/**
 * Date/time helpers for calendar and duty display.
 */

/**
 * YYYY-MM-DD in local time (for calendar keys, "today", request range).
 * @param {Date} d - Date
 * @returns {string}
 */
export function localDateString(d) {
  const y = d.getFullYear();
  const m = String(d.getMonth() + 1).padStart(2, "0");
  const day = String(d.getDate()).padStart(2, "0");
  return y + "-" + m + "-" + day;
}

/**
 * True if duty (start_at/end_at UTC) overlaps the local day YYYY-MM-DD.
 * @param {object} d - Duty with start_at, end_at
 * @param {string} dateKey - YYYY-MM-DD
 * @returns {boolean}
 */
export function dutyOverlapsLocalDay(d, dateKey) {
  const [y, m, day] = dateKey.split("-").map(Number);
  const dayStart = new Date(y, m - 1, day, 0, 0, 0, 0);
  const dayEnd = new Date(y, m - 1, day, 23, 59, 59, 999);
  const start = new Date(d.start_at);
  const end = new Date(d.end_at);
  return end > dayStart && start < dayEnd;
}

/**
 * True if duty overlaps any local day in the range [firstKey, lastKey] (inclusive).
 * @param {object} d - Duty with start_at, end_at
 * @param {string} firstKey - YYYY-MM-DD (first day of range)
 * @param {string} lastKey - YYYY-MM-DD (last day of range)
 * @returns {boolean}
 */
export function dutyOverlapsLocalRange(d, firstKey, lastKey) {
  const [y1, m1, day1] = firstKey.split("-").map(Number);
  const [y2, m2, day2] = lastKey.split("-").map(Number);
  const rangeStart = new Date(y1, m1 - 1, day1, 0, 0, 0, 0);
  const rangeEnd = new Date(y2, m2 - 1, day2, 23, 59, 59, 999);
  const start = new Date(d.start_at);
  const end = new Date(d.end_at);
  return end > rangeStart && start < rangeEnd;
}

/** @param {Date} d - Date */
export function firstDayOfMonth(d) {
  return new Date(d.getFullYear(), d.getMonth(), 1);
}

/** @param {Date} d - Date */
export function lastDayOfMonth(d) {
  return new Date(d.getFullYear(), d.getMonth() + 1, 0);
}

/** @param {Date} d - Date (returns Monday of that week) */
export function getMonday(d) {
  const day = d.getDay();
  const diff = d.getDate() - day + (day === 0 ? -6 : 1);
  return new Date(d.getFullYear(), d.getMonth(), diff);
}

/**
 * Format UTC date from ISO string as DD.MM for display.
 * @param {string} isoDateStr - ISO date string
 * @returns {string} DD.MM
 */
export function formatDateKey(isoDateStr) {
  const d = new Date(isoDateStr);
  const day = String(d.getDate()).padStart(2, "0");
  const month = String(d.getMonth() + 1).padStart(2, "0");
  return day + "." + month;
}

/**
 * Format YYYY-MM-DD as DD.MM for list header.
 * @param {string} key - YYYY-MM-DD
 * @returns {string} DD.MM
 */
export function dateKeyToDDMM(key) {
  return key.slice(8, 10) + "." + key.slice(5, 7);
}

/**
 * Format ISO date as HH:MM in local time.
 * @param {string} isoStr - ISO date string
 * @returns {string} HH:MM
 */
export function formatTimeLocal(isoStr) {
  const d = new Date(isoStr);
  return String(d.getHours()).padStart(2, "0") + ":" + String(d.getMinutes()).padStart(2, "0");
}

/**
 * Format ISO string as HH:MM (local).
 * @param {string} isoStr - ISO date string
 * @returns {string} HH:MM or ""
 */
export function formatHHMM(isoStr) {
  if (!isoStr) return "";
  const d = new Date(isoStr);
  const h = d.getHours();
  const m = d.getMinutes();
  return (h < 10 ? "0" : "") + h + ":" + (m < 10 ? "0" : "") + m;
}