Allow user to change first day of the week

Closes #421

CHANGELOG.md

@@ -6,6 +6,7 @@
 * Improved calculation of streaks for non-daily habits: performing habits on irregular weekdays will no longer break your streak.
 * Many more colors to choose from (now 20 in total).
 * Ability to customize how transparent the widgets are on your home screen.
+* Ability to customize the first day of the week.
 * Yes/No buttons on notifications, instead of just "Check".
 * Automatic dark theme according to phone settings (Android 10).
 * 25% smaller APK size and much smaller backup files.

android/uhabits-android/src/androidTest/java/org/isoron/uhabits/activities/common/views/ScoreChartTest.java

@@ -29,6 +29,8 @@ import org.isoron.uhabits.utils.*;
 import org.junit.*;
 import org.junit.runner.*;
 
+import java.util.*;
+
 @RunWith(AndroidJUnit4.class)
 @MediumTest
 public class ScoreChartTest extends BaseViewTest
@@ -80,7 +82,7 @@ public class ScoreChartTest extends BaseViewTest
     @Test
     public void testRender_withMonthlyBucket() throws Throwable
     {
-        view.setScores(habit.getScores().groupBy(DateUtils.TruncateField.MONTH));
+        view.setScores(habit.getScores().groupBy(DateUtils.TruncateField.MONTH, Calendar.SUNDAY));
         view.setBucketSize(30);
         view.invalidate();
 
@@ -97,7 +99,7 @@ public class ScoreChartTest extends BaseViewTest
     @Test
     public void testRender_withYearlyBucket() throws Throwable
     {
-        view.setScores(habit.getScores().groupBy(DateUtils.TruncateField.YEAR));
+        view.setScores(habit.getScores().groupBy(DateUtils.TruncateField.YEAR, Calendar.SUNDAY));
         view.setBucketSize(365);
         view.invalidate();
 

android/uhabits-android/src/androidTest/java/org/isoron/uhabits/widgets/FrequencyWidgetTest.java

@@ -28,6 +28,8 @@ import org.isoron.uhabits.core.models.*;
 import org.junit.*;
 import org.junit.runner.*;
 
+import java.util.*;
+
 @RunWith(AndroidJUnit4.class)
 @MediumTest
 public class FrequencyWidgetTest extends BaseViewTest
@@ -45,7 +47,7 @@ public class FrequencyWidgetTest extends BaseViewTest
         setTheme(R.style.WidgetTheme);
 
         habit = fixtures.createLongHabit();
-        FrequencyWidget widget = new FrequencyWidget(targetContext, 0, habit);
+        FrequencyWidget widget = new FrequencyWidget(targetContext, 0, habit, Calendar.SUNDAY);
         view = convertToView(widget, 400, 400);
     }
 

android/uhabits-android/src/androidTest/java/org/isoron/uhabits/widgets/HistoryWidgetTest.java

@@ -28,6 +28,8 @@ import org.isoron.uhabits.core.models.*;
 import org.junit.*;
 import org.junit.runner.*;
 
+import java.util.*;
+
 @RunWith(AndroidJUnit4.class)
 @MediumTest
 public class HistoryWidgetTest extends BaseViewTest
@@ -45,7 +47,7 @@ public class HistoryWidgetTest extends BaseViewTest
         setTheme(R.style.WidgetTheme);
 
         habit = fixtures.createLongHabit();
-        HistoryWidget widget = new HistoryWidget(targetContext, 0, habit);
+        HistoryWidget widget = new HistoryWidget(targetContext, 0, habit, Calendar.SUNDAY);
         view = convertToView(widget, 400, 400);
     }
 

android/uhabits-android/src/main/java/org/isoron/uhabits/activities/common/dialogs/HistoryEditorDialog.java

@@ -30,6 +30,7 @@ import android.util.*;
 import org.isoron.uhabits.*;
 import org.isoron.uhabits.activities.common.views.*;
 import org.isoron.uhabits.core.models.*;
+import org.isoron.uhabits.core.preferences.*;
 import org.isoron.uhabits.core.tasks.*;
 import org.isoron.uhabits.utils.*;
 
@@ -51,6 +52,8 @@ public class HistoryEditorDialog extends AppCompatDialogFragment
 
     private TaskRunner taskRunner;
 
+    private Preferences prefs;
+
     public HistoryEditorDialog()
     {
         this.controller = new Controller() {};
@@ -72,9 +75,11 @@ public class HistoryEditorDialog extends AppCompatDialogFragment
             (HabitsApplication) getActivity().getApplicationContext();
         habitList = app.getComponent().getHabitList();
         taskRunner = app.getComponent().getTaskRunner();
+        prefs = app.getComponent().getPreferences();
 
         historyChart = new HistoryChart(context);
         historyChart.setController(controller);
+        historyChart.setFirstWeekday(prefs.getFirstWeekday());
 
         if (savedInstanceState != null)
         {

android/uhabits-android/src/main/java/org/isoron/uhabits/activities/common/dialogs/WeekdayPickerDialog.java

@@ -29,6 +29,8 @@ import org.isoron.uhabits.*;
 import org.isoron.uhabits.core.models.*;
 import org.isoron.uhabits.core.utils.*;
 
+import java.util.*;
+
 /**
  * Dialog that allows the user to pick one or more days of the week.
  */
@@ -59,8 +61,9 @@ public class WeekdayPickerDialog extends AppCompatDialogFragment implements
         AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
         builder
             .setTitle(R.string.select_weekdays)
-            .setMultiChoiceItems(DateUtils.getLongDayNames(), selectedDays,
+            .setMultiChoiceItems(DateUtils.getLongWeekdayNames(Calendar.SATURDAY),
-                this)
+                    selectedDays,
+                    this)
             .setPositiveButton(android.R.string.yes, this)
             .setNegativeButton(android.R.string.cancel, (dialog, which) -> {
                 dismiss();

android/uhabits-android/src/main/java/org/isoron/uhabits/activities/common/views/FrequencyChart.java

