<?php
/** @package HolmesPortfolio_Forms */

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

final class HP_Forms_Draft {

	const LIFETIME_SECONDS = DAY_IN_SECONDS;
	const TRANSIENT_PREFIX = 'holmesforms_draft_';
	const SALT_SCHEME      = 'holmesforms_draft_token';
	const USED_PREFIX      = 'holmesforms_draft_used_';

	const DRAFT_ID_RANDOM_LENGTH = 16;
	const BIND_SECRET_LENGTH     = 32;
	const CLOCK_SKEW_SECONDS     = 5 * MINUTE_IN_SECONDS;
	const MAX_QUERY_PARAMETERS   = 30;

	private static $issued_secrets = array();

	public static function fetch( $key ) {
		$stored = get_transient( $key );
		if ( ! is_string( $stored ) ) {
			return $stored;
		}
		$data = json_decode( HP_Forms_Crypt::decrypt( $stored ), true );
		return is_array( $data ) ? $data : false;
	}

	public static function store( $key, array $data, $ttl ) {
		return set_transient( $key, HP_Forms_Crypt::encrypt( (string) wp_json_encode( $data ) ), $ttl );
	}

	public static function create( $form_id ) {
		$form_id  = absint( $form_id );
		$draft_id = sprintf( '%08x', time() ) . wp_generate_password( self::DRAFT_ID_RANDOM_LENGTH, false, false );

		return array(
			'token'    => self::signed_token( $form_id, $draft_id ),
			'draft_id' => $draft_id,
		);
	}

	public static function ensure( $draft_id, $form_id, array $meta = array() ) {
		$draft_id = self::clean_id( $draft_id );
		if ( is_array( self::fetch( self::TRANSIENT_PREFIX . $draft_id ) ) ) {
			return;
		}
		self::store( self::TRANSIENT_PREFIX . $draft_id, self::new_draft_data( (int) $form_id, $meta, time() ), self::LIFETIME_SECONDS );
	}

	public static function needs_new_token( $token ) {
		$parts = is_string( $token ) ? explode( '.', $token ) : array();
		if ( 3 !== count( $parts ) ) {
			return true;
		}
		list( $form_id, $draft_id, $signature ) = $parts;

		$draft_id = self::clean_id( $draft_id );
		if ( ! hash_equals( self::token_signature( absint( $form_id ), $draft_id ), (string) $signature ) || ! self::is_fresh( $draft_id ) ) {
			return true;
		}
		$draft = self::fetch( self::TRANSIENT_PREFIX . $draft_id );
		return ! is_array( $draft ) || ! empty( $draft['bind'] ) || empty( $draft['meta']['resume_key'] );
	}

	private static function new_draft_data( $form_id, array $meta, $started ) {
		return array(
			'form_id'  => (int) $form_id,
			'answers'  => array(),
			'meta'     => $meta,
			'started'  => (int) $started,
			'furthest' => 0,
		);
	}

	private static function is_fresh( $draft_id ) {
		$issued_at = hexdec( substr( (string) $draft_id, 0, 8 ) );
		return $issued_at > time() - self::LIFETIME_SECONDS && $issued_at < time() + self::CLOCK_SKEW_SECONDS;
	}

	private static function request_meta() {
		// phpcs:disable WordPress.Security.NonceVerification.Missing -- a visitor's form on a cached page has no nonce; the address is kept only if it is on this site.
		$url = '';
		foreach ( array( 'holmesforms_url', 'holmesforms_redirect' ) as $field_name ) {
			if ( ! empty( $_POST[ $field_name ] ) && is_string( $_POST[ $field_name ] ) ) {
				$url = esc_url_raw( wp_unslash( $_POST[ $field_name ] ) );
				break;
			}
		}
		// phpcs:enable
		if ( '' === $url && ! empty( $_SERVER['HTTP_REFERER'] ) ) {
			$url = esc_url_raw( wp_unslash( $_SERVER['HTTP_REFERER'] ) );
		}
		$home_url = set_url_scheme( trailingslashit( home_url() ), 'https' );
		$scheme   = strtolower( (string) wp_parse_url( $url, PHP_URL_SCHEME ) );
		if ( '' !== $url && ( ! in_array( $scheme, array( 'http', 'https' ), true ) || 0 !== strpos( set_url_scheme( trailingslashit( $url ), 'https' ), $home_url ) ) ) {
			$url = '';
		}
		$url   = remove_query_arg( array( 'holmesforms_resume', 'holmesforms_errors', 'holmesforms_error', 'holmesforms_sent', 'holmesforms_form' ), $url );
		$query = array();
		parse_str( (string) wp_parse_url( $url, PHP_URL_QUERY ), $raw_query );
		foreach ( (array) $raw_query as $key => $value ) {
			if ( is_scalar( $value ) && count( $query ) < self::MAX_QUERY_PARAMETERS ) {
				$query[ sanitize_key( $key ) ] = sanitize_text_field( (string) $value );
			}
		}
		return array(
			'url'   => explode( '?', $url )[0],
			'query' => $query,
		);
	}

