Merge pull request #233 from TelemetryDeck/feature/distinct-days-last…

…-month Add `distinctDaysUsedLastMonth` to better detect user engagement levels
TelemetryDeck · Feb 17, 2025 · 9c6644d · 9c6644d
2 parents 5f81340 + 731749e
commit 9c6644d
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diff --git a/Sources/TelemetryDeck/Helpers/SessionManager.swift b/Sources/TelemetryDeck/Helpers/SessionManager.swift
@@ -94,6 +94,17 @@ final class SessionManager: @unchecked Sendable {
         }
     }
 
+    var distinctDaysUsedLastMonthCount: Int {
+        let dateFormatter = ISO8601DateFormatter()
+        dateFormatter.formatOptions = [.withFullDate]
+
+        // Get date 30 days ago
+        let thirtyDaysAgoDate = Date().addingTimeInterval(-(30 * 24 * 60 * 60))
+        let thirtyDaysAgoFormatted = dateFormatter.string(from: thirtyDaysAgoDate)
+
+        return self.distinctDaysUsed.countISODatesOnOrAfter(cutoffISODate: thirtyDaysAgoFormatted)
+    }
+
     private var currentSessionStartedAt: Date = .distantPast
     private var currentSessionDuration: TimeInterval = .zero
 
@@ -263,3 +274,16 @@ final class SessionManager: @unchecked Sendable {
         #endif
     }
 }
+
+extension [String] {
+    /// Counts ISO-formatted date strings (YYYY-MM-DD) that are on or after the given date.
+    /// Uses string comparison since ISO dates sort alphabetically like dates chronologically.
+    ///
+    /// - Parameter cutoffISODate: The ISO date string to compare against
+    /// - Returns: Count of dates on or after the cutoff
+    func countISODatesOnOrAfter(cutoffISODate: String) -> Int {
+        // Simply filter strings that are >= the cutoff date string
+        // (works because: String compares alphabetically & ISO date format sorts dates alphabetically)
+        self.filter { $0 >= cutoffISODate }.count
+    }
+}
diff --git a/Sources/TelemetryDeck/Signals/Signal.swift b/Sources/TelemetryDeck/Signals/Signal.swift
@@ -119,6 +119,7 @@ public struct DefaultSignalPayload: Encodable {
                     "TelemetryDeck.Acquisition.firstSessionDate": SessionManager.shared.firstSessionDate,
                     "TelemetryDeck.Retention.averageSessionSeconds": "\(SessionManager.shared.averageSessionSeconds)",
                     "TelemetryDeck.Retention.distinctDaysUsed": "\(SessionManager.shared.distinctDaysUsed.count)",
+                    "TelemetryDeck.Retention.distinctDaysUsedLastMonth": "\(SessionManager.shared.distinctDaysUsedLastMonthCount)",
                     "TelemetryDeck.Retention.totalSessionsCount": "\(SessionManager.shared.totalSessionsCount)",
                 ],
                 uniquingKeysWith: { $1 }

diff --git a/Tests/TelemetryDeckTests/ArrayExtensionTests.swift b/Tests/TelemetryDeckTests/ArrayExtensionTests.swift
@@ -0,0 +1,86 @@
+@testable import TelemetryDeck
+import Testing
+
+enum ArrayExtensionTests {
+    enum CountISODatesOnOrAfter {
+        @Test
+        static func typicalCase() {
+            let dates = ["2025-01-01", "2025-01-15", "2025-02-01", "2025-03-01"]
+
+            #expect(dates.countISODatesOnOrAfter(cutoffISODate: "2025-01-15") == 3)
+            #expect(dates.countISODatesOnOrAfter(cutoffISODate: "2025-02-01") == 2)
+            #expect(dates.countISODatesOnOrAfter(cutoffISODate: "2025-03-02") == 0)
+        }
+
+        @Test
+        static func edgeCases() {
+            // Empty array
+            let emptyDates: [String] = []
+            #expect(emptyDates.countISODatesOnOrAfter(cutoffISODate: "2025-01-01") == 0)
+
+            // Single date, various cutoffs
+            let singleDate = ["2025-01-15"]
+            #expect(singleDate.countISODatesOnOrAfter(cutoffISODate: "2025-01-14") == 1)
+            #expect(singleDate.countISODatesOnOrAfter(cutoffISODate: "2025-01-15") == 1)
+            #expect(singleDate.countISODatesOnOrAfter(cutoffISODate: "2025-01-16") == 0)
+        }
+
+        @Test
+        static func duplicateDates() {
+            let datesWithDuplicates = [
+                "2025-01-01",
+                "2025-01-01",  // Duplicate
+                "2025-02-01",
+                "2025-02-01",  // Duplicate
+                "2025-03-01"
+            ]
+
+            #expect(datesWithDuplicates.countISODatesOnOrAfter(cutoffISODate: "2025-01-01") == 5)
+            #expect(datesWithDuplicates.countISODatesOnOrAfter(cutoffISODate: "2025-02-01") == 3)
+            #expect(datesWithDuplicates.countISODatesOnOrAfter(cutoffISODate: "2025-03-01") == 1)
+        }
+
+        @Test
+        static func complexDateRanges() {
+            let dates = [
+                "2020-12-31",  // End of 2020
+                "2021-01-01",  // Start of 2021
+                "2021-12-31",  // End of 2021
+                "2022-01-01",  // Start of 2022
+                "2022-09-30",  // End of September
+                "2022-10-01",  // Start of October
+                "2023-01-09",  // Single digit day
+                "2023-01-10",  // Double digit day
+                "2023-09-09",  // Both single digit
+                "2023-09-10",  // Mixed digits
+                "2023-10-09",  // Mixed digits different order
+                "2023-10-10",  // Both double digits
+                "2024-02-28",  // End of February
+                "2024-02-29",  // Leap year day
+                "2024-03-01",  // Start of March
+                "2025-01-01"   // Far future
+            ]
+
+            // Test year boundaries
+            #expect(dates.countISODatesOnOrAfter(cutoffISODate: "2020-12-31") == 16)
+            #expect(dates.countISODatesOnOrAfter(cutoffISODate: "2021-01-01") == 15)
+
+            // Test month transitions
+            #expect(dates.countISODatesOnOrAfter(cutoffISODate: "2022-09-30") == 12)
+            #expect(dates.countISODatesOnOrAfter(cutoffISODate: "2022-10-01") == 11)
+
+            // Test single/double digit transitions
+            #expect(dates.countISODatesOnOrAfter(cutoffISODate: "2023-01-09") == 10)
+            #expect(dates.countISODatesOnOrAfter(cutoffISODate: "2023-01-10") == 9)
+
+            // Test leap year period
+            #expect(dates.countISODatesOnOrAfter(cutoffISODate: "2024-02-28") == 4)
+            #expect(dates.countISODatesOnOrAfter(cutoffISODate: "2024-02-29") == 3)
+            #expect(dates.countISODatesOnOrAfter(cutoffISODate: "2024-03-01") == 2)
+
+            // Test future date
+            #expect(dates.countISODatesOnOrAfter(cutoffISODate: "2025-01-01") == 1)
+            #expect(dates.countISODatesOnOrAfter(cutoffISODate: "2025-01-02") == 0)
+        }
+    }
+}