<?php
function webinar_schedule_base_timezone(): DateTimeZone {
    static $timezone = null;

    if ($timezone === null) {
        $timezone = new DateTimeZone('Europe/Berlin');
    }

    return $timezone;
}

function webinar_default_title(): string {
    return 'Building Scalable Apps with AppWizzy';
}

function webinar_start_datetime(array $webinar): DateTimeImmutable {
    $scheduledAt = trim((string) ($webinar['scheduled_at'] ?? ''));

    if ($scheduledAt === '') {
        $scheduledAt = '2026-03-25 18:00:00';
    }

    return new DateTimeImmutable($scheduledAt, webinar_schedule_base_timezone());
}

function webinar_end_datetime(DateTimeImmutable $start, int $durationMinutes = 60): DateTimeImmutable {
    $durationMinutes = max(1, $durationMinutes);

    return $start->add(new DateInterval('PT' . $durationMinutes . 'M'));
}

function webinar_time_label(DateTimeInterface $start, string $timezone): string {
    $localStart = DateTimeImmutable::createFromInterface($start)->setTimezone(new DateTimeZone($timezone));

    return strtoupper($localStart->format('gA T'));
}

function webinar_utc_stamp(DateTimeInterface $dateTime): string {
    return DateTimeImmutable::createFromInterface($dateTime)
        ->setTimezone(new DateTimeZone('UTC'))
        ->format('Ymd\THis\Z');
}

function webinar_schedule_data(array $webinar, int $durationMinutes = 60): array {
    $title = trim((string) ($webinar['title'] ?? ''));
    if ($title === '') {
        $title = webinar_default_title();
    }

    $start = webinar_start_datetime($webinar);
    $end = webinar_end_datetime($start, $durationMinutes);

    $berlin = webinar_time_label($start, 'Europe/Berlin');
    $newYork = webinar_time_label($start, 'America/New_York');
    $losAngeles = webinar_time_label($start, 'America/Los_Angeles');

    return [
        'title' => $title,
        'start' => $start,
        'end' => $end,
        'date_long' => $start->format('l, F j, Y'),
        'berlin_label' => $berlin,
        'new_york_label' => $newYork,
        'los_angeles_label' => $losAngeles,
        'timezone_line' => $berlin . ' | ' . $newYork . ' | ' . $losAngeles,
        'hero_line' => strtoupper($start->format('l, F j') . ' | ' . $newYork . ' | ' . $losAngeles . ' | ' . $berlin),
        'calendar_sentence' => 'Professional Vibe-Coding Webinar. Join us on ' . $start->format('F jS') . ' at ' . $berlin . ' | ' . $newYork . ' | ' . $losAngeles . ' to learn the fastest way to go from an idea to a working app you own.',
        'calendar_description' => "Professional Vibe-Coding Webinar

Join us for this webinar on " . $start->format('F jS') . ' at ' . $berlin . ' | ' . $newYork . ' | ' . $losAngeles . '. The fastest way to go from an idea to a working app you own, running on your server, with your database, using real frameworks.',
    ];
}