@@ -69,8 +69,11 @@ public class FrequencyChart extends ScrollableChart
 
     @NonNull
     private HashMap<Timestamp, Integer[]> frequency;
+
     private int maxFreq;
 
+    private int firstWeekday = Calendar.SUNDAY;
+
     public FrequencyChart(Context context)
     {
         super(context);
@@ -98,6 +101,12 @@ public class FrequencyChart extends ScrollableChart
         postInvalidate();
     }
 
+    public void setFirstWeekday(int firstWeekday)
+    {
+        this.firstWeekday = firstWeekday;
+        postInvalidate();
+    }
+
     private int getMaxFreq(HashMap<Timestamp, Integer[]> frequency)
     {
         int maxValue = 1;
@@ -144,7 +153,6 @@ public class FrequencyChart extends ScrollableChart
         prevRect.setEmpty();
 
         GregorianCalendar currentDate = DateUtils.getStartOfTodayCalendar();
-
         currentDate.set(Calendar.DAY_OF_MONTH, 1);
         currentDate.add(Calendar.MONTH, -nColumns + 2 - getDataOffset());
 
@@ -193,11 +201,11 @@ public class FrequencyChart extends ScrollableChart
 
     private void drawColumn(Canvas canvas, RectF rect, GregorianCalendar date)
     {
-        Integer values[] = frequency.get(new Timestamp(date));
+        Integer[] values = frequency.get(new Timestamp(date));
         float rowHeight = rect.height() / 8.0f;
         prevRect.set(rect);
 
-        Integer[] localeWeekdayList = DateUtils.getLocaleWeekdayList();
+        int[] localeWeekdayList = DateUtils.getWeekdaySequence(firstWeekday);
         for (int j = 0; j < localeWeekdayList.length; j++)
         {
             rect.set(0, 0, baseSize, baseSize);
@@ -233,7 +241,7 @@ public class FrequencyChart extends ScrollableChart
         pText.setColor(textColor);
         pGrid.setColor(gridColor);
 
-        for (String day : DateUtils.getLocaleDayNames(Calendar.SHORT))
+        for (String day : DateUtils.getShortWeekdayNames(firstWeekday))
         {
             canvas.drawText(day, rGrid.right - columnWidth,
                 rGrid.top + rowHeight / 2 + 0.25f * em, pText);

android/uhabits-android/src/main/java/org/isoron/uhabits/activities/common/views/HistoryChart.java

@@ -93,6 +93,8 @@ public class HistoryChart extends ScrollableChart
 
     private boolean isNumerical = false;
 
+    private int firstWeekday = Calendar.SUNDAY;
+
     @NonNull
     private Controller controller;
 
@@ -210,6 +212,12 @@ public class HistoryChart extends ScrollableChart
         postInvalidate();
     }
 
+    public void setFirstWeekday(int firstWeekday)
+    {
+        this.firstWeekday = firstWeekday;
+        postInvalidate();
+    }
+
     protected void initPaints()
     {
         pTextHeader = new Paint();
@@ -293,7 +301,7 @@ public class HistoryChart extends ScrollableChart
     {
         float verticalOffset = pTextHeader.getFontSpacing() * 0.4f;
 
-        for (String day : DateUtils.getLocaleDayNames(Calendar.SHORT))
+        for (String day : DateUtils.getShortWeekdayNames(firstWeekday))
         {
             location.offset(0, columnWidth);
             canvas.drawText(day, location.left + headerTextOffset,
@@ -375,7 +383,7 @@ public class HistoryChart extends ScrollableChart
     {
         float width = 0;
 
-        for (String w : DateUtils.getLocaleDayNames(Calendar.SHORT))
+        for (String w : DateUtils.getShortWeekdayNames(firstWeekday))
             width = Math.max(width, pSquareFg.measureText(w));
 
         return width;
@@ -473,7 +481,7 @@ public class HistoryChart extends ScrollableChart
         int realWeekday =
             DateUtils.getStartOfTodayCalendar().get(Calendar.DAY_OF_WEEK);
         todayPositionInColumn =
-            (7 + realWeekday - baseDate.getFirstDayOfWeek()) % 7;
+            (7 + realWeekday - firstWeekday) % 7;
 
         baseDate.add(Calendar.DAY_OF_YEAR, -nDays);
         baseDate.add(Calendar.DAY_OF_YEAR, -todayPositionInColumn);

android/uhabits-android/src/main/java/org/isoron/uhabits/activities/habits/show/views/BarCard.java

@@ -28,6 +28,7 @@ import org.isoron.uhabits.*;
 import org.isoron.uhabits.R;
 import org.isoron.uhabits.activities.common.views.*;
 import org.isoron.uhabits.core.models.*;
+import org.isoron.uhabits.core.preferences.*;
 import org.isoron.uhabits.core.tasks.*;
 import org.isoron.uhabits.utils.*;
 
@@ -56,6 +57,9 @@ public class BarCard extends HabitCard
 
     private int bucketSize;
 
+    @Nullable
+    private Preferences prefs;
+
     public BarCard(Context context)
     {
         super(context);
@@ -84,6 +88,12 @@ public class BarCard extends HabitCard
 
     private void init()
     {
+        Context appContext = getContext().getApplicationContext();
+        if (appContext instanceof HabitsApplication)
+        {
+            HabitsApplication app = (HabitsApplication) appContext;
+            prefs = app.getComponent().getPreferences();
+        }
         inflate(getContext(), R.layout.show_habit_bar, this);
         ButterKnife.bind(this);
         boolSpinner.setSelection(1);
@@ -120,8 +130,11 @@ public class BarCard extends HabitCard
         {
             if (isCanceled()) return;
             List<Checkmark> checkmarks;
+            int firstWeekday = Calendar.SATURDAY;
+            if (prefs != null) firstWeekday = prefs.getFirstWeekday();
             if (bucketSize == 1) checkmarks = habit.getCheckmarks().getAll();
-            else checkmarks = habit.getCheckmarks().groupBy(getTruncateField(bucketSize));
+            else checkmarks = habit.getCheckmarks().groupBy(getTruncateField(bucketSize),
+                                                            firstWeekday);
             chart.setCheckmarks(checkmarks);
             chart.setBucketSize(bucketSize);
         }

android/uhabits-android/src/main/java/org/isoron/uhabits/activities/habits/show/views/FrequencyCard.java

