Feature the night underway instead of a 4am clock key

AGENTS.md

@@ -7,16 +7,20 @@ SwiftUI, SwiftData, and HealthKit and targets iOS 17+. See `README.md` for the p
 - No third‑party dependencies: there is no Swift Package Manager manifest, no CocoaPods/Carthage,
   and no package manager. The app uses only Apple system frameworks (`SwiftUI`, `SwiftData`,
   `HealthKit`, `Combine`, `Foundation`).
-- There are currently **no test targets** and **no lint config** (no `.swiftlint.yml` /
-  `.swift-format`) checked in.
+- Unit tests live in `Bedtime/BedtimeTests` (target `BedtimeTests`, Swift Testing). They cover
+ pure logic only — date/window math and formatting — and inject a fixed calendar rather than
+ relying on the machine's time zone. There is **no lint config** (no `.swiftlint.yml` /
+ `.swift-format`) checked in.
 
 ## Standard development (macOS + Xcode)
 
 On a macOS machine with Xcode 15+ installed:
 
 - Open and run: open `Bedtime/Bedtime.xcodeproj` in Xcode, select the `Bedtime` scheme, and run.
 - Build from CLI:
-  `xcodebuild -project Bedtime/Bedtime.xcodeproj -scheme Bedtime -destination 'platform=iOS Simulator,name=iPhone 15' build`
+ `xcodebuild -project Bedtime/Bedtime.xcodeproj -scheme Bedtime -destination 'platform=iOS Simulator,name=iPhone 15' build`
+- Run tests:
+ `xcodebuild -project Bedtime/Bedtime.xcodeproj -scheme Bedtime -destination 'platform=iOS Simulator,name=iPhone 15' test`
 - Run HealthKit features in the iOS Simulator. The Simulator starts with no sleep data, so seed it
   first: in a DEBUG build, use the debug buttons in `SettingsView` (backed by
   `DebugDataGenerator` / `HealthKitManager.generateFakeSleepData`), which write synthetic sleep‑stage

Bedtime/Bedtime.xcodeproj/project.pbxproj

@@ -6,8 +6,19 @@
 	objectVersion = 77;
 	objects = {
 
+/* Begin PBXContainerItemProxy section */
+		37B0000072E91B7E900D8ED8 /* PBXContainerItemProxy */ = {
+			isa = PBXContainerItemProxy;
+			containerPortal = 373AAED52E91B7E900D8ED84 /* Project object */;
+			proxyType = 1;
+			remoteGlobalIDString = 373AAEDC2E91B7E900D8ED84;
+			remoteInfo = Bedtime;
+		};
+/* End PBXContainerItemProxy section */
+
 /* Begin PBXFileReference section */
 		373AAEDD2E91B7E900D8ED84 /* Bedger.app */ = {isa = PBXFileReference; explicitFileType = wrapper.application; includeInIndex = 0; path = Bedger.app; sourceTree = BUILT_PRODUCTS_DIR; };
+		37B0000012E91B7E900D8ED8 /* BedtimeTests.xctest */ = {isa = PBXFileReference; explicitFileType = wrapper.cfbundle; includeInIndex = 0; path = BedtimeTests.xctest; sourceTree = BUILT_PRODUCTS_DIR; };
 /* End PBXFileReference section */
 
 /* Begin PBXFileSystemSynchronizedRootGroup section */
@@ -16,6 +27,11 @@
 			path = Bedtime;
 			sourceTree = "<group>";
 		};
+		37B0000022E91B7E900D8ED8 /* BedtimeTests */ = {
+			isa = PBXFileSystemSynchronizedRootGroup;
+			path = BedtimeTests;
+			sourceTree = "<group>";
+		};
 /* End PBXFileSystemSynchronizedRootGroup section */
 
 /* Begin PBXFrameworksBuildPhase section */
@@ -26,13 +42,21 @@
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};
+		37B0000042E91B7E900D8ED8 /* Frameworks */ = {
+			isa = PBXFrameworksBuildPhase;
+			buildActionMask = 2147483647;
+			files = (
+			);
+			runOnlyForDeploymentPostprocessing = 0;
+		};
 /* End PBXFrameworksBuildPhase section */
 
