#!/usr/bin/env ruby

require_relative '../common'

class Day05 < Day
  class Store
    def self.parse(input)
      stacks_data = input.take_while { |line| line != "" }
      instructions_data = input.drop_while { |line| !line.start_with?("move") }

      stacks = stacks_data.pop.tr_s(' ', ' ').strip.split(' ')
      crates = stacks_data.reverse

      Store.new(stacks.map do |stack|
        [
          stack,
          crates.map { |row| row[1 + 4 * (stack.to_i - 1)] }
            .take_while { |crate| crate != " " }
        ]
      end.to_h, instructions_data)
    end

    attr_reader :stacks

    def initialize(stacks, instructions)
      @stacks = stacks
      @instructions = instructions
    end

    def parse(instruction)
      count, from, to = instruction.match(/move ([0-9]+) from ([0-9]+) to ([0-9]+)/).captures
      [from, to, count.to_i]
    end

    def move_one_by_one(from, to, count)
      count.times { stacks[to] << stacks[from].pop }
    end

    def move_multiple(from, to, count)
      stacks[to] += stacks[from].pop(count)
    end

    def result_part1
      @instructions.each { |instruction| move_one_by_one(*parse(instruction)) }
      stacks.map { |_,v| v.last }.join
    end

    def result_part2
      @instructions.each { |instruction| move_multiple(*parse(instruction)) }
      stacks.map { |_,v| v.last }.join
    end
  end

  def part1
    Store.parse(stdin).result_part1
  end

  def part2
    Store.parse(stdin).result_part2
  end
end

Day05.run