<?php
/**
 * ICS calendar payload generator.
 *
 * @package Bookline
 */

declare( strict_types=1 );

namespace Bookline\Domain\Notification;

use DateTimeImmutable;
use DateTimeZone;

/**
 * Builds a minimal RFC 5545 VCALENDAR document.
 *
 * @since 0.1.0
 */
final class IcsGenerator {

	/**
	 * Generate an ICS document.
	 *
	 * @param string            $uid         Event UID.
	 * @param string            $summary     Summary.
	 * @param string            $description Description.
	 * @param DateTimeImmutable $start_utc   Start UTC.
	 * @param DateTimeImmutable $end_utc     End UTC.
	 * @param string|null       $location    Location text.
	 * @param string|null       $organizer   Organizer email.
	 *
	 * @since 0.1.0
	 */
	public function generate(
		string $uid,
		string $summary,
		string $description,
		DateTimeImmutable $start_utc,
		DateTimeImmutable $end_utc,
		?string $location = null,
		?string $organizer = null,
	): string {
		$utc   = new DateTimeZone( 'UTC' );
		$stamp = ( new DateTimeImmutable( 'now', $utc ) )->format( 'Ymd\THis\Z' );
		$dtstart = $start_utc->setTimezone( $utc )->format( 'Ymd\THis\Z' );
		$dtend   = $end_utc->setTimezone( $utc )->format( 'Ymd\THis\Z' );

		$lines = [
			'BEGIN:VCALENDAR',
			'VERSION:2.0',
			'PRODID:-//Bookline//EN',
			'CALSCALE:GREGORIAN',
			'METHOD:PUBLISH',
			'BEGIN:VEVENT',
			'UID:' . $this->escape( $uid ),
			'DTSTAMP:' . $stamp,
			'DTSTART:' . $dtstart,
			'DTEND:' . $dtend,
			'SUMMARY:' . $this->escape( $summary ),
			'DESCRIPTION:' . $this->escape( $description ),
		];

		if ( null !== $location && '' !== $location ) {
			$lines[] = 'LOCATION:' . $this->escape( $location );
		}
		if ( null !== $organizer && '' !== $organizer ) {
			$lines[] = 'ORGANIZER:mailto:' . $this->escape( $organizer );
		}

		$lines[] = 'END:VEVENT';
		$lines[] = 'END:VCALENDAR';

		return implode( "\r\n", $lines ) . "\r\n";
	}

	/**
	 * Escape ICS text values.
	 *
	 * @param string $value Raw.
	 */
	private function escape( string $value ): string {
		$value = str_replace( [ '\\', ';', ',', "\n", "\r" ], [ '\\\\', '\\;', '\\,', "\\n", '' ], $value );
		return $value;
	}
}