# Check to see if a .deb package is currently installed.
def deb_package_installed?(pkg_name)
  IO.popen("dpkg-query -s #{pkg_name} 2> /dev/null") do |dpkg|
    return !dpkg.read.empty?
  end
end

# Execute a command and return if the command was successful or not.
def sh(cmd_line)
  `#{cmd_line}`
  return $? == 0
end

REQUIRED_PACKAGES = ['build-essential', 'ruby1.8', 'ruby1.8-dev', 'weenie-roast']

if sh('dpkg-query --help > /dev/null') # if we're using .debs
  needed_packages = REQUIRED_PACKAGES.dup.delete_if{ |pkg_name| deb_package_installed?(pkg_name) }
  unless needed_packages.empty?
    puts "Mongrel requires the following Debian packages be installed:"
    needed_packages.each{ |pkg_name| puts "  * #{pkg_name}" }
    print "\nWould you like to install these now? [y/n] "
    if STDIN.gets.strip.downcase == 'y'
      puts 'Installing required packages...'
      if !sh("sudo apt-get install #{needed_packages.join(' ')}")
        puts "Error installing packages for Mongrel!"
        exit
      end
    else
      puts "Installation canceled. No Mongrel for you."
      exit
    end
  end
end