/*
 * Copyright (c) 2023 <NAME>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */
package days

import utils.*

fun main() {
    val (instructions, mappings) = readInput().let { lines ->
        val instructions = lines.first()
        val mappings = lines.drop(2).associate { line ->
            val targets = line.substringAfter('(').removeSuffix(")").split(", ").let { it[0] to it[1] }
            line.substringBefore(' ') to targets
        }

        instructions to mappings
    }

    fun findRequiredSteps(start: String, isDest: (String) -> Boolean): Long {
        var step = 0L
        var pos = start

        val instructionsItr = iterator {
            while (true) {
                yieldAll(instructions.asIterable())
            }
        }

        while (!isDest(pos)) {
            pos = when (val instruction = instructionsItr.next()) {
                'L' -> mappings[pos]!!.first
                'R' -> mappings[pos]!!.second
                else -> error("Unexpected instruction: $instruction")
            }

            step++
        }

        return step
    }

    tailrec fun gcd(x: Long, y: Long): Long =
        if (y == 0L) x else gcd(y, x % y)

    fun lcm(x: Long, y: Long): Long =
        if (x == 0L || y == 0L) 0 else (x * y) / gcd(x, y)

    fun solve(
        isStart: (String) -> Boolean,
        isDest: (String) -> Boolean
    ): Long =
        mappings.mapNotNull { (k, _) -> if (isStart(k)) k else null }
            .map { findRequiredSteps(it, isDest) }
            .reduce(::lcm)

    println("Part 1: ${solve(isStart = { it == "AAA" }, isDest = { it == "ZZZ" })}")
    println("Part 2: ${solve(isStart = { it.endsWith('A') }, isDest = { it.endsWith('Z') })}")
}