@@ -28,6 +28,7 @@ import org.isoron.uhabits.*;
 import org.isoron.uhabits.R;
 import org.isoron.uhabits.activities.common.views.*;
 import org.isoron.uhabits.core.models.*;
+import org.isoron.uhabits.core.preferences.*;
 import org.isoron.uhabits.core.tasks.*;
 import org.isoron.uhabits.utils.*;
 
@@ -43,6 +44,9 @@ public class FrequencyCard extends HabitCard
     @BindView(R.id.frequencyChart)
     FrequencyChart chart;
 
+    @Nullable
+    private Preferences prefs;
+
     public FrequencyCard(Context context)
     {
         super(context);
@@ -63,6 +67,12 @@ public class FrequencyCard extends HabitCard
 
     private void init()
     {
+        Context appContext = getContext().getApplicationContext();
+        if (appContext instanceof HabitsApplication)
+        {
+            HabitsApplication app = (HabitsApplication) appContext;
+            prefs = app.getComponent().getPreferences();
+        }
         inflate(getContext(), R.layout.show_habit_frequency, this);
         ButterKnife.bind(this);
         if (isInEditMode()) initEditMode();
@@ -84,6 +94,7 @@ public class FrequencyCard extends HabitCard
             if (isCanceled()) return;
             RepetitionList reps = getHabit().getRepetitions();
             HashMap<Timestamp, Integer[]> frequency = reps.getWeekdayFrequency();
+            if(prefs != null) chart.setFirstWeekday(prefs.getFirstWeekday());
             chart.setFrequency(frequency);
         }
 

android/uhabits-android/src/main/java/org/isoron/uhabits/activities/habits/show/views/HistoryCard.java

@@ -28,6 +28,7 @@ import org.isoron.uhabits.*;
 import org.isoron.uhabits.R;
 import org.isoron.uhabits.activities.common.views.*;
 import org.isoron.uhabits.core.models.*;
+import org.isoron.uhabits.core.preferences.*;
 import org.isoron.uhabits.core.tasks.*;
 import org.isoron.uhabits.utils.*;
 
@@ -41,9 +42,12 @@ public class HistoryCard extends HabitCard
     @BindView(R.id.title)
     TextView title;
 
-    @NonNull
+    @Nullable
     private Controller controller;
 
+    @Nullable
+    private Preferences prefs;
+
     public HistoryCard(Context context)
     {
         super(context);
@@ -59,16 +63,23 @@ public class HistoryCard extends HabitCard
     @OnClick(R.id.edit)
     public void onClickEditButton()
     {
-        controller.onEditHistoryButtonClick();
+        if(controller != null) controller.onEditHistoryButtonClick();
     }
 
-    public void setController(@NonNull Controller controller)
+    public void setController(@Nullable Controller controller)
     {
         this.controller = controller;
     }
 
     private void init()
     {
+        Context appContext = getContext().getApplicationContext();
+        if (appContext instanceof HabitsApplication)
+        {
+            HabitsApplication app = (HabitsApplication) appContext;
+            prefs = app.getComponent().getPreferences();
+        }
+
         inflate(getContext(), R.layout.show_habit_history, this);
         ButterKnife.bind(this);
         controller = new Controller() {};
@@ -107,7 +118,8 @@ public class HistoryCard extends HabitCard
         public void doInBackground()
         {
             if (isCanceled()) return;
-            int checkmarks[] = habit.getCheckmarks().getAllValues();
+            int[] checkmarks = habit.getCheckmarks().getAllValues();
+            if(prefs != null) chart.setFirstWeekday(prefs.getFirstWeekday());
             chart.setCheckmarks(checkmarks);
         }
 

android/uhabits-android/src/main/java/org/isoron/uhabits/activities/habits/show/views/ScoreCard.java

@@ -143,9 +143,12 @@ public class ScoreCard extends HabitCard
             if (isCanceled()) return;
             List<Score> scores;
             ScoreList scoreList = getHabit().getScores();
+            int firstWeekday = Calendar.SATURDAY;
+            if (prefs != null) firstWeekday = prefs.getFirstWeekday();
+            Log.d("ScoreCard", "firstWeekday="+firstWeekday);
 
             if (bucketSize == 1) scores = scoreList.toList();
-            else scores = scoreList.groupBy(getTruncateField(bucketSize));
+            else scores = scoreList.groupBy(getTruncateField(bucketSize), firstWeekday);
 
             chart.setScores(scores);
             chart.setBucketSize(bucketSize);

android/uhabits-android/src/main/java/org/isoron/uhabits/activities/settings/SettingsFragment.java

@@ -32,9 +32,12 @@ import org.isoron.uhabits.R;
 import org.isoron.uhabits.*;
 import org.isoron.uhabits.core.preferences.*;
 import org.isoron.uhabits.core.ui.*;
+import org.isoron.uhabits.core.utils.*;
 import org.isoron.uhabits.notifications.*;
 import org.isoron.uhabits.widgets.*;
 
+import java.util.*;
+
 import static android.media.RingtoneManager.*;
 import static android.os.Build.VERSION.*;
 import static org.isoron.uhabits.activities.habits.list.ListHabitsScreenKt.*;
@@ -143,6 +146,8 @@ public class SettingsFragment extends PreferenceFragmentCompat
             devCategory.setVisible(false);
         }
 
+        updateWeekdayPreference();
+
         if (SDK_INT < Build.VERSION_CODES.O)
             findPreference("reminderCustomize").setVisible(false);
         else
@@ -154,6 +159,19 @@ public class SettingsFragment extends PreferenceFragmentCompat
         updateSync();
     }
 
