Minor updates to schedule rotation form and preview (#2316)

- When editing a shift, use `shiftStart` as `rotationStart` value
(originally, `rotationStart` was most of the time the timestamp of
creation, which is confusing in the new form; otoh, for newly created
shifts, the `shiftStart` will match `rotationStart`)
- Since shift preview is requested starting the day before the start of
the week, sometimes the displayed preview is missing the last day of the
week (preview returns 7 days by default)

src/containers/RotationForm/RotationForm.tsx

@@ -370,10 +370,11 @@ const RotationForm = observer((props: RotationFormProps) => {
   useEffect(() => {
     if (shift) {
       setRotationName(getShiftName(shift));
-      const rotationStart = getDateTime(shift.rotation_start);
-      setRotationStart(rotationStart);
-      setRotationEnd(shift.until ? getDateTime(shift.until) : getDateTime(shift.shift_start).add(1, 'month'));
       const shiftStart = getDateTime(shift.shift_start);
+      // use shiftStart as rotationStart for existing shifts
+      // (original rotationStart defaulted to the shift creation timestamp)
+      setRotationStart(shiftStart);
+      setRotationEnd(shift.until ? getDateTime(shift.until) : getDateTime(shift.shift_start).add(1, 'month'));
       setShiftStart(shiftStart);
       const shiftEnd = getDateTime(shift.shift_end);
       setShiftEnd(shiftEnd);

src/models/schedule/schedule.ts

@@ -252,7 +252,7 @@ export class ScheduleStore extends BaseStore {
     const dayBefore = startMoment.subtract(1, 'day');
 
     const response = await makeRequest(`/oncall_shifts/preview/`, {
-      params: { date: getFromString(dayBefore) },
+      params: { date: getFromString(dayBefore), days: 8 },
       data: { type, schedule: scheduleId, shift_pk: shiftId === 'new' ? undefined : shiftId, ...params },
       method: 'POST',
     });