WIDTH  = 640
HEIGHT = 480

if Graphics.respond_to?(:width)
  WIDTH  = Graphics.width
  HEIGHT = Graphics.height
end


class Snow
  class Flake < Struct.new(:x, :y)
    def initialize(x = rand(WIDTH))
      self.x = x
      self.y = 0
    end
    def move(arr)
      self.y += 1
      return !is_ok?(arr)
    end
    def is_ok?(arr)
      return self.y < arr[self.x]
    end
  end

  def self.run
    snow = Snow.new
    self.integrate_graphics(snow)
  end

  def self.integrate_graphics(snow)
    Graphics.snow = snow
  end

  def initialize
    @bitmap = Bitmap.new(WIDTH,HEIGHT)
    @sprite = Sprite.new
    @color  = Color.new(255,255,255)
    @clear  = Color.new(0,0,0,0)
    @table  = Table.new(WIDTH,HEIGHT)
    @list   = []
    @bottom = Array.new(WIDTH,HEIGHT-1)

    @sprite.bitmap = @bitmap
    @sprite.z      = 9999
  end

  def update
    removed = []
    for flake in @list
      @bitmap.set_pixel(flake.x,flake.y,@clear)
      removed << flake if flake.move(@bottom)
      @bitmap.set_pixel(flake.x,flake.y,get_color)
    end

    for flake in removed
      @list.delete(flake)
      @bottom[flake.x] -= 1
    end

    for num in all_diff(1)
      flake = Flake.new
      if (flake.is_ok?(@bottom))
        @list << flake
        @bitmap.set_pixel(flake.x,flake.y,get_color)
      end
    end
  end

  def get_color
    return @color
  end

  def all_diff(num)
    arr = [rand(WIDTH)]
    while arr.size < num
      v = rand(WIDTH)
      arr << v unless arr.include?(v)
    end
    arr
  end
end

module Graphics
  @snow = nil
  class << self
    attr_accessor :snow
    alias_method(:update_snow, :update)

    def update(*args)
      snow.update if snow
      update_snow(*args)
    end
  end
end

Snow.run