<?php
/**
 * Local RFC 5545 calendar exports, without customer details or remote services.
 *
 * @package Abientot
 */

namespace Abientot\Support;

use DateTimeImmutable;
use InvalidArgumentException;

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

final class CalendarFile {
	/**
	 * @param array<string,mixed> $booking Appointment and public display details.
	 */
	public static function render( array $booking ): string {
		$dates = array();
		foreach ( array( 'start_utc', 'end_utc' ) as $key ) {
			$value = (string) ( $booking[ $key ] ?? '' );
			$date  = DateTimeImmutable::createFromFormat( '!Y-m-d H:i:s', $value, DateTimeHelper::utc_timezone() );
			if ( ! $date || $date->format( 'Y-m-d H:i:s' ) !== $value ) {
				throw new InvalidArgumentException( 'Invalid calendar date.' );
			}
			$dates[ $key ] = $date;
		}
		if ( $dates['end_utc'] <= $dates['start_utc'] ) {
			throw new InvalidArgumentException( 'Invalid calendar interval.' );
		}

		$lines = array(
			'BEGIN:VCALENDAR',
			'VERSION:2.0',
			'PRODID:-//Abientot//Booking//EN',
			'CALSCALE:GREGORIAN',
			'BEGIN:VEVENT',
			'UID:' . hash( 'sha256', home_url( '/' ) . '|' . (int) $booking['id'] ) . '@abientot',
			'DTSTAMP:' . gmdate( 'Ymd\THis\Z' ),
			'DTSTART:' . $dates['start_utc']->format( 'Ymd\THis\Z' ),
			'DTEND:' . $dates['end_utc']->format( 'Ymd\THis\Z' ),
			'SUMMARY:' . self::escape( (string) ( $booking['service'] ?? '' ) ),
			'LOCATION:' . self::escape( (string) ( $booking['location'] ?? '' ) ),
			'STATUS:' . ( 'confirmed' === ( $booking['status'] ?? '' ) ? 'CONFIRMED' : 'TENTATIVE' ),
			'END:VEVENT',
			'END:VCALENDAR',
		);

		return implode( "\r\n", array_map( array( self::class, 'fold' ), $lines ) ) . "\r\n";
	}

	private static function escape( string $value ): string {
		$value = wp_strip_all_tags( $value );
		$value = str_replace( array( "\r\n", "\r" ), "\n", $value );
		$value = preg_replace( '/[\x00-\x08\x0B\x0C\x0E-\x1F\x7F]/', '', $value );
		return str_replace( array( '\\', ';', ',', "\n" ), array( '\\\\', '\\;', '\\,', '\\n' ), $value );
	}

	/** Fold at 75 octets without splitting a UTF-8 character. */
	private static function fold( string $line ): string {
		$output = '';
		while ( strlen( $line ) > 75 ) {
			$length = 75;
			while ( ( ord( $line[ $length ] ) & 0xC0 ) === 0x80 ) {
				--$length;
			}
			$output .= substr( $line, 0, $length ) . "\r\n";
			$line    = ' ' . substr( $line, $length );
		}
		return $output . $line;
	}
}