--
--  gcsd
--
--  gcsd the generic command sequencer daemon can be used to serialize
--  commands sent over various paralell communication channels to a
--  single command output. It can be seen as a multiplexer for any
--  kind of communication between a single resource and various clients
--  which want to submit commands to it or query information from it.
--  gcsd is written in C and Lua. The goal is to provide an easy to
--  understand high level API based on Lua which can be used to
--  implement the business logic of the so formed multiplexer daemon.
--
--
--  Copyright (C) 2009-2010 Markus Grueneis <gimpf@spreadspace.org>
--                          Christian Pointner <equinox@spreadspace.org>
--
--  This file is part of gcsd.
--
--  gcsd is free software: you can redistribute it and/or modify
--  it under the terms of the GNU General Public License as published by
--  the Free Software Foundation, either version 3 of the License, or
--  any later version.
--
--  gcsd is distributed in the hope that it will be useful,
--  but WITHOUT ANY WARRANTY; without even the implied warranty of
--  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
--  GNU General Public License for more details.
--
--  You should have received a copy of the GNU General Public License
--  along with gcsd. If not, see <http://www.gnu.org/licenses/>.
--

command_queue = {}

command_queue.commands = {}
command_queue.current = nil

function command_queue:enqueue(command, expected_response, requester, timeout)
   if(not command) then
      log.printf(log.INFO, "ignoring empty command")
   end
   local new_cmd = {}
   new_cmd.command = command
   new_cmd.sent = false
   new_cmd.requester = requester
   if(expected_response and module_list.output.class.properties.type == defines.OUT_MODULE) then
      log.printf(log.WARNING, "output module doesn't support responses, ignoring expected response");
   else
      new_cmd.expected_response = expected_response
   end
   if(timeout) then
      new_cmd.timeout = timer.new(timeout)
   end

   table.insert(self.commands, new_cmd)
end

function command_queue:command_pending()
   return (self.current == nil and #self.commands > 0)
end

function command_queue:get_current_command()
   return self.current
end

function command_queue:get_expected_response()
   if(self.current == nil) then return end
   return self.current.expected_response
end

function command_queue:get_next_command()
   if(self.current ~= nil) then return nil end

   self.current = self.commands[1]
   return self.current.command
end

function command_queue:command_sent()
   if(self.current == nil) then return end

   self.current.sent = true
   if(self.current.timeout) then
      self.current.expiration_time = timer.now() + self.current.timeout
   end
   if(self.current.expected_response) then
      return self.current.expected_response
   end

   if(not self.current.expiration_time) then
      self:command_completed()
   end
end

function command_queue:check_timeout()
   if(self.current == nil or not self.current.sent) then return end
   if(not self.current.expiration_time) then return end

   if(timer.cmp(timer.now(), self.current.expiration_time) == 1) then
      log.printf(log.NOTICE, "command timed out")
      if(self.current.requester) then
         self.current.requester:process_timeout()
      end
      self:command_completed()
   end
end

function command_queue:command_completed(response)
   if(self.current == nil) then return end
   
   if(response and self.current.requester) then
      self.current.requester:process_response(response)
   end

   table.remove(self.commands, 1)
   self.current = nil
end