Add the preferences API for apps and users

src/Id/AnikeenId.php

@@ -2,6 +2,7 @@
 
 namespace Anikeen\Id;
 
+use Anikeen\Id\Concerns\ManagesPreferences;
 use Anikeen\Id\Concerns\ManagesPricing;
 use Anikeen\Id\Concerns\ManagesProducts;
 use Anikeen\Id\Concerns\ManagesShippingLabels;
@@ -23,6 +24,7 @@ use Illuminate\Contracts\Auth\Authenticatable;
 class AnikeenId
 {
     use OauthTrait;
+    use ManagesPreferences;
     use ManagesPricing;
     use ManagesProducts;
     use ManagesShippingLabels;

src/Id/Billable.php

@@ -9,6 +9,7 @@ use Anikeen\Id\Concerns\ManagesInvoices;
 use Anikeen\Id\Concerns\ManagesOrders;
 use Anikeen\Id\Concerns\ManagesPaymentMethods;
 use Anikeen\Id\Concerns\ManagesProfile;
+use Anikeen\Id\Concerns\ManagesUserPreferences;
 use Anikeen\Id\Concerns\ManagesSubscriptions;
 use Anikeen\Id\Concerns\ManagesTaxation;
 use Anikeen\Id\Concerns\ManagesTransactions;
@@ -27,6 +28,7 @@ trait Billable
     use ManagesSubscriptions;
     use ManagesTaxation;
     use ManagesTransactions;
+    use ManagesUserPreferences;
     use ManagesUserSshKeys;
 
     /*
@@ -40,6 +42,8 @@ trait Billable
     protected mixed $invoicesCache = null;
     protected mixed $ordersCache = null;
     protected mixed $paymentMethodsCache = null;
+    /** @var array<string, \Anikeen\Id\Resources\Preferences> by namespace */
+    protected array $preferencesCache = [];
     protected mixed $subscriptionsCache = null;
     protected mixed $transactionsCache = null;
     protected mixed $userDataCache = null;

