Added export/import features

src/lib/db.js

@@ -1,4 +1,5 @@
 import Dexie from 'dexie';
+import { BackupError, buildBackup, EXPORT_FORMAT, EXPORT_VERSION, parseBackup } from './backup.js';
 import { DAY, localDateKey } from './time.js';
 
 /**
@@ -238,3 +239,65 @@ export async function cleanupOldDays(retentionDays) {
   });
   return keys.length;
 }
+
+/**
+ * Write an imported dataset.
+ *
+ * `replace` wipes the local days and entries first and adopts the file's settings.
+ * `merge` adds only days the device does not already have and leaves settings
+ * alone — merging two devices' settings is meaningless, and keeping the local copy
+ * of a day the device already knows about never loses work that was done here.
+ *
+ * @param {{days: Array, entries: Array, settings: object|null}} payload
+ * @param {'merge'|'replace'} mode
+ * @returns {Promise<{added: number, skipped: number, entries: number}>}
+ */
+export function importBackup(payload, mode) {
+  if (mode !== 'merge' && mode !== 'replace') {
+    throw new BackupError('Mode d’import inconnu.');
+  }
+  // Validate again at the write boundary and turn Svelte state proxies into plain
+  // records. IndexedDB cannot structured-clone a proxy (DataCloneError).
+  const { days, entries, settings } = parseBackup(JSON.stringify({
+    ...payload,
+    format: EXPORT_FORMAT,
+    version: EXPORT_VERSION,
+  }));
+  return db.transaction('rw', db.days, db.entries, db.settings, async () => {
+    if (mode === 'replace') {
+      await db.days.clear();
+      await db.entries.clear();
+      await db.settings.clear();
+    }
+
+    const present = new Set((await db.days.toArray()).map((d) => d.date));
+    const incoming = days.filter((d) => !present.has(d.date));
+    const wanted = new Set(incoming.map((d) => d.date));
+    const incomingEntries = entries
+      .filter((e) => wanted.has(e.date))
+      .map(({ id, ...rest }) => rest);
+
+    if (incoming.length) await db.days.bulkAdd(incoming);
+    if (incomingEntries.length) await db.entries.bulkAdd(incomingEntries);
+
+    if (mode === 'replace' && settings) {
+      await db.settings.put({ key: 'app', value: settings });
+    }
+
+    return {
+      added: incoming.length,
+      skipped: days.length - incoming.length,
+      entries: incomingEntries.length,
+    };
+  });
+}
+
+/** A consistent snapshot of all three stores, even while another tab writes. */
+export function exportBackup() {
+  return db.transaction('r', db.days, db.entries, db.settings, async () => {
+    const [days, entries, settings] = await Promise.all([
+      db.days.toArray(), db.entries.toArray(), readSettings(),
+    ]);
+    return buildBackup({ days, entries, settings });
+  });
+}