rt_compose_tweet.rb

#!/usr/bin/env ruby

require 'optparse'

options = {}
OptionParser.new do |opts|
  opts.banner = "Usage: example.rb [options]"

  opts.on("-r", "--rt [Float]", Float, "Rt value") do |v|
    options[:rt] = v
  end
  opts.on("-c", "--cases [Integer]", Integer, "Number of cases today") do | v|
    options[:cases] = v
  end
  opts.on("-l", "--lower [Float]", Float, "Lower bound of Rt's 95% CI") do |v|
    options[:lower_bound] = v
  end
  opts.on("-u", "--upper [Float]", Float, "Upper bound of Rt's 95% CI") do |v|
    options[:upper_bound] = v
  end
end.parse!


def estimate(rt, days_from_now, cases)  
  ((rt**(1/2.9))**days_from_now * cases).floor
end

# formula given by Ryan Imgrund; 2.9 is the generation time
# https://twitter.com/imgrund/status/1467516798656466946
days_from_now = 24 - Time.now.day
xmas_estimate = estimate(options[:rt],days_from_now, options[:cases]) 

upper_estimate = estimate(options[:upper_bound],days_from_now,options[:cases])
lower_estimate = estimate(options[:lower_bound],days_from_now,options[:cases])

tweet = "Given an Rt value of #{options[:rt]} (95% CI: #{options[:lower_bound]}-#{options[:upper_bound]}) #{options[:cases]} cases today would lead to #{xmas_estimate} cases by December 24th (#{lower_estimate}- #{upper_estimate})"

# KLUDGE: quick DIY encoding that will be tolerated by Twitter
tweet = tweet.gsub("%", "%25").gsub(" ", "%20").gsub(":", "%3A")
p tweet
# p tweet.length
system("xdg-open", "https://twitter.com/compose/tweet?text=#{tweet}")