src/Id/Concerns/ManagesPreferences.php

@@ -0,0 +1,107 @@
+<?php
+
+namespace Anikeen\Id\Concerns;
+
+use Anikeen\Id\Exceptions\ApiException;
+use Anikeen\Id\Exceptions\PreconditionFailedException;
+use Anikeen\Id\Resources\Preference;
+use Anikeen\Id\Resources\Preferences;
+use Anikeen\Id\Support\AppRequest;
+use Anikeen\Id\Support\PreferenceRequest;
+
+/**
+ * Preferences of any user, with the app's own token (client credentials, scope
+ * `preferences:client`). Anikeen has to register the app for each namespace it uses: its own
+ * namespaces (read, write, lookup), read access to another app's namespace, or access to `global`.
+ * Without it every call fails with 403 "client_not_trusted" or 404 "namespace_not_found".
+ */
+trait ManagesPreferences
+{
+    /**
+     * All preferences of a user in a namespace, sorted by key.
+     *
+     * @throws ApiException 404 "namespace_not_found", "user_not_found" (also deleted users), …
+     */
+    public function preferencesByUserId(string $userId, string $namespace): Preferences
+    {
+        return Preferences::builder(fn () => AppRequest::send('GET', $this->userPreferencePath($userId, $namespace)));
+    }
+
+    /**
+     * One preference of a user.
+     *
+     * @throws ApiException 404 "preference_not_found" when the key isn't set, "user_not_found", …
+     */
+    public function preferenceByUserId(string $userId, string $namespace, string $key): Preference
+    {
+        return new Preference(fn () => AppRequest::send('GET', $this->userPreferencePath($userId, $namespace, $key)));
+    }
+
+    /**
+     * Set a preference of a user. The value is any JSON value (pass `(object) []` for `{}`), at
+     * most 2048 bytes and 4 levels deep. Writing the value already stored changes nothing and
+     * succeeds, also when a precondition would fail, so a retried write is safe.
+     *
+     * @param int|null $ifVersion only if the stored version is this one (`If-Match`)
+     * @param bool $createOnly only if the key isn't set yet (`If-None-Match: *`); not with $ifVersion
+     * @throws PreconditionFailedException 412 "preference_version_mismatch" / "preference_exists",
+     *     with currentVersion()
+     * @throws ApiException 403 "namespace_read_only", 409 "preference_value_taken" (a unique key),
+     *     422 "invalid_key", "forbidden_key", "value_too_large", "preference_limit_exceeded", …
+     */
+    public function setPreferenceByUserId(string $userId, string $namespace, string $key, mixed $value, ?int $ifVersion = null, bool $createOnly = false): Preference
+    {
+        $headers = PreferenceRequest::conditions($ifVersion, $createOnly);
+
+        return new Preference(fn () => AppRequest::send('PUT', $this->userPreferencePath($userId, $namespace, $key), ['value' => $value], [], $headers));
+    }
+
+    /**
+     * Delete a preference of a user.
+     *
+     * @param int|null $ifVersion only if the stored version is this one (`If-Match`)
+     * @throws PreconditionFailedException 412 "preference_version_mismatch", with currentVersion()
+     * @throws ApiException 404 "preference_not_found" when the key isn't set, …
+     */
+    public function deletePreferenceByUserId(string $userId, string $namespace, string $key, ?int $ifVersion = null): void
+    {
+        AppRequest::send('DELETE', $this->userPreferencePath($userId, $namespace, $key), null, [], PreferenceRequest::conditions($ifVersion));
+    }
+
+    /**
+     * The ID of the user holding a value of a unique key in one of the app's own namespaces, e.g.
+     * the user of a payment provider's customer ID. The value is sent in the body, never in the URL.
+     *
+     * @return string|null null when no (not deleted) user holds the value
+     * @throws ApiException 422 "key_not_unique", "invalid_unique_value", 403 "lookup_not_allowed", …
+     */
+    public function findUserIdByPreference(string $namespace, string $key, string $value): ?string
+    {
+        try {
+            $result = AppRequest::send('POST', PreferenceRequest::path('v1/client/preferences', $namespace, 'lookup'), [
+                'key' => $key,
+                'value' => $value,
+            ]);
+        } catch (ApiException $e) {
+            // only Anikeen ID's own answer means "nobody holds it", not e.g. an unknown namespace
+            if ($e->isNotFound() && $e->error === 'preference_not_found') {
+                return null;
+            }
+
+            throw $e;
+        }
+
+        return $result->data->user_id;
+    }
+
+    private function userPreferencePath(string $userId, string $namespace, ?string $key = null): string
+    {
+        $segments = [$userId, 'preferences', $namespace];
+
+        if ($key !== null) {
+            $segments[] = $key;
+        }
+
+        return PreferenceRequest::path('v1/client/users', ...$segments);
+    }
+}

