<?php
/** Read model: derive all reporting periods from the same daily counters. */
namespace EmbodiedAssistant;
if (!defined('ABSPATH')) { exit; }

class UsageReport {
    /** UTC calendar weeks start Monday. Include empty and partial periods. */
    public function group(array $daily, $from, $to, $period) {
        $period = in_array($period, array('day', 'week', 'month'), true) ? $period : 'day';
        $indexed = array_column($daily, null, 'usage_day');
        $rows = array();
        $day = new \DateTimeImmutable($from, new \DateTimeZone('UTC'));
        $last = new \DateTimeImmutable($to, new \DateTimeZone('UTC'));
        while ($day <= $last) {
            $date = $day->format('Y-m-d');
            $key = 'month' === $period ? $day->format('Y-m') : ('week' === $period ? $day->modify('monday this week')->format('Y-m-d') : $date);
            if (!isset($rows[$key])) { $rows[$key] = array('from' => $date, 'to' => $date, 'sessions' => 0, 'seconds' => 0); }
            $rows[$key]['to'] = $date;
            $rows[$key]['sessions'] += (int) ($indexed[$date]['sessions'] ?? 0);
            $rows[$key]['seconds'] += (int) ($indexed[$date]['seconds'] ?? 0);
            $day = $day->modify('+1 day');
        }
        return array_reverse(array_values($rows));
    }
}