Fix off-by-one in stats period start date and day count

LoopFollow/Stats/AggregatedStatsView.swift

@@ -28,7 +28,7 @@ struct AggregatedStatsView: View {
         let startOfToday = calendar.startOfDay(for: Date())
         let end = calendar.date(byAdding: .second, value: -1, to: startOfToday) ?? Date()
         let endDay = calendar.startOfDay(for: end)
-        let startDay = calendar.date(byAdding: .day, value: -7, to: endDay) ?? endDay
+        let startDay = calendar.date(byAdding: .day, value: -(7 - 1), to: endDay) ?? endDay
         let start = calendar.startOfDay(for: startDay)
         _startDate = State(initialValue: start)
         _endDate = State(initialValue: end)

LoopFollow/Stats/AggregatedStatsViewModel.swift

@@ -39,8 +39,11 @@ class AggregatedStatsViewModel: ObservableObject {
     }
 
     func updatePeriod(_ days: Int, completion: @escaping () -> Void = {}) {
-        let endDate = Date()
-        let startDate = dateTimeUtils.displayCalendar().date(byAdding: .day, value: -days, to: endDate) ?? endDate
+        let calendar = dateTimeUtils.displayCalendar()
+        let startOfToday = calendar.startOfDay(for: Date())
+        let endDate = calendar.date(byAdding: .second, value: -1, to: startOfToday) ?? Date()
+        let endDayStart = calendar.startOfDay(for: endDate)
+        let startDate = calendar.date(byAdding: .day, value: -(days - 1), to: endDayStart) ?? endDayStart
         updateDateRange(start: startDate, end: endDate, completion: completion)
     }
 

LoopFollow/Stats/DateRangePicker.swift

@@ -31,7 +31,9 @@ struct DateRangePicker: View {
 
     private var dayCount: Int {
         let calendar = dateTimeUtils.displayCalendar()
-        return calendar.dateComponents([.day], from: startDate, to: endDate).day ?? 0
+        let startDay = calendar.startOfDay(for: startDate)
+        let endDay = calendar.startOfDay(for: endDate)
+        return (calendar.dateComponents([.day], from: startDay, to: endDay).day ?? 0) + 1
     }
 
     private var lastFullDay: Date {
@@ -241,7 +243,7 @@ struct DateRangePicker: View {
         let calendar = dateTimeUtils.displayCalendar()
         endDate = lastFullDay
         let endDayStart = calendar.startOfDay(for: endDate)
-        let startDayStart = calendar.date(byAdding: .day, value: -days, to: endDayStart) ?? endDayStart
+        let startDayStart = calendar.date(byAdding: .day, value: -(days - 1), to: endDayStart) ?? endDayStart
         startDate = calendar.startOfDay(for: startDayStart)
         showStartDatePicker = false
         showEndDatePicker = false

LoopFollow/Stats/SimpleStatsViewModel.swift

@@ -66,7 +66,7 @@ class SimpleStatsViewModel: ObservableObject {
         let smbTotal = smbInPeriod.reduce(0.0) { $0 + $1.value }
         let totalBolusInPeriod = bolusTotal + smbTotal
 
-        let cutoffTime = Date().timeIntervalSince1970 - (Double(dataService.daysToAnalyze) * 24 * 60 * 60)
+        let cutoffTime = dataService.startDate.timeIntervalSince1970
         let allBolusDates = (bolusesInPeriod + smbInPeriod).map { $0.date }.filter { $0 >= cutoffTime }
         let actualDays = calculateActualDaysCovered(dates: allBolusDates, requestedDays: dataService.daysToAnalyze)
 
@@ -93,7 +93,7 @@ class SimpleStatsViewModel: ObservableObject {
 
         let totalCarbsInPeriod = dailyCarbs.values.reduce(0.0, +)
 
-        let daysWithData = max(dailyCarbs.count, 1)
+        let daysWithData = dataService.daysToAnalyze
 
         if daysWithData > 0 {
             avgCarbs = totalCarbsInPeriod / Double(daysWithData)
@@ -295,7 +295,7 @@ class SimpleStatsViewModel: ObservableObject {
         guard !dates.isEmpty else { return requestedDays }
 
         let calendar = dateTimeUtils.displayCalendar()
-        let cutoffTime = Date().timeIntervalSince1970 - (Double(requestedDays) * 24 * 60 * 60)
+        let cutoffTime = dataService.startDate.timeIntervalSince1970
         let filteredDates = dates.filter { $0 >= cutoffTime }
 
         var uniqueDays = Set<Date>()

LoopFollow/Stats/StatsDataService.swift

@@ -32,9 +32,11 @@ class StatsDataService {
     func updateDateRange(start: Date, end: Date) {
         startDate = start
         endDate = end
-        // Also update daysToAnalyze for compatibility with existing code
-        let daysBetween = dateTimeUtils.displayCalendar().dateComponents([.day], from: start, to: end).day ?? 14
-        daysToAnalyze = max(daysBetween, 1)
+        let calendar = dateTimeUtils.displayCalendar()
+        let startDay = calendar.startOfDay(for: start)
+        let endDay = calendar.startOfDay(for: end)
+        let daysBetween = calendar.dateComponents([.day], from: startDay, to: endDay).day ?? 13
+        daysToAnalyze = daysBetween + 1
     }
 
     func ensureDataAvailable(onProgress: @escaping () -> Void, completion: @escaping () -> Void) {