<?php

class EventPage extends Page
{
    public function sortedDates(): array
    {
        $groups = array_values($this->dates()->toStructure()->data());

        usort($groups, fn($a, $b) => strcmp(
            $this->firstDateOf($a),
            $this->firstDateOf($b)
        ));

        return $groups;
    }

    private function firstDateOf($group): string
    {
        $dates = array_filter(array_map(
            fn($item) => $item->date()->value(),
            array_values($group->dates()->toStructure()->data())
        ));

        return !empty($dates) ? min($dates) : '';
    }
}