<?php
/**
 * A2 Optimized Cache engine
 */

if ( ! defined( 'ABSPATH' ) ) {
	exit;
}

final class A2_Optimized_Cache_Engine {
	/**
	 * start engine
	 *
	 * @return  boolean  true if engine started, false otherwise
	 */

	public static function start() {
		if ( self::should_start() ) {
			new self();
		}

		return self::$started;
	}

	/**
	 * engine status
	 *
	 * @var     boolean
	 */

	public static $started = false;

	/**
	 * specific HTTP request headers from current request
	 *
	 */

	public static $request_headers;

	/**
	 * engine settings from disk or database
	 *
	 * @var     array
	 */

	public static $settings;

	/**
	 * constructor
	 *
	 */

	public function __construct() {
		// get request headers
		self::$request_headers = self::get_request_headers();

		// get settings from disk if directory index file
		if ( self::is_index() ) {
			self::$settings = A2_Optimized_Cache_Disk::get_settings();
		// get settings from database in late engine start otherwise
		} elseif ( class_exists( 'A2_Optimized_Cache' ) ) {
			self::$settings = A2_Optimized_Cache::get_settings();
			A2_Optimized_Cache::$options = self::$settings;
			A2_Optimized_Cache::$options['webp'] = self::$settings['convert_image_urls_to_webp'];
		}

		// check engine status
		if ( ! empty( self::$settings ) ) {
			self::$started = true;
		}
	}

	/**
	 * check if engine should start
	 *
	 * @return  boolean  true if engine should start, false otherwise
	 */

	public static function should_start() {
		// check if engine is running already
		if ( self::$started ) {
			return false;
		}

		// check if Ajax request in early engine start
		if ( defined( 'DOING_AJAX' ) && DOING_AJAX && ! class_exists( 'A2_Optimized_Cache' ) ) {
			return false;
		}

		// check if REST API request
		if ( defined( 'REST_REQUEST' ) && REST_REQUEST ) {
			return false;
		}

		// check if XMLRPC request
		if ( defined( 'XMLRPC_REQUEST' ) && XMLRPC_REQUEST ) {
			return false;
		}

		// check if Host request header is empty
		if ( empty( $_SERVER['HTTP_HOST'] ) ) {
			return false;
		}

		// check request URI
		if ( str_replace( [ '.ico', '.txt', '.xml', '.xsl' ], '', $_SERVER['REQUEST_URI'] ) !== $_SERVER['REQUEST_URI'] ) {
			return false;
		}

		return true;
	}

	/**
	 * start output buffering
	 *
	 */

	public static function start_buffering() {
		ob_start( 'self::end_buffering' );
	}

	/**
	 * end output buffering and cache page if applicable
	 *
	 * @param   string   $page_contents  contents of a page from the output buffer
	 * @param   integer  $phase          bitmask of PHP_OUTPUT_HANDLER_* constants
	 * @return  string   $page_contents  contents of a page from the output buffer
	 */

	private static function end_buffering($page_contents, $phase) {
		if ( $phase & PHP_OUTPUT_HANDLER_FINAL || $phase & PHP_OUTPUT_HANDLER_END ) {
			if ( ! self::is_cacheable( $page_contents ) || self::bypass_cache() ) {
				return $page_contents;
			}

			$page_contents = apply_filters( 'a2opt_cache_page_contents_before_store', $page_contents );

			A2_Optimized_Cache_Disk::cache_page( $page_contents );

			return $page_contents;
		}
	}

	/**
	 * get specific HTTP request headers from current request
	 *
	 * @return  array  $request_headers  specific HTTP request headers from current request
	 */

	private static function get_request_headers() {
		$request_headers = ( function_exists( 'apache_request_headers' ) ) ? apache_request_headers() : [];

