val input = readText("y2019/w1/d05/input.txt")

fun main() {
    val program = input.split(",").map(String::toInt).toMutableList()

    println("Part 1: " + run(program, listOf(1)))
    println("Part 2: " + run(program, listOf(5)))
}

private fun run(program: List<Int>, input: List<Int>): List<Int> {
    val memory = program.toMutableList()
    val inputLeft = ArrayDeque(input)
    val output = mutableListOf<Int>()

    var instrPtr = 0;

    loop@ while (true) {
        val instruction = memory[instrPtr].toString()

        val opCode = instruction.takeLast(2).toInt()
        val modes = instruction.dropLast(2).reversed().map { it.digit() }

        fun mode(offset: Int) = modes.getOrElse(offset - 1) { 0 }

        fun read(offset: Int) = when (val mode = mode(offset)) {
            0 -> memory[memory[instrPtr + offset]]
            1 -> memory[instrPtr + offset]
            else -> error("Unknown mode $mode")
        }

        fun write(offset: Int, value: Int) {
            check(mode(offset) == 0) { "Require mode 0 for writing, got ${mode(offset)}" }
            memory[memory[instrPtr + offset]] = value
        }

        when (opCode) {
            1, 2 -> { //add, mul
                val op: (Int, Int) -> Int = if (opCode == 1) Int::plus else Int::times
                write(3, op(read(1), read(2)))
                instrPtr += 4
            }
            3 -> { //input
                write(1, inputLeft.pop())
                instrPtr += 2
            }
            4 -> { //output
                output += read(1)
                instrPtr += 2
            }
            5, 6 -> { //jump-if-true, jump-if-false
                val expectTrue = opCode == 5
                if ((read(1) == 0) xor expectTrue)
                    instrPtr = read(2)
                else
                    instrPtr += 3
            }
            7, 8 -> { //lt, eq
                val cmp = if (opCode == 7) -1 else 0
                write(3, if (read(1).compareTo(read(2)) == cmp) 1 else 0)
                instrPtr += 4
            }
            99 -> break@loop
            else -> error("Unknown opCode $opCode")
        }
    }

    return output
}