calendarDaysNeed

/**
 * Calculates the end date of a task based on a start date, number of days to complete, and a list of holidays.
 * @param {*} startDate 
 * @param {*} daysToComplete 
 * @param {*} holidays 
 * @returns 
 */
function calculateEndDate(startDate, daysToComplete, holidays = []) {
  // Normalize holidays to a comparable string form for O(1) lookup.
  const holidaySets = new Set(
    holidays.map((date) => new Date(date).toDateString())
  );

  let current = new Date(startDate);
  let workdaysCompeleted = 0;

  // Move day-by-day until we finish the required number of working days.
  while (workdaysCompeleted < daysToComplete) {
    const day = current.getDay(); // index where 0 is Sun, 6 = Sat
    const isWeekend = day === 0 || day === 6;
    const isHoliday = holidaySets.has(current.toDateString());

    // Count only business days (not weekend, not holiday).
    if (!isWeekend && !isHoliday) {
      workdaysCompeleted++;
    }

    // Stop on the exact completion date; otherwise continue to next day.
    if (workdaysCompeleted < daysToComplete) {
      current.setDate(current.getDate() + 1);
    }
  }

  // Version 1 output: return the actual completion Date.
  return current;
}

const endDate = calculateEndDate(
  "2026-07-01", // startDate
  5,
  ["2026-07-03"]
);

console.log(endDate.toDateString()); // this will return the date

function calculateCalendarDaysNeeded(startDate, daysToComplete, holidays = []) {
  // Same business-day logic as calculateEndDate, but different output.
  const holidaySets = new Set(
    holidays.map(date => new Date(date).toDateString())
  );

  let current = new Date(startDate);
  let workdaysCompeleted = 0;
  let calendarDays = 0;

  while(workdaysCompeleted < daysToComplete) {
    const day = current.getDay();
    const isWeekend = day === 0 || day === 6;
    const isHoliday = holidaySets.has(current.toDateString());

    if (!isWeekend && !isHoliday) {
      workdaysCompeleted++;
    }

    // Count every traversed day, including weekends/holidays.
    calendarDays++;

    if (workdaysCompeleted < daysToComplete) {
      current.setDate(current.getDate() + 1);
    }
  }

  // Version 2 output: total calendar days needed to complete the work.
  return calendarDays;
}

console.log(
  calculateCalendarDaysNeeded("2026-07-01", 5, ["2026-07-03"])
);