		$request_headers = [
			'Accept' => ( isset( $request_headers['Accept'] ) ) ? $request_headers['Accept'] : ( ( isset( $_SERVER[ 'HTTP_ACCEPT' ] ) ) ? $_SERVER[ 'HTTP_ACCEPT' ] : '' ),
			'Accept-Encoding' => ( isset( $request_headers['Accept-Encoding'] ) ) ? $request_headers['Accept-Encoding'] : ( ( isset( $_SERVER[ 'HTTP_ACCEPT_ENCODING' ] ) ) ? $_SERVER[ 'HTTP_ACCEPT_ENCODING' ] : '' ),
			'Host' => ( isset( $request_headers['Host'] ) ) ? $request_headers['Host'] : ( ( isset( $_SERVER[ 'HTTP_HOST' ] ) ) ? $_SERVER[ 'HTTP_HOST' ] : '' ),
			'If-Modified-Since' => ( isset( $request_headers['If-Modified-Since'] ) ) ? $request_headers['If-Modified-Since'] : ( ( isset( $_SERVER[ 'HTTP_IF_MODIFIED_SINCE' ] ) ) ? $_SERVER[ 'HTTP_IF_MODIFIED_SINCE' ] : '' ),
			'User-Agent' => ( isset( $request_headers['User-Agent'] ) ) ? $request_headers['User-Agent'] : ( ( isset( $_SERVER[ 'HTTP_USER_AGENT' ] ) ) ? $_SERVER[ 'HTTP_USER_AGENT' ] : '' ),
			'X-Forwarded-Proto' => ( isset( $request_headers['X-Forwarded-Proto'] ) ) ? $request_headers['X-Forwarded-Proto'] : ( ( isset( $_SERVER[ 'HTTP_X_FORWARDED_PROTO' ] ) ) ? $_SERVER[ 'HTTP_X_FORWARDED_PROTO' ] : '' ),
			'X-Forwarded-Scheme' => ( isset( $request_headers['X-Forwarded-Scheme'] ) ) ? $request_headers['X-Forwarded-Scheme'] : ( ( isset( $_SERVER[ 'HTTP_X_FORWARDED_SCHEME' ] ) ) ? $_SERVER[ 'HTTP_X_FORWARDED_SCHEME' ] : '' ),
		];

		return $request_headers;
	}

	/**
	 * check if directory index file
	 *
	 * @return  boolean  true if directory index file, false otherwise
	 */

	private static function is_index() {
		if ( strtolower( basename( $_SERVER['SCRIPT_NAME'] ) ) === 'index.php' ) {
			return true;
		}

		return false;
	}

	/**
	 * check if page can be cached
	 *
	 * @param   string   $page_contents  contents of a page from the output buffer
	 * @return  boolean                  true if page contents are cacheable, false otherwise
	 */

	private static function is_cacheable($page_contents) {
		$has_html_tag = ( stripos( $page_contents, '<html' ) !== false );
		$has_html5_doctype = preg_match( '/^<!DOCTYPE.+html>/i', ltrim( $page_contents ) );
		$has_xsl_stylesheet = ( stripos( $page_contents, '<xsl:stylesheet' ) !== false || stripos( $page_contents, '<?xml-stylesheet' ) !== false );

		if ( $has_html_tag && $has_html5_doctype && ! $has_xsl_stylesheet ) {
			return true;
		}

		return false;
	}

	/**
	 * check permalink structure
	 *
	 * @return  boolean  true if request URI does not match permalink structure or if plain, false otherwise
	 */

	private static function is_wrong_permalink_structure() {
		// check if trailing slash is set and missing (ignoring root index and file extensions)
		if ( self::$settings['permalink_structure'] === 'has_trailing_slash' ) {
			if ( preg_match( '/\/[^\.\/\?]+(\?.*)?$/', $_SERVER['REQUEST_URI'] ) ) {
				return true;
			}
		}

		// check if trailing slash is not set and appended (ignoring root index and file extensions)
		if ( self::$settings['permalink_structure'] === 'no_trailing_slash' ) {
			if ( preg_match( '/\/[^\.\/\?]+\/(\?.*)?$/', $_SERVER['REQUEST_URI'] ) ) {
				return true;
			}
		}

		// check if custom permalink structure is not set
		if ( self::$settings['permalink_structure'] === 'plain' ) {
			return true;
		}

		return false;
	}

	/**
	 * check if page is excluded from cache
	 *
	 * @return  boolean  true if page is excluded from the cache, false otherwise
	 */

	private static function is_excluded() {
		// if post ID excluded
		if ( ! empty( self::$settings['excluded_post_ids'] ) && function_exists( 'is_singular' ) && is_singular() ) {
			$post_id = get_queried_object_id();
			$excluded_post_ids = array_map( 'absint', (array) explode( ',', self::$settings['excluded_post_ids'] ) );

			if ( in_array( $post_id, $excluded_post_ids, true ) ) {
				return true;
			}
		}

		// if page path excluded
		if ( ! empty( self::$settings['excluded_page_paths'] ) ) {
			$page_path = parse_url( $_SERVER['REQUEST_URI'], PHP_URL_PATH );

			if ( preg_match( self::$settings['excluded_page_paths'], $page_path ) ) {
				return true;
			}
		}

