<?php
/**
 * Backgrounds are just PNGs in img/bg/, generated by tools/background.py.
 * Drop a new one in and it joins the cycle automatically -- this list drives
 * both the CSS custom properties and the footer cycler.
 */

function bg_styles(): array
{
    static $names = null;
    if ($names !== null) {
        return $names;
    }
    $files = glob(__DIR__ . '/../img/bg/*.png') ?: [];
    $names = array_map(static fn($f) => pathinfo($f, PATHINFO_FILENAME), $files);
    sort($names);
    return $names;
}

function bg_default(): string
{
    $all = bg_styles();
    return in_array('flow', $all, true) ? 'flow' : ($all[0] ?? '');
}

/** A different style on every page load. */
function bg_pick(): string
{
    $all = bg_styles();
    return $all ? $all[random_int(0, count($all) - 1)] : '';
}