Git pre-commit hook to automatically run Jammit when assets are committed and add the processed files to the commit as well.

Jammit pre-commit hook

#!/usr/bin/env ruby
# This pre-commit hook automatically processes changed assets with Jammit
# and adds the changed files to the commit.

RAILS_ROOT = File.expand_path('.')
ASSET_DIR = File.join(RAILS_ROOT, 'public', 'assets')

status_lines = `git diff-index --cached HEAD`
files_committing = status_lines.map{|l| l.split(/\t/).last.strip }

unless files_committing.any?{|f| f['public/images/embed'] || f['public/stylesheets'] || f['public/javascripts'] || f['public/assets']}
  puts "\t* None of the changes being committed are asset files"
else
  puts "\t* About to commit changes to asset files."
  puts "\t* Processing with Jammit and adding output to commit before continuing..."
  
  # Spinner - based on http://snippets.dzone.com/posts/show/3760
  cr = "\r"             # move cursor to beginning of line
  clear = "\e[0K"       # ANSI escape code to clear line from cursor to end of line
  reset = cr + clear    # reset lines
  
  chars = [ "|", "/", "-", "\\" ]
  color = 32            # green
  str = "#{reset}\e[#{color};1m"

  worker = Thread.new do
    `cd #{RAILS_ROOT} && jammit\n`
    `git add #{ASSET_DIR}`
  end

  i = 0
  while worker.alive? do
    i += 1
    char = chars[ i % chars.length ]
    print "#{str}\t#{char}"
    sleep(0.2)
    $stdout.flush
  end
  print reset
  puts "\tDone!"
end