Git hook in ruby code to insert a JIRA link when commiting.

prepare-commit-msg

#!/usr/bin/env ruby

# This way you can customize which branches should be skipped when
# prepending commit message.
message_file = ARGV[0]
branches_to_skip = (ENV['BRANCHES_TO_SKIP'] || 'master').split(' ')
original_message = File.read(message_file)
current_branch = `git symbolic-ref --short HEAD`

# Don't do anything if the commit already has a link i.e. in the case of --amend
if !original_message.match(/Ticket/) && !branches_to_skip.include?(current_branch)
  match = current_branch.match(/([a-zA-Z]*-[0-9]*)/)
  if match
    ticket = match[1]
    jira_server = `git config jira.server`
    jira_link = "Ticket: #{jira_server.chomp}/browse/#{ticket}\n"

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

    # Need an extra line break when message is passed in as -m
    jira_link = "\n#{jira_link}" if ARGV[1] == "message"

    original_message.insert(jira_link_position, jira_link)
  end

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