src/Id/Concerns/ManagesUserPreferences.php

@@ -0,0 +1,96 @@
+<?php
+
+namespace Anikeen\Id\Concerns;
+
+use Anikeen\Id\Enums\SharedPreference;
+use Anikeen\Id\Exceptions\ApiException;
+use Anikeen\Id\Exceptions\PreconditionFailedException;
+use Anikeen\Id\Resources\Preference;
+use Anikeen\Id\Resources\Preferences;
+use Anikeen\Id\Support\PreferenceRequest;
+use GuzzleHttp\Exception\GuzzleException;
+
+/**
+ * The user's shared preferences (`global`, e.g. SharedPreference::APPEARANCE), with the user's
+ * token (scope `preferences` or `preferences:read`). User tokens reach `global` only; an app's
+ * own namespace needs the app token (AnikeenId::preferencesByUserId()).
+ */
+trait ManagesUserPreferences
+{
+    /**
+     * The user's shared preferences, sorted by key. Cached on this instance; set and delete clear it.
+     *
+     * @throws ApiException
+     */
+    public function globalPreferences(): Preferences
+    {
+        $namespace = SharedPreference::NAMESPACE;
+
+        if (!isset($this->preferencesCache[$namespace])) {
+            $anikeenId = $this->anikeenId();
+
+            $this->preferencesCache[$namespace] = Preferences::builder(
+                fn () => $anikeenId->get(PreferenceRequest::path('v1/preferences', $namespace))
+            );
+        }
+
+        return $this->preferencesCache[$namespace];
+    }
+
+    /**
+     * The value of a shared preference, or $default when the user hasn't set it.
+     *
+     * @throws ApiException
+     */
+    public function globalPreference(string $key, mixed $default = null): mixed
+    {
+        return $this->globalPreferences()->get($key, $default);
+    }
+
+    /**
+     * Set a shared preference of the user, e.g. setGlobalPreference(SharedPreference::APPEARANCE,
+     * Appearance::DARK). Only registered keys and values are accepted (422 "unknown_shared_key",
+     * "invalid_shared_value").
+     *
+     * @param int|null $ifVersion only if the stored version is this one (`If-Match`)
+     * @throws PreconditionFailedException 412 "preference_version_mismatch", with currentVersion()
+     * @throws ApiException
+     */
+    public function setGlobalPreference(string $key, mixed $value, ?int $ifVersion = null): Preference
+    {
+        $namespace = SharedPreference::NAMESPACE;
+        $headers = PreferenceRequest::conditions($ifVersion);
+        $anikeenId = $this->anikeenId();
+
+        try {
+            return new Preference(fn () => $anikeenId->put(PreferenceRequest::path('v1/preferences', $namespace, $key), ['value' => $value], [], null, $headers));
+        } finally {
+            unset($this->preferencesCache[$namespace]);
+        }
+    }
+
+    /**
+     * Delete a shared preference of the user.
+     *
+     * @param int|null $ifVersion only if the stored version is this one (`If-Match`)
+     * @throws PreconditionFailedException 412 "preference_version_mismatch", with currentVersion()
+     * @throws ApiException 404 "preference_not_found" when the key isn't set, …
+     */
+    public function deleteGlobalPreference(string $key, ?int $ifVersion = null): void
+    {
+        $namespace = SharedPreference::NAMESPACE;
+        $headers = PreferenceRequest::conditions($ifVersion);
+
+        try {
+            $result = $this->anikeenId()->delete(PreferenceRequest::path('v1/preferences', $namespace, $key), [], [], null, $headers);
+        } catch (GuzzleException $e) {
+            throw ApiException::unreachable($e);
+        } finally {
+            unset($this->preferencesCache[$namespace]);
+        }
+
+        if (!$result->success()) {
+            throw ApiException::fromResult($result);
+        }
+    }
+}

src/Id/Resources/Preference.php

@@ -0,0 +1,27 @@
+<?php
+
+namespace Anikeen\Id\Resources;
+
+/**
+ * A preference of a user: a JSON value under a namespace and a key. `version` is opaque: it only
+ * goes up (per user, not consecutive per key) and is what ifVersion (`If-Match`) compares.
+ * JSON objects come back as stdClass, so `{}` stays an object.
+ *
+ * @property string $namespace
+ * @property string $key
+ * @property mixed $value
+ * @property int $version
+ * @property string $updated_at
+ * @property object{type: string, client_id: ?string} $updated_by `type` "user" (written with a user token) or "app"
+ */
+class Preference extends BaseResource
+{
+    /**
+     * The write that returned this preference created the key (201). False for reads, updates and
+     * writes of the value already stored.
+     */
+    public function wasCreated(): bool
+    {
+        return $this->result->response()?->getStatusCode() === 201;
+    }
+}

