Generate a histogram of line changes (insertions + deletions) from a GitHub repo, bucketed by week

git-changes-histogram.rb

require 'time'

class Commit
  DATE = /^Date: +(\w{3} \w{3} \d{1,2}.+)$/
  MERGE = /^Merge: +([a-z0-9]+) ([a-z0-9]+)$/
  CHANGES = /^ *\d+ files? changed(?:, (\d+) insertions?...)?(?:, (\d+) deletions?...)? *$/

  attr_reader :sha

  def self.sha_for(pointer)
    `git rev-list -n 1 #{pointer}`.strip
  end

  def initialize(pointer)
    @sha = self.class.sha_for pointer
    @stat = `git show #{@sha} --stat`
  end

  def year_week
    @year_week ||= begin
      match = DATE.match(@stat)
      throw "No Date info in #{@stat}" unless match
      Time.parse(match[1]).strftime('%G-%V')
    end
  end

  def parent
    @parent ||= begin
      pointer = is_merge? ? MERGE.match(@stat)[1] : "#{@sha}~1"
      Commit.new(pointer)
    end
  end

  def change_count
    @change_count ||= begin
      match = CHANGES.match(@stat)
      raise "No change info in #{@stat}" unless match
      (match[1] || 0).to_i + (match[2] || 0).to_i
    end
  end

  def same_sha?(other)
    if other.is_a?(Commit)
      sha == other.sha
    else
      sha == self.class.sha_for(other)
    end
  end

  def is_merge?
    @is_merge ||= MERGE =~ @stat
  end

  def inspect
    "<Commit sha:#{sha.slice(0, 8)} bucket:#{year_week} lines:#{change_count}>"
  end
end

class Histogram
  def initialize
    @buckets ||= {}
  end

  def <<(commit)
    @buckets[commit.year_week] ||= 0
    @buckets[commit.year_week] += commit.change_count
  end

  def print
    @buckets.keys.sort.reverse.each do |week|
      puts "#{week}  #{@buckets[week]}"
    end
  end
end

def each_commit(start_pointer, end_pointer, &block)
  current = Commit.new(start_pointer)

  while !current.same_sha?(end_pointer)
    yield current
    current = current.parent
  end
end

def run
  if ARGV.length != 2
    puts 'USAGE: ruby git-changes-histogram.rb head head~1000'
  end

  histogram = Histogram.new
  each_commit ARGV[0], ARGV[1] do |commit|
    histogram << commit
  end
  histogram.print
end

run