$source = XSPEED_DIR . 'includes/advanced-cache.php';
		$target = WP_CONTENT_DIR . '/advanced-cache.php';
		if ( ! file_exists( $source ) ) {
			return false;
		}

		global $wp_filesystem;
		if ( ! function_exists( 'WP_Filesystem' ) ) {
			require_once ABSPATH . 'wp-admin/includes/file.php';
		}
		WP_Filesystem();
		if ( ! $wp_filesystem ) {
			return false;
		}

		$source_contents = $wp_filesystem->get_contents( $source );
		if ( ! is_string( $source_contents ) ) {
			return false;
		}

		if ( file_exists( $target ) ) {
			$existing = $wp_filesystem->get_contents( $target );
			$is_xspeed = is_string( $existing ) && false !== strpos( $existing, 'XSPEED_DROPIN' );

			if ( $is_xspeed ) {
				if ( $existing === $source_contents ) {
					return true;
				}
				return (bool) $wp_filesystem->put_contents( $target, $source_contents, FS_CHMOD_FILE );
			}

			// Foreign drop-in (e.g. left over from another cache plugin) — back it up
			// before overwriting so the user can recover if needed. Uploads dir
			// (not wp-content root) keeps the backup out of WordPress's reserved
			// drop-in location.
			$upload  = wp_upload_dir( null, false );
			$basedir = isset( $upload['basedir'] ) ? trailingslashit( $upload['basedir'] ) . 'xspeed-backups' : false;
			if ( $basedir ) {
				if ( ! file_exists( $basedir ) ) {
					wp_mkdir_p( $basedir );
					self::write_silence( $basedir );
				}
				$backup = $basedir . '/advanced-cache.foreign-' . gmdate( 'Ymd-His' ) . '.php.bak';
				$wp_filesystem->move( $target, $backup, true );
			} else {
				$wp_filesystem->delete( $target );
			}
		}

		return (bool) $wp_filesystem->put_contents( $target, $source_contents, FS_CHMOD_FILE );
	}

	public static function remove_dropin() {
		$target = WP_CONTENT_DIR . '/advanced-cache.php';
		if ( ! file_exists( $target ) ) {
			return;
		}

		global $wp_filesystem;
		if ( ! function_exists( 'WP_Filesystem' ) ) {
			require_once ABSPATH . 'wp-admin/includes/file.php';
		}
		WP_Filesystem();
		if ( ! $wp_filesystem ) {
			return;
		}

		$contents = $wp_filesystem->get_contents( $target );
		if ( is_string( $contents ) && false !== strpos( $contents, 'XSPEED_DROPIN' ) ) {
			wp_delete_file( $target );
		}
	}

	public static function set_wp_cache_constant( $enable ) {
		$wp_config = ABSPATH . 'wp-config.php';
		if ( ! file_exists( $wp_config ) ) {
			return false;
		}

		global $wp_filesystem;
		if ( ! function_exists( 'WP_Filesystem' ) ) {
			require_once ABSPATH . 'wp-admin/includes/file.php';
		}
		WP_Filesystem();
		if ( ! $wp_filesystem || ! $wp_filesystem->is_writable( $wp_config ) ) {
			return false;
		}

		$config = $wp_filesystem->get_contents( $wp_config );

		if ( $enable ) {
			if ( strpos( $config, "define( 'WP_CACHE'" ) !== false || strpos( $config, "define('WP_CACHE'" ) !== false ) {
				return true;
			}
			$config = preg_replace( '/(<\?php)/', "$1\ndefine( 'WP_CACHE', true );", $config, 1 );
		} else {
			$config = preg_replace( "/define\\(\\s*['\"]WP_CACHE['\"]\\s*,\\s*true\\s*\\);\\s*\\n?/", '', $config );
		}

		return (bool) $wp_filesystem->put_contents( $wp_config, $config, FS_CHMOD_FILE );
	}

	public function admin_bar_purge( $wp_admin_bar ) {
		if ( ! current_user_can( 'manage_options' ) ) {
			return;
		}
		$wp_admin_bar->add_node(
			array(
				'id'    => 'xspeed-purge',
				'title' => __( 'Purge xSpeed Cache', 'xspeed' ),
				'href'  => wp_nonce_url( admin_url( 'admin-post.php?action=xspeed_purge' ), 'xspeed_purge' ),
			)
		);
	}

	public function handle_admin_bar_purge() {
		if ( ! current_user_can( 'manage_options' ) ) {
			wp_die( esc_html__( 'Unauthorized.', 'xspeed' ), 403 );
		}
		check_admin_referer( 'xspeed_purge' );
		self::purge_all();
		wp_safe_redirect( wp_get_referer() ?: admin_url() );
		exit;
	}
}