<?php
/**
 * Delivery through the store owner's own CDN (1.8.0): picture addresses in the uploads folder point to the CDN address
 * on the public pages Image Manager delivers on, only after the CDN returned an exact copy of a new test file from this
 * site. Checked again every day; a failed check switches it off at once. No AffStackDev service.
 *
 * @package AffStackDevImageManager
 */

namespace AffStackDev\ImageManager;

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

/**
 * Delivery through the store owner's own CDN (a pull zone with an address of its own): addresses of pictures in the
 * uploads folder rewritten to it on public pages, switched on only after it returned a new test picture unchanged, and
 * checked again every day.
 */
final class CDN {
	public const HOOK = Hooks::CDN_CHECK;
	/** Attributes that can hold a picture address. */
	private const ATTRS = array( 'src', 'srcset', 'data-src', 'data-srcset', 'data-large_image', 'data-thumb', 'href', 'imagesrcset', 'poster', 'style' );
	/** Folders of the uploads folder that never go to a CDN (WooCommerce's downloads and logs). */
	private const PRIVATE_FOLDERS = array( 'woocommerce_uploads/', 'wc-logs/' );

	/**
	 * Whether Jetpack's image CDN is installed.
	 *
	 * @return bool True when it is.
	 */
	public static function jetpack(): bool {
		return class_exists( '\Automattic\Jetpack\Image_CDN\Image_CDN' ) || class_exists( '\Jetpack_Photon' );
	}
	/** On only with a saved address that passed its check, and never next to Jetpack's image CDN. */
	public static function active(): bool {
		$s = Settings::get();
		return $s['cdn'] && '' !== $s['cdn_url'] && ! empty( $s['cdn_state']['ok'] ) && ( $s['cdn_state']['url'] ?? '' ) === $s['cdn_url'] && ! self::jetpack();
	}
	/**
	 * A CDN address kept to HTTPS, a host of its own (not this site's) and an optional path; no user, query or fragment.
	 *
	 * @param string $url The CDN address asked for.
	 * @return string The address, or an empty string for none.
	 * @throws \RuntimeException With cdn_address when it is not such an address.
	 */
	public static function clean_url( string $url ): string {
		$url = trim( $url );
		if ( '' === $url ) {
			return '';
		}
		$p = wp_parse_url( $url );
		if ( ! is_array( $p ) || 'https' !== strtolower( (string) ( $p['scheme'] ?? '' ) ) || empty( $p['host'] ) || isset( $p['user'] ) || isset( $p['pass'] ) || isset( $p['query'] ) || isset( $p['fragment'] ) || strlen( $url ) > 200 ) {
			throw new \RuntimeException( 'cdn_address' );
		}
		$host = strtolower( (string) $p['host'] );
		if ( ! preg_match( '/^(?=.{1,190}$)([a-z0-9](?:[a-z0-9-]{0,61}[a-z0-9])?\.)+[a-z]{2,63}$/D', $host ) ) {
			throw new \RuntimeException( 'cdn_address' );
		}
		foreach ( array( home_url( '/' ), site_url( '/' ), wp_get_upload_dir()['baseurl'] ) as  $own ) {
			if ( strtolower( (string) wp_parse_url( $own, PHP_URL_HOST ) ) === $host ) {
				throw new \RuntimeException( 'cdn_same_host' );
			}
		}
		$path = isset( $p['path'] ) ? rtrim( (string) $p['path'], '/' ) : '';
		if ( '' !== $path && ! preg_match( '~^(/[A-Za-z0-9._-]+){1,4}$~D', $path ) ) {
			throw new \RuntimeException( 'cdn_address' );
		}
		return 'https://' . $host . ( isset( $p['port'] ) && 443 !== (int) $p['port'] ? ':' . (int) $p['port'] : '' ) . $path;
	}
	/**
	 * The CDN address of a file in the uploads folder: the CDN mirrors this site's paths.
	 *
	 * @param string $cdn  The CDN address.
	 * @param string $path The file's path on this site.
	 * @return string The file's CDN address.
	 */
	public static function address( string $cdn, string $path ): string {
		return rtrim( $cdn, '/' ) . '/' . ltrim( $path, '/' );
	}
	/**
	 * Check: a new test picture in Image Manager's own folder, asked for through the CDN, must come back byte for byte.
	 * The test picture is deleted afterwards. Returns the saved state.
	 *
	 * @param string $cdn The CDN address.
