Converts seconds to human reading duration like "4 days, 13 hours, 5 minutes, 49 seconds"

human_duration.php

<?php

function human_duration(int $seconds): string
{
    if ($seconds < 0) {
        return 'invalid';
    }

    if ($seconds === 0) {
        return 'now';
    }

    // Units
    $minute = 60;
    $hour = $minute * 60;
    $day = $hour * 24;
    $year = $day * 365;

    $parts = [ // Singular units, to easily add "s" when needed
        'year' => (int)floor($seconds / $year), // floor() returns float
        'day' => (int)floor($seconds % $year / $day),
        'hour' => (int)floor($seconds % $day / $hour),
        'minute' => (int)floor($seconds % $hour / $minute),
        'second' => $seconds % 60,
    ];

    // Keep significant parts
    $parts = array_filter($parts, fn ($value) => $value !== 0);

    // Build labels
    foreach ($parts as $unit => $value) {
        $parts[$unit] = $value . ' ' . $unit . ($value >= 2 ? 's' : '');
    }

    $result = implode(', ', $parts);

    return $result;
}