How to calculate shift time in js?

Question

JavaScript

Please help me write a function to calculate shifts.
The starting point is the current date, 00:00 hours, I get it using . Next, the beginning and end of the shift comes from the back in the form (in seconds, can be negative), which must be added to the reference point. Thus, I get the first shift: . In addition, a parameter comes from the back , which indicates how many shifts should be calculated. Changes should be sorted in descending order of dates. Input parameters:moment().startOf('day')"Start": 25200, "End": 684002020-08-07 07:00:00 - 2020-08-07 19:00:00"Amount"

Текущая дата:  2020-08-07 00:00:00,
Start: 07:00,
End: 19:00,
Amount: 5

Expected Result:

2020-08-07 07:00:00 - 2020-08-07 19:00:00
2020-08-06 19:00:00 - 2020-08-07 07:00:00
2020-08-06 07:00:00 - 2020-08-06 19:00:00
2020-08-05 19:00:00 - 2020-08-06 07:00:00
2020-08-05 07:00:00 - 2020-08-05 19:00:00

Answer 1

Something like this:

const today = moment().startOf('day');
const dateFormat = 'YYYY-MM-DD HH:mm:ss';
const mapFunc = ({ End, Start, Amount }) => {
  const points = [End, Start];
  const shift = moment(today).seconds(Start);
  const shifts = [];
  const order = Start > End;

  for (let i = 0; i < Amount; i++) {
    shifts.push(
      shift.format(dateFormat)
      + ' - '
      + shift
        .hours(0) // очищаем часы
        .minutes(0) // и минуты
        .seconds(points[i % 2]) // чередуем временную точку: чёт - End, нечёт - Start
        .add(i % 2 ^ order, 'd') // добавляем день если смена переходит на следующий
        .format(dateFormat)
    )
  }
  return shifts
}

console.log(mapFunc({
  "Start": 25200, 
  "End": 68400, 
  "Amount": 5
}));