--- Copas specific client handling module.
-- Typically this module is not used directly, but through `mqtt.loop` when
-- auto-detecting the environment.
-- @module mqtt.loop.copas

local copas = require "copas"
local log = require "mqtt.log"

local client_registry = {}

local _M = {}


--- Add MQTT client to the Copas scheduler.
-- Each received packet will be handled by a new thread, such that the thread
-- listening on the socket can return immediately.
-- The client will automatically be removed after it exits. It will set up a
-- thread to call `Client:check_keep_alive`.
-- @param cl mqtt-client to add to the Copas scheduler
-- @return `true` on success or `false` and error message on failure
function _M.add(cl)
	if client_registry[cl] then
		log:warn("MQTT client '%s' was already added to Copas", cl.opts.id)
		return false, "MQTT client was already added to Copas"
	end
	client_registry[cl] = true

	do -- make mqtt device async for incoming packets
		local handle_received_packet = cl.handle_received_packet
		local count = 0
		-- replace packet handler; create a new thread for each packet received
		cl.handle_received_packet = function(mqttdevice, packet)
			count = count + 1
			copas.addnamedthread(handle_received_packet, cl.opts.id..":receive_"..count, mqttdevice, packet)
			return true
		end
	end

	-- add keep-alive timer
	local timer = copas.addnamedthread(function()
		while client_registry[cl] do
			local next_check = cl:check_keep_alive()
			if next_check > 0 then
				copas.pause(next_check)
			end
		end
	end, cl.opts.id .. ":keep_alive")

	-- add client to connect and listen
	copas.addnamedthread(function()
		while client_registry[cl] do
			local timeout = cl:step()
			if not timeout then
				client_registry[cl] = nil -- exiting
				log:debug("MQTT client '%s' exited, removed from Copas", cl.opts.id)
				copas.wakeup(timer)
			else
				if timeout > 0 then
					copas.pause(timeout)
				end
			end
		end
	end, cl.opts.id .. ":listener")

	return true
end

return setmetatable(_M, {
	__call = function(self, ...)
		return self.add(...)
	end,
})