	 * @return array The check: address, time, result and reason.
	 */
	public static function check( string $cdn ): array {
		$state = array(
			'url'     => $cdn,
			'checked' => time(),
			'ok'      => false,
			'reason'  => '',
		);
		if ( self::jetpack() ) {
			$state['reason'] = 'cdn_jetpack';
			return $state;
		}
		$token = bin2hex( random_bytes( 12 ) );
		$name  = 'cdn-check-' . $token . '.png';
		$path  = '';
		try {
			$bytes = self::test_picture( $token );
			$path  = Settings::root( true ) . '/' . $name;
            // phpcs:ignore WordPress.WP.AlternativeFunctions.file_system_operations_file_put_contents -- A small generated test picture in Image Manager's own validated folder, deleted after the check.
			if ( Reviewed_Store::file_put_contents( $path, $bytes, LOCK_EX ) !== strlen( $bytes ) ) {
				$state['reason'] = 'cdn_storage';
				return $state;
			}
			$local    = wp_parse_url( trailingslashit( wp_get_upload_dir()['baseurl'] ) . 'affstackdev-image-manager/' . $name, PHP_URL_PATH );
			$response = wp_safe_remote_get(
				self::address( $cdn, (string) $local ),
				array(
					'timeout'             => 15,
					'redirection'         => 2,
					'limit_response_size' => 65536,
					'cookies'             => array(),
					'headers'             => array(
						'Accept'        => 'image/png',
						'Cache-Control' => 'no-cache',
					),
					'user-agent'          => 'AffStackDev-ImageManager/' . VERSION . ' cdn-check',
					'sslverify'           => true,
					'reject_unsafe_urls'  => true,
				)
			);
			if ( is_wp_error( $response ) ) {
				$state['reason'] = 'cdn_unreachable';
				return $state;
			}
			$code = (int) wp_remote_retrieve_response_code( $response );
			if ( 200 !== $code ) {
				$state['reason'] = 'cdn_status';
				$state['status'] = $code;
				return $state;
			}
			if ( ! hash_equals( hash( 'sha256', $bytes ), hash( 'sha256', (string) wp_remote_retrieve_body( $response ) ) ) ) {
				$state['reason'] = 'cdn_wrong_file';
				return $state;
			}
			$state['ok']     = true;
			$state['reason'] = 'cdn_ok';
			return $state;
		} catch ( \Throwable $e ) {
			$state['reason'] = 'cdn_storage';
			return $state;
		} finally {
			if ( '' !== $path && is_file( $path ) && ! is_link( $path ) ) {
				Reviewed_Store::wp_delete_file( $path );
			}
		}
	}
	/**
	 * A one-pixel PNG whose text chunk carries the token, so every check asks for a file no cache has seen.
	 *
	 * @param string $token A new random token.
	 * @return string The PNG's bytes.
	 */
	private static function test_picture( string $token ): string {
		$ihdr = pack( 'NNCCCCC', 1, 1, 8, 6, 0, 0, 0 );
		return "\x89PNG\r\n\x1a\n" . ImageInput::png_chunk( 'IHDR', $ihdr ) . ImageInput::png_chunk( 'tEXt', "Comment\0AffStackDev Image Manager CDN check " . $token )
			. ImageInput::png_chunk( 'IDAT', (string) gzcompress( "\0\0\0\0\0", 9 ) ) . ImageInput::png_chunk( 'IEND', '' );
	}
	/**
	 * Save the address and switch (Settings, CDN form). Switching on checks first; switching off never needs a check.
	 * Returns the state after saving.
	 *
	 * @param string $url The CDN address.
	 * @param bool   $on  True to switch the CDN on.
	 * @return array The CDN state after saving.
	 * @throws \RuntimeException With a reason code as its message when the step cannot be done.
