class Intcode
  attr_reader :memory, :pc, :stopped
  def initialize(memory)
    @initial_memory = memory
    @memory = memory.clone
    @pc = 0
    @stopped = true
  end

  def self.for(string)
    new string.split(",").map(&:to_i)
  end

  def run!
    @stopped = false
    @pc = 0
    step! until stopped
  end

  def reset!
    @memory = @initial_memory.clone
    @pc = 0
  end

  def step!
    case instruction
    when 1
      add!
    when 2
      multiply!
    when 99
      halt!
    else
      raise "invalid instuction #{instruction} at #{pc}"
    end
  end

  def add!
    v1 = peek(peek(pc + 1))
    v2 = peek(peek(pc + 2))
    log "adding #{v1} and #{v2}"
    poke(peek(pc + 3), v1 + v2)
    @pc += 4
  end

  def multiply!
    v1 = peek(peek(pc + 1))
    v2 = peek(peek(pc + 2))
    log "multiplying #{v1} and #{v2}"
    poke(peek(pc + 3), v1 * v2)
    @pc += 4
  end

  def halt!
    log "halting!"
    @stopped = true
  end

  def instruction
    peek pc
  end

  def peek(address)
    memory[address]
  end

  def poke(address, value)
    log "poking #{value} into #{address}"
    memory[address] = value
  end

  def log(message)
    puts message if logging?
  end

  def logging?
    false
  end
end