Initial commit

frontend/src/utils/time.ts

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+/**
+ * Time formatting utilities for baby sleep tracker
+ */
+
+/**
+ * Convert minutes after a reference time to clock time string
+ * @param minutes - minutes after reference time (can be negative)
+ * @param reference - reference time as HH:MM string
+ * @returns formatted time string like "07:15"
+ */
+export function formatMinutesAfter(minutes: number | null, reference: string = "04:00"): string {
+  if (minutes === null) return "N/A";
+
+  const [refHours, refMinutes] = reference.split(":").map(Number);
+  const totalRefMinutes = refHours * 60 + refMinutes;
+
+  const targetMinutes = totalRefMinutes + minutes;
+  // Handle wrap around midnight
+  const normalizedMinutes = ((targetMinutes % 1440) + 1440) % 1440;
+  const hours = Math.floor(normalizedMinutes / 60);
+  const mins = normalizedMinutes % 60;
+
+  return `${String(hours).padStart(2, "0")}:${String(mins).padStart(2, "0")}`;
+}
+
+/**
+ * Convert a Date to datetime-local input value format (local time)
+ * @param date - Date object
+ * @returns string in "YYYY-MM-DDTHH:MM" format
+ */
+export function toLocalDatetimeInputValue(date: Date): string {
+  const offset = date.getTimezoneOffset() * 60 * 1000;
+  const localDate = new Date(date.getTime() - offset);
+  return localDate.toISOString().slice(0, 16);
+}
+
+/**
+ * Format elapsed time in human-readable format
+ * @param startTime - start time as ISO string or Date
+ * @returns formatted string like "2h 35m" or "just now"
+ */
+export function formatElapsedTime(startTime: string | Date): string {
+  const start = typeof startTime === "string" ? new Date(startTime) : startTime;
+  const now = new Date();
+  const diffMs = now.getTime() - start.getTime();
+
+  if (diffMs < 0) return "just now";
+
+  const totalMinutes = Math.floor(diffMs / 60000);
+  const hours = Math.floor(totalMinutes / 60);
+  const minutes = totalMinutes % 60;
+
+  if (hours === 0 && minutes === 0) return "just now";
+  if (hours === 0) return `${minutes}m`;
+  if (minutes === 0) return `${hours}h`;
+  return `${hours}h ${minutes}m`;
+}
+
+/**
+ * Clamp a date to day boundaries (start or end of day)
+ * @param date - Date to clamp
+ * @param bound - 'start' for 00:00, 'end' for 23:59:59.999
+ * @returns new Date clamped to day boundary
+ */
+export function clampToDay(date: Date, bound: "start" | "end"): Date {
+  const result = new Date(date);
+  if (bound === "start") {
+    result.setHours(0, 0, 0, 0);
+  } else {
+    result.setHours(23, 59, 59, 999);
+  }
+  return result;
+}
+
+/**
+ * Parse HH:MM time string to Date on a given day
+ * @param timeStr - HH:MM format
+ * @param baseDate - base date (defaults to today)
+ * @returns Date object
+ */
+export function parseTime(timeStr: string, baseDate: Date = new Date()): Date {
+  const [hours, minutes] = timeStr.split(":").map(Number);
+  const result = new Date(baseDate);
+  result.setHours(hours, minutes, 0, 0);
+  return result;
+}
+
+/**
+ * Format minutes as hours and minutes string
+ * @param minutes - total minutes
+ * @returns formatted string like "12h 30m"
+ */
+export function formatMinutes(minutes: number): string {
+  const hours = Math.floor(minutes / 60);
+  const mins = minutes % 60;
+  if (hours === 0) return `${mins}m`;
+  if (mins === 0) return `${hours}h`;
+  return `${hours}h ${mins}m`;
+}
+
+/**
+ * Get date string for N days ago
+ * @param days - number of days ago
+ * @returns ISO date string (YYYY-MM-DD)
+ */
+export function getDaysAgo(days: number): string {
+  const date = new Date();
+  date.setDate(date.getDate() - days);
+  return date.toISOString().split("T")[0];
+}
+
+/**
+ * Get date string for today
+ * @returns ISO date string (YYYY-MM-DD)
+ */
+export function getToday(): string {
+  return new Date().toISOString().split("T")[0];
+}