diff --git a/2019/day13/intcode.rb b/2019/day13/intcode.rb
new file mode 100644
index 0000000..cee7224
--- /dev/null
+++ b/2019/day13/intcode.rb
@@ -0,0 +1,244 @@
+# frozen_string_literal: true
+
+require 'forwardable'
+
+module Intcode
+  def self.read(filename)
+    parse File.read(filename)
+  end
+
+  def self.parse(input)
+    parsed = input
+             .gsub(/^#.*$/, '')
+             .gsub('\s', '')
+             .split(',')
+             .map(&:to_i)
+    Program.new parsed
+  end
+
+  class Program
+    def initialize(mem)
+      @initial_state = mem
+    end
+
+    def as_memory
+      Memory.new(@initial_state.clone)
+    end
+
+    def run(&user_input)
+      Computer.new(as_memory).run(&user_input)
+    end
+  end
+
+  class Memory
+    extend Forwardable
+
+    def_delegator :@cells, :[]
+    def_delegator :@cells, :[]=
+
+    attr_accessor :relative_base
+
+    def initialize(cells)
+      @cells = cells
+      @relative_base = 0
+    end
+
+    def to_s
+      batch_size = 10
+      s = String.new
+      @cells.each_slice(batch_size).each_with_index do |batch, idx|
+        prefix = idx * batch_size
+        s << "#{prefix}: #{batch.join(' ')}\n"
+      end
+      s
+    end
+
+    def read(addr, mode)
+      # raise ArgumentError, "address out of range: #{addr}" if addr.negative? || addr >= @cells.length
+      return 0 if addr.negative? || addr >= @cells.length
+
+      case mode
+      when INDIRECT_MODE
+        read(@cells[addr], IMMEDIATE_MODE)
+      when IMMEDIATE_MODE
+        @cells[addr]
+      when RELATIVE_MODE
+        read(@cells[addr] + relative_base, IMMEDIATE_MODE)
+      else
+        raise ArgumentError, "unexpected mode: #{mode}"
+      end
+    end
+
+    def write(addr, mode, val)
+      raise ArgumentError, "address out of range: #{addr}" if addr.negative? || addr >= @cells.length
+
+      case mode
+      when INDIRECT_MODE
+        r = @cells[addr]
+        @cells[r] = val
+      when IMMEDIATE_MODE
+        raise ArgumentError, 'writes are not allowed in immediate mode'
+        @cells[addr]
+      when RELATIVE_MODE
+        r = @cells[addr] + relative_base
+        @cells[r] = val
+      else
+        raise ArgumentError, "unexpected mode: #{mode}"
+      end
+    end
+  end
+
+  INDIRECT_MODE = 0
+  IMMEDIATE_MODE = 1
+  RELATIVE_MODE = 2
+
+  class Computer
+    def initialize(mem, &block)
+      @mem = mem
+      @ip = 0
+      @input_block = block
+    end
+
+    def on_output(&block)
+      @output_block = block
+    end
+
+    def run
+      loop do
+        return if tick == :done_executing
+      end
+    end
+
+    def tick
+      opcode = operation(@mem[@ip])
+      case opcode
+      when 1
+        add!
+        nil
+      when 2
+        mul!
+        nil
+      when 3
+        input!(&@input_block)
+        nil
+      when 4
+        output!(&@output_block)
+      when 5
+        branch_if_not_zero!
+        nil
+      when 6
+        branch_if_zero!
+        nil
+      when 7
+        less_than!
+        nil
+      when 8
+        equal!
+        nil
+      when 9
+        move_relative_base!
+        nil
+      when 99
+        :done_executing
+      else
+        raise StandardError, "unexpected opcode: #{opcode}"
+      end
+    end
+
+    private
+
+    def add!
+      mode = modes(@mem[@ip])
+      a = @mem.read(@ip + 1, mode[0])
+      b = @mem.read(@ip + 2, mode[1])
+      @mem.write(@ip + 3, mode[2], a + b)
+      @ip += 4
+    end
+
+    def mul!
+      mode = modes(@mem[@ip])
+      a = @mem.read(@ip + 1, mode[0])
+      b = @mem.read(@ip + 2, mode[1])
+      @mem.write(@ip + 3, mode[2], a * b)
+      @ip += 4
+    end
+
+    def input!(&user_input)
+      mode = modes(@mem[@ip])
+      inp = input(&user_input)
+      @mem.write(@ip + 1, mode[0], inp)
+      @ip += 2
+    end
+
+    def output!(&user_output)
+      mode = modes(@mem[@ip])
+      output = @mem.read(@ip + 1, mode[0])
+      user_output.call output if block_given?
+      @ip += 2
+      output
+    end
+
+    def branch_if_not_zero!