 /* Begin PBXGroup section */
 		373AAED42E91B7E900D8ED84 = {
 			isa = PBXGroup;
 			children = (
 				373AAEDF2E91B7E900D8ED84 /* Bedtime */,
+				37B0000022E91B7E900D8ED8 /* BedtimeTests */,
 				373AAEDE2E91B7E900D8ED84 /* Products */,
 			);
 			sourceTree = "<group>";
@@ -41,6 +65,7 @@
 			isa = PBXGroup;
 			children = (
 				373AAEDD2E91B7E900D8ED84 /* Bedger.app */,
+				37B0000012E91B7E900D8ED8 /* BedtimeTests.xctest */,
 			);
 			name = Products;
 			sourceTree = "<group>";
@@ -70,6 +95,29 @@
 			productReference = 373AAEDD2E91B7E900D8ED84 /* Bedger.app */;
 			productType = "com.apple.product-type.application";
 		};
+		37B0000062E91B7E900D8ED8 /* BedtimeTests */ = {
+			isa = PBXNativeTarget;
+			buildConfigurationList = 37B0000092E91B7E900D8ED8 /* Build configuration list for PBXNativeTarget "BedtimeTests" */;
+			buildPhases = (
+				37B0000032E91B7E900D8ED8 /* Sources */,
+				37B0000042E91B7E900D8ED8 /* Frameworks */,
+				37B0000052E91B7E900D8ED8 /* Resources */,
+			);
+			buildRules = (
+			);
+			dependencies = (
+				37B0000082E91B7E900D8ED8 /* PBXTargetDependency */,
+			);
+			fileSystemSynchronizedGroups = (
+				37B0000022E91B7E900D8ED8 /* BedtimeTests */,
+			);
+			name = BedtimeTests;
+			packageProductDependencies = (
+			);
+			productName = BedtimeTests;
+			productReference = 37B0000012E91B7E900D8ED8 /* BedtimeTests.xctest */;
+			productType = "com.apple.product-type.bundle.unit-test";
+		};
 /* End PBXNativeTarget section */
 
 /* Begin PBXProject section */
@@ -83,6 +131,10 @@
 					373AAEDC2E91B7E900D8ED84 = {
 						CreatedOnToolsVersion = 26.0;
 					};
+					37B0000062E91B7E900D8ED8 = {
+						CreatedOnToolsVersion = 26.0;
+						TestTargetID = 373AAEDC2E91B7E900D8ED84;
+					};
 				};
 			};
 			buildConfigurationList = 373AAED82E91B7E900D8ED84 /* Build configuration list for PBXProject "Bedtime" */;
@@ -100,6 +152,7 @@
 			projectRoot = "";
 			targets = (
 				373AAEDC2E91B7E900D8ED84 /* Bedtime */,
+				37B0000062E91B7E900D8ED8 /* BedtimeTests */,
 			);
 		};
 /* End PBXProject section */
@@ -112,6 +165,13 @@
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};
+		37B0000052E91B7E900D8ED8 /* Resources */ = {
+			isa = PBXResourcesBuildPhase;
+			buildActionMask = 2147483647;
+			files = (
+			);
+			runOnlyForDeploymentPostprocessing = 0;
+		};
 /* End PBXResourcesBuildPhase section */
 
 /* Begin PBXSourcesBuildPhase section */
@@ -122,8 +182,23 @@
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};
+		37B0000032E91B7E900D8ED8 /* Sources */ = {
+			isa = PBXSourcesBuildPhase;
+			buildActionMask = 2147483647;
+			files = (
+			);
+			runOnlyForDeploymentPostprocessing = 0;
+		};
 /* End PBXSourcesBuildPhase section */
 
