main.js

/*
 * Your program must print string with the number of years and months and the total number of days between the dates.
 * Dates are provided in dd.mm.yyyy format.
 * You are not allowed to plug in JS libraries such as moment.js or date-fns directly into the code. All code need to be written in this file.
 * 
 * Result must be shown as a string in years, months and total days. If years or months are 0, then it should not be displayed in the output.
 *
 * Example:
 * Input: ['01.01.2000', '01.01.2016']
 * Output:
 * '16 years, total 5844 days'
 *
 * Example 2:
 * Input: ['01.11.2015', '01.02.2017']
 *
 * Output:
 * '1 year, 3 months, total 458 days'
*/
const dates = [
    ['01.01.2000', '01.01.2016'],
    ['01.01.2016', '01.08.2016'],
    ['01.11.2015', '01.02.2017'],
    ['17.12.2016', '16.01.2017'],
    ['01.01.2016', '01.01.2016'],
    ['28.02.2015', '13.04.2018'],
    ['28.01.2015', '28.02.2015'],
    ['17.03.2022', '17.03.2023'],
    ['17.02.2024', '17.02.2025'],
];

const monthDays = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];

function isLeapYear(year) {
    // check if year is leap year
    return ((year % 4 == 0) && (year % 100 != 0)) || (year % 400 == 0);
}

function getNumberOfYears(startDate, endDate) {
    const startDay = parseInt(startDate[0]), startMonth = parseInt(startDate[1]), startYear = parseInt(startDate[2])
    const endDay = parseInt(endDate[0]), endMonth = parseInt(endDate[1]), endYear = parseInt(endDate[2])

    // calculate number of years
    var years = endYear - startYear

    // check if starting month is higher than ending month
    // or if month is the same but starting day is higher than ending day
    // and subtract 1 year in those 2 cases because time between those dates
    // is less than 1 full year in those cases
    if((startMonth > endMonth) || (startMonth == endMonth && startDay > endDay)) {
        years--
    }

    return years
}

function getNumberOfMonths(startDate, endDate) {
    const startDay = parseInt(startDate[0]), startMonth = parseInt(startDate[1]), startYear = parseInt(startDate[2])
    const endDay = parseInt(endDate[0]), endMonth = parseInt(endDate[1]), endYear = parseInt(endDate[2])

    var months = 0

    // calculate number of months
    if(startYear == endYear) {
        months = endMonth - startMonth
    } else {
        if(startMonth < endMonth) {
            months = endMonth - startMonth
        } else if(startMonth > endMonth) {
            months = (12 - startMonth) + endMonth
        } else {
            if(startDay > endDay) {
                months = 12
            }
        }
    }

    // if starting day is higher than ending day then subtract one month from total
    if(startDay > endDay) {
        months--
    }

    return months
}

function getNumberOfDays(startDate, endDate) {
    const startDay = parseInt(startDate[0]), startMonth = parseInt(startDate[1]), startYear = parseInt(startDate[2])
    const endDay = parseInt(endDate[0]), endMonth = parseInt(endDate[1]), endYear = parseInt(endDate[2])
    var days = 0

    for(var currentYear = startYear; currentYear <= endYear; currentYear++) {

        // check if current year is start year, end year or in between
        if(currentYear == startYear) {
            var currentYearEndMonth = 12

            if(currentYear == endYear) {
                currentYearEndMonth = endMonth
            }

            for(var currentMonth = startMonth; currentMonth <= currentYearEndMonth; currentMonth++) {
                if(startMonth == endMonth && startYear == endYear) {
                    days += endDay - startDay
                } else if(currentMonth == startMonth) {
                    if(currentMonth == 2 && isLeapYear(currentYear)) {
                        days += 29 - startDay
                    } else {
                        days += monthDays[currentMonth-1] - startDay
                    }
                } else if(currentMonth == endMonth && startYear == endYear) {
                    days += endDay
                } else {
                    days += monthDays[currentMonth-1]

                    if(currentMonth == 2 && isLeapYear(currentYear)) {
                        days++
                    }
                }
            }
        } else if(currentYear == endYear) {
            var currentYearEndMonth = 12

            if(currentYear == endYear) {
                currentYearEndMonth = endMonth
            }

            for(var currentMonth = 1; currentMonth <= endMonth; currentMonth++) {
                if(currentMonth == endMonth) {
                    days += endDay
                } else {
                    days += monthDays[currentMonth-1]

                    if(currentMonth == 2 && isLeapYear(currentYear)) {
                        days++
                    }
                }
            }
        } else {
            // currentYear is in between starting and ending year
            // so we add all of the days within the year
            days += 365
            
            // add one additional day in case of leap year
            if(isLeapYear(currentYear)) {
                days++
            }
        }

        
    }

    return days
}

// Receive string of dates one after each other
function outputDate(dates) {
    var returnString = ''

    const startDate = dates[0].split('.')
    const endDate = dates[1].split('.')

    const years = getNumberOfYears(startDate, endDate)
    const months = getNumberOfMonths(startDate, endDate)
    const days = getNumberOfDays(startDate, endDate)

    // create year part of return string
    if(years > 0) {
        if(years == 1) {
            returnString += years + ' year, '
        } else {
            returnString += years + ' years, '
        }
    }
    // create month part of return string
    if(months > 0) {
        if(months == 1) {
            returnString += months + ' month, '
        } else {
            returnString += months + ' months, '
        }
    }
    // create total days part of return string
    if(days == 1) {
        returnString += 'total ' + days + ' day'
    } else {
        returnString += 'total ' + days + ' days'
    }

    return returnString;
}