local tOpen = { left = false, right = false, top = false, bottom = false, front = false, back = false }
local tValid = { left = true, right = true, top = true, bottom = true, front = true, back = true }

function open( sSide )
	if type( sSide ) ~= "string" then
		error( "string expected" )
	end
	if not tValid[sSide] then
		error( "Invalid side" )
	end
	tOpen[ sSide ] = true
end

function close( sSide )
	if type( sSide ) ~= "string" then
		error( "string expected" )
	end
	if not tValid[sSide] then
		error( "Invalid side" )
	end
	tOpen[ sSide ] = false
end

function send( sID, sMessage )
	local hasSent = false
	for i,v in pairs( tOpen ) do
		if v == true then
			local sCable = peripheral.wrap( i )
			sCable.send( sID, sMessage )
			hasSent = v
		end
	end
	return hasSent
end

function broadcast( sMessage )
	return send( -1, sMessage )
end

function announce()
	return broadcast( "" )
end

function receive( sTimeOut )
	local timer = nil
	local sEvent = "cable_message"
	if nTimeout then
		timer = os.startTimer( nTimeout )
		sEvent = nil
	end
	while true do
		local e, p1, p2, p3 = os.pullEvent( sEvent )
		if e == "cable_message" then
			return p1, p2, p3
		elseif e == "timer" and p1 == timer then
			return nil, nil, nil
		end
	end
end