src/Id/Resources/Preferences.php

@@ -0,0 +1,68 @@
+<?php
+
+namespace Anikeen\Id\Resources;
+
+/**
+ * The preferences of a user in one namespace, sorted by key (at most 50, no pagination).
+ */
+class Preferences extends BaseCollection
+{
+    /**
+     * The preference of a key; null when it isn't set. Reads the list, no request.
+     */
+    public function find(string $id): ?Preference
+    {
+        $data = $this->item($id);
+
+        if ($data === null) {
+            return null;
+        }
+
+        $result = clone $this->result;
+        $result->data = $data;
+
+        return new Preference(fn () => $result);
+    }
+
+    /**
+     * The value of a key, or $default when it isn't set.
+     */
+    public function get(string $key, mixed $default = null): mixed
+    {
+        $data = $this->item($key);
+
+        return $data !== null ? $data->value : $default;
+    }
+
+    public function has(string $key): bool
+    {
+        return $this->item($key) !== null;
+    }
+
+    /**
+     * The values by key.
+     *
+     * @return array<string, mixed>
+     */
+    public function values(): array
+    {
+        $values = [];
+
+        foreach ((array) $this->result->data as $data) {
+            $values[$data->key] = $data->value;
+        }
+
+        return $values;
+    }
+
+    private function item(string $key): ?object
+    {
+        foreach ((array) $this->result->data as $data) {
+            if (($data->key ?? null) === $key) {
+                return $data;
+            }
+        }
+
+        return null;
+    }
+}

src/Id/Support/PreferenceRequest.php

@@ -0,0 +1,42 @@
+<?php
+
+namespace Anikeen\Id\Support;
+
+use InvalidArgumentException;
+
+/**
+ * @internal paths and preconditions of the preferences API
+ */
+final class PreferenceRequest
+{
+    /**
+     * The path with every segment URL-encoded, e.g. path('v1/preferences', 'global', 'appearance').
+     */
+    public static function path(string $base, string ...$segments): string
+    {
+        return $base . '/' . implode('/', array_map('rawurlencode', $segments));
+    }
+
+    /**
+     * `If-Match: "<version>"` (only if the stored version is this one) or `If-None-Match: *`
+     * (only if the key isn't set yet).
+     *
+     * @return array<string, string>
+     */
+    public static function conditions(?int $ifVersion, bool $createOnly = false): array
+    {
+        if ($ifVersion !== null && $createOnly) {
+            throw new InvalidArgumentException('A write is either conditional on a version or create-only, not both.');
+        }
+
+        return match (true) {
+            $ifVersion !== null => ['If-Match' => sprintf('"%d"', $ifVersion)],
+            $createOnly => ['If-None-Match' => '*'],
+            default => [],
+        };
+    }
+
+    private function __construct()
+    {
+    }
+}

tests/Id/BillableModelTest.php

@@ -19,6 +19,8 @@ class BillableModelTest extends TestCase
                 foreach (['addresses', 'countries', 'defaultPaymentMethod', 'invoices', 'orders', 'paymentMethods', 'subscriptions', 'transactions', 'userData'] as $name) {
                     $this->{$name.'Cache'} = 'cached';
                 }
+
+                $this->preferencesCache['global'] = 'cached';
             }
         };
         $user->email = 'ada@example.com';

