refactor: Split EventFormFields.tsx into smaller modules

- Extract helper functions to utils/dateTimeHelpers.ts and utils/dateTimeFormatters.ts
- Extract validation logic to utils/formValidation.ts
- Extract FieldWithLabel component to components/FieldWithLabel.tsx
- Extract DateTimeFields component to components/DateTimeFields.tsx
- Extract all-day toggle logic to hooks/useAllDayToggle.ts
- Update imports in EventModal.tsx, EventUpdateModal.tsx, EventDisplay.tsx, eventHandlers.ts
- Maintain all existing functionality without breaking changes

src/components/Event/utils/formValidation.ts

@@ -0,0 +1,96 @@
+import { combineDateTime } from "./dateTimeHelpers";
+
+/**
+ * Validation parameters for event form
+ */
+export interface ValidationParams {
+  title: string;
+  startDate: string;
+  startTime: string;
+  endDate: string;
+  endTime: string;
+  allday: boolean;
+  showValidationErrors: boolean;
+}
+
+/**
+ * Validation result for event form
+ */
+export interface ValidationResult {
+  isValid: boolean;
+  errors: {
+    title: string;
+    dateTime: string;
+  };
+}
+
+/**
+ * Validate event form fields
+ * @param params - Validation parameters
+ * @returns Validation result with errors
+ */
+export function validateEventForm(params: ValidationParams): ValidationResult {
+  const {
+    title,
+    startDate,
+    startTime,
+    endDate,
+    endTime,
+    allday,
+    showValidationErrors,
+  } = params;
+
+  const isTitleValid = title.trim().length > 0;
+  const shouldShowTitleError = showValidationErrors && !isTitleValid;
+
+  let isDateTimeValid = true;
+  let dateTimeError = "";
+
+  // Validate start date
+  if (!startDate || startDate.trim() === "") {
+    isDateTimeValid = false;
+    dateTimeError = "Start date is required";
+  }
+  // Validate start time (if not all-day)
+  else if (!allday && (!startTime || startTime.trim() === "")) {
+    isDateTimeValid = false;
+    dateTimeError = "Start time is required";
+  }
+  // Validate end date
+  else if (!endDate || endDate.trim() === "") {
+    isDateTimeValid = false;
+    dateTimeError = "End date is required";
+  }
+  // Validate end time (if not all-day)
+  else if (!allday && (!endTime || endTime.trim() === "")) {
+    isDateTimeValid = false;
+    dateTimeError = "End time is required";
+  }
+  // Validate end > start
+  else {
+    const startDateTime = allday
+      ? new Date(startDate + "T00:00:00")
+      : new Date(combineDateTime(startDate, startTime));
+    const endDateTime = allday
+      ? new Date(endDate + "T00:00:00")
+      : new Date(combineDateTime(endDate, endTime));
+
+    if (isNaN(startDateTime.getTime()) || isNaN(endDateTime.getTime())) {
+      isDateTimeValid = false;
+      dateTimeError = "Invalid date/time";
+    } else if (endDateTime <= startDateTime) {
+      isDateTimeValid = false;
+      dateTimeError = "End time must be after start time";
+    }
+  }
+
+  const isValid = isTitleValid && isDateTimeValid;
+
+  return {
+    isValid,
+    errors: {
+      title: shouldShowTitleError ? "Title is required" : "",
+      dateTime: showValidationErrors ? dateTimeError : "",
+    },
+  };
+}