WinRTXamlToolkit.Controls.Calendar.ProcessSelection C# (CSharp) Method

        private void ProcessSelection(bool shift, DateTime? lastSelectedDate, int? index)
        {
            if (SelectionMode == CalendarSelectionMode.None && lastSelectedDate != null)
            {
                OnDayClick(lastSelectedDate.Value);
                return;
            }
            if (lastSelectedDate != null && IsValidKeyboardSelection(this, lastSelectedDate.Value))
            {
                if (SelectionMode == CalendarSelectionMode.SingleRange || SelectionMode == CalendarSelectionMode.MultipleRange)
                {
                    foreach (DateTime item in SelectedDates)
                    {
                        RemovedItems.Add(item);
                    }
                    SelectedDates.ClearInternal();
                    if (shift)
                    {
                        CalendarDayButton b;
                        _isShiftPressed = true;
                        if (HoverStart == null)
                        {
                            if (LastSelectedDate != null)
                            {
                                HoverStart = LastSelectedDate;
                            }
                            else
                            {
                                if (DateTimeHelper.CompareYearMonth(DisplayDateInternal, DateTime.Today) == 0)
                                {
                                    HoverStart = DateTime.Today;
                                }
                                else
                                {
                                    HoverStart = DisplayDateInternal;
                                }
                            }

                            b = FindDayButtonFromDay(HoverStart.Value);
                            if (b != null)
                            {
                                HoverStartIndex = b.Index;
                            }
                        }
                        // the index of the SelectedDate is always the last
                        // selectedDate's index
                        UnHighlightDays();
                        // If we hit a BlackOutDay with keyboard we do not
                        // update the HoverEnd
                        CalendarDateRange range;

                        if (DateTime.Compare(HoverStart.Value, lastSelectedDate.Value) < 0)
                        {
                            range = new CalendarDateRange(HoverStart.Value, lastSelectedDate.Value);
                        }
                        else
                        {
                            range = new CalendarDateRange(lastSelectedDate.Value, HoverStart.Value);
                        }

                        if (!BlackoutDates.ContainsAny(range))
                        {
                            HoverEnd = lastSelectedDate;

                            if (index.HasValue)
                            {
                                HoverEndIndex += index;
                            }
                            else
                            {
                                // For Home, End, PageUp and PageDown Keys there
                                // is no easy way to predict the index value
                                b = FindDayButtonFromDay(HoverEndInternal.Value);

                                if (b != null)
                                {
                                    HoverEndIndex = b.Index;
                                }
                            }
                        }

                        OnDayClick(HoverEnd.Value);
                        HighlightDays();
                    }
                    else
                    {
                        HoverStart = lastSelectedDate;
                        HoverEnd = lastSelectedDate;
                        AddSelection();
                        OnDayClick(lastSelectedDate.Value);
                    }
                }
                else
                {
                    // ON CLEAR 
                    LastSelectedDate = lastSelectedDate.Value;
                    if (SelectedDates.Count > 0)
                    {
                        SelectedDates[0] = lastSelectedDate.Value;
                    }
                    else
                    {
                        SelectedDates.Add(lastSelectedDate.Value);
                    }
                    OnDayClick(lastSelectedDate.Value);
                }
            }
        }