Disambiguate date picker when year or month differs (#496)

The Edit Datapoint screen contains a date picker. The Add Datapoint
screen, the lower part of the goal screen, did not contain a date
picker. Instead it contained a single digit to represent the date of the
to-be-created datapoint and furthermore sent this single digit to the
backend as part of `urtext`. The backend itself then interpreted the
values sent and really had no way to accurately map the "day of the
month" number to any particular year or month.

With this merge request, the Add Datapoint section has been given its
own date which is then sent to the backend when adding the new
datapoint. Since the app now provides all of year, month, and day, there
is less ambiguity related to the daystamp for the datapoint.

Furthermore, similar to how the [Android app /
Beedroid](#386 (comment))
handles this, the format shown varies: the (date) value shown is either
a simple single number (the day) when within the same month, the month
and day when no longer in the same month but still the same year, and
all three components when the point is for a different calendar year.

Fixes #386

BeeSwift/GoalViewController.swift

@@ -40,6 +40,9 @@ class GoalViewController: UIViewController,  UIScrollViewDelegate, DatapointTabl
     fileprivate let headerWidth = Double(1.0/3.0)
     fileprivate let viewGoalActivityType = "com.beeminder.viewGoal"
 
+    // date corresponding to the datapoint to be created
+    private var date: Date = Date()
+
     init(goal: Goal) {
         self.goal = goal
         super.init(nibName: nil, bundle: nil)
@@ -272,7 +275,7 @@ class GoalViewController: UIViewController,  UIScrollViewDelegate, DatapointTabl
         }
 
         self.navigationItem.rightBarButtonItems = [UIBarButtonItem(barButtonSystemItem: .action, target: self, action: #selector(self.actionButtonPressed))]
-        if (!self.goal.hideDataEntry) {
+        if !self.goal.hideDataEntry {
             self.navigationItem.rightBarButtonItems?.append(UIBarButtonItem(image: UIImage(named: "Timer"), style: .plain, target: self, action: #selector(self.timerButtonPressed)))
         }
 
@@ -368,12 +371,14 @@ class GoalViewController: UIViewController,  UIScrollViewDelegate, DatapointTabl
         var components = DateComponents()
         components.day = Int(self.dateStepper.value)
 
-        let newDate = (calendar as NSCalendar?)?.date(byAdding: components, to: Date(), options: [])
+        let now = Date()
+        guard let newDate = calendar.date(byAdding: components, to: now) else { return }
+        self.date = newDate
+
+        let isDifferentYear = calendar.component(.year, from: now) != calendar.component(.year, from: date)
+        let isDifferentMonth = calendar.component(.month, from: now) != calendar.component(.month, from: date)
 
-        let formatter = DateFormatter()
-        formatter.locale = Locale(identifier: "en_US")
-        formatter.dateFormat = "d"
-        self.dateTextField.text = formatter.string(from: newDate!)
+        self.dateTextField.text = DateFormatter.dateTextFieldString(from: self.date, isDifferentYear: isDifferentYear, isDifferentMonth: isDifferentMonth)
     }
 
     func setValueTextField() {
@@ -417,12 +422,12 @@ class GoalViewController: UIViewController,  UIScrollViewDelegate, DatapointTabl
     }
 
     func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
-        if (textField.isEqual(self.valueTextField)) {
+        if textField.isEqual(self.valueTextField) {
             // Only allow a single decimal separator (, or .)
             if textField.text!.components(separatedBy: ".").count > 1 {
                 if string == "." || string == "," { return false }
             }
-            if (string == ",") {
+            if string == "," {
                 textField.text = textField.text! + "."
                 return false
             }
@@ -436,9 +441,9 @@ class GoalViewController: UIViewController,  UIScrollViewDelegate, DatapointTabl
         }
         return true
     }
-
-    func urtextFromTextFields() -> String {
-        return "\(self.dateTextField.text!) \(self.valueTextField.text!) \"\(self.commentTextField.text!)\""
+    
+    private var urtext: String {
+        return "\(DateFormatter.urtextDateString(from: self.date)) \(self.valueTextField.text!) \"\(self.commentTextField.text!)\""
     }
 
     @objc func submitDatapoint() {
@@ -450,7 +455,7 @@ class GoalViewController: UIViewController,  UIScrollViewDelegate, DatapointTabl
             self.scrollView.scrollRectToVisible(CGRect(x: 0, y: 0, width: 0, height: 0), animated: true)
 
             do {
-                let _ = try await ServiceLocator.requestManager.addDatapoint(urtext: self.urtextFromTextFields(), slug: self.goal.slug)
+                let _ = try await ServiceLocator.requestManager.addDatapoint(urtext: self.urtext, slug: self.goal.slug)
                 self.commentTextField.text = ""
 
                 try await updateGoalAndInterface()
@@ -506,3 +511,50 @@ class GoalViewController: UIViewController,  UIScrollViewDelegate, DatapointTabl
         controller.dismiss(animated: true, completion: nil)
     }
 }
+
+
+private extension DateFormatter {
+    private static let urtextDateFormatter: DateFormatter = {
+            let formatter = DateFormatter()
+            formatter.locale = Locale(identifier: "en_US")
+            formatter.dateFormat = "yyyy MM dd"
+            return formatter
+        }()
+
+    static func urtextDateString(from date: Date) -> String {
+        urtextDateFormatter.string(from: date)
+    }
+}
+
+private extension DateFormatter {
+    private static let newDatapointDateDifferentYearDateFormatter: DateFormatter = {
+        let formatter = DateFormatter()
+        formatter.locale = Locale(identifier: "en_US")
+        formatter.dateFormat = "yyyy-MM-dd"
+        return formatter
+    }()
+
+    private static let newDatapointDateDifferentMonthDateFormatter: DateFormatter = {
+        let formatter = DateFormatter()
+        formatter.locale = Locale(identifier: "en_US")
+        formatter.dateFormat = "MMM d"
+        return formatter
+    }()
+
+    private static let newDatapointDateWithinSameMonthDateFormatter: DateFormatter = {
+        let formatter = DateFormatter()
+        formatter.locale = Locale(identifier: "en_US")
+        formatter.dateFormat = "d"
+        return formatter
+    }()
+
+    static func dateTextFieldString(from date: Date, isDifferentYear: Bool, isDifferentMonth: Bool) -> String {
+        if isDifferentYear {
+            return newDatapointDateDifferentYearDateFormatter.string(from: date)
+        } else if isDifferentMonth {
+            return newDatapointDateDifferentMonthDateFormatter.string(from: date)
+        } else {
+            return newDatapointDateWithinSameMonthDateFormatter.string(from: date)
+        }
+    }
+}