	/** @return string The form's page address, query included. */
	public static function page_url( array $draft ) {
		$url = isset( $draft['meta']['url'] ) ? (string) $draft['meta']['url'] : '';
		if ( '' !== $url && ! empty( $draft['meta']['query'] ) && is_array( $draft['meta']['query'] ) ) {
			$url = add_query_arg( array_map( 'rawurlencode', $draft['meta']['query'] ), $url );
		}
		return $url;
	}

	public static function load( $token ) {
		$parts = is_string( $token ) ? explode( '.', $token ) : array();
		if ( 3 !== count( $parts ) ) {
			return null;
		}

		list( $form_id, $draft_id, $signature ) = $parts;

		$form_id  = absint( $form_id );
		$draft_id = self::clean_id( $draft_id );

		if ( ! hash_equals( self::token_signature( $form_id, $draft_id ), (string) $signature ) ) {
			return null;
		}

		if ( ! self::is_fresh( $draft_id ) ) {
			return null;
		}
		$draft = self::fetch( self::TRANSIENT_PREFIX . $draft_id );
		if ( ! is_array( $draft ) ) {
			if ( false !== get_transient( self::USED_PREFIX . $draft_id ) ) {
				return null;
			}
			$draft = self::new_draft_data( $form_id, self::request_meta(), hexdec( substr( $draft_id, 0, 8 ) ) );
			self::store( self::TRANSIENT_PREFIX . $draft_id, $draft, self::LIFETIME_SECONDS );
		}
		if ( ! isset( $draft['form_id'] ) || (int) $draft['form_id'] !== $form_id ) {
			return null;
		}

		$bind_header = isset( $_SERVER['HTTP_X_HPF_BIND'] ) ? preg_replace( '/[^A-Za-z0-9]/', '', sanitize_text_field( wp_unslash( $_SERVER['HTTP_X_HPF_BIND'] ) ) ) : '';
		if ( ! empty( $draft['bind'] ) ) {
			$is_bound = false;
			foreach ( array( $bind_header, isset( self::$issued_secrets[ $draft_id ] ) ? self::$issued_secrets[ $draft_id ] : '' ) as $candidate ) {
				if ( '' !== $candidate && hash_equals( (string) $draft['bind'], self::bind_hash( $draft_id, $candidate ) ) ) {
					$is_bound = true;
				}
			}
			if ( ! $is_bound ) {
				return null;
			}
		} elseif ( ( ( defined( 'REST_REQUEST' ) && REST_REQUEST ) || wp_doing_ajax() ) && ! headers_sent() ) {
			$secret        = strlen( $bind_header ) >= self::BIND_SECRET_LENGTH ? $bind_header : wp_generate_password( self::BIND_SECRET_LENGTH, false, false );
			$draft['bind'] = self::bind_hash( $draft_id, $secret );
			self::store( self::TRANSIENT_PREFIX . $draft_id, $draft, self::LIFETIME_SECONDS );
			self::$issued_secrets[ $draft_id ] = $secret;
			header( 'X-HPF-Bind: ' . $secret );
		}

		return array(
			'form_id'  => $form_id,
			'draft_id' => $draft_id,
			'answers'  => isset( $draft['answers'] ) && is_array( $draft['answers'] ) ? $draft['answers'] : array(),
			'meta'     => isset( $draft['meta'] ) && is_array( $draft['meta'] ) ? $draft['meta'] : array(),
			'started'  => isset( $draft['started'] ) ? (int) $draft['started'] : time(),
			'review'   => ! empty( $draft['review'] ),
			'kept'     => isset( $draft['kept'] ) && is_array( $draft['kept'] ) ? $draft['kept'] : array(),
			'changing' => isset( $draft['changing'] ) ? (string) $draft['changing'] : '',
		);
	}

	public static function merge_answers( $draft_id, array $answers ) {
		$key   = self::TRANSIENT_PREFIX . self::clean_id( $draft_id );
		$draft = self::fetch( $key );
		if ( ! is_array( $draft ) ) {
			return;
		}

