git post-receive hook for Flowdock emails

#!/usr/bin/env ruby

# This git post-receive hook generates a nice-looking email about
# the recent commits. It can be used to send e-mail to the team's
# Flowdock account, for example.
#
# Just copy it to your git repository's hooks/post-receive and make
# sure you have ruby, rubygems and gem 'grit' installed.

require 'stringio'
require 'rubygems'
require 'grit'
require 'md5'
require 'cgi'

# These two configuration variables need to be set.
DESCRIPTION = "MyApp Frontend"
RECIPIENTS = "myflow@mycompany.flowdock.com"

def generate_email_header
  puts <<-END_OF_HEADERS
To: #{$recipients}
Subject: #{$subject_prefix}#{$subject}#{$subject_suffix}
Content-Type: text/html; charset="utf-8"
X-Git-Refname: #{$refname}
X-Git-Oldrev: #{$oldrev}
X-Git-Newrev: #{$newrev}

  END_OF_HEADERS
end

def generate_email_body
  commits_to_html
end

def commits_to_html
  $commits.reverse.each do |c|
    short, long = c.message.split(/\n+/, 2)

    puts "<div style=\"margin-bottom: 10px\"><div class=\"ui-corner-all\" style=\"background:url(http://gravatar.com/avatar/#{MD5::md5(c.author.email)}?s=30)
 no-repeat scroll center;height:30px;width:30px;float:left;margin-right:5px;\">&nbsp;</div>"
    puts "<div style=\"padding-left: 35px;\">#{CGI.escapeHTML(short)}<br/>"

    if long
      long.gsub!(/\n/, '<br />')
      puts '<p style="margin:5px 0px; padding: 0 5px; border-left: 3px solid #ccc">' + long + '</p>'
    end

    puts "<span style=\"font-size: 90%; color: #333\"><code>#{c.id_abbrev}</code> <a href=\"mailto:#{CGI.escapeHTML(c.author.email)}\">#{CGI.escapeHTML(c.aut
hor.name)}</a> on #{c.date.strftime("%b %d, %H:%M")}</span></div></div>"
  end
end
repo = Grit::Repo.new(".")

if ARGV.empty?
  strio = StringIO.new
  $stdout = strio
  $oldrev, $newrev, $refname = gets.split()
else
  $oldrev, $newrev, $refname = ARGV
end

# Don't do anything if it's not a branch update(?)
exit unless $refname =~ %r{refs/heads/}

branch = $refname.scan(%r{[^/]+$}).to_s

$description = DESCRIPTION
$recipients = RECIPIENTS
$subject = "#{DESCRIPTION}: branch #{branch} updated"
$subject_suffix = " ##{branch} #push"

begin
  $commits = repo.commits_between($oldrev, $newrev)

  generate_email_header
  generate_email_body

  if strio
    strio.rewind()
    email = strio.read()

    IO.popen("/usr/sbin/sendmail -t", "w+") do |pipe|
      pipe.write email
      pipe.close_write
    end
  end
rescue => e
  puts "post-receive script failed: #{e.inspect}"
  puts
  puts "oldrev: #{$oldrev}"
  puts "newrev: #{$newrev}"
  puts "refname: #{$refname}"
end