tests/Id/EndpointsTest.php

@@ -283,4 +283,133 @@ class EndpointsTest extends TestCase
 
         $this->assertSame(['items' => [], 'billing_address' => ['country_iso' => 'DE']], $this->sentJson(0));
     }
+
+    private function preference(string $namespace, string $key, mixed $value, int $version = 7): array
+    {
+        return ['namespace' => $namespace, 'key' => $key, 'value' => $value, 'version' => $version, 'updated_at' => '2026-11-06T10:00:00.000000Z', 'updated_by' => ['type' => 'app', 'client_id' => 'app-client']];
+    }
+
+    private function conditions(int $index): array
+    {
+        $request = $this->sent[$index]['request'];
+
+        return [$request->getHeaderLine('If-Match'), $request->getHeaderLine('If-None-Match')];
+    }
+
+    public function test_global_preferences_of_the_user(): void
+    {
+        $this->respond(200, ['data' => [$this->preference('global', 'appearance', 'dark')]]);
+
+        $preferences = $this->owner()->globalPreferences();
+
+        $this->assertSame('dark', $preferences->get('appearance'));
+        $this->assertSame('GET /api/v1/preferences/global Bearer user-token', $this->sentCall(0));
+    }
+
+    public function test_global_preference_with_a_default(): void
+    {
+        $this->respond(200, ['data' => [$this->preference('global', 'appearance', 'light')]]);
+
+        $owner = $this->owner();
+
+        $this->assertSame('light', $owner->globalPreference('appearance'));
+        $this->assertSame('system', $owner->globalPreference('unknown', 'system'));
+        $this->assertCount(1, $this->sent);
+        $this->assertSame('GET /api/v1/preferences/global Bearer user-token', $this->sentCall(0));
+    }
+
+    public function test_set_global_preference(): void
+    {
+        $this->respond(201, ['data' => $this->preference('global', 'appearance', 'dark', 8)]);
+        $this->respond(200, ['data' => $this->preference('global', 'appearance', 'light', 9)]);
+
+        $created = $this->owner()->setGlobalPreference('appearance', 'dark');
+        $updated = $this->owner()->setGlobalPreference('appearance', 'light', ifVersion: 8);
+
+        $this->assertTrue($created->wasCreated());
+        $this->assertFalse($updated->wasCreated());
+        $this->assertSame(9, $updated->version);
+        $this->assertSame('PUT /api/v1/preferences/global/appearance Bearer user-token', $this->sentCall(0));
+        $this->assertSame(['value' => 'dark'], $this->sentJson(0));
+        $this->assertSame(['', ''], $this->conditions(0));
+        $this->assertSame(['"8"', ''], $this->conditions(1));
+    }
+
+    public function test_delete_global_preference(): void
+    {
+        $this->respond(204);
+        $this->respond(204);
+
+        $this->owner()->deleteGlobalPreference('appearance');
+        $this->owner()->deleteGlobalPreference('appearance', ifVersion: 9);
+
+        $this->assertSame('DELETE /api/v1/preferences/global/appearance Bearer user-token', $this->sentCall(0));
+        $this->assertSame('', (string) $this->sent[0]['request']->getBody());
+        $this->assertSame(['', ''], $this->conditions(0));
+        $this->assertSame(['"9"', ''], $this->conditions(1));
+    }
+
+    public function test_preferences_by_user_id(): void
+    {
