Generate a list of pay periods (two per month) between two dates, using XQuery

pay-periods-between-dates.xq

xquery version "3.1";

import module namespace functx="http://www.functx.com";

(: Calculate the number of months between two dates, rounding down :)
declare function local:months-between-dates-floor($start-date as xs:date, $end-date as xs:date) {
    local:months-between-dates-floor($start-date, $end-date, xs:yearMonthDuration("P0M"))
};

(: A helper function for local:months-between-dates-floor :)
declare %private function local:months-between-dates-floor($start-date as xs:date, $end-date as xs:date, $months as xs:yearMonthDuration) {
    if ($start-date + xs:yearMonthDuration("P1M") gt $end-date) then
        $months
    else
        local:months-between-dates-floor($start-date + xs:yearMonthDuration("P1M"), $end-date, $months + xs:yearMonthDuration("P1M"))
};

(: Generate a list of pay periods, two per month, between two dates :)
declare function local:pay-periods-between-dates($start as xs:string, $end as xs:string) {
    let $start-date := $start => xs:date()
    let $end-date := $end => xs:date()
    let $months := local:months-between-dates-floor($start-date, $end-date)
    return
        array {
            for $m in 1 to months-from-duration($months) + 1
            let $months-offset := xs:yearMonthDuration("P" || $m || "M") - xs:yearMonthDuration("P1M")
            let $period1-start := $start-date + $months-offset
            let $period1-end := $start-date + $months-offset + xs:dayTimeDuration("P14D")
            let $period2-start := $period1-end + xs:dayTimeDuration("P1D")
            let $period2-end := functx:date($period1-start => year-from-date(), $period1-start => month-from-date(), $period1-start => functx:days-in-month())
            return 
                (
                    if ($period1-end le $end-date) then
                        map { 
                            "period": ($m - 1) * 2 + 1,
                            "start": $period1-start,
                            "end": $period1-end
                        }
                    else
                        (),
                    if ($period2-end le $end-date) then
                        map { 
                            "period": ($m - 1) * 2 + 2,
                            "start": $period2-start,
                            "end": $period2-end
                        }
                    else
                        ()
                )
        }
};

local:pay-periods-between-dates("2020-01-01", "2020-12-31")

pay-periods-between-dates_results.xq

[
    {
        "period": 1,
        "start": "2020-01-01",
        "end": "2020-01-15"
    },
    {
        "period": 2,
        "start": "2020-01-16",
        "end": "2020-01-31"
    },
    {
        "period": 3,
        "start": "2020-02-01",
        "end": "2020-02-15"
    },
    {
        "period": 4,
        "start": "2020-02-16",
        "end": "2020-02-29"
    },
    {
        "period": 5,
        "start": "2020-03-01",
        "end": "2020-03-15"
    },
    {
        "period": 6,
        "start": "2020-03-16",
        "end": "2020-03-31"
    },
    {
        "period": 7,
        "start": "2020-04-01",
        "end": "2020-04-15"
    },
    {
        "period": 8,
        "start": "2020-04-16",
        "end": "2020-04-30"
    },
    {
        "period": 9,
        "start": "2020-05-01",
        "end": "2020-05-15"
    },
    {
        "period": 10,
        "start": "2020-05-16",
        "end": "2020-05-31"
    },
    {
        "period": 11,
        "start": "2020-06-01",
        "end": "2020-06-15"
    },
    {
        "period": 12,
        "start": "2020-06-16",
        "end": "2020-06-30"
    },
    {
        "period": 13,
        "start": "2020-07-01",
        "end": "2020-07-15"
    },
    {
        "period": 14,
        "start": "2020-07-16",
        "end": "2020-07-31"
    },
    {
        "period": 15,
        "start": "2020-08-01",
        "end": "2020-08-15"
    },
    {
        "period": 16,
        "start": "2020-08-16",
        "end": "2020-08-31"
    },
    {
        "period": 17,
        "start": "2020-09-01",
        "end": "2020-09-15"
    },
    {
        "period": 18,
        "start": "2020-09-16",
        "end": "2020-09-30"
    },
    {
        "period": 19,
        "start": "2020-10-01",
        "end": "2020-10-15"
    },
    {
        "period": 20,
        "start": "2020-10-16",
        "end": "2020-10-31"
    },
    {
        "period": 21,
        "start": "2020-11-01",
        "end": "2020-11-15"
    },
    {
        "period": 22,
        "start": "2020-11-16",
        "end": "2020-11-30"
    },
    {
        "period": 23,
        "start": "2020-12-01",
        "end": "2020-12-15"
    },
    {
        "period": 24,
        "start": "2020-12-16",
        "end": "2020-12-31"
    }
]