✨(frontend) sync user and frontend language

On Language change in the frontend,
the user language is updated via API.
If user language is available, it will
be preferred and set in the frontend.

CHANGELOG.md

@@ -21,6 +21,7 @@ and this project adheres to
 - 🌐(backend) add german translation #259
 - ♻️(frontend) simplify stores #402
 - ✨(frontend) update $css Box props type to add styled components RuleSet #423
+- ✨(frontend) sync user and frontend language #401
 
 ## Fixed
 

src/backend/core/api/serializers.py

@@ -18,7 +18,7 @@ class UserSerializer(serializers.ModelSerializer):
 
     class Meta:
         model = models.User
-        fields = ["id", "email", "full_name", "short_name"]
+        fields = ["id", "email", "full_name", "short_name", "language"]
         read_only_fields = ["id", "email", "full_name", "short_name"]
 
 

src/frontend/apps/e2e/__tests__/app-impress/language.spec.ts

@@ -1,20 +1,23 @@
-import { expect, test } from '@playwright/test';
+import { Page, expect, test } from '@playwright/test';
 
 test.beforeEach(async ({ page }) => {
   await page.goto('/');
 });
 
 test.describe('Language', () => {
-  test('checks the language picker', async ({ page }) => {
+  test('checks language switching', async ({ page }) => {
+    const header = page.locator('header').first();
+
+    // initial language should be english
     await expect(
       page.getByRole('button', {
         name: 'Create a new document',
       }),
     ).toBeVisible();
 
-    const header = page.locator('header').first();
-    await header.getByRole('combobox').getByText('English').click();
-    await header.getByRole('option', { name: 'Français' }).click();
+    // switch to french
+    await waitForLanguageSwitch(page, Languages.French);
+
     await expect(
       header.getByRole('combobox').getByText('Français'),
     ).toBeVisible();
@@ -63,12 +66,41 @@ test.describe('Language', () => {
     // Check for English 404 response
     await check404Response('Not found.');
 
-    // Switch language to French
-    const header = page.locator('header').first();
-    await header.getByRole('combobox').getByText('English').click();
-    await header.getByRole('option', { name: 'Français' }).click();
+    await waitForLanguageSwitch(page, Languages.French);
 
     // Check for French 404 response
     await check404Response('Pas trouvé.');
   });
 });
+
+test.afterEach(async ({ page }) => {
+  // Switch back to English - important for other tests to run, as this updates the language in the user entity
+  // and in turn updates the language of the frontend.
+  // Therefore continuing tests, messages that are expected to be english would be french
+  await waitForLanguageSwitch(page, Languages.English);
+});
+
+// eslint-disable-next-line @typescript-eslint/no-unused-vars
+enum Languages {
+  English = 'English',
+  French = 'Français',
+}
+const serverSideLanguageValues: Record<Languages, string> = {
+  [Languages.English]: 'en-us',
+  [Languages.French]: 'fr-fr',
+};
+async function waitForLanguageSwitch(page: Page, lang: Languages) {
+  const header = page.locator('header').first();
+  await header.getByRole('combobox').click();
+
+  const [response] = await Promise.all([
+    page.waitForResponse(
+      (resp) =>
+        resp.url().includes('/user') && resp.request().method() === 'PATCH',
+    ),
+    header.getByRole('option', { name: lang }).click(),
+  ]);
+
+  const updatedUserResponse = await response.json();
+  expect(updatedUserResponse.language).toBe(serverSideLanguageValues[lang]);
+}

src/frontend/apps/impress/src/core/AppProvider.tsx

@@ -3,10 +3,11 @@ import { QueryClient, QueryClientProvider } from '@tanstack/react-query';
 import { useEffect } from 'react';
 
 import { useCunninghamTheme } from '@/cunningham';
-import '@/i18n/initI18n';
+import { LANGUAGES_ALLOWED } from '@/i18n/conf';
+import i18n from '@/i18n/initI18n';
 import { useResponsiveStore } from '@/stores/';
 
-import { Auth } from './auth/';
+import { Auth, useAuthStore } from './auth/';
 
 /**
  * QueryClient:
@@ -26,6 +27,7 @@ const queryClient = new QueryClient({
 
 export function AppProvider({ children }: { children: React.ReactNode }) {
   const { theme } = useCunninghamTheme();
+  const { userData } = useAuthStore();
 
   const initializeResizeListener = useResponsiveStore(
     (state) => state.initializeResizeListener,
@@ -36,6 +38,16 @@ export function AppProvider({ children }: { children: React.ReactNode }) {
     return cleanupResizeListener;
   }, [initializeResizeListener]);
 
