gistfile1.txt

    static func deletePersistentHistoryIfPossible() {
        let ONE_DAY_DURATION: Int64 = 1*24*60*60*1000
        let SEVEN_DAYS_DURATION: Int64 = 7*24*60*60*1000
        let FOURTEEN_DAYS_DURATION: Int64 = 14*24*60*60*1000
        
        let lastDeletePersistentHistoryTimestamp = WeNoteOptions.lastDeletePersistentHistoryTimestamp
        let currentTimeMillis = Date.currentTimeMillis
        
        let iCloudLastSyncInfo = WeNoteOptions.INSTANCE.iCloudLastSyncInfo
        
        if !WeNoteOptions.isiCloudSync {
            // https://stackoverflow.com/questions/72733892/how-should-we-handle-history-tracking-transactions-purging-if-we-allow-users-to
            return
        }
        
        if iCloudLastSyncInfo.timestamp <= 0 {
            // We have never success in iCloud sync.
            return
        }
        
        if currentTimeMillis <= FOURTEEN_DAYS_DURATION {
            // Something went wrong on currentTimeMillis.
            return
        }
        
        if lastDeletePersistentHistoryTimestamp <= 0 {
            // First time to perform WeNoteOptions.lastDeletePersistentHistoryTimestamp update.
            WeNoteOptions.lastDeletePersistentHistoryTimestamp = currentTimeMillis
            return
        }
        
        if lastDeletePersistentHistoryTimestamp > currentTimeMillis {
            // Perhaps previous WeNoteOptions.lastDeletePersistentHistoryTimestamp is holding wrong information.
            WeNoteOptions.lastDeletePersistentHistoryTimestamp = currentTimeMillis
            return
        }
        
        let duration = currentTimeMillis - lastDeletePersistentHistoryTimestamp
        
        if duration < ONE_DAY_DURATION {
            // Return early without updating WeNoteOptions.lastDeletePersistentHistoryTimestamp. Avoding performing
            // deleteHistory too frequent.
            return
        }
        
        // https://stackoverflow.com/questions/72557060/what-is-the-right-way-to-perform-persistent-history-purging-without-affecting-t
        if duration > (SEVEN_DAYS_DURATION) {
            // The user hasn't launched the app for more than 7 days. Most probably CloudKit has not yet consume the
            // history transactions. Update WeNoteOptions.lastDeletePersistentHistoryTimestamp then return early.
            
            WeNoteOptions.lastDeletePersistentHistoryTimestamp = currentTimeMillis
            return
        }
        
        let date0 = Date(timeMillis: currentTimeMillis - FOURTEEN_DAYS_DURATION)
        let date1: Date
        
        if (iCloudLastSyncInfo.timestamp - SEVEN_DAYS_DURATION) > 0 {
            date1 = Date(timeMillis: iCloudLastSyncInfo.timestamp - SEVEN_DAYS_DURATION)
        } else {
            date1 = date0
        }
        
        let backgroundContext = CoreDataStack.INSTANCE.backgroundContext
        
        backgroundContext.performAndWait {
            let bestDate = date0 < date1 ? date0 : date1
            let purgeHistoryRequest = NSPersistentHistoryChangeRequest.deleteHistory(before: bestDate)
            do {
                try backgroundContext.execute(purgeHistoryRequest)
            } catch {
                error_log(error)
            }
        }

        WeNoteOptions.lastDeletePersistentHistoryTimestamp = currentTimeMillis
    }