+    private void updateWeekdayPreference()
+    {
+        if (prefs == null) return;
+        ListPreference weekdayPref = (ListPreference) findPreference("pref_first_weekday");
+        int currentFirstWeekday = prefs.getFirstWeekday();
+        String[] dayNames = DateUtils.getLongWeekdayNames(Calendar.SATURDAY);
+        String[] dayValues = {"7", "1", "2", "3", "4", "5", "6"};
+        weekdayPref.setEntries(dayNames);
+        weekdayPref.setEntryValues(dayValues);
+        weekdayPref.setDefaultValue(Integer.toString(currentFirstWeekday));
+        weekdayPref.setSummary(dayNames[currentFirstWeekday % 7]);
+    }
+
     @Override
     public void onSharedPreferenceChanged(SharedPreferences sharedPreferences,
                                           String key)
@@ -163,6 +181,7 @@ public class SettingsFragment extends PreferenceFragmentCompat
             Log.d("SettingsFragment", "updating widgets");
             widgetUpdater.updateWidgets();
         }
+        if (key.equals("pref_first_weekday")) updateWeekdayPreference();
         BackupManager.dataChanged("org.isoron.uhabits");
         updateSync();
     }

android/uhabits-android/src/main/java/org/isoron/uhabits/utils/AndroidDateUtils.java

@@ -41,8 +41,8 @@ public class AndroidDateUtils
 
     public static String formatWeekdayList(Context context, boolean weekday[])
     {
-        String shortDayNames[] = org.isoron.uhabits.core.utils.DateUtils.getShortDayNames();
+        String shortDayNames[] = org.isoron.uhabits.core.utils.DateUtils.getShortWeekdayNames(Calendar.SATURDAY);
-        String longDayNames[] = org.isoron.uhabits.core.utils.DateUtils.getLongDayNames();
+        String longDayNames[] = org.isoron.uhabits.core.utils.DateUtils.getLongWeekdayNames(Calendar.SATURDAY);
         StringBuilder buffer = new StringBuilder();
 
         int count = 0;

android/uhabits-android/src/main/java/org/isoron/uhabits/widgets/BaseWidgetProvider.java

@@ -40,6 +40,7 @@ public abstract class BaseWidgetProvider extends AppWidgetProvider
     private HabitList habits;
 
     private Preferences preferences;
+
     private WidgetPreferences widgetPrefs;
 
     public static void updateAppWidget(@NonNull AppWidgetManager manager,
@@ -195,4 +196,9 @@ public abstract class BaseWidgetProvider extends AppWidgetProvider
         preferences = app.getComponent().getPreferences();
         widgetPrefs = app.getComponent().getWidgetPreferences();
     }
+
+    public Preferences getPreferences()
+    {
+        return preferences;
+    }
 }

android/uhabits-android/src/main/java/org/isoron/uhabits/widgets/FrequencyWidget.kt

@@ -29,7 +29,8 @@ import org.isoron.uhabits.widgets.views.*
 class FrequencyWidget(
         context: Context,
         widgetId: Int,
-        private val habit: Habit
+        private val habit: Habit,
+        private val firstWeekday: Int
 ) : BaseWidget(context, widgetId) {
 
     override fun getOnClickPendingIntent(context: Context) =
@@ -40,6 +41,7 @@ class FrequencyWidget(
         widgetView.setTitle(habit.name)
         widgetView.setBackgroundAlpha(preferedBackgroundAlpha)
         (widgetView.dataView as FrequencyChart).apply {
+            setFirstWeekday(firstWeekday)
             setColor(PaletteUtils.getColor(context, habit.color))
             setFrequency(habit.repetitions.weekdayFrequency)
         }

android/uhabits-android/src/main/java/org/isoron/uhabits/widgets/FrequencyWidgetProvider.kt

@@ -24,7 +24,10 @@ import android.content.*
 class FrequencyWidgetProvider : BaseWidgetProvider() {
     override fun getWidgetFromId(context: Context, id: Int): BaseWidget {
         val habits = getHabitsFromWidgetId(id)
-        if (habits.size == 1) return FrequencyWidget(context, id, habits[0])
+        if (habits.size == 1) return FrequencyWidget(context,
+                                                     id,
+                                                     habits[0],
+                                                     preferences.firstWeekday)
         else return StackWidget(context, id, StackWidgetType.FREQUENCY, habits)
     }
 }

android/uhabits-android/src/main/java/org/isoron/uhabits/widgets/HistoryWidget.kt

@@ -30,7 +30,8 @@ import org.isoron.uhabits.widgets.views.*
 class HistoryWidget(
         context: Context,
         id: Int,
-        private val habit: Habit
+        private val habit: Habit,
+        private val firstWeekday: Int
 ) : BaseWidget(context, id) {
 
     override fun getOnClickPendingIntent(context: Context): PendingIntent {
@@ -41,6 +42,7 @@ class HistoryWidget(
         val widgetView = view as GraphWidgetView
         widgetView.setBackgroundAlpha(preferedBackgroundAlpha)
         (widgetView.dataView as HistoryChart).apply {
+            setFirstWeekday(firstWeekday)
             setColor(PaletteUtils.getColor(context, habit.color))
             setCheckmarks(habit.checkmarks.allValues)
         }

android/uhabits-android/src/main/java/org/isoron/uhabits/widgets/HistoryWidgetProvider.kt

@@ -23,7 +23,10 @@ import android.content.*
 class HistoryWidgetProvider : BaseWidgetProvider() {
     override fun getWidgetFromId(context: Context, id: Int): BaseWidget {
         val habits = getHabitsFromWidgetId(id)
-        if (habits.size == 1) return HistoryWidget(context, id, habits[0])
+        if (habits.size == 1) return HistoryWidget(context,
+                                                   id,
+                                                   habits[0],
+                                                   preferences.firstWeekday)
         else return StackWidget(context, id, StackWidgetType.HISTORY, habits)
     }
 }

android/uhabits-android/src/main/java/org/isoron/uhabits/widgets/ScoreWidget.kt

@@ -40,7 +40,8 @@ class ScoreWidget(
         val size = ScoreCard.BUCKET_SIZES[prefs.defaultScoreSpinnerPosition]
         val scores = when(size) {
             1 -> habit.scores.toList()
-            else -> habit.scores.groupBy(ScoreCard.getTruncateField(size))
+            else -> habit.scores.groupBy(ScoreCard.getTruncateField(size),
+                                         prefs.firstWeekday)
         }
 
         val widgetView = view as GraphWidgetView

android/uhabits-android/src/main/java/org/isoron/uhabits/widgets/StackWidgetService.java

