<?php

namespace App\Http\Controllers;

use App\Models\CalendarInstance;
use Illuminate\Support\Facades\Response;
use Carbon\Carbon;

class IcsController extends Controller
{
    public function download(string $calendarUri)
    {
        $instance = CalendarInstance::where('uri', $calendarUri)->firstOrFail();

        $calendar = $instance->calendar()->with(['events.meta'])->firstOrFail();
        $timezone = $instance->timezone ?? 'UTC';

        $ical = $this->generateICalendarFeed($calendar->events, $timezone);

        return Response::make($ical, 200, [
            'Content-Type' => 'text/calendar; charset=utf-8',
            'Content-Disposition' => 'inline; filename="' . $calendarUri . '.ics"',
        ]);
    }

    protected function generateICalendarFeed($events, string $tz): string
    {
        $output = [];
        $output[] = 'BEGIN:VCALENDAR';
        $output[] = 'VERSION:2.0';
        $output[] = 'PRODID:-//Kithkin Calendar//EN';
        $output[] = 'CALSCALE:GREGORIAN';
        $output[] = 'METHOD:PUBLISH';

        foreach ($events as $event) {
            $meta = $event->meta;

            if (!$meta || !$meta->start_at || !$meta->end_at) {
                continue;
            }

            $start = Carbon::parse($meta->start_at)->timezone($tz)->format('Ymd\THis');
            $end = Carbon::parse($meta->end_at)->timezone($tz)->format('Ymd\THis');

            $output[] = 'BEGIN:VEVENT';
            $output[] = 'UID:' . $event->uid;
            $output[] = 'SUMMARY:' . $this->escape($meta->title ?? '(Untitled)');
            $output[] = 'DESCRIPTION:' . $this->escape($meta->description ?? '');
            $output[] = 'DTSTART;TZID=' . $tz . ':' . $start;
            $output[] = 'DTEND;TZID=' . $tz . ':' . $end;
            $output[] = 'DTSTAMP:' . Carbon::parse($event->lastmodified)->format('Ymd\THis\Z');
            if ($meta->location) {
                $output[] = 'LOCATION:' . $this->escape($meta->location);
            }
            $output[] = 'END:VEVENT';
        }

        $output[] = 'END:VCALENDAR';

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

    protected function escape(?string $text): string
    {
        return str_replace(['\\', ';', ',', "\n"], ['\\\\', '\;', '\,', '\n'], $text ?? '');
    }
}