final touches for beta skymoney (at least i think)

web/src/utils/timezone.ts

@@ -0,0 +1,156 @@
+/**
+ * Timezone utility functions for consistent date handling across the application.
+ * 
+ * All dates should be:
+ * 1. Stored in the backend as UTC ISO strings
+ * 2. Displayed to users in their saved timezone
+ * 3. Input from users interpreted in their saved timezone
+ * 
+ * The user's timezone is stored in the database and should be fetched from the dashboard.
+ */
+
+/**
+ * Get today's date in the user's timezone as YYYY-MM-DD format.
+ * This should be used for date inputs to ensure consistency with user's timezone.
+ * 
+ * @param userTimezone - IANA timezone string (e.g., "America/New_York")
+ * @returns Date string in YYYY-MM-DD format
+ */
+export function getTodayInTimezone(userTimezone: string): string {
+  const now = new Date();
+  // Use Intl.DateTimeFormat to get the date in the user's timezone
+  const formatter = new Intl.DateTimeFormat('en-CA', { // en-CA gives YYYY-MM-DD format
+    timeZone: userTimezone,
+    year: 'numeric',
+    month: '2-digit',
+    day: '2-digit',
+  });
+  return formatter.format(now);
+}
+
+/**
+ * Convert a date input string (YYYY-MM-DD) to an ISO string that represents
+ * midnight in the user's timezone.
+ * 
+ * This should be used when sending date-only data to the backend.
+ * 
+ * @param dateString - Date in YYYY-MM-DD format
+ * @param userTimezone - IANA timezone string
+ * @returns ISO string representing midnight in the user's timezone
+ */
+export function dateStringToUTCMidnight(dateString: string, userTimezone: string): string {
+  // Parse the date string as-is (YYYY-MM-DD)
+  const [year, month, day] = dateString.split('-').map(Number);
+  
+  // Create a date object representing midnight in the user's timezone
+  // We format a string that includes timezone info
+  const dateStr = `${year}-${String(month).padStart(2, '0')}-${String(day).padStart(2, '0')}T00:00:00`;
+  
+  // Get the date/time string in the user's timezone to calculate offset
+  const tzDate = new Date(new Date(dateStr).toLocaleString('en-US', { timeZone: userTimezone }));
+  const utcDate = new Date(new Date(dateStr).toLocaleString('en-US', { timeZone: 'UTC' }));
+  const offset = tzDate.getTime() - utcDate.getTime();
+  
+  // Create final date adjusted for timezone
+  const adjustedDate = new Date(Date.UTC(year, month - 1, day, 0, 0, 0) - offset);
+  
+  return adjustedDate.toISOString();
+}
+
+/**
+ * Format an ISO date string for display in the user's timezone.
+ * 
+ * @param isoString - ISO date string from backend
+ * @param userTimezone - IANA timezone string
+ * @param options - Intl.DateTimeFormatOptions for formatting
+ * @returns Formatted date string
+ */
+export function formatDateInTimezone(
+  isoString: string,
+  userTimezone: string,
+  options: Intl.DateTimeFormatOptions = { year: 'numeric', month: 'short', day: 'numeric' }
+): string {
+  const date = new Date(isoString);
+  return new Intl.DateTimeFormat('en-US', {
+    ...options,
+    timeZone: userTimezone,
+  }).format(date);
+}
+
+/**
+ * Convert an ISO string to YYYY-MM-DD format in the user's timezone.
+ * This is useful for populating date inputs.
+ * 
+ * @param isoString - ISO date string from backend
+ * @param userTimezone - IANA timezone string
+ * @returns Date string in YYYY-MM-DD format
+ */
+export function isoToDateString(isoString: string, userTimezone: string): string {
+  const date = new Date(isoString);
+  const formatter = new Intl.DateTimeFormat('en-CA', {
+    timeZone: userTimezone,
+    year: 'numeric',
+    month: '2-digit',
+    day: '2-digit',
+  });
+  return formatter.format(date);
+}
+
+/**
+ * Get the current date and time as an ISO string in UTC.
+ * This should be used for timestamps (not date-only fields).
+ * 
+ * @returns ISO string in UTC
+ */
+export function getCurrentTimestamp(): string {
+  return new Date().toISOString();
+}
+
+/**
+ * Compare two date strings (YYYY-MM-DD) to determine if date1 is before date2.
+ * This is timezone-safe because it compares date strings directly.
+ * 
+ * @param date1 - First date string
+ * @param date2 - Second date string
+ * @returns true if date1 is before date2
+ */
+export function isDateBefore(date1: string, date2: string): boolean {
+  return date1 < date2;
+}
+
+/**
+ * Compare two date strings (YYYY-MM-DD) to determine if date1 is after date2.
+ * This is timezone-safe because it compares date strings directly.
+ * 
+ * @param date1 - First date string
+ * @param date2 - Second date string
+ * @returns true if date1 is after date2
+ */
+export function isDateAfter(date1: string, date2: string): boolean {
+  return date1 > date2;
+}
+
+/**
+ * Add days to a date string, accounting for the user's timezone.
+ * 
+ * @param dateString - Date in YYYY-MM-DD format
+ * @param days - Number of days to add
+ * @param userTimezone - IANA timezone string
+ * @returns New date string in YYYY-MM-DD format
+ */
+export function addDaysToDate(dateString: string, days: number, userTimezone: string): string {
+  const baseISO = dateStringToUTCMidnight(dateString, userTimezone);
+  const base = new Date(baseISO);
+  base.setUTCDate(base.getUTCDate() + days);
+  return isoToDateString(base.toISOString(), userTimezone);
+}
+
+/**
+ * Get the user's browser timezone as a fallback.
+ * This should only be used when the backend timezone is not available.
+ * 
+ * @returns IANA timezone string
+ */
+export function getBrowserTimezone(): string {
+  return Intl.DateTimeFormat().resolvedOptions().timeZone;
+}