		// if query string excluded
		if ( ! empty( $_GET ) ) {
			// set regex matching query strings that should bypass the cache
			if ( ! empty( self::$settings['excluded_query_strings'] ) ) {
				$query_string_regex = self::$settings['excluded_query_strings'];
			} else {
				$query_string_regex = '/^(?!(fbclid|ref|mc_(cid|eid)|utm_(source|medium|campaign|term|content|expid)|gclid|fb_(action_ids|action_types|source)|age-verified|usqp|cn-reloaded|_ga|_ke)).+$/';
			}

			$query_string = parse_url( $_SERVER['REQUEST_URI'], PHP_URL_QUERY );

			if ( preg_match( $query_string_regex, $query_string ) ) {
				return true;
			}
		}

		// if cookie excluded
		if ( ! empty( $_COOKIE ) ) {
			// set regex matching cookies that should bypass the cache
			if ( ! empty( self::$settings['excluded_cookies'] ) ) {
				$cookies_regex = self::$settings['excluded_cookies'];
			} else {
				if (file_exists(ABSPATH . 'wp-content/plugins/woocommerce/woocommerce.php') || class_exists( 'WooCommerce' )) {
					$cookies_regex = '/^(wp-postpass|wordpress_logged_in|comment_author|woocommerce_cart_hash|woocommerce_items_in_cart|woocommerce_recently_viewed)_/';
				} else {
					$cookies_regex = '/^(wp-postpass|wordpress_logged_in|comment_author)_/';
				}
			}
			// bypass cache if an excluded cookie is found
			foreach ( $_COOKIE as $key => $value) {
				if ( preg_match( $cookies_regex, $key ) ) {
					return true;
				}
			}
		}

		return false;
	}

	/**
	 * check if search page
	 *
	 * @return  boolean  true if search page, false otherwise
	 */

	private static function is_search() {
		if ( apply_filters( 'a2opt_cache_exclude_search', is_search() ) ) {
			return true;
		}

		return false;
	}

	/**
	 * check if mobile template
	 *
	 * @return  boolean  true if mobile template, false otherwise
	 */

	private static function is_mobile() {
		return ( strpos( TEMPLATEPATH, 'wptouch' ) || strpos( TEMPLATEPATH, 'carrington' ) || strpos( TEMPLATEPATH, 'jetpack' ) || strpos( TEMPLATEPATH, 'handheld' ) );
	}

	/**
	 * check if cache should be bypassed
	 *
	 * @return  boolean  true if cache should be bypassed, false otherwise
	 */

	private static function bypass_cache() {
		// bypass cache hook
		if ( apply_filters( 'a2opt_cache_bypass_cache', false ) ) {
			return true;
		}

		// check request method
		if ( ! isset( $_SERVER['REQUEST_METHOD'] ) || $_SERVER['REQUEST_METHOD'] !== 'GET' ) {
			return true;
		}

		// check HTTP status code
		if ( http_response_code() !== 200 ) {
			return true;
		}

		// check DONOTCACHEPAGE constant
		if ( defined( 'DONOTCACHEPAGE' ) && DONOTCACHEPAGE ) {
			return true;
		}

		// check conditional tags
		if ( self::is_wrong_permalink_structure() || self::is_excluded() ) {
			return true;
		}

		// check conditional tags when output buffering has ended
		if ( class_exists( 'WP' ) ) {
			if ( is_admin() || self::is_search() || is_feed() || is_trackback() || is_robots() || is_preview() || post_password_required() || self::is_mobile() ) {
				return true;
			}
		}

		return false;
	}

	/**
	 * deliver cache
	 *
	 * @return  boolean  false if cached page was not delivered
	 */

	public static function deliver_cache() {
		$cache_file = A2_Optimized_Cache_Disk::get_cache();

		if ( A2_Optimized_Cache_Disk::cache_exists( $cache_file ) && ! A2_Optimized_Cache_Disk::cache_expired( $cache_file ) && ! self::bypass_cache()  ) {
			// set X-Cache-Handler response header
			header( 'X-Cache-Handler: cache-enabler-engine' );

			// return 304 Not Modified with empty body if applicable
			if ( strtotime( self::$request_headers['If-Modified-Since'] >= filemtime( $cache_file ) ) ) {
				header( $_SERVER['SERVER_PROTOCOL'] . ' 304 Not Modified', true, 304 );
				exit;
			}

			// set Content-Encoding response header if applicable
			if ( strpos( basename( $cache_file ), 'gz' ) !== false ) {
				header( 'Content-Encoding: gzip' );
			}

			// deliver cache
			readfile( $cache_file );

			exit;
		}

		return false;
	}
}