manyike/current-month-week-number

"use strict";
const moment = require('moment');
/*
 * DateOfTheCurrentMonth is a number e.g 13 for 13th of the current month
 * Get the weekNumber for the current month
 */
function weekNumberOfCurrentMonth(dateOfTheCurrentMonth) {
    if(!dateOfTheCurrentMonth) return undefined;

    let endOfMonth = moment().endOf('month');
    let beginningOfMonth = moment().startOf('month').day(); // numeric representation of weekday for the day the month begins
    let totalNumberOfDaysInAMonth = endOfMonth.date();
    let thisMonthTracker = {};
    let weekCounter = 1;

    for (let i = 1; i <= totalNumberOfDaysInAMonth; i++) {
        if(beginningOfMonth === 6) {
            thisMonthTracker[i] = weekCounter;
            weekCounter++;
            beginningOfMonth = 0;
        } else {
            thisMonthTracker[i] = weekCounter;
            beginningOfMonth++;
        }
    }

    return thisMonthTracker[dateOfTheCurrentMonth.toString()];
}

function weekNumberForGivenDate (fullYear, fullMonth, dateOfTheMonth) {

    if (!fullYear || !fullMonth || !dateOfTheMonth) {
        return undefined;
    }

    if (fullYear.length > 4) {
        return 'full year should be four digits e.g 2017'
    }

    if (parseInt(fullMonth, 10) > 12 || parseInt(fullMonth, 10) < 1) {
        return 'Full month should be between 1 and 12'
    }

    if (fullMonth.length > 1 && parseInt(fullMonth, 10) < 10) {
        return 'Month should be between 1 and 12 i.e >=1 and <=12 and not 01 or 09';
    }

    if (dateOfTheMonth.length > 1 && parseInt(dateOfTheMonth, 10) < 10) {
        return 'dateOfTheMonth should be between 1 and 31 i.e >=1 and <=31 and not 01 or 09';
    }

    if (parseInt(dateOfTheMonth, 10) > 31) {
        return 'dateOfTheMonth should be between 1 and 31 i.e >=1 and <=31';
    }

    let paddedDayOfTheMonth = parseInt(dateOfTheMonth, 10) > 9 ? dateOfTheMonth : '0' + dateOfTheMonth;
    let paddedMonth = parseInt(fullMonth, 10) > 9 ? fullMonth : '0' + fullMonth;

    if (!moment(`${fullYear}-${paddedMonth}-${paddedDayOfTheMonth}`).isValid()) {
        return 'supplied date is not valid';
    }
    let endOfMonth = moment(`${fullYear}-${paddedMonth}-${paddedDayOfTheMonth}`).endOf('month');
    let beginningOfMonth = moment(`${fullYear}-${paddedMonth}-${paddedDayOfTheMonth}`).startOf('month').day(); // numeric representation of weekday for the day the month begins
    let totalNumberOfDaysInAMonth = endOfMonth.date();
    let thisMonthTracker = {};
    let weekCounter = 1;

    for (let i = 1; i <= totalNumberOfDaysInAMonth; i++) {
        if (beginningOfMonth === 6) {
            thisMonthTracker[i] = weekCounter;
            weekCounter++;
            beginningOfMonth = 0;
        } else {
            thisMonthTracker[i] = weekCounter;
            beginningOfMonth++;
        }
    }
    return thisMonthTracker[dateOfTheMonth.toString()];
}

module.exports = {
    weekNumberOfCurrentMonth,
    weekNumberForGivenDate
};