Calendar Interaction System

Overview

16 partial files under Calendar/BeepCalendar.Interactions.*.cs handle all pointer/touch/mouse events. The system uses view-mode-specific hit testing, drag mode resolution driven by the hit-test result, event creation proposals during drag, and a commitment pipeline that integrates with the undo/redo history stack. The ResolveDragMode() method returns a CalendarInteractionMode enum that determines subsequent behavior. Four interaction events (InteractionStarted, InteractionUpdated, InteractionCompleted, InteractionCancelled) provide hooks for external observers.

Pointer Events (4 Files)

Drag Modes

ResolveDragMode(CalendarInteractionHitTestResult) determines the CalendarInteractionMode:

Hit Testing (8 Files, 7 Views)

private CalendarInteractionHitTestResult ResolveInteractionTarget(Point loc)
{
    switch (_state.ViewMode)
    {
        case CalendarViewMode.Month:    return ResolveMonthInteraction(loc);
        case CalendarViewMode.Week:
        case CalendarViewMode.WorkWeek: return ResolveWeekInteraction(loc);
        case CalendarViewMode.Day:      return ResolveDayInteraction(loc);
        case CalendarViewMode.Agenda:   return ResolveAgendaInteraction(loc);
        case CalendarViewMode.Timeline: return ResolveTimelineInteraction(loc);
        case CalendarViewMode.List:     return ResolveListInteraction(loc);
        default: return new CalendarInteractionHitTestResult
            { TargetKind = EmptySurface, RequestedMode = SelectDate };
    }
}

8 specialized hit-testing files: HitTesting.cs (dispatcher above), HitTesting.Views.cs, HitTesting.MonthView.cs, HitTesting.WeekView.cs, HitTesting.DayView.cs, HitTesting.TimelineView.cs, HitTesting.TimedView.cs, HitTesting.Helpers.cs. Each resolves whether the click hit an event block (EventBlock), a date cell (DateCell), or empty space (EmptySurface). Returns a CalendarInteractionHitTestResult with TargetKind, RequestedMode, Location, and Date properties.

Timing & Snapping

InteractionSnapIntervalMinutes (default 15) causes event start/end times to snap to the nearest N-minute interval during drag operations. The snapping logic spans three files: Interactions.Timing.cs (base timing), Timing.Snap.cs (snap calculation), Timing.Snap.Location.cs (pixel-to-time conversion with snap). For ResizeStart/ResizeEnd modes, only the affected edge snaps; the opposite anchor remains fixed.

Creation Proposals

During drag-to-create operations, a visual "ghost" rectangle is rendered showing the proposed event at the snapped time interval. The ghost updates in real-time as the user drags, giving live visual feedback of the event that will be created on mouse-up. Two files: Interactions.Proposals.cs (proposal lifecycle management — create, update, clear) and Proposals.CreationRange.cs (calculates proposal start/end times from drag rectangle extents).

Commitment Pipeline (4 Files)

On mouse-up, CommitInteractionMutation(Point location, Point delta) dispatches:

• Commit.cs — Dispatch hub: routes to NewEvent, Copy, or ExistingEvent handler based on drag mode and modifier state
• Commit.NewEvent.cs — Creates event from proposal, routes through EventMutating → CRUD → EventMutated → History push
• Commit.Copy.cs — Clones the source event and creates the copy at the drop location (activated by Ctrl+drag of existing event)
• Commit.ExistingEvent.cs — Mutates an existing event's properties (start, end, date) in place. Routes through EventMutating/EventMutated with modification kind

Copy-Modifier (Ctrl+Drag)

IsCopyModifierDown() checks whether Ctrl or Ctrl+Shift is pressed. When true, dragging an existing event creates a copy at the drop location instead of moving the original. This enables quick event duplication workflows common in modern calendar applications.

CalendarViewStateHelper

Internal static helper in Calendar/Helpers/CalendarViewStateHelper.cs. Builds and returns a populated DayCellState data object:

internal static DayCellState BuildDayCellState(
    DateTime cellDate,
    DateTime currentMonthAnchor,
    DateTime selectedDate,
    DateTime? hoveredDate,
    DateTime focusedDate,
    bool isKeyboardFocusVisible,
    int eventCount,
    int maxEventsPerCell)
// Returns DayCellState with computed flags:
//   IsCurrentMonth, IsToday, IsSelected, IsHovered,
//   IsWeekend (Saturday/Sunday), IsFocused,
//   EventCount, HasMoreEvents (eventCount > maxEventsPerCell)

File Inventory

Code Examples

// Interaction events
cal.InteractionStarted += (s, e) =>
    Console.WriteLine($"Started: {e.Mode} at {e.Location}");

cal.InteractionUpdated += (s, e) =>
    Console.WriteLine($"Updated: dragged to {e.Location}");

cal.InteractionCompleted += (s, e) =>
    Console.WriteLine($"Completed: {e.Mode}");

// Snap interval
cal.InteractionSnapIntervalMinutes = 30;  // Snap to :00 and :30

// Create event on drop
cal.CreateEventRequested += (s, e) =>
{
    e.CreatedEvent = new CalendarEvent
    {
        Title = "New Event",
        Start = e.RequestedStart,
        End = e.RequestedStart.AddHours(1)
    };
};