Kotlin: Custom Range - Restaurant delivery time options

customRange.kt

data class Restaurant(
    val id: Long,
    val name: String,
    val openTime: Date,
    val closeTime: Date
) {
    private val deliveryTimeStep: Long = 15 * 60 * 1000

    fun getDeliveryTimeOptions(): DeliveryTimeOptions {
        return openTime..closeTime step deliveryTimeStep
    }
}

class DeliveryTimeOptions(
    override val start: Date,
    override val endInclusive: Date,
    private val stepTime: Long = 3_600_000
) : ClosedRange<Date>, Iterable<Date> {

    override fun iterator(): Iterator<Date> {
        return DeliveryTimeIterator(start, endInclusive, stepTime)
    }

    infix fun step(stepTime: Long) = DeliveryTimeOptions(start, endInclusive, stepTime)
}

class DeliveryTimeIterator(
    private val start: Date,
    private val endInclusive: Date,
    private val stepTime: Long
): Iterator<Date> {
    private var currentValue = start.time


    override fun hasNext(): Boolean {
        return currentValue <= endInclusive.time
    }

    override fun next(): Date {
        val next = currentValue
        currentValue += stepTime
        return Date(next)
    }
}

operator fun Date.rangeTo(other: Date) = DeliveryTimeOptions(this, other)

fun main() {
  val openTime = Calendar.getInstance().apply {
        set(Calendar.HOUR_OF_DAY, 9)
        set(Calendar.MINUTE, 0)
        set(Calendar.SECOND, 0)
    }

    val closeTime = Calendar.getInstance().apply {
        set(Calendar.HOUR_OF_DAY, 17)
        set(Calendar.MINUTE, 0)
        set(Calendar.SECOND, 0)
    }

    val restaurant = Restaurant(
        id = 42L,
        name = "FooBar",
        openTime = openTime.time,
        closeTime = closeTime.time
    )

    restaurant.getDeliveryTimeOptions().toList()
        .forEach { println(it) }
}

Output:
Fri Nov 20 09:00:00 CET 2020
Fri Nov 20 09:15:00 CET 2020
Fri Nov 20 09:30:00 CET 2020
...
Fri Nov 20 16:30:00 CET 2020
Fri Nov 20 16:45:00 CET 2020
Fri Nov 20 17:00:00 CET 2020

Article "Guide: Ranges in Kotlin": https://alexzh.com/guide-ranges-and-progressions-in-kotlin/