// Hilfsfunktionen für Zeit-/Datumsberechnungen rund um das Arbeitszeitkonto.

const WEEKDAY_NAMES = ['So', 'Mo', 'Di', 'Mi', 'Do', 'Fr', 'Sa'];

/** "08:30" -> 510 (Minuten seit Mitternacht) */
function timeToMinutes(value) {
  const [h, m] = String(value).split(':').map(Number);
  return h * 60 + m;
}

/** 95 -> "1:35" (immer positiv, ohne Vorzeichen) */
function minutesToHM(totalMinutes) {
  const abs = Math.abs(Math.round(totalMinutes));
  const h = Math.floor(abs / 60);
  const m = abs % 60;
  return `${h}:${String(m).padStart(2, '0')}`;
}

/** 95 -> "+1:35", -30 -> "-0:30" */
function formatBalance(minutes) {
  const sign = minutes < 0 ? '−' : '+';
  return `${sign}${minutesToHM(minutes)}`;
}

/** Prüft, ob ein Datum (YYYY-MM-DD) laut Einstellungen ein Arbeitstag ist. */
function isWorkDay(dateStr, workDays) {
  const day = new Date(`${dateStr}T00:00:00`).getDay();
  return Array.isArray(workDays) && workDays.includes(day);
}

/**
 * Summiert alle Einzelpausen.
 * @param {Array<{start: string, end: string}>} breaks
 * @returns {number} Gesamte Pausenzeit in Minuten
 */
function computeTotalBreakMinutes(breaks) {
  if (!Array.isArray(breaks)) return 0;
  return breaks.reduce((total, b) => {
    if (!b || !b.start || !b.end) return total;
    const duration = timeToMinutes(b.end) - timeToMinutes(b.start);
    return total + Math.max(0, duration);
  }, 0);
}

/**
 * Berechnet die tatsächlich geleisteten Netto-Minuten.
 * @param {string} startTime  z. B. "08:00"
 * @param {string} endTime    z. B. "17:00"
 * @param {Array<{start: string, end: string}>} breaks  Pausenzeiten
 * @returns {number}
 */
function computeWorkedMinutes(startTime, endTime, breaks) {
  const gross = timeToMinutes(endTime) - timeToMinutes(startTime);
  const totalBreak = computeTotalBreakMinutes(breaks);
  return gross - totalBreak;
}

/** Saldo (Über-/Minusstunden) eines einzelnen Tages in Minuten. */
function computeBalanceMinutes(workedMinutes, dateStr, settings) {
  const targetMinutes = isWorkDay(dateStr, settings.workDays)
    ? settings.targetHoursPerDay * 60
    : 0;
  return workedMinutes - targetMinutes;
}

/** "2026-06-23" -> "Di, 23.06.2026" */
function formatDateDisplay(dateStr) {
  const date = new Date(`${dateStr}T00:00:00`);
  return new Intl.DateTimeFormat('de-DE', {
    weekday: 'short',
    day: '2-digit',
    month: '2-digit',
    year: 'numeric',
  }).format(date);
}

/** "2026-06" -> "Juni 2026" */
function formatMonthDisplay(yearMonth) {
  const date = new Date(`${yearMonth}-01T00:00:00`);
  return new Intl.DateTimeFormat('de-DE', { month: 'long', year: 'numeric' }).format(date);
}

module.exports = {
  WEEKDAY_NAMES,
  timeToMinutes,
  minutesToHM,
  formatBalance,
  isWorkDay,
  computeTotalBreakMinutes,
  computeWorkedMinutes,
  computeBalanceMinutes,
  formatDateDisplay,
  formatMonthDisplay,
};