# frozen_string_literal: true

require 'set'
require_relative 'intcode'

Point = Struct.new(:x, :y) do
  def to_s
    "(#{x}, #{y})"
  end
end

class Hull
  def initialize
    @panels = Hash.new { |hash, key| hash[key] = :black }
    @painted = Set.new
  end

  def color_at(point)
    @panels[point]
  end

  def paint(point, color)
    @painted << point
    @panels[point] = color
  end

  def painted
    @painted.count
  end
end

class DoneExecuting < StandardError; end

class Robot
  def initialize(program, hull)
    @computer = Intcode::Computer.new(program.as_memory) { on_input }
    @hull = hull
    @facing = :up
    @position = Point.new(0, 0)
  end

  def step
    color_output = nil
    direction_output = nil

    color_output = tick until color_output
    direction_output = tick until direction_output

    @hull.paint(@position, color(color_output))
    @facing = turn(@facing, direction_output)
    @position = move(@position, @facing)
  end

  def tick
    ret = @computer.tick
    raise DoneExecuting if ret == :done_executing

    ret
  end

  def on_input
    color = @hull.color_at(@position)
    case color
    when :black
      0
    when :white
      1
    else
      raise ArgumentError, "unexpected color: #{color}"
    end
  end

  def color(code)
    case code
    when 0
      :black
    when 1
      :white
    else
      raise ArgumentError, "unexpected color code: #{code}"
    end
  end

  DIRECTIONS = %i[up right down left].freeze

  def turn(facing, direction_code)
    idx = DIRECTIONS.index(facing)
    case direction_code
    when 0
      # left 90 degrees (ccw)
      next_idx = (idx - 1) % DIRECTIONS.length
    when 1
      # right 90 degrees (cw)
      next_idx = (idx + 1) % DIRECTIONS.length
    else
      raise ArgumentError, "unexpected direction code: #{direction_code}"
    end
    DIRECTIONS.fetch(next_idx)
  end

  def move(pos, direction)
    case direction
    when :up
      Point.new(pos.x, pos.y - 1)
    when :down
      Point.new(pos.x, pos.y + 1)
    when :left
      Point.new(pos.x - 1, pos.y)
    when :right
      Point.new(pos.x + 1, pos.y)
    else
      raise ArgumentError, "unexpected direction: #{direction}"
    end
  end
end

program = Intcode.read(File.join(__dir__, 'input'))
hull = Hull.new
robot = Robot.new(program, hull)

loop do
  robot.step
rescue DoneExecuting
  break
end

puts hull.painted