local mcSerial = {}
local inst = mc.mcGetInstance()

rs232 = require("luars232")
port_name = "COM1"
local out = io.stderr
local read_len = 1 -- read one byte
local timeout = 5 -- in miliseconds
local ResponseTimer = 5 --Time to delay for drive response in milliseconds
local max_flush = 4096 --Maximum number of characters to flush from the buffer while reading
local max_length = 18 --Longest Serial Packet


----------------------------------
-- mcSerial.OpenPort() --
----------------------------------
function mcSerial.OpenPort()
	--mc.mcCntlSetLastError(inst, "Starting Serial Port Open Function")
	--This function uses the RS232 library to open a serial port using the global variable port_name
	--Port settings are assigned immediately
	local ES = ""
	local RS = ""
	local RV = 0
	
	--Open Serial port using the RS232 library and check for errors
	e, p = rs232.open(port_name)
	--mc.mcCntlSetLastError(inst, "Attepted to Open Port - Checking for Errors")
	if e ~= rs232.RS232_ERR_NOERROR then; ES = "F0101"..string.format("%02X",e)..":"; return ES; end
	--mc.mcCntlSetLastError(inst, "Port Open - No Errors, Applying Settings")
	-- set port settings
	assert(p:set_baud_rate(rs232.RS232_BAUD_38400) == rs232.RS232_ERR_NOERROR)
	assert(p:set_data_bits(rs232.RS232_DATA_8) == rs232.RS232_ERR_NOERROR)
	assert(p:set_parity(rs232.RS232_PARITY_NONE) == rs232.RS232_ERR_NOERROR)
	assert(p:set_stop_bits(rs232.RS232_STOP_1) == rs232.RS232_ERR_NOERROR)
	assert(p:set_flow_control(rs232.RS232_FLOW_OFF)  == rs232.RS232_ERR_NOERROR)
	
	--mc.mcCntlSetLastError(inst, "Serial Port Open - Settings Applied")
	
	WriteRegister("SerialOpen", 1)
	return ES
end

----------------------------------
-- mcSerial.ClosePort() --
----------------------------------
function mcSerial.ClosePort()
	local ES = ""
	local RS = ""
	local RV = 0
	
	p:close()
	
	WriteRegister("SerialOpen", 0)
	return ES
end

----------------------------------
-- mcSerial.DebugWrite() --
----------------------------------
function mcSerial.DebugWrite(string)
	local ES = ""
	local RS = ""
	local RV = 0
	
	RV, len_written = p:write(string, timeout) --write the string over the serial port
	if (RV ~= rs232.RS232_ERR_NOERROR) then; ES = "F0601"..string.format("%02X",RV)..":" ; return ES; end
	
	return ES
end

----------------------------------
-- mcSerial.FlushBuffer() --
----------------------------------
function mcSerial.FlushBuffer()
	--Windows automatically fills a serial buffer with characters (up to 4096 I think)
	--This function reads the entire buffer to empty it out
	local ES = ""
	local RS = ""
	local RV = 0
	local data_read
	local size

	--RV, data_read, size = p:read(max_flush, timeout)
	RV = p:flush()
	if RV ~= rs232.RS232_ERR_NOERROR then; ES = "F0201"..string.format("%02X",RV)..":"; return ES; end
	return ES
end

----------------------------------
-- mcSerial.AppendChecksum(string) --
----------------------------------
function mcSerial.AppendChecksum(str)
	--This function is for use with Ultra 3000 serial host commands
	--This function takes a string input then calculates two character checksum
	--The input string is concatenated with a leading colon, a trailing checksum, and a trailing carriage return
	local ES = ""
	local RS = ""
	local RV = 0
	local ccSum = 0
	local rString = ""
	
	--mc.mcCntlSetLastError(inst, "Entering Append Checksum, Input Data is :"..str)
	local len = string.len(str)
	--mc.mcCntlSetLastError(inst, "String Length is "..tostring(len))
	
	if len == 0 then; ES = "F030101:"; rString = ""; return ES, rString; end
	if len > 70 then; ES = "F030102:"; rString = ""; return ES, rString; end
	
	for i=1,len,1 do 
		ccSum = ccSum + str:byte(i)
		--mc.mcCntlSetLastError(inst, "Checksum Index "..tostring(i).." Current Sum = "..tostring(ccSum))
	end 
	local output = string.format("%X", bit32.band(256-ccSum)) 
	--mc.mcCntlSetLastError(inst, "Calculated Checksum = "..output)
	local checksum =  string.sub(output,-2,-1)
	--mc.mcCntlSetLastError(inst, "Truncated Checksum = "..checksum)
	rString = ':'..str..checksum.."\r"
	--mc.mcCntlSetLastError(inst, "String to be Returned is "..rString)
	return ES, rString
end 