+        $this->respond(200, ['data' => [$this->preference('acme', 'plan', 'pro'), $this->preference('acme', 'theme', ['accent' => 'blue'])]]);
+
+        $preferences = app(AnikeenId::class)->preferencesByUserId('01JUSER', 'acme');
+
+        $this->assertEquals(['plan' => 'pro', 'theme' => (object) ['accent' => 'blue']], $preferences->values());
+        $this->assertSame('blue', $preferences->find('theme')->value->accent);
+        $this->assertNull($preferences->find('missing'));
+        $this->assertSame('GET /api/v1/client/users/01JUSER/preferences/acme Bearer app-token', $this->sentCall(0));
+    }
+
+    public function test_preference_by_user_id(): void
+    {
+        $this->respond(200, ['data' => $this->preference('acme', 'plan', 'pro')]);
+
+        $preference = app(AnikeenId::class)->preferenceByUserId('01JUSER', 'acme', 'plan');
+
+        $this->assertSame('pro', $preference->value);
+        $this->assertSame(7, $preference->version);
+        $this->assertSame('GET /api/v1/client/users/01JUSER/preferences/acme/plan Bearer app-token', $this->sentCall(0));
+    }
+
+    public function test_set_preference_by_user_id(): void
+    {
+        $this->respond(200, ['data' => $this->preference('acme', 'plan', 'pro')]);
+        $this->respond(200, ['data' => $this->preference('acme', 'plan', 'pro')]);
+        $this->respond(201, ['data' => $this->preference('acme', 'plan', 'pro')]);
+
+        $anikeenId = app(AnikeenId::class);
+        $anikeenId->setPreferenceByUserId('01JUSER', 'acme', 'plan', 'pro');
+        $anikeenId->setPreferenceByUserId('01JUSER', 'acme', 'plan', 'pro', ifVersion: 7);
+        $anikeenId->setPreferenceByUserId('01JUSER', 'acme', 'plan', 'pro', createOnly: true);
+
+        $this->assertSame('PUT /api/v1/client/users/01JUSER/preferences/acme/plan Bearer app-token', $this->sentCall(0));
+        $this->assertSame(['value' => 'pro'], $this->sentJson(0));
+        $this->assertSame(['', ''], $this->conditions(0));
+        $this->assertSame(['"7"', ''], $this->conditions(1));
+        $this->assertSame(['', '*'], $this->conditions(2));
+    }
+
+    public function test_delete_preference_by_user_id(): void
+    {
+        $this->respond(204);
+        $this->respond(204);
+
+        app(AnikeenId::class)->deletePreferenceByUserId('01JUSER', 'acme', 'plan');
+        app(AnikeenId::class)->deletePreferenceByUserId('01JUSER', 'acme', 'plan', ifVersion: 7);
+
+        $this->assertSame('DELETE /api/v1/client/users/01JUSER/preferences/acme/plan Bearer app-token', $this->sentCall(0));
+        $this->assertSame(['', ''], $this->conditions(0));
+        $this->assertSame(['"7"', ''], $this->conditions(1));
+    }
+
+    public function test_find_user_id_by_preference(): void
+    {
+        $this->respond(200, ['data' => ['user_id' => '01JUSER', 'namespace' => 'acme', 'key' => 'customer_id', 'version' => 7, 'updated_at' => '2026-11-06T10:00:00.000000Z']]);
+
+        $this->assertSame('01JUSER', app(AnikeenId::class)->findUserIdByPreference('acme', 'customer_id', 'cus_123'));
+        $this->assertSame('POST /api/v1/client/preferences/acme/lookup Bearer app-token', $this->sentCall(0));
+        $this->assertSame(['key' => 'customer_id', 'value' => 'cus_123'], $this->sentJson(0));
+        $this->assertSame('', $this->sent[0]['request']->getUri()->getQuery());
+    }
 }

