Do not assume current stopwatch lap has positive duration

am: f8e562f6

* commit 'f8e562f6':
  Do not assume current stopwatch lap has positive duration

src/com/android/deskclock/data/Stopwatch.java

@@ -61,7 +61,11 @@ public final class Stopwatch {
             return mAccumulatedTime;
         }
 
-        return mAccumulatedTime + (now() - mLastStartTime);
+        // In practice, "now" can be any value due to device reboots. When the real-time clock
+        // is reset, there is no more guarantee that "now" falls after the last start time. To
+        // ensure the stopwatch is monotonically increasing, normalize negative time segments to 0,
+        final long timeSinceStart = now() - mLastStartTime;
+        return mAccumulatedTime + Math.max(0, timeSinceStart);
     }
 
     /**
@@ -79,7 +83,7 @@ public final class Stopwatch {
             return this;
         }
 
-        return new Stopwatch(RUNNING, now(), mAccumulatedTime);
+        return new Stopwatch(RUNNING, now(), getTotalTime());
     }
 
     /**
@@ -90,8 +94,7 @@ public final class Stopwatch {
             return this;
         }
 
-        final long accumulatedTime = mAccumulatedTime + (now() - mLastStartTime);
-        return new Stopwatch(PAUSED, Long.MIN_VALUE, accumulatedTime);
+        return new Stopwatch(PAUSED, Long.MIN_VALUE, getTotalTime());
     }
 
     /**

src/com/android/deskclock/data/StopwatchModel.java

@@ -175,21 +175,17 @@ final class StopwatchModel {
     }
 
     /**
-     * @param time a point in time after the end of the last lap
-     * @return the elapsed time between the given {@code time} and the end of the previous lap
+     * In practice, {@code time} can be any value due to device reboots. When the real-time clock is
+     * reset, there is no more guarantee that this time falls after the last recorded lap.
+     *
+     * @param time a point in time expected, but not required, to be after the end of the prior lap
+     * @return the elapsed time between the given {@code time} and the end of the prior lap;
+     *      negative elapsed times are normalized to {@code 0}
      */
     long getCurrentLapTime(long time) {
         final Lap previousLap = getLaps().get(0);
-
-        final long last = previousLap.getAccumulatedTime();
-        final long lapTime = time - last;
-
-        if (lapTime < 0) {
-            final String message = String.format("time (%d) must exceed last lap (%d)", time, last);
-            throw new IllegalArgumentException(message);
-        }
-
-        return lapTime;
+        final long currentLapTime = time - previousLap.getAccumulatedTime();
+        return Math.max(0, currentLapTime);
     }
 
     /**