KantSites/src/Content/Consent.php

<?php

namespace App\Content;

use Symfony\Component\HttpFoundation\Cookie;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\Response;

/**
 * The visitor's decision about groups of content that may not load without consent.
 *
 * Two things matter here, and the banner is the smaller one. The banner only asks; what makes the
 * answer worth anything is that an embed does not load until it has been given - that is why
 * `granted()` is asked in the renderer and not only in the template.
 *
 * The decision lives in one first-party cookie and nowhere else: no server record, no identifier,
 * no third party. The cookie holds the version of the question, the groups that were granted and
 * when - nothing about the person. It is deliberately not signed: it describes what this browser
 * chose, so a forged value can only change what that same browser gets shown.
 */
final class Consent
{
    public const COOKIE = 'kant_consent';

    /**
     * Necessary content is not a group: it is what remains when nothing is granted, and it is
     * never asked about. Only these two can be asked about.
     */
    public const GROUPS = [
        'statistics' => 'Statistik',
        'external' => 'Externe Inhalte',
    ];

    public const GROUP_HELP = [
        'statistics' => 'Messung, wie die Website benutzt wird.',
        'external' => 'Inhalte von anderen Anbietern, etwa Karten, Videos, Bewertungen oder ein Chat. Sie sehen die Adresse dieser Seite und deine IP-Adresse, sobald sie geladen werden.',
    ];

    /**
     * Half a year, then the question is asked again. Long enough not to be a nuisance, short
     * enough that a decision is not silently eternal.
     */
    public const MAX_AGE = 15552000;

    /** Raise this when the groups or their meaning change: an old answer then no longer counts. */
    public const VERSION = 1;

    public function __construct(private SiteSettings $settings)
    {
    }

    /** Which groups this site asks about at all. Empty means: nothing to consent to. */
    public function askedGroups(): array
    {
        $settings = $this->settings->load();
        if (!$settings['consentBanner']) {
            return [];
        }

        return array_values(array_intersect(array_keys(self::GROUPS), $settings['consentGroups']));
    }

    /**
     * The stored decision, or null when there is none that still counts.
     *
     * @return array{granted: list<string>, at: int}|null
     */
    public function decision(Request $request): ?array
    {
        $raw = $request->cookies->get(self::COOKIE);
        if (!is_string($raw) || strlen($raw) > 200) {
            return null;
        }
        $parts = explode('|', $raw);
        if (3 !== count($parts) || (string) self::VERSION !== $parts[0]) {
            return null;
        }
        $at = filter_var($parts[2], FILTER_VALIDATE_INT);
        if (false === $at || $at <= 0 || $at + self::MAX_AGE < time()) {
            return null;
        }
        $granted = array_values(array_intersect(
            array_keys(self::GROUPS),
            '' === $parts[1] ? [] : explode(',', $parts[1]),
        ));

        return ['granted' => $granted, 'at' => $at];
    }

    /**
     * Whether a group may load.
     *
     * A group this site never asks about counts as granted: otherwise switching the banner off
     * would silently hide content that needs no consent.
     */
    public function granted(Request $request, string $group): bool
    {
        if (!in_array($group, $this->askedGroups(), true)) {
            return true;
        }

        return in_array($group, $this->decision($request)['granted'] ?? [], true);
    }

    /** Whether this request should be shown the question. */
    public function needsBanner(Request $request): bool
    {
        return [] !== $this->askedGroups() && null === $this->decision($request);
    }

    /** @param list<string> $groups */
    public function remember(Request $request, Response $response, array $groups): void
    {
        $granted = array_values(array_intersect($this->askedGroups(), $groups));
        $response->headers->setCookie(Cookie::create(
            self::COOKIE,
            sprintf('%d|%s|%d', self::VERSION, implode(',', $granted), time()),
            time() + self::MAX_AGE,
            '/',
            null,
            $request->isSecure(),
            // No script needs to read it: the banner is rendered by the server.
            true,
            false,
            Cookie::SAMESITE_LAX,
        ));
    }

    public function forget(Response $response): void
    {
        $response->headers->clearCookie(self::COOKIE, '/');
    }

    /**
     * The two mandatory pages, as link path => label, for the note every page carries.
     *
     * It sits in this class because the templates already have it at hand, and because the note
     * belongs next to the consent link: both are things a visitor must be able to reach from
     * anywhere, not things an editor can delete out of the footer by accident.
     *
     * @return array<string, string>
     */
    public function legalLinks(): array
    {
        $settings = $this->settings->load();
        $links = [];
        foreach (['privacyPath' => 'Datenschutz', 'imprintPath' => 'Impressum'] as $key => $label) {
            if ('' !== $settings[$key]) {
                $links[$settings[$key]] = $label;
            }
        }

        return $links;
    }

    /** What the banner and the consent page need to render. */
    public function state(Request $request): array
    {
        $settings = $this->settings->load();
        $decision = $this->decision($request);

        return [
            'groups' => array_map(
                static fn (string $group): array => [
                    'key' => $group,
                    'name' => self::GROUPS[$group],
                    'help' => self::GROUP_HELP[$group],
                    'granted' => in_array($group, $decision['granted'] ?? [], true),
                ],
                $this->askedGroups(),
            ),
            'decided' => null !== $decision,
            'decidedAt' => $decision['at'] ?? null,
            'text' => $settings['consentText'],
            'title' => $settings['consentTitle'],
            'layout' => $settings['consentLayout'],
            'privacyPath' => $settings['privacyPath'],
            'imprintPath' => $settings['imprintPath'],
        ];
    }

    /**
     * Die Gestaltung des Hinweises als CSS-Variablen für den Kopf der Seite.
     *
     * Das Stylesheet kennt die Standardwerte; hier stehen nur die Abweichungen, die jemand in den
     * Einstellungen gewählt hat. Die Form bestimmt zwei Radien auf einmal - Fläche und Knöpfe
     * gehören zusammen, und zwei Regler dafür wären zwei Regler, die man gegeneinander verstellt.
     */
    public function styles(array $theme): string
    {
        $settings = $this->settings->load();
        if (!$settings['consentBanner']) {
            return '';
        }
        [$box, $button] = match ($settings['consentShape']) {
            'rund' => ['28px', '999px'],
            'eckig' => ['0', '0'],
            default => ['18px', '10px'],
        };
        $values = ['--kant-consent-radius:'.$box, '--kant-consent-button-radius:'.$button];
        foreach (['consentColor' => '--kant-consent-bg', 'consentInk' => '--kant-consent-ink', 'consentAccent' => '--kant-consent-accent', 'consentAccentInk' => '--kant-consent-accent-ink'] as $field => $variable) {
            $value = Theme::cssColor((string) $settings[$field], $theme);
            if (null !== $value) {
                $values[] = $variable.':'.$value;
            }
        }

        return ':root{'.implode(';', $values).'}';
    }
}