tests/Id/PreferencesTest.php

@@ -0,0 +1,226 @@
+<?php
+
+namespace Anikeen\Id\Tests;
+
+use Anikeen\Id\AnikeenId;
+use Anikeen\Id\Billable;
+use Anikeen\Id\Enums\Appearance;
+use Anikeen\Id\Enums\SharedPreference;
+use Anikeen\Id\Exceptions\ApiException;
+use Anikeen\Id\Exceptions\PreconditionFailedException;
+use Illuminate\Database\Eloquent\Model;
+use InvalidArgumentException;
+
+class PreferencesTest extends TestCase
+{
+    private function owner(): Model
+    {
+        $owner = new class extends Model {
+            use Billable;
+
+            protected $guarded = [];
+        };
+        $owner->anikeen_id = '01JUSER';
+        $owner->anikeen_id_access_token = 'user-token';
+
+        return $owner;
+    }
+
+    private function preference(string $key, mixed $value, int $version = 7): array
+    {
+        return ['data' => ['namespace' => 'global', 'key' => $key, 'value' => $value, 'version' => $version, 'updated_at' => '2026-11-06T10:00:00.000000Z', 'updated_by' => ['type' => 'user', 'client_id' => 'app-client']]];
+    }
+
+    private function path(int $index): string
+    {
+        return $this->sent[$index]['request']->getUri()->getPath();
+    }
+
+    public function test_the_lookup_returns_null_when_nobody_holds_the_value(): void
+    {
+        $this->respond(404, ['message' => 'The preference is not set.', 'error' => 'preference_not_found']);
+
+        $this->assertNull(app(AnikeenId::class)->findUserIdByPreference('acme', 'customer_id', 'cus_123'));
+    }
+
+    public function test_the_lookup_throws_on_other_not_found_answers(): void
+    {
+        $this->respond(404, ['message' => 'The namespace does not exist.', 'error' => 'namespace_not_found']);
+
+        try {
+            app(AnikeenId::class)->findUserIdByPreference('acme', 'customer_id', 'cus_123');
+            $this->fail('no exception');
+        } catch (ApiException $e) {
+            $this->assertSame(404, $e->status);
+            $this->assertSame('namespace_not_found', $e->error);
+        }
+    }
+
+    public function test_the_lookup_throws_on_a_404_without_an_error_code(): void
+    {
+        $this->respond(404, ['message' => 'Not Found']);
+
+        $this->expectException(ApiException::class);
+
+        app(AnikeenId::class)->findUserIdByPreference('acme', 'customer_id', 'cus_123');
+    }
+
+    public function test_the_lookup_throws_on_validation_errors(): void
+    {
+        $this->respond(422, ['message' => 'The key is not unique.', 'error' => 'key_not_unique']);
+
+        try {
+            app(AnikeenId::class)->findUserIdByPreference('acme', 'plan', 'pro');
+            $this->fail('no exception');
+        } catch (ApiException $e) {
+            $this->assertSame('key_not_unique', $e->error);
+        }
+    }
+
+    public function test_a_failed_app_write_carries_the_current_version(): void
+    {
+        $this->respond(412, ['message' => 'The preference has another version.', 'error' => 'preference_version_mismatch', 'current_version' => 12]);
+
+        try {
+            app(AnikeenId::class)->setPreferenceByUserId('01JUSER', 'acme', 'plan', 'pro', ifVersion: 7);
+            $this->fail('no exception');
+        } catch (PreconditionFailedException $e) {
+            $this->assertSame(412, $e->status);
+            $this->assertSame('preference_version_mismatch', $e->error);
+            $this->assertSame(12, $e->currentVersion());
+        }
+    }
+
+    public function test_a_create_only_write_of_a_set_key_fails(): void
+    {
+        $this->respond(412, ['message' => 'The preference is already set.', 'error' => 'preference_exists', 'current_version' => 3]);
+
+        try {
+            app(AnikeenId::class)->setPreferenceByUserId('01JUSER', 'acme', 'plan', 'pro', createOnly: true);
+            $this->fail('no exception');
+        } catch (PreconditionFailedException $e) {
+            $this->assertSame('preference_exists', $e->error);
+            $this->assertSame(3, $e->currentVersion());
+        }
+    }
+
+    public function test_a_failed_user_write_carries_the_current_version(): void
+    {
+        $this->respond(412, ['message' => 'The preference has another version.', 'error' => 'preference_version_mismatch', 'current_version' => null]);
+        $this->respond(412, ['message' => 'The preference has another version.', 'error' => 'preference_version_mismatch', 'current_version' => 5]);
+
+        foreach ([
+            fn () => $this->owner()->setGlobalPreference('appearance', 'dark', ifVersion: 4),
+            fn () => $this->owner()->deleteGlobalPreference('appearance', ifVersion: 4),
+        ] as $i => $call) {
+            try {
