Theme Performance and Caching

$ucid = (int) Money::getUCID();

$rows = Cache::remember('website', 'acme_footer_' . $ucid . '_' . Language::selected(), 3600,
    fn (): array => Products::group_cards($ucid));

$out = Cache::remember('website', 'software_store_' . $categoryId . '_' . $ucid . '_' . Language::selected(), 3600,
    function () use ($ucid, $categoryId): array {
        // one query, many rows, shaped for the template
        return $this->build($categoryId, $ucid);
    });

// OUTSIDE the producer: this must run on every request, cached or not.
$ctx = ['currency' => $ucid, 'category' => $categoryId];
Hook::runRefs('filter:product.software_list', $out, $ctx);

return $out;

// coremio/classes/Cache.php
// Returns whatever the producer returns: array, string, int, object.
public static function remember(string $name, string $key, int $ttl, callable $producer);

// coremio/classes/Cache.php
public static function getInstance(): self;

public function store($key, $data, $expiration = 86400): bool;   // $expiration = 0 never expires
public function retrieve($key, $timestamp = false);              // null when missing or unreadable
public function isCached($key): bool;                            // also drops the entry if expired
public function erase($key): self;                               // drops one entry
public function eraseAll(): self;                                // empties the bucket this instance points at
public function clear($keys = []): void;                         // named buckets, or no argument = every bucket

/*
 * ONE handler per theme: the view layer keeps only the last returned value, so a second
 * registration would drop every key set here. Add keys, do not add a second Hook::add.
 */
Hook::add("filter:template.variables", 1, function ($template, $data) {
    $data["footer_groups"] = acme_footer_groups();

    return $data;
});

if (!function_exists('acme_footer_groups')) {
    /**
     * Product group cards for the footer strip. Runs on every website page, so the query
     * behind it is cached; the value is shared by every visitor, which is exactly why the
     * key has to carry the two things that make it visitor-specific.
     */
    function acme_footer_groups(): array
    {
        // Same request, several partials: skip even the key building.
        static $rows = null;
        if ($rows !== null) return $rows;

        // Currency comes from the visitor, links come from the selected language.
        // Both go in the key, or the first visitor's version is served to everyone.
        $ucid = (int) Money::getUCID();

        $rows = Cache::remember('website', 'acme_footer_groups_' . $ucid . '_' . Language::selected(), 3600,
            fn (): array => Products::group_cards($ucid));

        return $rows;
    }
}