Calculate libyear for a ruby project over time, for charting progress

libyear-per-month.rb

# To generate the input file, I ran this:
#   
#    git log --merges --date-order --pretty="format:%h%d %aI" > first-commit-per-month.txt
#
# ... and then manually edited the file to have only the first commit per month. it'd
# be neat to geneate the list of target commits automatically.
#
# Note: this doesn't work with upstreamn libyears-bundler, because https://github.com/jaredbeck/libyear-bundler/issues/4
# However, my very hacky fork can do it: https://github.com/yob/libyear-bundler

File.open("first-commit-per-month.txt", "r") do |file|
  file.each_line do |line|
    sha, timestamp = *line.split(" ")
    date = timestamp[0,10]
    datetime = Time.iso8601(timestamp)

    # print commit sha and timestamp
    puts "********************************"
    puts "#{sha},#{date}"
    puts "********************************"

    # ensure we have a clean working directory
    system("git reset --hard > /dev/null")

    # checkout the target git sha
    system("git checkout #{sha} > /dev/null")

    # append libyear-bundler to the Gemfile and then run bundle to update Gemfile.lock
    system("echo 'gem \"libyear-bundler\" , github: \"yob/libyear-bundler\"' >> Gemfile")
    Bundler.with_unbundled_env do
      system("bundle > /dev/null")
    end

    # Run libyear to print the aggregate number of years this project is behind
    system("libyear-bundler --cache=/usr/local/bundle/libyear.yml --libyears --grand-total --max-time=\"#{datetime.iso8601}\"")
  end
end