+                $call();
+                $this->fail('no exception');
+            } catch (PreconditionFailedException $e) {
+                $this->assertSame([null, 5][$i], $e->currentVersion());
+            }
+        }
+    }
+
+    public function test_a_write_is_either_conditional_or_create_only(): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+
+        try {
+            app(AnikeenId::class)->setPreferenceByUserId('01JUSER', 'acme', 'plan', 'pro', ifVersion: 7, createOnly: true);
+        } finally {
+            $this->assertCount(0, $this->sent);
+        }
+    }
+
+    public function test_writes_clear_the_cached_preferences(): void
+    {
+        $owner = $this->owner();
+
+        $this->respond(200, ['data' => [$this->preference('appearance', 'light')['data']]]);
+        $this->respond(200, $this->preference('appearance', 'dark', 8));
+        $this->respond(200, ['data' => [$this->preference('appearance', 'dark', 8)['data']]]);
+        $this->respond(204);
+        $this->respond(200, ['data' => []]);
+
+        $this->assertSame('light', $owner->globalPreference(SharedPreference::APPEARANCE));
+        $this->assertSame('light', $owner->globalPreference(SharedPreference::APPEARANCE)); // cached
+        $owner->setGlobalPreference(SharedPreference::APPEARANCE, Appearance::DARK);
+        $this->assertSame('dark', $owner->globalPreference(SharedPreference::APPEARANCE));
+        $owner->deleteGlobalPreference(SharedPreference::APPEARANCE);
+        $this->assertSame(Appearance::SYSTEM, $owner->globalPreference(SharedPreference::APPEARANCE, Appearance::SYSTEM));
+
+        $this->assertCount(5, $this->sent);
+        $this->assertSame(['GET', 'PUT', 'GET', 'DELETE', 'GET'], array_map(fn ($sent) => $sent['request']->getMethod(), $this->sent));
+    }
+
+    public function test_a_failed_write_clears_the_cached_preferences_too(): void
+    {
+        $owner = $this->owner();
+
+        $this->respond(200, ['data' => [$this->preference('appearance', 'light')['data']]]);
+        $this->respond(412, ['message' => 'x', 'error' => 'preference_version_mismatch', 'current_version' => 9]);
+        $this->respond(200, ['data' => [$this->preference('appearance', 'dark', 9)['data']]]);
+
+        $owner->globalPreferences();
+
+        try {
+            $owner->setGlobalPreference('appearance', 'dark', ifVersion: 7);
+        } catch (PreconditionFailedException) {
+        }
+
+        $this->assertSame('dark', $owner->globalPreference('appearance'));
+        $this->assertCount(3, $this->sent);
+    }
+
+    public function test_path_segments_are_encoded(): void
+    {
+        $this->respond(200, ['data' => []]);
+        $this->respond(204);
+        $this->respond(200, ['data' => ['user_id' => '01JUSER']]);
+
+        $anikeenId = app(AnikeenId::class);
+        $anikeenId->preferencesByUserId('a/b', 'x y');
+        $anikeenId->deletePreferenceByUserId('01JUSER', 'acme', '../key?');
+        $anikeenId->findUserIdByPreference('ac/me', 'k', 'v');
+
+        $this->assertSame('/api/v1/client/users/a%2Fb/preferences/x%20y', $this->path(0));
+        $this->assertSame('/api/v1/client/users/01JUSER/preferences/acme/..%2Fkey%3F', $this->path(1));
+        $this->assertSame('/api/v1/client/preferences/ac%2Fme/lookup', $this->path(2));
+    }
+
+    public function test_values_round_trip_as_json(): void
+    {
+        $this->respond(201, $this->preference('settings', (object) []));
+
+        $preference = app(AnikeenId::class)->setPreferenceByUserId('01JUSER', 'acme', 'settings', (object) []);
+
+        $this->assertSame('{"value":{}}', (string) $this->sent[0]['request']->getBody());
+        $this->assertEquals((object) [], $preference->value);
+    }
+
+    public function test_a_deleted_user_is_not_found(): void
+    {
+        $this->respond(404, ['message' => 'The user does not exist.', 'error' => 'user_not_found']);
+
+        try {
+            app(AnikeenId::class)->preferenceByUserId('01JGONE', 'acme', 'plan');
+            $this->fail('no exception');
+        } catch (ApiException $e) {
+            $this->assertTrue($e->isNotFound());
+            $this->assertSame('user_not_found', $e->error);
+        }
+    }
+
+    public function test_an_unreachable_service_is_temporary(): void
+    {
+        $this->http->append(new \GuzzleHttp\Exception\ConnectException('down', new \GuzzleHttp\Psr7\Request('DELETE', 'x')));
+
+        try {
+            $this->owner()->deleteGlobalPreference('appearance');
+            $this->fail('no exception');
+        } catch (ApiException $e) {
+            $this->assertTrue($e->isTemporary());
+        }
+    }
+}