<?php
/**
 * Page Cache class.
 *
 * @package SpeedNest
 */

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

/**
 * Class WPSCO_Page_Cache
 *
 * Implements high-speed page caching for anonymous visitors with pre-gzipped assets.
 * Delivers sub-50ms TTFB for maximum Google PageSpeed performance.
 */
class WPSCO_Page_Cache {

    /**
     * Whether output buffering is active.
     *
     * @var bool
     */
    private $buffer_active = false;

    /**
     * Constructor.
     */
    public function __construct() {
        if ( $this->should_cache() ) {
            // Serve cache as early as possible on init, fallback to template_redirect.
            add_action( 'init', array( $this, 'maybe_serve_cache' ), 1 );
            add_action( 'template_redirect', array( $this, 'maybe_serve_cache' ), 0 );

            // WordPress 6.9+ standardized template enhancement output buffer support.
            add_filter( 'wp_should_output_buffer_template_for_enhancement', '__return_true' );
            add_filter( 'wp_template_enhancement_output_buffer', array( $this, 'filter_template_enhancement_buffer' ), 20, 2 );

            add_action( 'template_redirect', array( $this, 'start_buffer' ), 1 );
        }
    }

    /**
     * Check if the current request should be cached.
     *
     * @return bool
     */
    private function should_cache() {
        if ( is_admin() ) {
            return false;
        }

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

        if ( wpsco_get_setting( 'emergency_disable', false ) ) {
            return false;
        }

        return true;
    }

    /**
     * Try to serve a cached page.
     */
    public function maybe_serve_cache() {
        if ( headers_sent() ) {
            return;
        }

        // Instant force-purge action for administrators via URL (?wpsco_purge=1 or ?wpsco_purge_all=1 or ?purge=1).
        // phpcs:ignore WordPress.Security.NonceVerification.Recommended -- Administrative cache purge parameter check.
        if ( isset( $_GET['wpsco_purge'] ) || isset( $_GET['wpsco_purge_all'] ) || isset( $_GET['purge'] ) ) {
            // phpcs:ignore WordPress.Security.NonceVerification.Recommended -- Administrative cache purge parameter check.
            if ( function_exists( 'current_user_can' ) && current_user_can( 'manage_options' ) && isset( $_GET['_wpnonce'] ) && wp_verify_nonce( sanitize_text_field( wp_unslash( $_GET['_wpnonce'] ) ), 'wpsco_purge_cache' ) ) {
                $purger = new WPSCO_Cache_Purger();
                // phpcs:ignore WordPress.Security.NonceVerification.Recommended -- Nonce verified above.
                if ( isset( $_GET['wpsco_purge_all'] ) ) {
                    $purger->purge_everything();
                } else {
                    $cache_file = $this->get_cache_file_path();
                    wp_delete_file( $cache_file );
                    wp_delete_file( $cache_file . '.gz' );
                }
                header( 'X-WP-Speed-Cache: PURGED' );
                header( 'Cache-Control: no-cache, no-store, must-revalidate, max-age=0' );
                header( 'Pragma: no-cache' );
                return;
            }
        }

        if ( wpsco_is_cache_excluded() ) {
            header( 'X-WP-Speed-Cache: BYPASS' );
            header( 'Cache-Control: no-cache, no-store, must-revalidate, max-age=0' );
            header( 'Pragma: no-cache' );
            return;
        }

        $cache_file = $this->get_cache_file_path();

        if ( ! file_exists( $cache_file ) ) {
            return;
        }

        $ttl       = (int) wpsco_get_setting( 'page_cache_ttl', 3600 );
        $file_time = filemtime( $cache_file );

        if ( ( time() - $file_time ) > $ttl ) {
            wp_delete_file( $cache_file );
            wp_delete_file( $cache_file . '.gz' );
            return;
        }

        $gz_file              = $cache_file . '.gz';
        $http_accept_encoding = isset( $_SERVER['HTTP_ACCEPT_ENCODING'] ) ? sanitize_text_field( wp_unslash( $_SERVER['HTTP_ACCEPT_ENCODING'] ) ) : '';
        $accept_gzip          = ! empty( $http_accept_encoding ) && stripos( $http_accept_encoding, 'gzip' ) !== false;
        $remaining            = max( 0, min( 120, $ttl - ( time() - $file_time ) ) );

