Improves date handling and event stacking

Enhances date validation and timezone handling using DateService, ensuring data integrity and consistency.

Refactors event rendering and dragging to correctly handle date transformations.

Adds a test plan for event stacking and z-index management.

Fixes edge cases in navigation and date calculations for week/year boundaries and DST transitions.

src/managers/AllDayManager.ts

@@ -1,7 +1,7 @@
 // All-day row height management and animations
 
 import { eventBus } from '../core/EventBus';
-import { ALL_DAY_CONSTANTS } from '../core/CalendarConfig';
+import { ALL_DAY_CONSTANTS, calendarConfig } from '../core/CalendarConfig';
 import { AllDayEventRenderer } from '../renderers/AllDayEventRenderer';
 import { AllDayLayoutEngine, EventLayout } from '../utils/AllDayLayoutEngine';
 import { ColumnBounds, ColumnDetectionUtils } from '../utils/ColumnDetectionUtils';
@@ -18,6 +18,7 @@ import { DragOffset, MousePosition } from '../types/DragDropTypes';
 import { CoreEvents } from '../constants/CoreEvents';
 import { EventManager } from './EventManager';
 import { differenceInCalendarDays } from 'date-fns';
+import { DateService } from '../utils/DateService';
 
 /**
  * AllDayManager - Handles all-day row height animations and management
@@ -26,6 +27,7 @@ import { differenceInCalendarDays } from 'date-fns';
 export class AllDayManager {
   private allDayEventRenderer: AllDayEventRenderer;
   private eventManager: EventManager;
+  private dateService: DateService;
 
   private layoutEngine: AllDayLayoutEngine | null = null;
 
@@ -43,6 +45,8 @@ export class AllDayManager {
   constructor(eventManager: EventManager) {
     this.eventManager = eventManager;
     this.allDayEventRenderer = new AllDayEventRenderer();
+    const timezone = calendarConfig.getTimezone?.();
+    this.dateService = new DateService(timezone);
 
     // Sync CSS variable with TypeScript constant to ensure consistency
     document.documentElement.style.setProperty('--single-row-height', `${ALL_DAY_CONSTANTS.EVENT_HEIGHT}px`);
@@ -420,9 +424,9 @@ export class AllDayManager {
     newEndDate.setDate(newEndDate.getDate() + durationDays);
     newEndDate.setHours(originalEndDate.getHours(), originalEndDate.getMinutes(), originalEndDate.getSeconds(), originalEndDate.getMilliseconds());
 
-    // Update data attributes with new dates
-    dragEndEvent.draggedClone.dataset.start = newStartDate.toISOString();
-    dragEndEvent.draggedClone.dataset.end = newEndDate.toISOString();
+    // Update data attributes with new dates (convert to UTC)
+    dragEndEvent.draggedClone.dataset.start = this.dateService.toUTC(newStartDate);
+    dragEndEvent.draggedClone.dataset.end = this.dateService.toUTC(newEndDate);
 
     const droppedEvent: CalendarEvent = {
       id: eventId,

src/managers/CalendarManager.ts

@@ -42,7 +42,7 @@ export class CalendarManager {
         this.eventRenderer = eventRenderer;
         this.scrollManager = scrollManager;
         this.eventFilterManager = new EventFilterManager();
-        const timezone = calendarConfig.getTimezone?.() || 'Europe/Copenhagen';
+        const timezone = calendarConfig.getTimezone?.();
         this.dateService = new DateService(timezone);
         this.setupEventListeners();
     }

src/managers/EventManager.ts

@@ -30,7 +30,7 @@ export class EventManager {
 
     constructor(eventBus: IEventBus) {
         this.eventBus = eventBus;
-        const timezone = calendarConfig.getTimezone?.() || 'Europe/Copenhagen';
+        const timezone = calendarConfig.getTimezone?.();
         this.dateService = new DateService(timezone);
     }
 
@@ -156,20 +156,23 @@ export class EventManager {
             return null;
         }
 
-        try {
-            if (isNaN(event.start.getTime())) {
-                console.warn(`EventManager: Invalid event start date for event ${id}:`, event.start);
-                return null;
-            }
-
-            return {
-                event,
-                eventDate: event.start
-            };
-        } catch (error) {
-            console.warn(`EventManager: Failed to parse event date for event ${id}:`, error);
+        // Validate event dates
+        const validation = this.dateService.validateDate(event.start);
+        if (!validation.valid) {
+            console.warn(`EventManager: Invalid event start date for event ${id}:`, validation.error);
             return null;
         }
+
+        // Validate date range
+        if (!this.dateService.isValidRange(event.start, event.end)) {
+            console.warn(`EventManager: Invalid date range for event ${id}: start must be before end`);
+            return null;
+        }
+
+        return {
+            event,
+            eventDate: event.start
+        };
     }
 
     /**

src/managers/GridManager.ts

@@ -137,7 +137,7 @@ export class GridManager {
         const weekEnd = this.getWeekEnd(this.currentDate);
         return this.dateService.formatDateRange(weekStart, weekEnd);
       case 'month':
-        return this.currentDate.toLocaleDateString('en-US', { month: 'long', year: 'numeric' });
+        return this.dateService.formatMonthYear(this.currentDate);
       default:
         const defaultWeekStart = this.getISOWeekStart(this.currentDate);
         const defaultWeekEnd = this.getWeekEnd(this.currentDate);

src/managers/NavigationManager.ts

@@ -90,17 +90,22 @@ export class NavigationManager {
     this.eventBus.on(CoreEvents.DATE_CHANGED, (event: Event) => {
       const customEvent = event as CustomEvent;
       const dateFromEvent = customEvent.detail.currentDate;
-      
+
       // Validate date before processing
       if (!dateFromEvent) {
+        console.warn('NavigationManager: No date provided in DATE_CHANGED event');
         return;
       }
-      
+
       const targetDate = new Date(dateFromEvent);
-      if (isNaN(targetDate.getTime())) {
+
+      // Use DateService validation
+      const validation = this.dateService.validateDate(targetDate);
+      if (!validation.valid) {
+        console.warn('NavigationManager: Invalid date received:', validation.error);
         return;
       }
-      
+
       this.navigateToDate(targetDate);
     });
 

src/managers/WorkHoursManager.ts

@@ -38,7 +38,7 @@ export class WorkHoursManager {
   private workSchedule: WorkScheduleConfig;
 
   constructor() {
-    const timezone = calendarConfig.getTimezone?.() || 'Europe/Copenhagen';
+    const timezone = calendarConfig.getTimezone?.();
     this.dateService = new DateService(timezone);
     
     // Default work schedule - will be loaded from JSON later