+/* Begin PBXTargetDependency section */
+		37B0000082E91B7E900D8ED8 /* PBXTargetDependency */ = {
+			isa = PBXTargetDependency;
+			target = 373AAEDC2E91B7E900D8ED84 /* Bedtime */;
+			targetProxy = 37B0000072E91B7E900D8ED8 /* PBXContainerItemProxy */;
+		};
+/* End PBXTargetDependency section */
+
 /* Begin XCBuildConfiguration section */
 		373AAEEC2E91B7EA00D8ED84 /* Debug */ = {
 			isa = XCBuildConfiguration;
@@ -322,6 +397,48 @@
 			};
 			name = Release;
 		};
+		37B00000A2E91B7E900D8ED8 /* Debug */ = {
+			isa = XCBuildConfiguration;
+			buildSettings = {
+				BUNDLE_LOADER = "$(TEST_HOST)";
+				CODE_SIGN_STYLE = Automatic;
+				CURRENT_PROJECT_VERSION = 1;
+				DEVELOPMENT_TEAM = 9J44X82D53;
+				GENERATE_INFOPLIST_FILE = YES;
+				MARKETING_VERSION = 0.9.0;
+				PRODUCT_BUNDLE_IDENTIFIER = com.burnsides.bedtime.tests;
+				PRODUCT_NAME = "$(TARGET_NAME)";
+				SWIFT_APPROACHABLE_CONCURRENCY = YES;
+				SWIFT_DEFAULT_ACTOR_ISOLATION = MainActor;
+				SWIFT_EMIT_LOC_STRINGS = NO;
+				SWIFT_UPCOMING_FEATURE_MEMBER_IMPORT_VISIBILITY = YES;
+				SWIFT_VERSION = 5.0;
+				TARGETED_DEVICE_FAMILY = "1,2";
+				TEST_HOST = "$(BUILT_PRODUCTS_DIR)/Bedger.app/$(BUNDLE_EXECUTABLE_FOLDER_PATH)/Bedger";
+			};
+			name = Debug;
+		};
+		37B00000B2E91B7E900D8ED8 /* Release */ = {
+			isa = XCBuildConfiguration;
+			buildSettings = {
+				BUNDLE_LOADER = "$(TEST_HOST)";
+				CODE_SIGN_STYLE = Automatic;
+				CURRENT_PROJECT_VERSION = 1;
+				DEVELOPMENT_TEAM = 9J44X82D53;
+				GENERATE_INFOPLIST_FILE = YES;
+				MARKETING_VERSION = 0.9.0;
+				PRODUCT_BUNDLE_IDENTIFIER = com.burnsides.bedtime.tests;
+				PRODUCT_NAME = "$(TARGET_NAME)";
+				SWIFT_APPROACHABLE_CONCURRENCY = YES;
+				SWIFT_DEFAULT_ACTOR_ISOLATION = MainActor;
+				SWIFT_EMIT_LOC_STRINGS = NO;
+				SWIFT_UPCOMING_FEATURE_MEMBER_IMPORT_VISIBILITY = YES;
+				SWIFT_VERSION = 5.0;
+				TARGETED_DEVICE_FAMILY = "1,2";
+				TEST_HOST = "$(BUILT_PRODUCTS_DIR)/Bedger.app/$(BUNDLE_EXECUTABLE_FOLDER_PATH)/Bedger";
+			};
+			name = Release;
+		};
 /* End XCBuildConfiguration section */
 
 /* Begin XCConfigurationList section */
@@ -343,6 +460,15 @@
 			defaultConfigurationIsVisible = 0;
 			defaultConfigurationName = Release;
 		};
+		37B0000092E91B7E900D8ED8 /* Build configuration list for PBXNativeTarget "BedtimeTests" */ = {
+			isa = XCConfigurationList;
+			buildConfigurations = (
+				37B00000A2E91B7E900D8ED8 /* Debug */,
+				37B00000B2E91B7E900D8ED8 /* Release */,
+			);
+			defaultConfigurationIsVisible = 0;
+			defaultConfigurationName = Release;
+		};
 /* End XCConfigurationList section */
 	};
 	rootObject = 373AAED52E91B7E900D8ED84 /* Project object */;

Bedtime/Bedtime/Constants.swift

@@ -12,6 +12,9 @@ class Constants {
     static let iconWidth: CGFloat = 30
     static let cardHeaderSpacing: CGFloat = 12
     static let sleepHistoryDays = 30
+    /// The wee hours, when a night with no sleep recorded yet falls back to the night
+    /// before: sleep may still be in progress, or the tracker may not have synced.
+    static let weeHours = 0..<4
     /// Only suggest opening source apps that have written sleep data within this window.
     static let recentSourceAppLookbackDays = 7
     /// Allowed lookback for sleep-bank / insight window selection (Settings slider, insights, list handle).

