refactor: scanAndCount - use channel to synchronize data with the main goroutine

internal/bundb/bundb.go

@@ -46,44 +46,60 @@ func sortDirectionToString(sd domain.SortDirection) (string, error) {
 	return "", fmt.Errorf("%w: %d", domain.ErrUnsupportedSortDirection, sd)
 }
 
+type scanAndCountResult struct {
+	count int
+	err   error
+}
+
 func scanAndCount(
 	ctx context.Context,
 	countQ *bun.SelectQuery,
 	scanQ *bun.SelectQuery,
 ) (int, error) {
 	var wg sync.WaitGroup
-	var mu sync.Mutex
+	ch := make(chan scanAndCountResult)
+
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+
+		count, err := countQ.Count(ctx)
+		if err != nil {
+			ch <- scanAndCountResult{err: err}
+			return
+		}
+		ch <- scanAndCountResult{count: count}
+	}()
+
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+
+		if err := scanQ.Scan(ctx); err != nil {
+			ch <- scanAndCountResult{err: err}
+		}
+	}()
+
+	go func() {
+		wg.Wait()
+		close(ch)
+	}()
+
 	var count int
-	var err error
+	var firstErr error
 
-	wg.Add(1)
-	go func() {
-		defer wg.Done()
-
-		var countErr error
-		if count, countErr = countQ.Count(ctx); countErr != nil {
-			mu.Lock()
-			if err == nil {
-				err = countErr
-			}
-			mu.Unlock()
+	for res := range ch {
+		if firstErr == nil && res.err != nil {
+			firstErr = res.err
+			continue
 		}
-	}()
 
-	wg.Add(1)
-	go func() {
-		defer wg.Done()
+		count = res.count
+	}
 
-		if scanErr := scanQ.Scan(ctx); scanErr == nil {
-			mu.Lock()
-			if err == nil {
-				err = scanErr
-			}
-			mu.Unlock()
-		}
-	}()
+	if firstErr != nil {
+		return 0, firstErr
+	}
 
-	wg.Wait()
-
-	return count, err
+	return count, nil
 }