Tweak snapIntervalsTogether so that "1 time every x days" habits work better

android/uhabits-core/src/main/java/org/isoron/uhabits/core/models/CheckmarkList.java

@@ -122,22 +122,28 @@ public abstract class CheckmarkList
     }
 
     /**
-     * Starting from the oldest interval, this function tries to slide the
+     * Starting from the second newest interval, this function tries to slide the
      * intervals backwards into the past, so that gaps are eliminated and
-     * streaks are maximized. When it detects that sliding an interval
-     * would not help fixing any gap, it leaves the interval unchanged.
+     * streaks are maximized.
      */
     static void snapIntervalsTogether(@NonNull ArrayList<Interval> intervals)
     {
-        for (int i = 1; i < intervals.size(); i++)
+        int n = intervals.size();
+        for (int i = n - 2; i >= 0; i--)
         {
             Interval curr = intervals.get(i);
-            Interval prev = intervals.get(i - 1);
+            Interval next = intervals.get(i + 1);
 
-            int gap = prev.end.daysUntil(curr.begin) - 1;
-            if (gap <= 0 || curr.end.minus(gap).isOlderThan(curr.center)) continue;
-            intervals.set(i, new Interval(curr.begin.minus(gap), curr.center,
-                curr.end.minus(gap)));
+            int gapNextToCurrent = next.begin.daysUntil(curr.end);
+            int gapCenterToEnd = curr.center.daysUntil(curr.end);
+
+            if (gapNextToCurrent >= 0)
+            {
+                int shift = Math.min(gapCenterToEnd, gapNextToCurrent + 1);
+                intervals.set(i, new Interval(curr.begin.minus(shift),
+                                              curr.center,
+                                              curr.end.minus(shift)));
+            }
         }
     }
 

android/uhabits-core/src/test/java/org/isoron/uhabits/core/models/CheckmarkListTest.java

@@ -319,16 +319,31 @@ public class CheckmarkListTest extends BaseUnitTest
     public void test_snapIntervalsTogether_1() throws Exception
     {
         ArrayList<CheckmarkList.Interval> original = new ArrayList<>();
-        original.add(new CheckmarkList.Interval(day(40), day(40), day(34)));
-        original.add(new CheckmarkList.Interval(day(25), day(25), day(19)));
-        original.add(new CheckmarkList.Interval(day(16), day(16), day(10)));
+        original.add(new CheckmarkList.Interval(day(27), day(27), day(21)));
+        original.add(new CheckmarkList.Interval(day(20), day(20), day(14)));
+        original.add(new CheckmarkList.Interval(day(12), day(12), day(6)));
         original.add(new CheckmarkList.Interval(day(8), day(8), day(2)));
 
         ArrayList<CheckmarkList.Interval> expected = new ArrayList<>();
-        expected.add(new CheckmarkList.Interval(day(40), day(40), day(34)));
-        expected.add(new CheckmarkList.Interval(day(25), day(25), day(19)));
-        expected.add(new CheckmarkList.Interval(day(18), day(16), day(12)));
-        expected.add(new CheckmarkList.Interval(day(11), day(8), day(5)));
+        expected.add(new CheckmarkList.Interval(day(29), day(27), day(23)));
+        expected.add(new CheckmarkList.Interval(day(22), day(20), day(16)));
+        expected.add(new CheckmarkList.Interval(day(15), day(12), day(9)));
+        expected.add(new CheckmarkList.Interval(day(8), day(8), day(2)));
+
+        CheckmarkList.snapIntervalsTogether(original);
+        assertThat(original, equalTo(expected));
+    }
+
+    @Test
+    public void test_snapIntervalsTogether_2() throws Exception
+    {
+        ArrayList<CheckmarkList.Interval> original = new ArrayList<>();
+        original.add(new CheckmarkList.Interval(day(11), day(8), day(5)));
+        original.add(new CheckmarkList.Interval(day(6), day(4), day(0)));
+
+        ArrayList<CheckmarkList.Interval> expected = new ArrayList<>();
+        expected.add(new CheckmarkList.Interval(day(13), day(8), day(7)));
+        expected.add(new CheckmarkList.Interval(day(6), day(4), day(0)));
 
         CheckmarkList.snapIntervalsTogether(original);
         assertThat(original, equalTo(expected));

android/uhabits-core/src/test/java/org/isoron/uhabits/core/models/ScoreListTest.java

@@ -153,9 +153,9 @@ public class ScoreListTest extends BaseUnitTest
             habit.getScores().groupBy(DateUtils.TruncateField.MONTH, Calendar.SATURDAY);
 
         assertThat(list.size(), equalTo(5));
-        assertThat(list.get(0).getValue(), closeTo(0.653659, E));
-        assertThat(list.get(1).getValue(), closeTo(0.622715, E));
-        assertThat(list.get(2).getValue(), closeTo(0.520997, E));
+        assertThat(list.get(0).getValue(), closeTo(0.687724, E));
+        assertThat(list.get(1).getValue(), closeTo(0.636747, E));
+        assertThat(list.get(2).getValue(), closeTo(0.533860, E));
     }
 
     @Test