Utility to find first discontinuity in timeline (#99)

Author: jolarsen

src/main/java/no/nav/fpsak/tidsserie/LocalDateTimeline.java

@@ -476,23 +476,32 @@ public <T, R> LocalDateTimeline<R> union(LocalDateTimeline<T> other, final Local
     /**
      * Whether this timeline is continuous and not empty for its entire interval.
      *
-     * @return true if continuous and not empty for whole matchInterval
+     * @return true if continuous
      */
     public boolean isContinuous() {
+        return firstDiscontinuity() == null;
+    }
+
+    /**
+     * Return the first interval, if any, not covered by the timeline. Utility when full disjoint is not needed
+     *
+     * @return null if continuous, first interval
+     */
+    public LocalDateInterval firstDiscontinuity() {
         if (segments.size() == 1) {
-            return true;
+            return null;
         }
 
         LocalDateInterval lastInterval = null;
         for (LocalDateSegment<V> entry : segments) {
             if (lastInterval != null) {
                 if (!lastInterval.abuts(entry.getLocalDateInterval())) {
-                    return false;
+                    return new LocalDateInterval(lastInterval.getTomDato().plusDays(1), entry.getLocalDateInterval().getFomDato().minusDays(1));
                 }
             }
             lastInterval = entry.getLocalDateInterval();
         }
-        return true;
+        return null;
     }
 
     /**

src/test/java/no/nav/fpsak/tidsserie/LocalDateTimelineTest.java

@@ -26,12 +26,19 @@ class LocalDateTimelineTest {
     void skal_opprette_kontinuerlig_tidslinje() {
         LocalDateTimeline<String> tidslinje = basicContinuousTimeline();
         assertThat(tidslinje.isContinuous()).isTrue();
+        assertThat(tidslinje.firstDiscontinuity()).isNull();
     }
 
     @Test
     void skal_opprette_ikke_kontinuerlig_tidslinje() {
         LocalDateTimeline<String> tidslinje = basicDiscontinuousTimeline();
         assertThat(tidslinje.isContinuous()).isFalse();
+        var firstDiscontinuedInterval = tidslinje.firstDiscontinuity();
+        assertThat(firstDiscontinuedInterval).isNotNull();
+        // tidslinje = Timeline of two intervals A,C. Verify that full timeline A,B,C - A,C = B = discontinuity
+        var continuousTimeline = new LocalDateTimeline<>(tidslinje.getMinLocalDate(), tidslinje.getMaxLocalDate(), "hello world");
+        assertThat(continuousTimeline.disjoint(tidslinje).getLocalDateIntervals().stream().findFirst().orElseThrow()).isEqualTo(firstDiscontinuedInterval);
+
     }
 
     @Test