function sameDay(due, now) {
    return (
        due.getFullYear() == now.getFullYear() &&
        due.getMonth() == now.getMonth() &&
        due.getDate() == now.getDate()
    )
}

function dayDiff(due, now, stopAt) {
    // due and now are both Date objects
    // if due has the same day as now (i.e. due is today), return 0
    // if due is tomorrow, return 1, the day after that 2, yesterday -1, etc.
    // when the absolute value of diff reaches stopAt, return stopAt
    let diff = 0
    const step = (due > now) ? 1 : -1
    while (!sameDay(due, now)) {
        now.setDate(now.getDate() + step)
        diff += step
        if (Math.abs(diff) >= stopAt) {
            return stopAt
        }
    }
    return diff
}

function humanDue(isoDue) {
    // converts ISO 8601 datetime string to relative time, e.g. tomorrow midnight
    const daysOfWeek = [
        i18n("Sunday"),
        i18n("Monday"),
        i18n("Tuesday"),
        i18n("Wednesday"),
        i18n("Thursday"),
        i18n("Friday"),
        i18n("Saturday"),
    ]

    try {
        let due = new Date(isoDue)
        if (due.toString() == "Invalid Date") {
            console.warn(`Cannot parse due date: ${isoDue}`)
            return isoDue
        }

        let now = new Date()
        const pastDue = (due <= now)
        const dayDifference = dayDiff(due, now, 8)
        let humanDueString = ""

        if (dayDifference <= -2) {
            humanDueString = Qt.formatDate(due)
        } else if (dayDifference == -1) {
            humanDueString = i18n("Yesterday")
        } else if (dayDifference == 0) {
            humanDueString = i18n("Today")
        } else if (dayDifference == 1) {
            humanDueString = i18n("Tomorrow")
        } else if (dayDifference <= 6) {
            humanDueString = daysOfWeek[due.getDay()]
        } else {
            humanDueString = Qt.formatDate(due)
        }

        humanDueString += " " + Qt.formatTime(due)
        return humanDueString
    } catch (e) {
        return isoDue // screw it
    }
}

function dueLabelText() {
    if (type != "assignment") { return "" }
    if (submitted) { return i18n("Submitted") }
    if (!dueAt) { return i18n("Due date not announced") }
    return i18n("Due: ") + humanDue(dueAt)
}