Snowflakes falling in terminal in Ruby

snow.rb

# Seen on https://connectified.com/@ruby_discussions@mastodon.social/109993732600145441.
# Fixed data structure bug, added drift & other changes/improvements.

# Ruby version doing the same calculations as the elixir version in snow.exs

HEIGHT = `tput lines`.to_i
WIDTH = `tput cols`.to_i
SLEEP_DURATION = 0.5
LIFETIME = HEIGHT + 30
WIND_SPEED = [-2.0, -1.5, -1.0, -0.5, 0.0, 0.5, 1.0, 1.5, 2.0].sample * [-2.0, -1.5, -1.0, -0.5, 0.0, 0.5, 1.0, 1.5, 2.0].sample / 4.21
FLAKES_PER_ROW = 5

def clear_screen = puts "\e\[2J"

def string_to_move_cursor(x, y) = "\e\[#{y};#{x}H"

def print_cursor_top_left
  print "#{string_to_move_cursor(0, 0)}#{Time.now.strftime('%Y-%m-%d %H:%M:%S.%6N')}\nwind: #{WIND_SPEED.round(4)}#{string_to_move_cursor(0, 0)}"
end

def print_position(x, y, string)
  if x >= 0 and x < WIDTH and y >= 0 and y < HEIGHT
    print "#{string_to_move_cursor(x, y)}#{string}"
    print_cursor_top_left
  end
end

def erase_position(x, y)
  if x >= 0 and x < WIDTH and y >= 0 and y < HEIGHT
    print_position(x, y, " ")
    print_cursor_top_left
  end
end

def twinkle_print_position(x, y)
  if rand < 0.94
    print_position(x, y, colorless_flake)
  else
    print_position(x, y, colorful_flake)
  end
end

def colorless_flake
  # "\e[37m*\e[0m" is grey. Distinctive in some color configs and nigh-indistinguishable in others
  ["*", "*", "*", "*", "\e[37m*\e[0m"].sample
end

def colorful_flake
  # red is too vibrant: "\e[31m*\e[0m"
  ["\e[32m*\e[0m", "\e[33m*\e[0m", "\e[34m*\e[0m", "\e[35m*\e[0m", "\e[36m*\e[0m"].sample
end

trap("SIGINT") { puts "Bye!" ; exit! }

def run
  clear_screen
  snowfall([])
end

def snowfall(flakes)
  loop do
    FLAKES_PER_ROW.times {
      # the calculated area extends off-screen to the left and right
      flakes << {x: rand(3 * WIDTH) - WIDTH - 1, y: 0, lifetime: LIFETIME}
    }

    flakes.map! do |flake|
      x, y, lifetime = flake[:x], flake[:y], flake[:lifetime]

      # Erase flake.
      erase_position(x, y) unless lifetime == LIFETIME # newly-born, hasn't been drawn yet.

      lifetime -= 1

      # Only keep & process flakes that haven't gone too wide or reached the end of their lifetime.
      if x >= -WIDTH && x < 2 * WIDTH && lifetime > 0

        # Calculate wind- and random-drifted new x position, and extra drop in y position,
        # as long as the flake hasn't reached the ground yet.
        if y < HEIGHT - 1
          random_horizontal_drift = rand
          x = random_horizontal_drift < 0.1 ? x-1 : random_horizontal_drift > 0.9 ? x+1 : x
          x += 1 if WIND_SPEED > 0 && rand < WIND_SPEED
          x -= 1 if WIND_SPEED < 0 && rand < 0 - WIND_SPEED

          # A slight chance to drift one extra unit lower.
          y += 1 if rand < 0.1
        end

        # Fall the usual one unit if the flake still hasn't reached the ground yet.
        y += 1 if y < HEIGHT - 1

        twinkle_print_position(x, y)

        {x: x, y: y, lifetime: lifetime}
      end
    end.compact!

    sleep SLEEP_DURATION
  end
end

run