class Computer
  attr_reader :data
  def initialize(data)
    @data = data
    @program_counter = 0
    @halted = true
  end

  def run
    @halted = false
    while !@halted
      instruction_range = data[@program_counter..(@program_counter + 3)]
      opcode = OpCode.for(self, *instruction_range)
      opcode.execute
      @program_counter += 4
    end
  end

  def read(index)
    data[index]
  end

  def write(index, value)
    data[index] = value
  end

  def halt
    @halted = true
  end

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

  def self.from_file(file_path)
    from_string(File.read file_path)
  end
end

class OpCode
  attr_reader :computer
  def initialize(computer)
    @computer = computer
  end

  def self.for(computer, *args)
    case args[0]
    when 1
      OpCode1.new(computer, *args[1..])
    when 2
      OpCode2.new(computer, *args[1..])
    when 99
      OpCode99.new(computer)
    end
  end
end

class OpCode1 < OpCode
  attr_reader :destination, :first_position, :second_position
  def initialize(computer, arg1, arg2, arg3)
    super(computer)
    @first_position = arg1
    @second_position = arg2
    @destination = arg3
  end

  def value_to_write
    computer.read(first_position) + computer.read(second_position)
  end
  
  def execute
    computer.write destination, value_to_write
  end
end

class OpCode2 < OpCode1
  def value_to_write
    computer.read(first_position) * computer.read(second_position)
  end
end

class OpCode99 < OpCode
  def execute
    computer.halt
  end
end

c = Computer.from_file("../data/2019/2/input.txt")
c.write(1, 12)
c.write(2, 2)
c.run
puts "Part 1: #{c.read(0)}"