Solution to return filenames

index.php

<?php
/**
 * Solution to return image names
 *
 * @param string $S
 *
 * @return string
 */
function solution($S)
{
    $rawPhotos = explode("\n", $S);
    $locations = $finalNames = $photos = $locationArray = [];
    foreach ($rawPhotos as $index => $rawPhoto) {
        list($filename, $location, $datetime) = explode(",", $rawPhoto);
        if (empty($locations[trim($location)][$filename])) {
            $locations[trim($location)][$filename] = 0;
        }
        $locations[trim($location)][$filename] = count($locations[trim($location)]);
        $locationArray[trim($location)] = empty($locationArray[trim($location)]) ? 1 : $locationArray[trim($location)]+1;
        $photos[] = [
            'index'     => $index,
            'filename'  => $filename,
            'date'      => trim($datetime),
            'location'  => trim($location)
        ];
    }
    usort($photos, function ($a, $b) {
        return strtotime($a['date']) - strtotime($b['date']);
    });
    foreach ($photos as $index => $photo) {
        $strPad = strlen((string)($locationArray[$photo['location']]));
        $number = str_pad($locations[$photo['location']][$photo['filename']], $strPad, '0', STR_PAD_LEFT);
        $finalNames[$photo['index']] = $photo['location'] . $number . '.'. pathinfo($photo['filename'], PATHINFO_EXTENSION);
    }
    return implode("\n", $finalNames);
}