        // Send cache headers.
        header( 'X-WP-Speed-Cache: HIT' );
        header( 'X-WP-Speed-Cache-Age: ' . ( time() - $file_time ) );
        header( 'Cache-Control: public, max-age=' . $remaining . ', must-revalidate' );
        header( 'Vary: Accept-Encoding, User-Agent' );
        header( 'Content-Type: text/html; charset=UTF-8' );

        // Serve compressed if client supports gzip.
        if ( $accept_gzip ) {
            header( 'Content-Encoding: gzip' );
            if ( file_exists( $gz_file ) ) {
                $gz_content = wpsco_read_file( $gz_file );
                if ( false !== $gz_content ) {
                    echo $gz_content; // phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped -- Pre-compressed gzipped HTML cache output.
                    exit;
                }
            }

            $content = wpsco_read_file( $cache_file );
            if ( false !== $content ) {
                echo gzencode( $content, 6 ); // phpcs:ignore
                exit;
            }
        }

        $content = wpsco_read_file( $cache_file );
        if ( false !== $content ) {
            echo $content; // phpcs:ignore
            exit;
        }
    }

    /**
     * Start output buffering.
     */
    public function start_buffer() {
        if ( wpsco_is_cache_excluded() ) {
            return;
        }

        // If WordPress 6.9+ core template enhancement output buffer is active, let core manage it.
        if ( function_exists( 'has_filter' ) && has_filter( 'wp_template_enhancement_output_buffer' ) && did_action( 'wp_finalized_template_enhancement_output_buffer' ) ) {
            return;
        }

        $this->buffer_active = true;
        ob_start( array( $this, 'save_cache' ) );
        add_action( 'shutdown', array( $this, 'end_buffer' ), 0 );
    }

    /**
     * Explicitly close and flush the output buffer at shutdown to prevent buffer-stack misalignment.
     */
    public function end_buffer() {
        if ( $this->buffer_active && ob_get_level() > 0 ) {
            $this->buffer_active = false;
            ob_end_flush();
        }
    }

    /**
     * WordPress 6.9+ template enhancement output buffer callback.
     *
     * @param string $buffer   Rendered HTML output.
     * @param string $original Original HTML before core enhancements.
     * @return string
     */
    public function filter_template_enhancement_buffer( $buffer, $original = '' ) {
        $this->buffer_active = true;
        return $this->save_cache( $buffer );
    }

    /**
     * Save the output buffer to cache.
     *
     * @param string $buffer Page output.
     * @return string
     */
    public function save_cache( $buffer ) {
        if ( ! $this->buffer_active || empty( $buffer ) ) {
            return $buffer;
        }

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

        if ( wpsco_is_woocommerce_nocache_page() || wpsco_is_cache_excluded() ) {
            return $buffer;
        }

        // Add speed cache stamp.
        $timestamp = gmdate( 'Y-m-d H:i:s' );
        $buffer   .= "\n<!-- Cached by SpeedNest on {$timestamp} UTC -->";

        $cache_file = $this->get_cache_file_path();

        // Save raw HTML via safe WordPress Filesystem API.
        wpsco_write_file( $cache_file, $buffer );

        // Save pre-compressed GZIP copy for instant delivery.
        if ( function_exists( 'gzencode' ) ) {
            wpsco_write_file( $cache_file . '.gz', gzencode( $buffer, 6 ) );
        }

        if ( ! headers_sent() ) {
            header( 'X-WP-Speed-Cache: MISS' );
        }

        return $buffer;
    }

    /**
     * Get the cache file path for the current request.
     *
     * @return string
     */
    private function get_cache_file_path() {
        $request = isset( $_SERVER['REQUEST_URI'] ) ? sanitize_text_field( wp_unslash( $_SERVER['REQUEST_URI'] ) ) : '/';
        $parsed  = wp_parse_url( $request );
        $path    = isset( $parsed['path'] ) ? $parsed['path'] : '/';
        $path    = wpsco_sanitize_cache_path( $path );

        if ( empty( $path ) ) {
            $path = 'index';
        }

        $host = isset( $_SERVER['HTTP_HOST'] ) ? sanitize_text_field( wp_unslash( $_SERVER['HTTP_HOST'] ) ) : 'default';
        $host = preg_replace( '/[^a-zA-Z0-9\.\-]/', '', $host );

        $suffix = '';
        if ( wp_is_mobile() ) {
            $suffix = '-mobile';
        }

        return wpsco_get_cache_dir( 'html/' . $host . '/' . $path . $suffix . '.html' );
    }
}