<?php

declare(strict_types=1);

namespace App\Services;

use App\Dto\IcsContentDto;

class IcsGeneratorService
{
    public function __construct(
        private readonly string $appName
    ) {
        if (empty($this->appName)) {
            throw new \InvalidArgumentException('App name must be provided for ICS generation.');
        }
    }

    public function generate(IcsContentDto $event): string
    {
        $dateFormat = 'Ymd\THis\Z';
        $lines      = [
            'BEGIN:VCALENDAR',
            'VERSION:2.0',
            'PRODID:-//' . $this->appName . '//NONSGML v1.0//EN',
            'BEGIN:VEVENT',
            'UID:' . $event->uid,
            'DTSTAMP:' . now()->setTimezone('UTC')->format($dateFormat),
            'DTSTART:' . $event->startsAt->setTimezone('UTC')->format($dateFormat),
            'DTEND:' . $event->endsAt->setTimezone('UTC')->format($dateFormat),
            'SUMMARY:' . $this->escape($event->summary),
            'DESCRIPTION:' . $this->escape($event->description),
        ];

        if ($event->url) {
            $lines[] = 'URL:' . $this->escape($event->url);
        }

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

        // NOTE: ICS files must have CRLF line endings
        return implode("\r\n", $lines) . "\r\n";
    }

    private function escape(string $text): string
    {
        $text = str_replace('\\', '\\\\', $text);
        $text = str_replace(';', '\;', $text);
        $text = str_replace(',', '\,', $text);
        $text = str_replace("\n", '\n', $text);

        return $text;
    }
}