		$draft['answers'] = array_merge(
			isset( $draft['answers'] ) && is_array( $draft['answers'] ) ? $draft['answers'] : array(),
			$answers
		);

		self::store( $key, $draft, self::LIFETIME_SECONDS );
	}

	public static function forget_answers( $draft_id, array $keys ) {
		if ( ! $keys ) {
			return;
		}
		$key   = self::TRANSIENT_PREFIX . self::clean_id( $draft_id );
		$draft = self::fetch( $key );
		if ( ! is_array( $draft ) || empty( $draft['answers'] ) ) {
			return;
		}
		foreach ( $keys as $answer_key ) {
			unset( $draft['answers'][ $answer_key ] );
		}
		self::store( $key, $draft, self::LIFETIME_SECONDS );
	}

	public static function set_review( $draft_id, $is_review ) {
		$key   = self::TRANSIENT_PREFIX . self::clean_id( $draft_id );
		$draft = self::fetch( $key );
		if ( ! is_array( $draft ) ) {
			return;
		}
		if ( $is_review ) {
			$draft['review'] = true;
		} else {
			unset( $draft['review'] );
		}
		self::store( $key, $draft, self::LIFETIME_SECONDS );
	}

	public static function keep_page( $draft_id, $page_id, array $answers ) {
		self::patch(
			$draft_id,
			static function ( array $draft ) use ( $page_id, $answers ) {
				if ( ! isset( $draft['kept'] ) || ! is_array( $draft['kept'] ) ) {
					$draft['kept'] = array();
				}
				$draft['kept'][ $page_id ] = $answers;
				return $draft;
			}
		);
	}

	public static function drop_kept( $draft_id, $page_id ) {
		self::patch(
			$draft_id,
			static function ( array $draft ) use ( $page_id ) {
				unset( $draft['kept'][ $page_id ] );
				if ( empty( $draft['kept'] ) ) {
					unset( $draft['kept'] );
				}
				return $draft;
			}
		);
	}

	public static function forget_everywhere( $draft_id, array $keys ) {
		if ( ! $keys ) {
			return;
		}
		self::patch(
			$draft_id,
			static function ( array $draft ) use ( $keys ) {
				foreach ( $keys as $key ) {
					unset( $draft['answers'][ $key ] );
					foreach ( array_keys( isset( $draft['kept'] ) && is_array( $draft['kept'] ) ? $draft['kept'] : array() ) as $page_id ) {
						unset( $draft['kept'][ $page_id ][ $key ] );
					}
				}
				return $draft;
			}
		);
	}

	/** @param string $page_id The page opened from Check your answers, or '' once it is confirmed or cancelled. */
	public static function set_changing( $draft_id, $page_id ) {
		self::patch(
			$draft_id,
			static function ( array $draft ) use ( $page_id ) {
				if ( '' === $page_id ) {
					unset( $draft['changing'] );
				} else {
					$draft['changing'] = $page_id;
				}
				return $draft;
			}
		);
	}

	private static function patch( $draft_id, callable $change ) {
		$key   = self::TRANSIENT_PREFIX . self::clean_id( $draft_id );
		$draft = self::fetch( $key );
		if ( ! is_array( $draft ) ) {
			return;
		}
		self::store( $key, $change( $draft ), self::LIFETIME_SECONDS );
	}

	/** @return bool True when it is a new furthest page. */
	public static function mark_furthest( $draft_id, $position ) {
		$key   = self::TRANSIENT_PREFIX . self::clean_id( $draft_id );
		$draft = self::fetch( $key );
		if ( ! is_array( $draft ) ) {
			return false;
		}
		$position = max( 1, (int) $position );
		if ( $position <= (int) ( $draft['furthest'] ?? 0 ) ) {
			return false;
		}
		$draft['furthest'] = $position;
		self::store( $key, $draft, self::LIFETIME_SECONDS );
		return true;
	}

	public static function was_sent( $token ) {
		$parts = is_string( $token ) ? explode( '.', $token ) : array();
		if ( 3 !== count( $parts ) ) {
			return false;
		}
		$draft_id = self::clean_id( $parts[1] );
		return hash_equals( self::token_signature( absint( $parts[0] ), $draft_id ), (string) $parts[2] )
			&& false !== get_transient( self::USED_PREFIX . $draft_id );
	}

	public static function destroy( $draft_id ) {
		$draft_id = self::clean_id( $draft_id );
		delete_transient( self::TRANSIENT_PREFIX . $draft_id );
		$seconds_left = hexdec( substr( $draft_id, 0, 8 ) ) + self::LIFETIME_SECONDS - time();
		if ( $seconds_left > 0 ) {
			set_transient( self::USED_PREFIX . $draft_id, 1, $seconds_left );
		}
	}

	public static function clean_id( $draft_id ) {
		return preg_replace( '/[^A-Za-z0-9]/', '', (string) $draft_id );
	}

	private static function bind_hash( $draft_id, $secret ) {
		return hash_hmac( 'sha256', 'bind|' . $draft_id . '|' . $secret, wp_salt( self::SALT_SCHEME ) );
	}

	private static function signed_token( $form_id, $draft_id ) {
		return $form_id . '.' . $draft_id . '.' . self::token_signature( $form_id, $draft_id );
	}

	private static function token_signature( $form_id, $draft_id ) {
		return hash_hmac( 'sha256', $form_id . '|' . $draft_id, wp_salt( self::SALT_SCHEME ) );
	}
}