Process list with merge function

mergewindow.kt

fun <T> MutableList<T>.processWindowWith(
    withinWindow: (List<T>, T) -> Boolean,
    process: (MutableList<T>) -> Unit,
): MutableList<T> {

    if (isEmpty()) {
        return this
    }

    var lastWindowMerged: MutableList<T>? = null

    val merged = fold(mutableListOf<MutableList<T>>()) { acc, record ->
        val last = acc.lastOrNull()
        if (last == null) {
            acc += mutableListOf(record)
        } else if (withinWindow(last, record)) {
            last += record
        } else {
            process(last)
            lastWindowMerged = last
            acc += mutableListOf(record)
        }
        acc
    }

    if (lastWindowMerged != merged.last()) {
        process(merged.last())
    }

    clear()
    addAll(merged.flatten())

    return this
}