Fix streaks not to begin or end with skipped days

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

@@ -107,6 +107,17 @@ public abstract class RepetitionList
     @Nullable
     public abstract Repetition getOldest();
 
+    /**
+     * Returns the oldest successful repetition in the list.
+     * <p>
+     * If the list is empty, returns null. Repetitions in the future are
+     * discarded.
+     *
+     * @return oldest sucessful repetition in the list, or null if list is empty.
+     */
+    @Nullable
+    public abstract Repetition getOldestSuccessful();
+
     @Nullable
     /**
      * Returns the newest repetition in the list.

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

@@ -113,7 +113,7 @@ public abstract class StreakList
         Streak newestStreak = getNewestComputed();
         if (newestStreak != null) return newestStreak.getStart();
 
-        Repetition oldestRep = habit.getRepetitions().getOldest();
+        Repetition oldestRep = habit.getRepetitions().getOldestSuccessful();
         if (oldestRep != null) return oldestRep.getTimestamp();
         return null;
     }
@@ -131,18 +131,32 @@ public abstract class StreakList
     {
         ArrayList<Timestamp> list = new ArrayList<>();
         Timestamp current = beginning;
-        list.add(current);
+        Timestamp lastSuccesful = beginning;
+        boolean isInStreak = false;
 
-        for (int i = 1; i < checks.length; i++)
+        for (int i = checks.length - 1; i >= 0; --i)
         {
-            current = current.plus(1);
-            int j = checks.length - i - 1;
+            boolean isCurrentChecked = (
+                    checks[i] == Checkmark.CHECKED_EXPLICITLY ||
+                        checks[i] == Checkmark.CHECKED_IMPLICITLY
+            );
+            if (habit.getData().type == Habit.NUMBER_HABIT || isCurrentChecked) {
+                lastSuccesful = current;
+            }
+
+            if (isInStreak && checks[i] == 0) {
+                list.add(lastSuccesful);
+                isInStreak = false;
+            }
+            if (!isInStreak && isCurrentChecked) {
+                list.add(current);
+                isInStreak = true;
+            }
 
-            if ((checks[j + 1] == 0 && checks[j] > 0)) list.add(current);
-            if ((checks[j + 1] > 0 && checks[j] == 0)) list.add(current.minus(1));
+            current = current.plus(1);
         }
 
-        if (list.size() % 2 == 1) list.add(current);
+        if (isInStreak) list.add(lastSuccesful);
 
         return list;
     }

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

@@ -92,6 +92,29 @@ public class MemoryRepetitionList extends RepetitionList
         return oldestRep;
     }
 
+    @Nullable
+    @Override
+    public Repetition getOldestSuccessful()
+    {
+        Timestamp oldestTimestamp = Timestamp.ZERO.plus(1000000);
+        Repetition oldestRep = null;
+
+        for (Repetition rep : list)
+        {
+            if (habit.getData().type == Habit.YES_NO_HABIT
+                    && rep.getValue() == Checkmark.SKIPPED_EXPLICITLY) {
+                continue;
+            }
+            if (rep.getTimestamp().isOlderThan(oldestTimestamp))
+            {
+                oldestRep = rep;
+                oldestTimestamp = rep.getTimestamp();
+            }
+        }
+
+        return oldestRep;
+    }
+
     @Nullable
     @Override
     public Repetition getNewest()

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

@@ -100,6 +100,13 @@ public class SQLiteRepetitionList extends RepetitionList
         return list.getOldest();
     }
 
+    @Override
+    public Repetition getOldestSuccessful()
+    {
+        loadRecords();
+        return list.getOldestSuccessful();
+    }
+
     @Override
     public Repetition getNewest()
     {