+      mode = modes(@mem[@ip])
+      a = @mem.read(@ip + 1, mode[0])
+      b = @mem.read(@ip + 2, mode[1])
+      @ip = a.zero? ? @ip + 3 : b
+    end
+
+    def branch_if_zero!
+      mode = modes(@mem[@ip])
+      a = @mem.read(@ip + 1, mode[0])
+      b = @mem.read(@ip + 2, mode[1])
+      @ip = a.zero? ? b : @ip + 3
+    end
+
+    def less_than!
+      mode = modes(@mem[@ip])
+      a = @mem.read(@ip + 1, mode[0])
+      b = @mem.read(@ip + 2, mode[1])
+      val = a < b ? 1 : 0
+      @mem.write(@ip + 3, mode[2], val)
+      @ip += 4
+    end
+
+    def equal!
+      mode = modes(@mem[@ip])
+      a = @mem.read(@ip + 1, mode[0])
+      b = @mem.read(@ip + 2, mode[1])
+      val = a == b ? 1 : 0
+      @mem.write(@ip + 3, mode[2], val)
+      @ip += 4
+    end
+
+    def move_relative_base!
+      mode = modes(@mem[@ip])
+      delta = @mem.read(@ip + 1, mode[0])
+      @mem.relative_base += delta
+      @ip += 2
+    end
+
+    def input
+      if block_given?
+        inp = yield
+        raise "Invalid input: #{inp.inspect}" unless inp.is_a?(Numeric)
+
+        return inp
+      end
+
+      print 'input> '
+      gets.to_i
+    end
+
+    def operation(cell)
+      (cell % 100)
+    end
+
+    def modes(cell)
+      m = Hash.new(0)
+      (cell / 100).truncate.digits.each_with_index do |d, i|
+        m[i] = d
+      end
+      m
+    end
+  end
+end
diff --git a/2019/day13/part1.rb b/2019/day13/part1.rb
new file mode 100644
index 0000000..f983a2c
--- /dev/null
+++ b/2019/day13/part1.rb
@@ -0,0 +1,133 @@
+# frozen_string_literal: true
+
+require_relative 'intcode'
+
+Cell = Struct.new(:x, :y)
+
+class Screen
+  attr_reader :tiles
+
+  def initialize
+    @tiles = {}
+  end
+
+  def draw(x, y, tile)
+    @tiles[Cell.new(x, y)] = tile
+  end
+
+  def to_s
+    tl, br = corners
+
+    s = String.new
+    (tl.y..br.y).each do |y|
+      (tl.x..br.x).each do |x|
+        s << char(Cell.new(x, y))
+      end
+      s << "\n"
+    end
+    s
+  end
+
+  private
+
+  def corners
+    min_x = +Float::INFINITY
+    min_y = +Float::INFINITY
+    max_x = -Float::INFINITY
+    max_y = -Float::INFINITY
+
+    @tiles.keys.each do |p|
+      min_x = [min_x, p.x].min
+      min_y = [min_y, p.y].min
+      max_x = [max_x, p.x].max
+      max_y = [max_y, p.y].max
+    end
+
+    upper_left = Cell.new(min_x, min_y)
+    lower_right = Cell.new(max_x, max_y)
+    [upper_left, lower_right]
+  end
+
+  def char(cell)
+    tile = @tiles[cell]
+    case tile
+    when :empty
+      ' '
+    when :wall
+      '#'
+    when :block
+      'x'
+    when :horizontal_paddle
+      '_'
+    when :ball
+      'o'
+    when nil
+      ' '
+    else
+      raise StandardError, "Unexpected tile #{tile}"
+    end
+  end
+end
+
+class DoneExecuting < StandardError; end
+
+class Game
+  def initialize(program, screen)
+    @computer = Intcode::Computer.new(program.as_memory) { on_input }
+    @screen = screen
+  end
+
+  def on_input
+    raise NotImplementedError
+  end
+
+  def run
+    loop do
+      step
+      system 'clear'
+      puts @screen
+      sleep 0.01
+      blocks = @screen.tiles.values.count { |val| val == :block }
+      puts blocks
+    rescue DoneExecuting
+      nil
+    end
+  end
+
+  def step
+    x = next_output
+    y = next_output
+    tile_id = next_output
+
+    case tile_id
+    when 0
+      @screen.draw(x, y, :empty)
+    when 1
+      @screen.draw(x, y, :wall)
+    when 2
+      @screen.draw(x, y, :block)
+    when 3
+      @screen.draw(x, y, :horizontal_paddle)
+    when 4
+      @screen.draw(x, y, :ball)
+    end
+  end
+
+  def next_output
+    out = nil
+    out = tick until out
+    out
+  end
+
+  def tick
+    ret = @computer.tick
+    raise DoneExecuting if ret == :done_executing
+
+    ret
+  end
+end
+
+program = Intcode.read(File.join(__dir__, 'input'))
+screen = Screen.new
+game = Game.new(program, screen)
+game.run