Bedtime/Bedtime/ContentView.swift

@@ -25,19 +25,16 @@ struct ContentView: View {
         _healthKitManager = StateObject(wrappedValue: HealthKitManager(sourcePreferences: sourcePrefs))
     }
 
-    private var lastNightKey: Date {
-        let calendar = Calendar.current
-        return calendar.startOfDay(
-            for: calendar.date(byAdding: .hour, value: -4, to: Date()) ?? Date()
-        )
+    private var featuredNight: Date {
+        SleepDay.featured(in: healthKitManager.sleepSessions)
     }
 
-    var lastNightData: [SleepSession]? {
-        healthKitManager.sleepSessions[lastNightKey]
+    var featuredNightData: [SleepSession]? {
+        healthKitManager.sleepSessions[featuredNight]
     }
 
     private var recentSourceAppLinks: [SleepSourceAppLink] {
-        guard healthKitManager.allSleepSessions[lastNightKey] == nil else { return [] }
+        guard healthKitManager.allSleepSessions[featuredNight] == nil else { return [] }
         return ViewModel.recentSourceAppLinks(sleepSessions: healthKitManager.allSleepSessions)
     }
 
@@ -119,7 +116,7 @@ struct ContentView: View {
                         HealthKitAuthorizationCard(healthKitManager: healthKitManager)
                     case .hasRequested:
                         if isBeforeEvening {
-                            LastNightCard(sleepSessions: lastNightData,
+                            LastNightCard(sleepSessions: featuredNightData,
                                           goal: userPreferences.sleepGoalHours,
                                           sourceAppLinks: recentSourceAppLinks)
                         } else {
@@ -153,7 +150,7 @@ struct ContentView: View {
                                 wakeTime: wakeTimeBinding
                             )
                         } else {
-                            LastNightCard(sleepSessions: lastNightData,
+                            LastNightCard(sleepSessions: featuredNightData,
                                           goal: userPreferences.sleepGoalHours,
                                           sourceAppLinks: recentSourceAppLinks)
                         }

Bedtime/Bedtime/Models/SleepData.swift

@@ -29,9 +29,7 @@ struct SleepSession {
     }
 
     var dateForGrouping: Date {
-        let midpoint = startDate.addingTimeInterval(duration / 2)
-        let shiftedMidpoint = midpoint.addingTimeInterval(TimeInterval(6 * 60 * 60))
-        return Calendar.current.startOfDay(for: shiftedMidpoint)
+        SleepDay.containing(startDate.addingTimeInterval(duration / 2))
     }
 }
 

Bedtime/Bedtime/Utils/SleepDay.swift

@@ -0,0 +1,54 @@
+//
+//  SleepDay.swift
+//  Bedtime
+//
+
+import Foundation
+
+/// The calendar day a stretch of sleep is credited to.
+///
+/// Sleep that crosses midnight belongs to the day it ends on, so sleep days are cut
+/// at 6pm rather than midnight: shifting an instant forward six hours and taking that
+/// day's start files an evening bedtime and the morning it leads into under one day.
+enum SleepDay {
+    /// How far an instant is shifted before its day is taken, which puts the boundary
+    /// between one sleep day and the next at 6pm.
+    static let shift: TimeInterval = 6 * 60 * 60
+
+    /// The sleep day `date` belongs to. Applied to a session's midpoint this buckets
+    /// the session; applied to `now` it gives the sleep day currently underway.
+    static func containing(_ date: Date, calendar: Calendar = .current) -> Date {
+        calendar.startOfDay(for: date.addingTimeInterval(shift))
+    }
+
+    /// The sleep day before `day`.
+    static func previous(before day: Date, calendar: Calendar = .current) -> Date? {
+        calendar.date(byAdding: .day, value: -1, to: day)
+    }
+
+    /// The sleep day a summary should feature, given the nights that have data.
+    ///
+    /// Prefers the day underway, so waking briefly at 2am shows tonight's sleep so far
+    /// rather than yesterday's total. During `Constants.weeHours` that day can have
+    /// nothing recorded yet — sleep is still in progress, or the tracker hasn't synced —
+    /// so it falls back to the night before. Later in the day an empty night stays
+    /// empty, leaving the no-data state free to prompt a sync instead of resurrecting
+    /// older sleep.
+    static func featured<Sessions>(
+        in nights: [Date: Sessions],
+        now: Date = Date(),
+        calendar: Calendar = .current
+    ) -> Date {
+        let nightUnderway = containing(now, calendar: calendar)
+        let nothingRecordedYet = nights[nightUnderway] == nil
+        let stillTheWeeHours = Constants.weeHours.contains(calendar.component(.hour, from: now))
+
+        if nothingRecordedYet,
+           stillTheWeeHours,
+           let previousNight = previous(before: nightUnderway, calendar: calendar) {
+            return previousNight
+        }
+
+        return nightUnderway
+    }
+}