# 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

def executable_exists?(name, harmless_option = '-h')
  IO.popen("/usr/bin/env #{name} #{harmless_option} 2>/dev/null", 'r') do |bin|
    return !bin.read.empty?
  end  
end

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

if RUBY_PLATFORM !~ /mswin32/ && executable_exists?('dpkg-query') # if we're not on Windows and we're using .debs
  if deb_package_installed?('ruby1.8') # if we're using the package
    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 "\nWarning: There's a very good chance that you won't be able to compile"
        puts "         Mongrel. Unless you have a C compiler and Ruby's development"
        puts "         files installed, Mongrel won't work."
        print "\nAre you sure you want to continue? [y/n] "
        exit if STDIN.gets.strip.downcase != 'y'
      end
    end
  elsif executable_exists?('ruby') # if we're using a source install
    puts "\nWarning: It looks like you've installed Ruby from source. Make sure"
    puts "         you also have all the development headers for Ruby. Without"
    puts "         those, Mongrel won't be able to compile its C extension."
  else # can't find Ruby, can't find the packages... and yet we're running... odd
    puts "\nWarning: Cannot detect your Ruby installation. Installing Mongrel may"
    puts "         or may not work. Here be dragons."
  end
end