class C
  def initialize
    @size_x = 20
    @size_y = 20
    @dots = []
    @sushis = []
  end

  def dot!(loc)
    if 0 <= loc[0] && loc[0] < @size_x &&
        0 <= loc[1] && loc[1] < @size_y
      @dots += [loc]
    else
      raise "Out of boundary: #{loc}"
    end
  end

  def sushi!(loc)
    if 0 <= loc[0] && loc[0] < @size_x &&
        0 <= loc[1] && loc[1] < @size_y
      @sushis += [loc]
    else
      raise "Out of boundary: #{loc}"
    end
  end

  # Bresenham's algorithm
  def draw_line!(loc0, loc1)
    if loc0 == loc1
      dot!(lot0)
      return
    end

    sushi!(loc0)
    sushi!(loc1)

    (x0, y0) = loc0
    (x1, y1) = loc1
    dx = (x1 - x0).abs
    dy = (y1 - y0).abs
    step_x = x0 == x1 ? 0 : x0 < x1 ? 1 : -1
    step_y = y0 == y1 ? 0 : y0 < y1 ? 1 : -1
    # step_y = dy == 0 ? 0 : dy < 0 ? -1 : 1

    f = 0
    if dx > dy
      y = y0
      x0.step(x1, step_x).each do |x|
        if f > 0
          y += step_y
          dot!([x, y])
          f += 2*dy - 2*dx
        else
          dot!([x, y])
          f += 2*dy
        end
      end
    else
      x = x0
      y0.step(y1, step_y).each do |y|
        if f > 0
          x += step_x
          dot!([x, y])
          f += 2*dx - 2*dy
        else
          dot!([x, y])
          f += 2*dx
        end
      end
    end
  rescue
    p [loc0, loc1]
    raise
  end

  def fill_rect!(loc0, loc1)
    (x0, y0) = loc0
    (x1, y1) = loc1
    dx = x1 - x0
    dy = y1 - y0
    step_x = dx < 0 ? -1 : 1
    step_y = dy < 0 ? -1 : 1

    x0.step(x1, step_x).each do |x|
      y0.step(y1, step_y) do |y|
        dot!([x, y])
      end
    end
  end

  def to_a
    Array.new(@size_x) {|x|
      Array.new(@size_y) {|y|
        case [x, y]
        when *@sushis
          '🍣'
        when *@dots
          '⬛'
        else
          '　'
        end
      }.join('') + '|'
    }
  end

  def to_s
    [
      '--' * @size_x,
      *to_a(),
      '--' * @size_x,
    ].join("\n")
  end
end

c = C.new

# c.draw_line!(*)
# puts c
# exit

c.draw_line!([rand(20), rand(20)], [rand(20), rand(20)])
c.draw_line!([rand(20), rand(20)], [rand(20), rand(20)])
c.draw_line!([0, 0], [19, 0])
c.draw_line!([0, 0], [0, 19])
c.draw_line!([19, 19], [19, 0])
c.draw_line!([19, 19], [0, 19])

# c.fill_rect!([rand(20), rand(20)], [rand(20), rand(20)])

puts c.to_a