mastodon_usernum.rb

require 'csv'
require 'json'
require 'net/http'
require 'uri'

def jsontocsv(instance_name)
    target_url = 'https://instances.mastodon.xyz/api/instances/history.json?instance=' + 
                 instance_name + '&start=0&end=' + Date.today.to_time.to_i.to_s
    parsed = JSON.parse(Net::HTTP.get(URI.parse(target_url)))

    csv_filename = instance_name + '.csv'
    CSV.open(csv_filename, 'w') do |file|
        parsed.each { |item|
            file << [Time.at(item['date']).strftime('%Y-%m-%d %H:%M:%S'), item['users'].to_s]
        }
    end
end

jsontocsv(ARGV[0])