#!/usr/bin/env ruby
require 'mail'

# This script is a dead-simple Mail Delivery Agent (MDA) that exports the parts of the received email as
# environment variables and calls a shell script that can make use of these variables to further process
# the mail.
mail = Mail.new(ARGF.read)

# Expose mail properties as environment variables
%w[date message_id from to subject body].each{|field|
  value = mail.send(field.to_sym)
  value = value.join(',') if value.respond_to?(:join)
  ENV["TWMAIL_#{field.upcase}"] = Shellwords.escape(value.to_s)
}

# The hook to be executed is read from the environment variable TWMAIL_HOOK
# If none is set, this script will assume that twmail_on_new_mail is in the
# $PATH and executable.
cmd = ENV["TWMAIL_HOOK"] || 'twmail_hook'

# Call hook script
%x[#{cmd}]