I Caught a Big Bug

Today I upgraded the calendar library I use in Moodsmitten to its master branch. Previously, I was using a random branch that supported Swift 3, but it’s since been merged. There were a couple of big changes with methods, but it didn’t seem like a big deal. Except… it was!

Turns out, I overlooked one of the most important things about calendars, and it seemed like the past version of JTAppleCalendar, Swift 2.1, or my non-refactored date methods hid my logic errors. I neglected dealing with timezone in DateFormatter. Trying to use my newly refactored date class resulted in days that were a day or more before the expected result. I fixed this up, setting all dates to GMT +0000, but there’s a huge problem. When I try running 1.0 and upgrade to 1.1, all of the data disappears, because the Dates in the calendar are different from the new GMT +0000 dates!

I always knew that migrations were a fact of life, but until Moodsmitten I never had to deal with preserving data integrity in an upgrade. 1.1 has to migrate Core Data’s persistent store to a shared location in order to have the today extension and the watchOS app. I made a DataMigrationDelegate and set it to a new DataMigrator class. The lone delegate method is called after a 1.0->1.1 migration has occurred In the delegate it was a matter of making a little loop writing to Core Data:

func migrationCompleted() {
    guard let days = dayService.getAllDays() else {
      print("can't get days")
     return
    }
    days.forEach {
       day in
         guard let date = day.date else {
         return
      }
     day.date? = DateLib.sanitizeDate(date) // set up a date with the proper timezone
      coreDataStack.saveContext(managedObjectContext)
     }
  }

I’m Lucky

I’m very lucky to have caught this bug and averted a v1.1 train wreck wrought with all past thought records from v1.0 disappearing. It took an entire afternoon to figure this out, but I’m a more experienced developer because of it.

UPDATE 2016-10-22

I decided to do the date calculations at run-time when the calendar is shown. I don’t want to touch the data, especially when I consider CloudKit syncing. It’s a recipe for disaster. I’m not thrilled with this solution because it’s slightly expensive, but it’s safer.

func calendar(_ calendar: JTAppleCalendarView, willDisplayCell cell: JTAppleDayCellView, date: Date, cellState: CellState) {

        var myCalendar = Calendar(identifier: .gregorian)
        myCalendar.timeZone = NSTimeZone.local
        var mood = -999
        var days = dayService.days
        if let index = days.index(where: {
        let argDay = myCalendar.component(.day, from: $0.date!)
        let argMonth = myCalendar.component(.month, from: $0.date!)
        let argYear = myCalendar.component(.year, from: $0.date!)
        let dateDay = myCalendar.component(.day, from: date)
        let dateMonth = myCalendar.component(.month, from: date)
        let dateYear = myCalendar.component(.year, from: date)

        return argDay == dateDay && argMonth == dateMonth && argYear == dateYear }) {
        mood = Int(days[index].mood!)
        }

        (cell as! CalendarCell).setupCellBeforeDisplay(cellState, date: date, mood: mood, selectedDate: selectedDate!)

    }

UPDATE 2016-10-27

Making that date-checking loop freezes the calendar for a couple seconds, which is unacceptable. Today I figured out that making Core Data queries is much faster and there is no lag. This is probably because Core Data is using really performant faulting.

func calendar(_ calendar: JTAppleCalendarView, willDisplayCell cell: JTAppleDayCellView, date: Date, cellState: CellState) {

            var myCalendar = Calendar(identifier: .gregorian)
            myCalendar.timeZone = NSTimeZone.local
            var mood = -999

            if let day = dayService.getDay(date) {
                mood = Int(day.mood!)
            }

            (cell as! CalendarCell).setupCellBeforeDisplay(cellState, date: date, mood: mood, selectedDate: selectedDate!)

        }

Support Moodsmitten

Did I mention that Moodsmitten 1.0 is already on the App Store? It’s free-to-download with a $4.99 in-app purchase to unlock all functionality. If you’re into CBT or need a place to challenge your automatic thoughts, look no further!

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