@@ -9,6 +9,7 @@ import android.widget.*;
 
 import org.isoron.uhabits.*;
 import org.isoron.uhabits.core.models.*;
+import org.isoron.uhabits.core.preferences.*;
 import org.isoron.uhabits.core.utils.*;
 
 import java.util.*;
@@ -87,18 +88,19 @@ class StackRemoteViewsFactory implements RemoteViewsService.RemoteViewsFactory
     }
 
     @NonNull
-    private BaseWidget constructWidget(@NonNull Habit habit)
+    private BaseWidget constructWidget(@NonNull Habit habit,
+                                       @NonNull Preferences prefs)
     {
         switch (widgetType)
         {
             case CHECKMARK:
                 return new CheckmarkWidget(context, widgetId, habit);
             case FREQUENCY:
-                return new FrequencyWidget(context, widgetId, habit);
+                return new FrequencyWidget(context, widgetId, habit, prefs.getFirstWeekday());
             case SCORE:
                 return new ScoreWidget(context, widgetId, habit);
             case HISTORY:
-                return new HistoryWidget(context, widgetId, habit);
+                return new HistoryWidget(context, widgetId, habit, prefs.getFirstWeekday());
             case STREAKS:
                 return new StreakWidget(context, widgetId, habit);
         }
@@ -136,6 +138,7 @@ class StackRemoteViewsFactory implements RemoteViewsService.RemoteViewsFactory
         Log.i("StackRemoteViewsFactory", "onDataSetChanged started");
 
         HabitsApplication app = (HabitsApplication) context.getApplicationContext();
+        Preferences prefs = app.getComponent().getPreferences();
         HabitList habitList = app.getComponent().getHabitList();
         Bundle options = AppWidgetManager.getInstance(context).getAppWidgetOptions(widgetId);
         ArrayList<RemoteViews> newRemoteViews = new ArrayList<>();
@@ -147,7 +150,7 @@ class StackRemoteViewsFactory implements RemoteViewsService.RemoteViewsFactory
             Habit h = habitList.getById(id);
             if (h == null) throw new HabitNotFoundException();
 
-            BaseWidget widget = constructWidget(h);
+            BaseWidget widget = constructWidget(h, prefs);
             widget.setDimensions(getDimensionsFromOptions(context, options));
 
             RemoteViews landscapeViews = widget.getLandscapeRemoteViews();

android/uhabits-android/src/main/res/values/strings.xml

@@ -242,5 +242,6 @@
     <string name="database">Database</string>
     <string name="widget_opacity_title">Widget opacity</string>
     <string name="widget_opacity_description">Makes widgets more transparent or more opaque in your home screen.</string>
+    <string name="first_day_of_the_week">First day of the week</string>
 
 </resources>

android/uhabits-android/src/main/res/xml/preferences.xml

@@ -55,6 +55,11 @@
                 android:title="@string/widget_opacity_title"
                 app:iconSpaceReserved="false" />
 
+        <ListPreference
+                android:key="pref_first_weekday"
+                android:title="@string/first_day_of_the_week"
+                app:iconSpaceReserved="false" />
+
     </PreferenceCategory>
 
     <PreferenceCategory

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

@@ -412,7 +412,7 @@ public abstract class CheckmarkList
     }
 
     @NonNull
-    public List<Checkmark> groupBy(DateUtils.TruncateField field)
+    public List<Checkmark> groupBy(DateUtils.TruncateField field, int firstWeekday)
     {
         List<Checkmark> checks = getAll();
 
@@ -422,7 +422,7 @@ public abstract class CheckmarkList
 
         for (Checkmark rep : checks)
         {
-            Timestamp tt = rep.getTimestamp().truncate(field);
+            Timestamp tt = rep.getTimestamp().truncate(field, firstWeekday);
             if (count == 0 || !truncatedTimestamps[count - 1].equals(tt))
                 truncatedTimestamps[count++] = tt;
 

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

@@ -129,10 +129,10 @@ public abstract class ScoreList implements Iterable<Score>
         return values;
     }
 
-    public List<Score> groupBy(DateUtils.TruncateField field)
+    public List<Score> groupBy(DateUtils.TruncateField field, int firstWeekday)
     {
         computeAll();
-        HashMap<Timestamp, ArrayList<Double>> groups = getGroupedValues(field);
+        HashMap<Timestamp, ArrayList<Double>> groups = getGroupedValues(field, firstWeekday);
         List<Score> scores = groupsToAvgScores(groups);
         Collections.sort(scores, (s1, s2) -> s2.compareNewer(s1));
         return scores;
@@ -293,14 +293,18 @@ public abstract class ScoreList implements Iterable<Score>
     }
 
     @NonNull
-    private HashMap<Timestamp, ArrayList<Double>> getGroupedValues(DateUtils.TruncateField field)
+    private HashMap<Timestamp, ArrayList<Double>> getGroupedValues(DateUtils.TruncateField field,
+                                                                   int firstWeekday)
     {
         HashMap<Timestamp, ArrayList<Double>> groups = new HashMap<>();
 
         for (Score s : this)
         {
             Timestamp groupTimestamp = new Timestamp(
-                DateUtils.truncate(field, s.getTimestamp().getUnixTime()));
+                DateUtils.truncate(
+                        field,
+                        s.getTimestamp().getUnixTime(),
+                        firstWeekday));
 
             if (!groups.containsKey(groupTimestamp))
                 groups.put(groupTimestamp, new ArrayList<>());

