// whatsappImportHistory reads batch names and live cutoffs from both logs.
// Imported chat-days belong only to the target log, which is first.
func whatsappImportHistory(target, root []DatedMessage, names map[string]WhatsAppChat, cutoffs map[string]time.Time, location *time.Location) (map[string]bool, error) {
// whatsappImportHistory reads batch names and live cutoffs from both logs.
// Imported chat-days belong only to the target log, which is first.
func whatsappImportHistory(target, root []DatedMessage, names map[string]WhatsAppChat, cutoffs map[string]time.Time, location *time.Location) (map[string]bool, error) {