skip-unavailable-dates.js

// given a date range
// and some unavailable dates
// construct multiple allocations to fit around them
// e.g., 21st - 28th with 23rd & 24th unavailable
// gives us 2 allocations: 21st - 22nd and 25th - 28th

import moment from 'moment';

function getDatesInRange(startDate, endDate) {
  const dates = [];
  let start = moment(startDate).clone();

  while (start.isSameOrBefore(endDate, "day")) {
    dates.push(start.format("YYYY-MM-DD"));
    start = start.add(1, "day");
  }
  
  return dates;
}

const startDate = moment('2020-01-01');
const endDate = moment('2020-01-14');
const unavailableDates = ['2020-01-08', '2020-01-11', '2020-01-01', '2020-01-09'];
const originalDates = getDatesInRange(startDate, endDate);
const availableDates = originalDates.filter(oD => !unavailableDates.includes(oD));

// https://stackoverflow.com/a/51420305
const groupedDateRanges = availableDates.reduce((acc, date) => {
  const group = acc[acc.length - 1];

  if (moment(date).diff(moment(group[group.length - 1] || date), 'days') > 1) {
    acc.push([date])
  } else {
    group.push(date);
  }

  return acc;
}, [[]]);

const allocationDates = groupedDateRanges.map((range) => {
  return {
    start: range[0],
    end: range[range.length - 1],
    days: moment(range[range.length - 1]).diff(range[0], 'd') + 1
  } 
});