time-spent.rb

require 'csv'
require 'json'
require 'time'

users = {}

CSV.new(ARGF, headers: true).each do |row|
  STDERR.print '.'
  user_id = row["user_id"]
  metadata = JSON.parse(row["metadata"])
  started = Time.parse(metadata.fetch("started_at"))
  finish = Time.parse(metadata.fetch("finished_at"))

  next unless user_id

  users[user_id] ||= {time: 0, classifications: 0}
  users[user_id][:time] += finish - started
  users[user_id][:classifications] += 1
  users[user_id][:first_seen] ||= started
  users[user_id][:last_seen] = finish
end

STDERR.puts " done\n\n"

CSV.new(STDOUT).tap do |csv|
  csv << ["user_id", "time_spent", "classifications_count", "first_seen", "last_seen"]
  users.each do |user_id, data|
    csv << [user_id, data[:time], data[:classifications], data[:first_seen], data[:last_seen]]
  end
end