	 */
	public static function save( string $url, bool $on ): array {
		$held = Reviewed_Store::enter( 8 );
		try {
			if ( ! current_user_can( 'manage_options' ) ) {
				throw new \RuntimeException( 'image_access_denied' );
			}
			$cdn = self::clean_url( $url );
			$s   = Settings::fresh();
			if ( $on && ! $s['public_policy'] ) {
				throw new \RuntimeException( 'Please confirm that these are public website images.' );
			}
			if ( $on && '' === $cdn ) {
				throw new \RuntimeException( 'cdn_address' );
			}
			if ( $on && self::jetpack() ) {
				throw new \RuntimeException( 'cdn_jetpack' );
			}
			$state   = $on ? self::check( $cdn ) : array(
				'url'     => $cdn,
				'checked' => 0,
				'ok'      => false,
				'reason'  => '',
			);
			$enabled = $on && ! empty( $state['ok'] );
			Settings::patch(
				array(
					'cdn'        => $enabled,
					'cdn_url'    => $cdn,
					'cdn_state'  => $state,
					'generation' => (int) $s['generation'] + 1,
				)
			);
			self::schedule( $enabled );
			if ( $enabled !== (bool) $s['cdn'] ) {
				Activity::add( $enabled ? 'cdn_on' : 'cdn_off' );
			}
			return $state;
		} finally {
			Reviewed_Store::leave( $held );
		}
	}
	/**
	 * Schedule the daily check while the CDN is on; clear it when off.
	 *
	 * @param bool $on Whether the CDN is on.
	 */
	public static function schedule( bool $on ): void {
		if ( ! $on ) {
			Reviewed_Store::wp_clear_scheduled_hook( self::HOOK );
			return;
		}
		if ( ! wp_next_scheduled( self::HOOK ) ) {
			Reviewed_Store::wp_schedule_event( time() + DAY_IN_SECONDS, 'daily', self::HOOK );
		}
	}
	/**
	 * The daily check. A CDN that no longer returns this site's file stops being used at once.
	 *
	 * @throws \RuntimeException What a step inside threw, passed on after cleaning up.
	 */
	public static function scheduled(): void {
		try {
			$held = Reviewed_Store::enter();
		} catch ( \RuntimeException $e ) {
			if ( Reviewed_Store::busy( $e ) ) {
				return;
			} throw $e;
		} // Busy: tomorrow's run checks.
		try {
			$s = Settings::fresh();
			if ( ! $s['cdn'] || '' === $s['cdn_url'] ) {
				self::schedule( false );
				return;
			}
			$state = self::check( (string) $s['cdn_url'] );
			if ( empty( $state['ok'] ) ) {
				$state['stopped'] = time();
				Settings::patch(
					array(
						'cdn'        => false,
						'cdn_state'  => $state,
						'generation' => (int) $s['generation'] + 1,
					)
				);
				self::schedule( false );
				Activity::add( 'cdn_stopped' );
				return;
			}
			Settings::patch( array( 'cdn_state' => $state ) );
		} finally {
			Reviewed_Store::leave( $held );
		}
	}

	/* ---- The page a visitor gets ---- */

	/**
	 * Rewrite a public page's picture addresses to the CDN, where delivery allows it: a pass on the page's whole HTML
	 * through WordPress's template enhancement output buffer (Hooks::PAGE_HTML), last of Image Manager's passes.
	 */
	public static function start_buffer(): void {
		if ( ! self::active() || ! Delivery::allowed( 'cdn' ) ) {
			return;
		}
		$cdn = (string) Settings::get()['cdn_url'];
		add_filter(
			Hooks::PAGE_HTML,
			static function ( string $html ) use ( $cdn ): string {
				try {
					return self::rewrite( $html, $cdn );
				} catch ( \Throwable $e ) {
					return $html;
				} // An address change never breaks a page: the site keeps serving its own.
			},
			Hooks::PASS_CDN
		);
	}
	/**
	 * Every picture address in the uploads folder (same host, absolute, protocol-relative or root-relative) in a value.
	 *
	 * @param string $value An attribute or style value.
	 * @param string $cdn   The CDN address.
	 * @return string The value with those addresses pointing to the CDN.
	 */
	public static function value( string $value, string $cdn ): string {
		$u = wp_parse_url( wp_get_upload_dir()['baseurl'] );
		if ( ! is_array( $u ) || empty( $u['host'] ) ) {
			return $value;
		}
		$host    = preg_quote( strtolower( (string) $u['host'] ), '~' ) . ( isset( $u['port'] ) ? ':' . (int) $u['port'] : '' );
		$raw     = rtrim( (string) ( $u['path'] ?? '' ), '/' );
		$pattern = '~(?:(?:https?:)?//' . $host . '|(?<=^|[\s,("\'=]))(' . preg_quote( $raw, '~' ) . '/[^\s,"\'()<>?#]+\.(?:jpe?g|png|gif|webp|avif))(\?[^\s,"\'()<>#]*)?(?=$|[\s,"\'()<>#])~i';
		$out     = preg_replace_callback(
			$pattern,
			static function ( $m ) use ( $cdn, $raw ) {
				$relative = substr( $m[1], strlen( $raw ) + 1 );
				foreach ( self::PRIVATE_FOLDERS as  $folder ) {
					if ( str_starts_with( $relative, $folder ) ) {
						return $m[0];
					}
				}
				if ( str_contains( $m[1], '..' ) ) {
					return $m[0];
				}
				return self::address( $cdn, $m[1] ) . ( $m[2] ?? '' );
			},
			$value
		);
		return is_string( $out ) ? $out : $value;
	}
	/**
	 * Bounded attribute pass over the finished page. Only addresses change.
