perf(offline): parallelise note caching with batched writes

Fetch blobs with a concurrency of 8 instead of one at a time, batch
PouchDB writes via bulkUpdate, filter already-cached files up front,
and run the README fetch in parallel with the worker loop.

src/hooks/useOfflineNotes.hook.ts

@@ -3,11 +3,31 @@ import { computed, ref } from "vue"
 
 import { data, generateId } from "@/data/data"
 import { DataType } from "@/data/DataType.enum"
-import { prepareNoteCache } from "@/modules/note/cache/prepareNoteCache"
+import { buildNoteDocs } from "@/modules/note/cache/prepareNoteCache"
 import { Note } from "@/modules/note/models/Note"
 import { getMainReadme, queryFileContent } from "@/modules/repo/services/repo"
 import { useUserRepoStore } from "@/modules/repo/store/userRepo.store"
 
+const CONCURRENCY = 8
+const BULK_FLUSH_SIZE = 50
+
+const runWithConcurrency = async <T>(
+  items: T[],
+  limit: number,
+  worker: (item: T) => Promise<void>
+) => {
+  let cursor = 0
+  const next = async (): Promise<void> => {
+    const i = cursor++
+    if (i >= items.length) return
+    await worker(items[i])
+    return next()
+  }
+  await Promise.all(
+    Array.from({ length: Math.min(limit, items.length) }, next)
+  )
+}
+
 export const useOfflineNotes = () => {
   const store = useUserRepoStore()
   const totalOfNotes = computed(() => store.files.length)
@@ -30,40 +50,51 @@ export const useOfflineNotes = () => {
 
     const cachedNotesSet = new Set(cachedNotesFromSha.map((note) => note._id))
 
-    noteCompleted.value = 0
+    const filesToFetch = store.files.filter(
+      (file) =>
+        file.sha && !cachedNotesSet.has(generateId(DataType.Note, file.sha))
+    )
+
+    noteCompleted.value = store.files.length - filesToFetch.length
     failedNotes.value = 0
 
-    for (const file of store.files) {
-      noteCompleted.value++
-
-      if (
-        !file.sha ||
-        cachedNotesSet.has(generateId(DataType.Note, file.sha))
-      ) {
-        continue
-      }
-
-      const { saveCacheNote } = prepareNoteCache(file.sha, file.path)
-
-      const contentFile = await queryFileContent(
-        store.user,
-        store.repo,
-        file.sha
-      )
-
-      if (!contentFile) {
-        failedNotes.value++
-        continue
-      }
-
-      saveCacheNote(contentFile)
+    const pendingDocs: Note[] = []
+    const flush = async () => {
+      if (!pendingDocs.length) return
+      const batch = pendingDocs.splice(0, pendingDocs.length)
+      await data.bulkUpdate(batch)
     }
 
-    try {
-      await getMainReadme(store.user, store.repo)
-    } catch {
+    const fetchWork = runWithConcurrency(
+      filesToFetch,
+      CONCURRENCY,
+      async (file) => {
+        try {
+          const content = await queryFileContent(
+            store.user,
+            store.repo,
+            file.sha!
+          )
+          if (!content) {
+            failedNotes.value++
+            return
+          }
+          pendingDocs.push(...buildNoteDocs(file.sha!, file.path, content))
+          if (pendingDocs.length >= BULK_FLUSH_SIZE) {
+            await flush()
+          }
+        } finally {
+          noteCompleted.value++
+        }
+      }
+    )
+
+    const readmeWork = getMainReadme(store.user, store.repo).catch(() => {
       failedNotes.value++
-    }
+    })
+
+    await Promise.all([fetchWork, readmeWork])
+    await flush()
   }
   const { execute, isLoading } = useAsyncState(cacheAllNotes, null, {
     immediate: false