Merge pull request #342 from tidepool-org/ps2/LOOP-2492/use-glucose-velocity

LOOP-2492: Use glucose velocity instead of ICE for meal detection

Author: ps2

Loop/Models/LoopConstants.swift

@@ -52,4 +52,9 @@ enum LoopConstants {
     static let defaultWatchCarbPickerValue = 15 // grams
 
     static let defaultWatchBolusPickerValue = 1.0 // %
+    
+    /// Missed Meal warning constants
+    static let missedMealWarningGlucoseRiseThreshold = 3.0 // mg/dL/m
+    static let missedMealWarningGlucoseRecencyWindow = TimeInterval(minutes: 20)
+    static let missedMealWarningVelocitySampleMinDuration = TimeInterval(minutes: 12)
 }

Loop/View Controllers/CarbEntryViewController.swift

@@ -216,23 +216,29 @@ final class CarbEntryViewController: LoopChartsTableViewController, Identifiable
     private var foodKeyboard: EmojiInputController!
 
     private func updateDisplayAccurateCarbEntryWarning() {
-        deviceManager.loopManager.getLoopState { [weak self] (_, state) in
-            let endDate = Date()
-            let startDate = endDate.addingTimeInterval(.minutes(-20))
-            let threshold = HKQuantity(unit: GlucoseEffectVelocity.unit, doubleValue: 3)
-
-            let filteredInsulinCounteractionEffects = state.insulinCounteractionEffects.filterDateRange(startDate, endDate)
+        let now = Date()
+        let startDate = now.addingTimeInterval(-LoopConstants.missedMealWarningGlucoseRecencyWindow)
 
+        deviceManager.glucoseStore.getGlucoseSamples(start: startDate, end: nil) { [weak self] (result) -> Void in
             DispatchQueue.main.async {
-                // at least 3 insulin counteraction effects are required to calculate the average
-                guard filteredInsulinCounteractionEffects.count >= 3,
-                    let averageInsulinCounteractionEffect = filteredInsulinCounteractionEffects.average(unit: GlucoseEffectVelocity.unit) else
-                {
+                switch result {
+                case .failure:
                     self?.shouldDisplayAccurateCarbEntryWarning = false
-                    return
+                case .success(let samples):
+                    let filteredSamples = samples.filterDateRange(startDate, now)
+                    guard let startSample = filteredSamples.first, let endSample = filteredSamples.last else {
+                        self?.shouldDisplayAccurateCarbEntryWarning = false
+                        return
+                    }
+                    let duration = endSample.startDate.timeIntervalSince(startSample.startDate)
+                    guard duration >= LoopConstants.missedMealWarningVelocitySampleMinDuration else {
+                        self?.shouldDisplayAccurateCarbEntryWarning = false
+                        return
+                    }
+                    let delta = endSample.quantity.doubleValue(for: .milligramsPerDeciliter) - startSample.quantity.doubleValue(for: .milligramsPerDeciliter)
+                    let velocity = delta / duration.minutes // Unit = mg/dL/m
+                    self?.shouldDisplayAccurateCarbEntryWarning = velocity > LoopConstants.missedMealWarningGlucoseRiseThreshold
                 }
-
-                self?.shouldDisplayAccurateCarbEntryWarning = averageInsulinCounteractionEffect >= threshold
             }
         }
     }