	 *
	 * @param string $html The page.
	 * @param string $cdn  The CDN address.
	 * @return string The page with its picture addresses on the CDN.
	 */
	public static function rewrite( string $html, string $cdn ): string {
		if ( '' === $html || strlen( $html ) > 2097152 || ! class_exists( '\WP_HTML_Tag_Processor' ) ) {
			return $html;
		}
		foreach ( headers_list() as  $header ) {
			if ( preg_match( '/^content-type:\s*([^;]+)/i', $header, $m ) && ! in_array( strtolower( trim( $m[1] ) ), array( 'text/html', 'application/xhtml+xml' ), true ) ) {
				return $html;
			}
		}
		$p = new \WP_HTML_Tag_Processor( $html );
		if ( ! method_exists( $p, 'set_attribute' ) ) {
			return $html;
		}
		$n       = 0;
		$changed = 0;
		while ( $n++ < 20000 && $p->next_tag() ) {
			$tag = $p->get_tag();
			if ( in_array( $tag, array( 'SCRIPT', 'STYLE' ), true ) ) {
				continue;
			}
			foreach ( self::ATTRS as  $attr ) {
				$value = $p->get_attribute( $attr );
				if ( ! is_string( $value ) || '' === $value ) {
					continue;
				}
				if ( 'href' === $attr && ! in_array( $tag, array( 'A', 'LINK' ), true ) ) {
					continue;
				}
				if ( 'LINK' === $tag && 'href' === $attr && 'preload' !== strtolower( (string) $p->get_attribute( 'rel' ) ) ) {
					continue;
				}
				$new = self::value( $value, $cdn );
				if ( $new !== $value ) {
					$p->set_attribute( $attr, $new );
					++$changed;
				}
			}
		}
		return $changed ? $p->get_updated_html() : $html;
	}
	/**
	 * The words for a CDN check's reason.
	 *
	 * @param string $reason The reason code.
	 * @param int    $status The HTTP status the CDN answered with, when it is about one.
	 * @return string The translated words.
	 */
	public static function human( string $reason, int $status = 0 ): string {
		$messages = array(
			'cdn_ok'          => __( 'Checked: the CDN fetched a new test picture from this site and returned it unchanged.', 'affstackdev-image-manager' ),
			'cdn_unreachable' => __( 'The CDN address did not answer (or this server may not connect to it). Pictures come from your site.', 'affstackdev-image-manager' ),
			/* translators: %d: HTTP status code, such as 404. */
			'cdn_status'      => sprintf( __( 'The CDN answered with status %d instead of the test picture. Check that the CDN pulls from this site (its origin is this site’s address). Pictures come from your site.', 'affstackdev-image-manager' ), $status ),
			'cdn_wrong_file'  => __( 'The CDN returned a different file than this site has. If it optimizes or converts pictures itself, switch that off for this site. Pictures come from your site.', 'affstackdev-image-manager' ),
			'cdn_storage'     => __( 'Image Manager could not write its test picture in the uploads folder. Check Tools for storage status.', 'affstackdev-image-manager' ),
			'cdn_jetpack'     => __( 'Jetpack’s image CDN is active. Use one CDN for pictures: switch Jetpack’s image CDN off to use your own.', 'affstackdev-image-manager' ),
			'cdn_address'     => __( 'Enter the CDN address as https://cdn.example.com (an optional path is allowed, nothing after it).', 'affstackdev-image-manager' ),
			'cdn_same_host'   => __( 'That is this site’s own address. Enter the CDN’s own address, such as https://example.b-cdn.net.', 'affstackdev-image-manager' ),
		);
		return $messages[ $reason ] ?? __( 'The CDN check could not finish. Pictures come from your site.', 'affstackdev-image-manager' );
	}
}