2021 Day5

class Line(_start:Pair<Int, Int>, _end:Pair<Int, Int>) {
    val diagonal = _start.first != _end.first && _start.second != _end.second
    private val inverted = !diagonal &&  (_start.first > _end.first || _start.second > _end.second)
    private val start = if (inverted) _end else _start
    private val end = if (inverted) _start else _end
    val points = when {
        diagonal -> pointsOnDiagonal()
        start.first == end.first -> (start.second..end.second).map { start.first to it }
        else -> (start.first..end.first).map { it to start.second }
    }

    private fun pointsOnDiagonal(): List<Pair<Int, Int>> {
        val first = start.first range end.first
        val second = (start.second range end.second).toList()
        return first.mapIndexed{index, x -> x to second[index]}
    }
}

private infix fun Int.range(other: Int) = if (this < other) (this .. other) else (this downTo other)

private val String.asLine: Line
    get() = this.split(" -> ").map { pair -> pair.split(",").map { coord -> coord.toInt() }}
        .let { Line(it[0][0] to it[0][1], it[1][0] to it [1][1]) }