package com.s13g.aoc.aoc2021

import com.s13g.aoc.Result
import com.s13g.aoc.Solver
import kotlin.math.sign

/**
 * --- Day 5: Hydrothermal Venture ---
 * https://adventofcode.com/2021/day/5
 */
class Day5 : Solver {
  override fun solve(lines: List<String>): Result {
    val regex = """([0-9]+),([0-9]+) -> ([0-9]+),([0-9]+)""".toRegex()
    val input = lines.map { regex.find(it)!!.destructured }
      .map { (x1, y1, x2, y2) -> Line(Point(x1.toInt(), y1.toInt()), Point(x2.toInt(), y2.toInt())) }
    val area = mutableListOf<Point>()
    for (i in input) {
      val validForA = i.a.x == i.b.x || i.a.y == i.b.y
      val dir = Point((i.b.x - i.a.x).sign, (i.b.y - i.a.y).sign)
      area.add(Point(i.a.x, i.a.y, validForA))
      while (i.a != i.b) {
        i.a.x += dir.x
        i.a.y += dir.y
        area.add(Point(i.a.x, i.a.y, validForA))
      }
    }
    val partA = area.filter { it.partA }.groupBy { it }.count { it.value.size > 1 }
    val partB = area.groupBy { "${it.x},${it.y}" }.count { it.value.size > 1 }
    return Result("$partA", "$partB")
  }

  private data class Point(var x: Int, var y: Int, val partA: Boolean = false)
  private data class Line(val a: Point, val b: Point)
}
