babymonitor/frontend/src/utils/time.ts

/**
 * 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")}`;
}

/**
 * Adjust minutes by the local timezone offset
 * @param utcMinutes - minutes from UTC midnight
 * @returns adjusted minutes for local time
 */
export function adjustForTimezone(utcMinutes: number): number {
  const offsetInMinutes = new Date().getTimezoneOffset();
  return utcMinutes - offsetInMinutes;
}

/**
 * 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);
}

export function formatElapsedTime(utcTimestamp: string): string {
  let isoString = utcTimestamp;
  if (utcTimestamp.includes(' ')) {
    isoString = utcTimestamp.replace(' ', 'T');
  }
  if (!isoString.endsWith('Z')) {
    isoString += 'Z';
  }
  const then = new Date(isoString);
  const now = new Date();
   const diffMs = now.getTime() - then.getTime();
  const diffMins = Math.floor(diffMs / 60000);
  const hours = Math.floor(diffMins / 60);
  const mins = diffMins % 60;

  if (hours > 0) return `${hours}h ${mins}m`;
  return `${mins}m`;
}

/**
 * Format a Date or ISO string to a human-readable datetime string (YYYY-MM-DD HH:mm)
 * @param date - Date object or ISO string
 * @returns formatted datetime string
 */
export function formatDateTime(date: Date | string): string {
  let dateToParse = date;
  if (typeof date === 'string' && !date.endsWith('Z') && !date.includes('+')) {
    dateToParse = date + 'Z';
  }
  const d = typeof dateToParse === 'string' ? new Date(dateToParse) : dateToParse;
  return d.toLocaleString('sv-SE', {
    year: 'numeric',
    month: '2-digit',
    day: '2-digit',
    hour: '2-digit',
    minute: '2-digit',
    hour12: false
  }).replace(',', ' ');
}

/**
 * Convert a datetime-local input value to an ISO UTC string
 * @param inputValue - datetime-local string (YYYY-MM-DDTHH:mm)
 * @returns ISO UTC string
 */
export function toUTCFromLocalInput(inputValue: string): string {
  const d = new Date(inputValue);
  return d.toISOString();
}

/**
 * Calculate duration in minutes between two dates or ISO strings
 * @param start - Start date object or ISO string
 * @param end - End date object or ISO string
 * @returns duration in minutes
 */
export function getDurationMinutes(start: Date | string, end: Date | string): number {
  const startDate = typeof start === 'string' ? new Date(start) : start;
  const endDate = typeof end === 'string' ? new Date(end) : end;
  return Math.round((endDate.getTime() - startDate.getTime()) / 60000);
}

/**
 * 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
 * @throws Error if timeStr is invalid
 */
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;
}

/**
 * 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];
}

/**
 * Convert HH:MM time string to total minutes from start of day
 * @param timeStr - HH:MM format
 * @returns total minutes
 */
export function timeToMinutes(timeStr: string): number {
  const [hours, minutes] = timeStr.split(":").map(Number);
  return hours * 60 + minutes;
}

/**
 * Get the offset from a reference time in local minutes
 * @param utcMinutesFromMidnight - minutes from UTC midnight
 * @param referenceHHMM - reference time as HH:MM string
 * @returns local offset from reference in minutes
 */
export function getLocalOffsetFromReference(utcMinutesFromMidnight: number, referenceHHMM: string): number {
  const localMinsFromMidnight = adjustForTimezone(utcMinutesFromMidnight);
  return localMinsFromMidnight - timeToMinutes(referenceHHMM);
}

/**
 * Convert total minutes to a human-readable string (e.g., "1h 30m" or "45m")
 * @param totalMinutes - Total number of minutes
 * @returns Formatted string
 */
export function formatMinutes(totalMinutes: number): string {
  const hours = Math.floor(totalMinutes / 60);
  const mins = totalMinutes % 60;

  if (hours > 0) {
    return `${hours}h ${mins}m`;
  }
  return `${mins}m`;
}