Refactor code structure and remove redundant changes

src-old/lib/dateUtils.ts

@@ -0,0 +1,200 @@
+/**
+ * Date Utility Functions for Timezone-Agnostic Date Handling
+ * 
+ * This module provides utilities for handling calendar dates (not moments in time)
+ * without timezone shifts. All dates are stored as YYYY-MM-DD strings in the database
+ * using the DATE type (not TIMESTAMP).
+ * 
+ * Key Principle: Calendar dates like "January 1, 2024" should remain "2024-01-01"
+ * regardless of user timezone. We never use UTC conversion for DATE fields.
+ * 
+ * @see docs/DATE_HANDLING.md for full documentation
+ */
+
+/**
+ * Converts a Date object to YYYY-MM-DD string in LOCAL timezone
+ * 
+ * This prevents timezone shifts where selecting "Jan 1, 2024" could
+ * save as "2023-12-31" or "2024-01-02" due to UTC conversion.
+ * 
+ * @param date - Date object to convert
+ * @returns YYYY-MM-DD formatted string in local timezone
+ * 
+ * @example
+ * // User in UTC-8 selects Jan 1, 2024 11:00 PM
+ * const date = new Date('2024-01-01T23:00:00-08:00');
+ * toDateOnly(date); // Returns "2024-01-01" ✅ (NOT "2024-01-02")
+ */
+export function toDateOnly(date: Date): string {
+  const year = date.getFullYear();
+  const month = String(date.getMonth() + 1).padStart(2, '0');
+  const day = String(date.getDate()).padStart(2, '0');
+  return `${year}-${month}-${day}`;
+}
+
+/**
+ * Parses a YYYY-MM-DD string to a Date object at midnight local time
+ * 
+ * @param dateString - YYYY-MM-DD formatted string
+ * @returns Date object set to midnight local time
+ * 
+ * @example
+ * parseDateOnly('2024-01-01'); // Returns Date object for Jan 1, 2024 00:00:00 local
+ */
+export function parseDateOnly(dateString: string): Date {
+  const [year, month, day] = dateString.split('-').map(Number);
+  return new Date(year, month - 1, day);
+}
+
+/**
+ * Gets current date as YYYY-MM-DD string in local timezone
+ * 
+ * @returns Current date in YYYY-MM-DD format
+ * 
+ * @example
+ * getCurrentDateLocal(); // "2024-01-15"
+ */
+export function getCurrentDateLocal(): string {
+  return toDateOnly(new Date());
+}
+
+/**
+ * Formats a date string for display based on precision
+ * 
+ * @param dateString - YYYY-MM-DD formatted string
+ * @param precision - Display precision: 'day', 'month', or 'year'
+ * @returns Formatted display string
+ * 
+ * @example
+ * formatDateDisplay('2024-01-01', 'year');  // "2024"
+ * formatDateDisplay('2024-01-01', 'month'); // "January 2024"
+ * formatDateDisplay('2024-01-01', 'day');   // "January 1, 2024"
+ */
+export function formatDateDisplay(
+  dateString: string | null | undefined,
+  precision: 'day' | 'month' | 'year' = 'day'
+): string {
+  if (!dateString) return '';
+  
+  const date = parseDateOnly(dateString);
+  
+  switch (precision) {
+    case 'year':
+      return date.getFullYear().toString();
+    case 'month':
+      return date.toLocaleDateString('en-US', { year: 'numeric', month: 'long' });
+    case 'day':
+    default:
+      return date.toLocaleDateString('en-US', { 
+        year: 'numeric', 
+        month: 'long', 
+        day: 'numeric' 
+      });
+  }
+}
+
+/**
+ * Validates YYYY-MM-DD date format
+ * 
+ * @param dateString - String to validate
+ * @returns true if valid YYYY-MM-DD format
+ * 
+ * @example
+ * isValidDateString('2024-01-01'); // true
+ * isValidDateString('01/01/2024'); // false
+ * isValidDateString('2024-1-1');   // false
+ */
+export function isValidDateString(dateString: string): boolean {
+  return /^\d{4}-\d{2}-\d{2}$/.test(dateString);
+}
+
+/**
+ * Checks if a date is within a valid range
+ * 
+ * @param dateString - YYYY-MM-DD formatted string
+ * @param minYear - Minimum allowed year (default: 1800)
+ * @param maxYear - Maximum allowed year (default: current year + 10)
+ * @returns true if date is within range
+ */
+export function isDateInRange(
+  dateString: string,
+  minYear: number = 1800,
+  maxYear: number = new Date().getFullYear() + 10
+): boolean {
+  if (!isValidDateString(dateString)) return false;
+  
+  const year = parseInt(dateString.split('-')[0]);
+  return year >= minYear && year <= maxYear;
+}
+
+/**
+ * Compares two date strings
+ * 
+ * @param date1 - First date in YYYY-MM-DD format
+ * @param date2 - Second date in YYYY-MM-DD format
+ * @returns -1 if date1 < date2, 0 if equal, 1 if date1 > date2
+ */
+export function compareDateStrings(date1: string, date2: string): number {
+  if (date1 === date2) return 0;
+  return date1 < date2 ? -1 : 1;
+}
+
+/**
+ * Safely parses a date value (string or Date) for display formatting
+ * Ensures YYYY-MM-DD strings are interpreted as local dates, not UTC
+ * 
+ * This prevents timezone bugs where "1972-10-01" would display as
+ * "September 30, 1972" for users in negative UTC offset timezones.
+ * 
+ * @param date - Date string (YYYY-MM-DD) or Date object
+ * @returns Date object in local timezone
+ * 
+ * @example
+ * // User in UTC-8 viewing "1972-10-01"
+ * parseDateForDisplay("1972-10-01"); // Returns Oct 1, 1972 00:00 PST ✅
+ * // NOT Sep 30, 1972 16:00 PST (what new Date() would create)
+ */
+export function parseDateForDisplay(date: string | Date): Date {
+  if (date instanceof Date) {
+    return date;
+  }
+  // If it's a YYYY-MM-DD string, use parseDateOnly for local interpretation
+  if (typeof date === 'string' && /^\d{4}-\d{2}-\d{2}$/.test(date)) {
+    return parseDateOnly(date);
+  }
+  // Fallback for other date strings (timestamps, ISO strings, etc.)
+  return new Date(date);
+}
+
+/**
+ * Creates a date string for a specific precision
+ * Sets the date to the first day of the period for month/year precision
+ * 
+ * @param date - Date object
+ * @param precision - 'day', 'month', or 'year'
+ * @returns YYYY-MM-DD formatted string
+ * 
+ * @example
+ * const date = new Date('2024-06-15');
+ * toDateWithPrecision(date, 'year');  // "2024-01-01"
+ * toDateWithPrecision(date, 'month'); // "2024-06-01"
+ * toDateWithPrecision(date, 'day');   // "2024-06-15"
+ */
+export function toDateWithPrecision(
+  date: Date,
+  precision: 'day' | 'month' | 'year'
+): string {
+  const year = date.getFullYear();
+  const month = date.getMonth() + 1;
+  const day = date.getDate();
+  
+  switch (precision) {
+    case 'year':
+      return `${year}-01-01`;
+    case 'month':
+      return `${year}-${String(month).padStart(2, '0')}-01`;
+    case 'day':
+    default:
+      return `${year}-${String(month).padStart(2, '0')}-${String(day).padStart(2, '0')}`;
+  }
+}