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

@@ -143,13 +143,17 @@ public final class Timestamp
         return DateFormats.getCSVDateFormat().format(new Date(unixTime));
     }
 
+    /**
+     * Returns an integer corresponding to the day of the week. Saturday maps
+     * to 0, Sunday maps to 1, and so on.
+     */
     public int getWeekday()
     {
         return toCalendar().get(DAY_OF_WEEK) % 7;
     }
 
-    public Timestamp truncate(DateUtils.TruncateField field)
+    Timestamp truncate(DateUtils.TruncateField field, int firstWeekday)
     {
-        return new Timestamp(DateUtils.truncate(field, unixTime));
+        return new Timestamp(DateUtils.truncate(field, unixTime, firstWeekday));
     }
 }

android/uhabits-core/src/main/java/org/isoron/uhabits/core/preferences/Preferences.java

@@ -333,6 +333,19 @@ public class Preferences
         return Integer.parseInt(storage.getString("pref_widget_opacity", "102"));
     }
 
+    /**
+     * @return An integer representing the first day of the week. Sunday
+     * corresponds to 1, Monday to 2, and so on, until Saturday, which is
+     * represented by 7. By default, this is based on the current system locale,
+     * unless the user changed this in the settings.
+     */
+    public int getFirstWeekday()
+    {
+        String weekday = storage.getString("pref_first_weekday", "");
+        if (weekday.isEmpty()) return DateUtils.getFirstWeekdayNumberAccordingToLocale();
+        return Integer.parseInt(weekday);
+    }
+
     public interface Listener
     {
         default void onCheckmarkSequenceChanged()

android/uhabits-core/src/main/java/org/isoron/uhabits/core/utils/DateUtils.java

@@ -22,6 +22,7 @@ package org.isoron.uhabits.core.utils;
 import android.support.annotation.*;
 
 import org.isoron.uhabits.core.models.*;
+import org.jetbrains.annotations.*;
 
 import java.util.*;
 
@@ -73,23 +74,6 @@ public abstract class DateUtils
         return day;
     }
 
-    private static String[] getDayNames(int format)
-    {
-        String[] wdays = new String[7];
-
-        Calendar day = new GregorianCalendar();
-        day.set(DAY_OF_WEEK, Calendar.SATURDAY);
-
-        for (int i = 0; i < wdays.length; i++)
-        {
-            wdays[i] =
-                day.getDisplayName(DAY_OF_WEEK, format, getLocale());
-            day.add(DAY_OF_MONTH, 1);
-        }
-
-        return wdays;
-    }
-
     public static long getLocalTime()
     {
         if (fixedLocalTime != null) return fixedLocalTime;
@@ -100,19 +84,25 @@ public abstract class DateUtils
     }
 
     /**
-     * @return array with weekday names starting according to locale settings,
+     * Returns an array of strings with the names for each day of the week,
-     * e.g. [Mo,Di,Mi,Do,Fr,Sa,So] in Germany
+     * in either SHORT or LONG format. The first entry corresponds to the
+     * first day of the week, according to the provided argument.
+     *
+     * @param format Either GregorianCalendar.SHORT or LONG
+     * @param firstWeekday An integer representing the first day of the week,
+     *                     following java.util.Calendar conventions. That is,
+     *                     Saturday corresponds to 7, and Sunday corresponds
+     *                     to 1.
      */
-    public static String[] getLocaleDayNames(int format)
+    @NotNull
+    private static String[] getWeekdayNames(int format, int firstWeekday)
     {
         String[] days = new String[7];
-
         Calendar calendar = new GregorianCalendar();
-        calendar.set(DAY_OF_WEEK, calendar.getFirstDayOfWeek());
+        calendar.set(DAY_OF_WEEK, firstWeekday);
-        for (int i = 0; i < days.length; i++)
+        for (int i = 0; i < days.length; i++) {
-        {
             days[i] = calendar.getDisplayName(DAY_OF_WEEK, format,
-                getLocale());
+                    getLocale());
             calendar.add(DAY_OF_MONTH, 1);
         }
 
@@ -120,30 +110,63 @@ public abstract class DateUtils
     }
 
     /**
-     * @return array with week days numbers starting according to locale
+     * Returns a vector of exactly seven integers, where the first integer is
-     * settings, e.g. [2,3,4,5,6,7,1] in Europe
+     * the provided firstWeekday number, and each subsequent number is the
+     * previous number plus 1, wrapping back to 1 after 7. For example,
+     * providing 3 as firstWeekday returns {3,4,5,6,7,1,2}
+     *
+     * This function is supposed to be used to construct a sequence of weekday
+     * number following java.util.Calendar conventions.
      */
-    public static Integer[] getLocaleWeekdayList()
+    public static int[] getWeekdaySequence(int firstWeekday)
     {
-        Integer[] dayNumbers = new Integer[7];
+        return new int[]
-        Calendar calendar = new GregorianCalendar();
-        calendar.set(DAY_OF_WEEK, calendar.getFirstDayOfWeek());
-        for (int i = 0; i < dayNumbers.length; i++)
         {
-            dayNumbers[i] = calendar.get(DAY_OF_WEEK);
+                (firstWeekday - 1) % 7 + 1,
-            calendar.add(DAY_OF_MONTH, 1);
+                (firstWeekday) % 7 + 1,
-        }
+                (firstWeekday + 1) % 7 + 1,
-        return dayNumbers;
+                (firstWeekday + 2) % 7 + 1,
+                (firstWeekday + 3) % 7 + 1,
+                (firstWeekday + 4) % 7 + 1,
+                (firstWeekday + 5) % 7 + 1,
+        };
     }
 
-    public static String[] getLongDayNames()
+    /**
+     * @return An integer representing the first day of the week, according to
+     * the current locale. Sunday corresponds to 1, Monday to 2, and so on,
+     * until Saturday, which is represented by 7. This is consistent
+     * with java.util.Calendar constants.
+     */
+    public static int getFirstWeekdayNumberAccordingToLocale()
     {
-        return getDayNames(GregorianCalendar.LONG);
+        return new GregorianCalendar().getFirstDayOfWeek();
     }
 
