Formats a dates (start,end) range in Kotlin, presenting the result in a collapsed date range format.

CollapseDateRanges.kt

import java.text.SimpleDateFormat
import java.util.Date
import java.util.Locale.ENGLISH

/**
 * Creates a "collapsed" date range String representing the period of time
 * between two Dates.
 *
 * @author marlonlom
 */
object CollapseDateRanges {

    private val YEAR_FORMAT = SimpleDateFormat("yyyy", ENGLISH)
    private val MONTH_FORMAT = SimpleDateFormat("MMM", ENGLISH)
    private val DAY_FORMAT = SimpleDateFormat("dd", ENGLISH)
    private val DAY_MONTH_FORMAT = SimpleDateFormat("dd MMM", ENGLISH)
    private val DAY_MONTH_YEAR_FORMAT = SimpleDateFormat("dd MMM/yy", ENGLISH)

    /**
     * Returns a "collapsed" date range String representing the period of time
     * between two Date parameters.
     * <br/>
     * Example: August 19 as a {@code startDate} and August 30 as an {@code endDate}
     * will return "19 - 30 AUG", August 28 as a {@code startDate}
     * and September 7 as an {@code endDate} will return "28 AUG - 07 SEP".
     * <br/><br/>
     * This means if you pass this two dates which cannot
     * collapse into a shorter form, then the longer form is returned.
     * <br/><br/>
     * Years are not ignored, and the start and end dates are not checked to ensure we
     * are not going backwards in time (Aug 10 - July 04 is not checked).
     *
     * @param startDate
     *            the start Date in the range.
     * @param endDate
     *            the end Date in the range.
     * @return a String representation of the range between the two dates given.
     */
    @JvmStatic
    fun collapseDate(startDate: Date, endDate: Date): String {
        val formattedDateRange: String

        // Get a comparison result to determine if the Years are the same
        val startDateYear = YEAR_FORMAT.format(startDate)
        val endDateYear = YEAR_FORMAT.format(endDate)

        // Get a comparison result to determine if the Months are the same
        val startDateMonth = MONTH_FORMAT.format(startDate)
        val endDateMonth = MONTH_FORMAT.format(endDate)

        formattedDateRange = if (startDateMonth == endDateMonth && startDateYear == endDateYear) {
            "${DAY_FORMAT.format(startDate)} - ${DAY_MONTH_FORMAT.format(endDate).toUpperCase(ENGLISH)}"
        } else if (startDateMonth == endDateMonth && startDateYear == endDateYear) {
            // Months don't match, but, years match, split the string across both months
            "${DAY_MONTH_FORMAT.format(startDate).toUpperCase(ENGLISH)} - ${DAY_MONTH_FORMAT.format(endDate).toUpperCase(ENGLISH)}"
        }else {
            // Months don't match, also, years don't match, split the string across both months and years
            "${DAY_MONTH_YEAR_FORMAT.format(startDate).toUpperCase(ENGLISH)} - ${DAY_MONTH_YEAR_FORMAT.format(endDate).toUpperCase(ENGLISH)}"
        }

        return formattedDateRange
    }

}