Ruby git hook example prepare-commit-msg that parses pivotal story id and inserts it and a link in the commit message

prepare-commit-msg

#!/usr/bin/env ruby
# parse Pivotal ticket names out of branches named similar to
#      xxxx-9999-xxxx-xxxx
# make sure the hook has permissions to execute after copying it over

message_file = ARGV[0]
original_message = File.read(message_file)

# Don't do anything if the commit already has a pivotal id i.e. in the case of --amend
unless original_message.match(/\[\d+\]/)
  message = ""

  current_branch = `git rev-parse --abbrev-ref HEAD`
  match = current_branch.match(/[a-zA-Z]+-([0-9]+)-/)

  if match
    pivotal_id = match[1]
    pivotal_link = "https://www.pivotaltracker.com/story/show/#{pivotal_id}"
    line_break_match = original_message.match(/\n/)
    if line_break_match
      id_position = line_break_match.offset(0)[0]
    else
      id_position = original_message.length - 1
    end
    original_message.insert(id_position, " [#{pivotal_id}]")

    # Insert pivotal link immediately before comments begin
    # Match where there are 3 or more lines of comments
    comment_match = original_message.match(/((^\#.*$\n){3})/)
    if comment_match
      pivotal_link_position = comment_match.offset(0)[0]
    else
      pivotal_link_position = original_message.length - 1
    end

    # Need an extra line break when message is passed in as -m
    if ARGV[1] == "message"
      pivotal_link_string = "\n\n#{pivotal_link}\n"
    else
      pivotal_link_string = "\n#{pivotal_link}\n"
    end
    original_message.insert(pivotal_link_position, pivotal_link_string)
  end

  message = message + original_message

  File.open(message_file, 'w') { |f| f.write message }
end