Add Timer.recordInterval method (#83)

* Add Timer.recordInterval method

Co-authored-by: Konrad `ktoso` Malawski <ktoso@apple.com>

Sources/CoreMetrics/Metrics.swift

@@ -12,6 +12,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+import Dispatch
+
 // MARK: User API
 
 extension Counter {

Sources/Metrics/Metrics.swift

@@ -33,6 +33,15 @@ public extension Timer {
         }
         return try body()
     }
+
+    /// Record the time interval (with nanosecond precision) between the passed `since` dispatch time and `end` dispatch time.
+    ///
+    /// - parameters:
+    ///   - since: Start of the interval as `DispatchTime`.
+    ///   - end: End of the interval, defaulting to `.now()`.
+    func recordInterval(since: DispatchTime, end: DispatchTime = .now()) {
+        self.recordNanoseconds(end.uptimeNanoseconds - since.uptimeNanoseconds)
+    }
 }
 
 public extension Timer {

Tests/MetricsTests/MetricsTests+XCTest.swift

@@ -28,6 +28,7 @@ extension MetricsExtensionsTests {
             ("testTimerBlock", testTimerBlock),
             ("testTimerWithTimeInterval", testTimerWithTimeInterval),
             ("testTimerWithDispatchTime", testTimerWithDispatchTime),
+            ("testTimerWithDispatchTimeInterval", testTimerWithDispatchTimeInterval),
             ("testTimerUnits", testTimerUnits),
             ("testPreferDisplayUnit", testPreferDisplayUnit),
         ]

Tests/MetricsTests/MetricsTests.swift

@@ -78,6 +78,23 @@ class MetricsExtensionsTests: XCTestCase {
         XCTAssertEqual(testTimer.values[4].1, 0, "expected value to match")
     }
 
+    func testTimerWithDispatchTimeInterval() {
+        let metrics = TestMetrics()
+        MetricsSystem.bootstrapInternal(metrics)
+
+        let name = "timer-\(UUID().uuidString)"
+
+        let timer = Timer(label: name)
+        let start = DispatchTime.now()
+        let end = DispatchTime(uptimeNanoseconds: start.uptimeNanoseconds + 1000 * 1000 * 1000)
+        timer.recordInterval(since: start, end: end)
+
+        let testTimer = timer.handler as! TestTimer
+        XCTAssertEqual(testTimer.values.count, 1, "expected number of entries to match")
+        XCTAssertEqual(UInt64(testTimer.values.first!.1), end.uptimeNanoseconds - start.uptimeNanoseconds, "expected value to match")
+        XCTAssertEqual(metrics.timers.count, 1, "timer should have been stored")
+    }
+
     func testTimerUnits() throws {
         let metrics = TestMetrics()
         MetricsSystem.bootstrapInternal(metrics)