+  useEffect(() => {
+    if (userData?.language) {
+      Object.keys(LANGUAGES_ALLOWED).forEach((key) => {
+        if (userData.language.includes(key) && i18n.language !== key) {
+          void i18n.changeLanguage(key);
+        }
+      });
+    }
+  }, [userData?.language]);
+
   return (
     <QueryClientProvider client={queryClient}>
       <CunninghamProvider theme={theme}>

src/frontend/apps/impress/src/core/auth/api/types.ts

@@ -1,13 +1,17 @@
+import { UserLanguage } from '@/i18n/types';
+
 /**
  * Represents user retrieved from the API.
  * @interface User
  * @property {string} id - The id of the user.
  * @property {string} email - The email of the user.
  * @property {string} name - The name of the user.
+ * @property {string} language - The language of the user.
  */
 export interface User {
   id: string;
   email: string;
   full_name: string;
   short_name: string;
+  language: UserLanguage;
 }

src/frontend/apps/impress/src/features/language/LanguagePicker.tsx

@@ -6,6 +6,8 @@ import styled from 'styled-components';
 import { Box, Text } from '@/components/';
 import { LANGUAGES_ALLOWED } from '@/i18n/conf';
 
+import { useSetUserLanguage } from './api/useChangeUserLanguage';
+
 const SelectStyled = styled(Select)<{ $isSmall?: boolean }>`
   flex-shrink: 0;
   width: auto;
@@ -33,6 +35,7 @@ const SelectStyled = styled(Select)<{ $isSmall?: boolean }>`
 
 export const LanguagePicker = () => {
   const { t, i18n } = useTranslation();
+  const { mutateAsync: setUserLanguage } = useSetUserLanguage();
   const { preload: languages } = i18n.options;
 
   const optionsPicker = useMemo(() => {
@@ -63,13 +66,22 @@ export const LanguagePicker = () => {
       showLabelWhenSelected={false}
       clearable={false}
       hideLabel
-      defaultValue={i18n.language}
+      value={i18n.language}
       className="c_select__no_bg"
       options={optionsPicker}
       onChange={(e) => {
-        i18n.changeLanguage(e.target.value as string).catch((err) => {
-          console.error('Error changing language', err);
-        });
+        void i18n
+          .changeLanguage(e.target.value as string)
+          .catch((err) => {
+            console.error('Error changing language', err);
+          })
+          .then(() => {
+            setUserLanguage({
+              language: i18n.language === 'fr' ? 'fr-fr' : 'en-us',
+            }).catch((err) => {
+              console.error('Error changing users language', err);
+            });
+          });
       }}
     />
   );

src/frontend/apps/impress/src/features/language/api/useChangeUserLanguage.tsx

@@ -0,0 +1,50 @@
+import { useMutation, useQueryClient } from '@tanstack/react-query';
+
+import { APIError, errorCauses, fetchAPI } from '@/api';
+import { User, useAuthStore } from '@/core';
+
+interface SetUserLanguageParams {
+  language: User['language'];
+}
+
+export const setUserLanguage = async ({
+  language,
+}: SetUserLanguageParams): Promise<User> => {
+  const { userData } = useAuthStore.getState();
+
+  if (!userData?.id) {
+    console.warn('Id of user is needed for this request.');
+    return {} as Promise<User>;
+  }
+
+  const response = await fetchAPI(`users/${userData.id}/`, {
+    method: 'PATCH',
+    body: JSON.stringify({
+      language,
+    }),
+  });
+
+  if (!response.ok) {
+    throw new APIError(
+      `Failed to change the user language to ${language}`,
+      await errorCauses(response, {
+        value: language,
+        type: 'language',
+      }),
+    );
+  }
+
+  return response.json() as Promise<User>;
+};
+
+export function useSetUserLanguage() {
+  const queryClient = useQueryClient();
+  return useMutation<User, APIError, SetUserLanguageParams>({
+    mutationFn: setUserLanguage,
+    onSuccess: () => {
+      void queryClient.invalidateQueries({
+        queryKey: ['set-user-language'],
+      });
+    },
+  });
+}

src/frontend/apps/impress/src/features/service-worker/ApiPlugin.ts

@@ -216,6 +216,7 @@ export class ApiPlugin implements WorkboxPlugin {
             email: 'dummy-email',
             full_name: 'dummy-full-name',
             short_name: 'dummy-short-name',
+            language: 'en-us',
           },
           abilities: {
             destroy: false,