1 files changed, 104 insertions, 0 deletions

diff --git a/packages/main/src/i18n/I18nStore.ts b/packages/main/src/i18n/I18nStore.ts
new file mode 100644
index 0000000..d833e8a
--- /dev/null
+++ b/packages/main/src/i18n/I18nStore.ts
@@ -0,0 +1,104 @@
+/*
+ * Copyright (C)  2022 Kristóf Marussy <kristof@marussy.com>
+ *
+ * This file is part of Sophie.
+ *
+ * Sophie is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import type { i18n, TFunction } from 'i18next';
+import { IAtom, createAtom } from 'mobx';
+
+import { getLogger } from '../utils/log';
+
+const log = getLogger('I18nStore');
+
+export type UseTranslationResult =
+  | { ready: true; i18n: i18n; t: TFunction }
+  | { ready: false };
+
+export default class I18nStore {
+  private readonly languageChangedAtom: IAtom;
+
+  private readonly namespaceLoadedAtoms: Map<string, IAtom> = new Map();
+
+  private readonly notifyLanguageChange = () =>
+    this.languageChangedAtom.reportObserved();
+
+  constructor(private readonly i18next: i18n) {
+    this.languageChangedAtom = createAtom(
+      'i18next',
+      () => i18next.on('languageChanged', this.notifyLanguageChange),
+      () => i18next.off('languageChanged', this.notifyLanguageChange),
+    );
+  }
+
+  useTranslation(ns?: string): UseTranslationResult {
+    const observed = this.languageChangedAtom.reportObserved();
+    const namespaceToLoad =
+      ns ?? this.i18next.options.defaultNS ?? 'translation';
+    if (
+      this.i18next.isInitialized &&
+      this.i18next.hasLoadedNamespace(namespaceToLoad)
+    ) {
+      return {
+        ready: true,
+        i18n: this.i18next,
+        // eslint-disable-next-line unicorn/no-null -- `i18next` API requires `null`.
+        t: this.i18next.getFixedT(null, namespaceToLoad),
+      };
+    }
+    if (observed) {
+      this.loadNamespace(namespaceToLoad);
+    }
+    return { ready: false };
+  }
+
+  private loadNamespace(ns: string): void {
+    const existingAtom = this.namespaceLoadedAtoms.get(ns);
+    if (existingAtom !== undefined) {
+      existingAtom.reportObserved();
+      return;
+    }
+    const atom = createAtom(`i18next-${ns}`);
+    this.namespaceLoadedAtoms.set(ns, atom);
+    atom.reportObserved();
+
+    const loaded = () => {
+      this.namespaceLoadedAtoms.delete(ns);
+      atom.reportChanged();
+    };
+
+    const loadAsync = async () => {
+      await this.i18next.loadNamespaces([ns]);
+      if (this.i18next.isInitialized) {
+        setImmediate(loaded);
+        return;
+      }
+      const initialized = () => {
+        setImmediate(() => {
+          this.i18next.off('initialized', initialized);
+          loaded();
+        });
+      };
+      this.i18next.on('initialized', initialized);
+    };
+
+    loadAsync().catch((error) => {
+      log.error('Failed to load translations for namespace', ns, error);
+      setImmediate(loaded);
+    });
+  }
+}