-    public static String[] getShortDayNames()
+    /**
+     * @return A vector of strings with the long names for the week days,
+     * according to the current locale. The first entry corresponds to Saturday,
+     * the second entry corresponds to Monday, and so on.
+     *
+     * @param firstWeekday Either Calendar.SATURDAY, Calendar.MONDAY, or other
+     *                     weekdays defined in this class.
+     */
+    public static String[] getLongWeekdayNames(int firstWeekday)
     {
-        return getDayNames(SHORT);
+        return getWeekdayNames(GregorianCalendar.LONG, firstWeekday);
+    }
+
+    /**
+     * Returns a vector of strings with the short names for the week days,
+     * according to the current locale. The first entry corresponds to Saturday,
+     * the second entry corresponds to Monday, and so on.
+     *
+     * @param firstWeekday Either Calendar.SATURDAY, Calendar.MONDAY, or other
+     *                     weekdays defined in this class.
+     */
+    public static String[] getShortWeekdayNames(int firstWeekday)
+    {
+        return getWeekdayNames(GregorianCalendar.SHORT, firstWeekday);
     }
 
     @NonNull
@@ -206,10 +229,13 @@ public abstract class DateUtils
         return Locale.getDefault();
     }
 
-    public static Long truncate(TruncateField field, long timestamp)
+    public static Long truncate(TruncateField field,
+                                long timestamp,
+                                int firstWeekday)
     {
         GregorianCalendar cal = DateUtils.getCalendar(timestamp);
 
+
         switch (field)
         {
             case MONTH:
@@ -217,7 +243,6 @@ public abstract class DateUtils
                 return cal.getTimeInMillis();
 
             case WEEK_NUMBER:
-                int firstWeekday = cal.getFirstDayOfWeek();
                 int weekday = cal.get(DAY_OF_WEEK);
                 int delta = weekday - firstWeekday;
                 if (delta < 0) delta += 7;

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

@@ -388,20 +388,20 @@ public class CheckmarkListTest extends BaseUnitTest
         Habit habit = fixtures.createLongNumericalHabit(timestamp(2014, JUNE, 1));
         CheckmarkList checkmarks = habit.getCheckmarks();
 
-        List<Checkmark> byMonth = checkmarks.groupBy(MONTH);
+        List<Checkmark> byMonth = checkmarks.groupBy(MONTH, Calendar.SATURDAY);
         assertThat(byMonth.size(), equalTo(25)); // from 2013-01-01 to 2015-01-01
         assertThat(byMonth.get(0), equalTo(new Checkmark(timestamp(2015, JANUARY, 1), 0)));
         assertThat(byMonth.get(6), equalTo(new Checkmark(timestamp(2014, JULY, 1), 0)));
         assertThat(byMonth.get(12), equalTo(new Checkmark(timestamp(2014, JANUARY, 1), 1706)));
         assertThat(byMonth.get(18), equalTo(new Checkmark(timestamp(2013, JULY, 1), 1379)));
 
-        List<Checkmark> byQuarter = checkmarks.groupBy(QUARTER);
+        List<Checkmark> byQuarter = checkmarks.groupBy(QUARTER, Calendar.SATURDAY);
         assertThat(byQuarter.size(), equalTo(9)); // from 2013-Q1 to 2015-Q1
         assertThat(byQuarter.get(0), equalTo(new Checkmark(timestamp(2015, JANUARY, 1), 0)));
         assertThat(byQuarter.get(4), equalTo(new Checkmark(timestamp(2014, JANUARY, 1), 4964)));
         assertThat(byQuarter.get(8), equalTo(new Checkmark(timestamp(2013, JANUARY, 1), 4975)));
 
-        List<Checkmark> byYear = checkmarks.groupBy(YEAR);
+        List<Checkmark> byYear = checkmarks.groupBy(YEAR, Calendar.SATURDAY);
         assertThat(byYear.size(), equalTo(3)); // from 2013 to 2015
         assertThat(byYear.get(0), equalTo(new Checkmark(timestamp(2015, JANUARY, 1), 0)));
         assertThat(byYear.get(1), equalTo(new Checkmark(timestamp(2014, JANUARY, 1), 8227)));

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

@@ -150,7 +150,7 @@ public class ScoreListTest extends BaseUnitTest
     {
         Habit habit = fixtures.createLongHabit();
         List<Score> list =
-            habit.getScores().groupBy(DateUtils.TruncateField.MONTH);
+            habit.getScores().groupBy(DateUtils.TruncateField.MONTH, Calendar.SATURDAY);
 
         assertThat(list.size(), equalTo(5));
         assertThat(list.get(0).getValue(), closeTo(0.653659, E));

android/uhabits-core/src/test/java/org/isoron/uhabits/core/utils/DateUtilsTest.java

@@ -34,6 +34,9 @@ import static org.isoron.uhabits.core.utils.DateUtils.removeTimezone;
 
 public class DateUtilsTest extends BaseUnitTest
 {
+
+    int firstWeekday = SUNDAY;
+
     @Before
     @Override
     public void setUp() throws Exception
@@ -61,18 +64,29 @@ public class DateUtilsTest extends BaseUnitTest
         long t1 = unixTime(2015, Calendar.JANUARY, 16);
         long t2 = unixTime(2015, Calendar.JANUARY, 17);
 
-        assertThat(DateUtils.truncate(field, t0), equalTo(expected));
+        assertThat(DateUtils.truncate(field, t0, firstWeekday), equalTo(expected));
-        assertThat(DateUtils.truncate(field, t1), equalTo(expected));
+        assertThat(DateUtils.truncate(field, t1, firstWeekday), equalTo(expected));
-        assertThat(DateUtils.truncate(field, t2), equalTo(expected));
+        assertThat(DateUtils.truncate(field, t2, firstWeekday), equalTo(expected));
 
         expected = unixTime(2015, Calendar.JANUARY, 18);
         t0 = unixTime(2015, Calendar.JANUARY, 18);
         t1 = unixTime(2015, Calendar.JANUARY, 19);
         t2 = unixTime(2015, Calendar.JANUARY, 24);
 
