require 'tempfile'

module Rgpg
  module GpgHelper
    def self.generate_key_pair(key_base_name, recipient, real_name)
      public_key_file_name = "#{key_base_name}.pub"
      private_key_file_name = "#{key_base_name}.sec"
      script = generate_key_script(public_key_file_name, private_key_file_name, recipient, real_name)
      script_file = Tempfile.new('gpg-script')
      begin
        script_file.write(script)
        script_file.close
        result = system("gpg --batch --gen-key #{script_file.path}")
        raise RuntimeError.new('gpg failed') unless result
      ensure
        script_file.close
        script_file.unlink
      end
    end

    def self.encrypt_file(public_key_file_name, input_file_name, output_file_name)
      raise ArgumentError.new("Public key file \"#{public_key_file_name}\" does not exist") unless File.exist?(public_key_file_name)
      raise ArgumentError.new("Input file \"#{input_file_name}\" does not exist") unless File.exist?(input_file_name)

      recipient = get_recipient(public_key_file_name)
      with_temporary_encrypt_keyring(public_key_file_name) do |keyring_file_name|
        run_gpg(
          '--keyring', keyring_file_name,
          '--output', output_file_name,
          '--encrypt',
          '--recipient', recipient,
          '--yes',
          '--trust-model', 'always',
          input_file_name
        )
      end
    end

    def self.decrypt_file(public_key_file_name, private_key_file_name, input_file_name, output_file_name)
      raise ArgumentError.new("Public key file \"#{public_key_file_name}\" does not exist") unless File.exist?(public_key_file_name)
      raise ArgumentError.new("Private key file \"#{public_key_file_name}\" does not exist") unless File.exist?(private_key_file_name)
      raise ArgumentError.new("Input file \"#{input_file_name}\" does not exist") unless File.exist?(input_file_name)

      recipient = get_recipient(private_key_file_name)
      with_temporary_decrypt_keyrings(public_key_file_name, private_key_file_name) do |keyring_file_name, secret_keyring_file_name|
        run_gpg(
          '--keyring', keyring_file_name,
          '--secret-keyring', secret_keyring_file_name,
          '--output', output_file_name,
          '--decrypt',
          '--yes',
          '--trust-model', 'always',
          input_file_name
        )
      end
    end

    private

    def self.run_gpg(*args)
      fragments = [
        'gpg',
        '--no-default-keyring'
      ] + args
      command_line = fragments.join(' ')

      output_file = Tempfile.new('gpg-output')
      begin
        output_file.close
        result = system("#{command_line} > #{output_file.path} 2>&1")
      ensure
        output_file.unlink
      end
      raise RuntimeError.new('gpg failed') unless result
    end

    def self.generate_key_script(public_key_file_name, private_key_file_name, recipient, real_name)
      <<-EOS
  %echo Generating a standard key
  Key-Type: DSA
  Key-Length: 1024
  Subkey-Type: ELG-E
  Subkey-Length: 1024
  Name-Real: #{real_name}
  Name-Comment: Key automatically generated by rgpg
  Name-Email: #{recipient}
  Expire-Date: 0
  %pubring #{public_key_file_name}
  %secring #{private_key_file_name}
  # Do a commit here, so that we can later print "done" :-)
  %commit
  %echo done
      EOS
    end

    def self.get_recipient(key_file_name)
      result = `gpg #{key_file_name}`.lines.first.chomp
      raise RuntimeError.new('gpg failed') unless $?
      result =~ /^(pub|sec)\s+\d+D\/([0-9a-fA-F]{8}).+<(.+)>/ or raise RuntimeError.new('Invalid output')
      key_id = $2
      recipient = $3
      recipient
    end

    def self.with_temporary_encrypt_keyring(public_key_file_name)
      with_temporary_keyring_file do |keyring_file_name|
        run_gpg(
          '--keyring', keyring_file_name,
          '--import', public_key_file_name
        )
        yield keyring_file_name
      end
    end

    def self.with_temporary_decrypt_keyrings(public_key_file_name, private_key_file_name)
      with_temporary_keyring_file do |keyring_file_name|
        with_temporary_keyring_file do |secret_keyring_file_name|
          run_gpg(
            '--keyring', keyring_file_name,
            '--secret-keyring', secret_keyring_file_name,
            '--import', private_key_file_name
          )
          yield keyring_file_name, secret_keyring_file_name
        end
      end
    end

    def self.with_temporary_keyring_file
      keyring_file = Tempfile.new('gpg-key-ring')
      begin
        keyring_file_name = keyring_file.path
        keyring_file.close
        keyring_file.unlink
        yield keyring_file_name
      ensure
        File.unlink(keyring_file_name) if File.exist?(keyring_file_name)
        backup_keyring_file_name = "#{keyring_file_name}~"
        File.unlink(backup_keyring_file_name) if File.exist?(backup_keyring_file_name)
      end
    end
  end
end