landingpage-haus-schleusingen/app/Controllers/LocaleSwitcher.php

<?php

declare(strict_types=1);

namespace App\Controllers;

use App\Core\I18n;
use App\Core\Locale;

/**
 * Renders the language switcher widget. Pure HTML generation — no
 * side effects, no header writing.
 *
 * Single <details>-based dropdown shown at every viewport. The
 * trigger is a flag-sized button (24×16 SVG + tiny caret) that
 * opens to a menu of all 4 supported locales.
 *
 * Each menu option gets:
 *   - an inline 24×16 SVG flag,
 *   - `hreflang` and `lang` for SEO and screen readers,
 *   - `aria-current="true"` on the active option.
 *
 * The active option is rendered as a <span> (not a link) so it
 * cannot be reactivated. The trigger and every menu option are
 * ≥44px touch targets via CSS.
 */
final class LocaleSwitcher
{
    public function __construct(
        private readonly string $currentLocale,
        private readonly string $currentPath,
    ) {
    }

    public function render(): string
    {
        $path      = $this->sanitisePath($this->currentPath);
        $ariaLabel = htmlspecialchars(
            I18n::t('locale.switcher.aria', [], $this->currentLocale),
            ENT_QUOTES,
            'UTF-8',
        );

        $currentName = htmlspecialchars(
            I18n::t('locale.' . $this->currentLocale, [], $this->currentLocale),
            ENT_QUOTES,
            'UTF-8',
        );
        $currentCode = htmlspecialchars($this->currentLocale, ENT_QUOTES, 'UTF-8');
        $currentFlag = self::flagImg($this->currentLocale);

        $html  = '<details class="locale-switcher">';
        $html .= '<summary class="locale-switcher__trigger"'
               . ' aria-label="' . $ariaLabel . '"'
               . ' title="' . $currentName . '"'
               . '>';
        $html .= '<span class="locale-switcher__current" lang="' . $currentCode . '">';
        $html .= $currentFlag;
        $html .= '</span>';
        $html .= '<span class="locale-switcher__caret" aria-hidden="true">▾</span>';
        $html .= '</summary>';
        $html .= '<ul class="locale-switcher__menu" role="list">';
        foreach (Locale::SUPPORTED as $code) {
            $isCurrent = $code === $this->currentLocale;
            $name      = htmlspecialchars(
                I18n::t('locale.' . $code, [], $this->currentLocale),
                ENT_QUOTES,
                'UTF-8',
            );
            $codeAttr  = htmlspecialchars($code, ENT_QUOTES, 'UTF-8');
            $flag      = self::flagImg($code);

            $html .= '<li>';
            if ($isCurrent) {
                $html .= '<span class="locale-switcher__option is-current"'
                       . ' aria-current="true"'
                       . ' lang="' . $codeAttr . '">'
                       . $flag
                       . '<span class="locale-switcher__label">' . $name . '</span>'
                       . '</span>';
            } else {
                $url = '/locale?set=' . rawurlencode($code) . '&amp;return=' . rawurlencode($path);
                $html .= '<a class="locale-switcher__option"'
                       . ' href="' . $url . '"'
                       . ' hreflang="' . $codeAttr . '"'
                       . ' lang="' . $codeAttr . '"'
                       . ' rel="alternate"'
                       . '>'
                       . $flag
                       . '<span class="locale-switcher__label">' . $name . '</span>'
                       . '</a>';
            }
            $html .= '</li>';
        }
        $html .= '</ul>';
        $html .= '</details>';

        return $html;
    }

    /**
     * Country flag for the given locale. Renders a 24×18 <img>
     * pointing at the official flag-icons SVG asset shipped under
     * public/img/flags/. 4:3 aspect (de/gb/ua/ru), crisp at any DPI,
     * no external CDN dependency.
     *
     * Decorative: `alt=""` (the visible locale-switcher label and
     * the <a>'s `hreflang`/`lang` carry the accessible name).
     */
    public static function flagImg(string $locale): string
    {
        $src = self::flagSource($locale);
        // 32×24 = ~4:3, large enough that the flag is the visual
        // anchor of the option. No loading="lazy" — these are 4
        // small SVGs that must be ready the moment the <details>
        // opens (lazy would cause a flash of empty boxes).
        return '<img class="flag" src="' . $src . '" alt="" width="32" height="24">';
    }

    /**
     * Map our locale codes to flag-icons file names. Locale "en"
     * is en-GB per ADR-002, so the asset is "gb.svg". Anything we
     * do not know falls back to a transparent 1×1 gif so the layout
     * stays intact and the alt text (from the surrounding <a>) is
     * the only signal.
     */
    private static function flagSource(string $locale): string
    {
        $file = match ($locale) {
            'de' => 'de',
            'en' => 'gb',
            'uk' => 'ua',
            'ru' => 'ru',
            default => null,
        };
        if ($file === null) {
            return 'data:image/gif;base64,R0lGODlhAQABAAAAACwAAAAAAQABAAACAkQBADs=';
        }
        return '/img/flags/' . $file . '.svg';
    }

    /**
     * Make sure the path is safe to embed as a query string value and
     * a redirect target. Drops query/fragment, keeps only the path.
     */
    private function sanitisePath(string $path): string
    {
        $path = parse_url($path, PHP_URL_PATH) ?: '/';
        if ($path === '' || $path[0] !== '/') {
            return '/';
        }
        return $path;
    }
}