-        assertThat(DateUtils.truncate(field, t0), equalTo(expected));
+        assertThat(DateUtils.truncate(field, t0, firstWeekday), equalTo(expected));
-        assertThat(DateUtils.truncate(field, t1), equalTo(expected));
+        assertThat(DateUtils.truncate(field, t1, firstWeekday), equalTo(expected));
-        assertThat(DateUtils.truncate(field, t2), equalTo(expected));
+        assertThat(DateUtils.truncate(field, t2, firstWeekday), equalTo(expected));
+
+
+        firstWeekday = WEDNESDAY;
+        expected = unixTime(2015, Calendar.JANUARY, 7);
+        t0 = unixTime(2015, Calendar.JANUARY, 7);
+        t1 = unixTime(2015, Calendar.JANUARY, 9);
+        t2 = unixTime(2015, Calendar.JANUARY, 13);
+
+        assertThat(DateUtils.truncate(field, t0, firstWeekday), equalTo(expected));
+        assertThat(DateUtils.truncate(field, t1, firstWeekday), equalTo(expected));
+        assertThat(DateUtils.truncate(field, t2, firstWeekday), equalTo(expected));
     }
 
     @Test
@@ -85,18 +99,18 @@ public class DateUtilsTest extends BaseUnitTest
 
         DateUtils.TruncateField field = DateUtils.TruncateField.MONTH;
 
-        assertThat(DateUtils.truncate(field, t0), equalTo(expected));
+        assertThat(DateUtils.truncate(field, t0, firstWeekday), equalTo(expected));
-        assertThat(DateUtils.truncate(field, t1), equalTo(expected));
+        assertThat(DateUtils.truncate(field, t1, firstWeekday), equalTo(expected));
-        assertThat(DateUtils.truncate(field, t2), equalTo(expected));
+        assertThat(DateUtils.truncate(field, t2, firstWeekday), equalTo(expected));
 
         expected = unixTime(2016, DECEMBER, 1);
         t0 = unixTime(2016, DECEMBER, 1);
         t1 = unixTime(2016, DECEMBER, 15);
         t2 = unixTime(2016, DECEMBER, 31);
 
-        assertThat(DateUtils.truncate(field, t0), equalTo(expected));
+        assertThat(DateUtils.truncate(field, t0, firstWeekday), equalTo(expected));
-        assertThat(DateUtils.truncate(field, t1), equalTo(expected));
+        assertThat(DateUtils.truncate(field, t1, firstWeekday), equalTo(expected));
-        assertThat(DateUtils.truncate(field, t2), equalTo(expected));
+        assertThat(DateUtils.truncate(field, t2, firstWeekday), equalTo(expected));
     }
 
     @Test
@@ -109,18 +123,18 @@ public class DateUtilsTest extends BaseUnitTest
         long t1 = unixTime(2016, FEBRUARY, 15);
         long t2 = unixTime(2016, MARCH, 30);
 
-        assertThat(DateUtils.truncate(field, t0), equalTo(expected));
+        assertThat(DateUtils.truncate(field, t0, firstWeekday), equalTo(expected));
-        assertThat(DateUtils.truncate(field, t1), equalTo(expected));
+        assertThat(DateUtils.truncate(field, t1, firstWeekday), equalTo(expected));
-        assertThat(DateUtils.truncate(field, t2), equalTo(expected));
+        assertThat(DateUtils.truncate(field, t2, firstWeekday), equalTo(expected));
 
         expected = unixTime(2016, APRIL, 1);
         t0 = unixTime(2016, APRIL, 1);
         t1 = unixTime(2016, MAY, 30);
         t2 = unixTime(2016, JUNE, 20);
 
-        assertThat(DateUtils.truncate(field, t0), equalTo(expected));
+        assertThat(DateUtils.truncate(field, t0, firstWeekday), equalTo(expected));
-        assertThat(DateUtils.truncate(field, t1), equalTo(expected));
+        assertThat(DateUtils.truncate(field, t1, firstWeekday), equalTo(expected));
-        assertThat(DateUtils.truncate(field, t2), equalTo(expected));
+        assertThat(DateUtils.truncate(field, t2, firstWeekday), equalTo(expected));
     }
 
     @Test
@@ -133,18 +147,18 @@ public class DateUtilsTest extends BaseUnitTest
         long t1 = unixTime(2016, FEBRUARY, 25);
         long t2 = unixTime(2016, DECEMBER, 31);
 
-        assertThat(DateUtils.truncate(field, t0), equalTo(expected));
+        assertThat(DateUtils.truncate(field, t0, firstWeekday), equalTo(expected));
-        assertThat(DateUtils.truncate(field, t1), equalTo(expected));
+        assertThat(DateUtils.truncate(field, t1, firstWeekday), equalTo(expected));
-        assertThat(DateUtils.truncate(field, t2), equalTo(expected));
+        assertThat(DateUtils.truncate(field, t2, firstWeekday), equalTo(expected));
 
         expected = unixTime(2017, JANUARY, 1);
         t0 = unixTime(2017, JANUARY, 1);
         t1 = unixTime(2017, MAY, 30);
         t2 = unixTime(2017, DECEMBER, 31);
 
-        assertThat(DateUtils.truncate(field, t0), equalTo(expected));
+        assertThat(DateUtils.truncate(field, t0, firstWeekday), equalTo(expected));
-        assertThat(DateUtils.truncate(field, t1), equalTo(expected));
+        assertThat(DateUtils.truncate(field, t1, firstWeekday), equalTo(expected));
-        assertThat(DateUtils.truncate(field, t2), equalTo(expected));
+        assertThat(DateUtils.truncate(field, t2, firstWeekday), equalTo(expected));
     }
 
     @Test