----------------------------------
-- mcSerial.Hex2Num(string) --
----------------------------------
function mcSerial.Hex2Num(str)
	--This function converts a hexidecimal number to decimal using twos complement
	--This function returns the decimal number (or nil) and an error code
	local ES = ""
	local RS = ""
	local RV = 0
	local hexNum = nil
	
	local len = string.len(str)
	if len == 0 then; ES = "F040101:"; hexNum = nil; return ES, hexNum; end
	
	hexNum = tonumber(str,16)
	if len == 2 then
		if hexNum >= 128 then
			hexNum = hexNum - 256
		end
	elseif len == 4 then
		if hexNum >= 32768 then
			hexNum = hexNum - 65536
		end
	elseif len == 8 then
		if hexNum >= 2147484148 then
			hexNum = hexNum - 4294967296
		end
	else; ES = "F040102:"; hexNum = nil; return ES, hexNum;
	end
	return ES, hexNum
end

----------------------------------
-- mcSerial.WriteRead(string) --
----------------------------------
function mcSerial.WriteRead(tString)
	--mc.mcCntlSetLastError(inst, "Starting Serial Routine Write/Read ")
	--This function is in charge of writing to the Ultra 3000 and handling reponses
	local ES = ""
	local RS = ""
	local RV = 0
	
	local rString = ""
	--local sError = 0
	local data = ""
	local len_written = 0
	local data_read = ""
	local size 
	local checkVerify = ""
	
	--mc.mcCntlSetLastError(inst, "Flushing Buffer")
	RS = mcSerial.FlushBuffer()
	if (RS ~= "") then; ES = "F050101:"..RS ; data = ""; return ES, data; end
	--mc.mcCntlSetLastError(inst, "Buffer Flush Complete, Writing String ="..tString)
	
	RV, len_written = p:write(tString, timeout) --write the string over the serial port
	if (RV ~= rs232.RS232_ERR_NOERROR) then; ES = "F0502"..string.format("%02X",RV)..":" ; data = ""; return ES, data; end
	--mc.mcCntlSetLastError(inst, "Write Complete, Starting Delay")
	
	wx.wxMilliSleep(2) --Sleep 2 milliseconds
	
	--mc.mcCntlSetLastError(inst, "Delay Complete, Looking for Drive Response")
	--read serial buffer until a colon is found
	for i = 0, max_flush, 1 do --Flush the buffer until a colon is found, routine resumes here after timer expiration
		RV, data_read, size = p:read(1, timeout)
		--RV, data_read, size = p:read(1)
		
		--mc.mcCntlSetLastError(inst, "Index = "..tostring(i).." Data = "..tostring(data_read))
		
		if (RV ~= rs232.RS232_ERR_NOERROR) then; ES = "F0503"..string.format("%02X",RV)..":" ; data = ""; return ES, data; end
		
		if (data_read == "") then; ES = "F050401:"; data = ""; return ES, data; end
		
		if (i == max_flush)  then; ES = "F050402:"; data = ""; return ES, data; end 
	
		if data_read == ":" then break end
	end
	--mc.mcCntlSetLastError(inst, "Colon Found, Starting Data Read")
	--read serial buffer and concatenate a string until a <cr> is found
	for i = 0,max_length,1 do --Flush the buffer until a colon is found, routine resumes here after timer expiration
		RV, data_read, size = p:read(1, timeout)
		if (RV ~= rs232.RS232_ERR_NOERROR) then; ES = "F0505"..string.format("%02X",RV)..":" ; data = ""; return ES, data; end
		
		if (data_read == nil or i == max_length) then; ES = "F050601:"; data = ""; return ES, data; end
		
		rString = rString..data_read
		if data_read == "\r" then break end
	end
	--mc.mcCntlSetLastError(inst, "Data Read Complete, Validating Checksum")
	--validate checksum
	RS, checkVerify = mcSerial.AppendChecksum(string.sub(rString, 1,-4))
	if (RS ~= "") then; ES = "F050701:"..RS ; return ES; end
	
	if (string.sub(rString, -3, -2) ~= string.sub(checkVerify,-3,-2)) then; ES = "F050801:"; data = ""; return ES, data; end
	--mc.mcCntlSetLastError(inst, "Checksum OK, Checking for Exceptions")
	
	--check if drive exception was received by checking if the received parameter code equals the transmitted parameter code + 0x800
	if (string.sub(rString,3,5) == string.format("%x",tonumber("0x800")+tonumber(string.sub(tString,4,6),16))) then; ES = "F050901:"; data = ""; return ES, data; end
	--mc.mcCntlSetLastError(inst, "No Exceptions, Verifying Sender")
	
	--check if address, parameter, and function match what was sent, if so return data, else return error
	if (string.sub(rString,1,6) == string.sub(tString,2,7)) then
		data = string.sub(rString,7,-4)
		--mc.mcCntlSetLastError(inst, "Sender Verified, Returning Data")
		return ES, data
	else; ES = "F050A01:"; data = ""; return ES, data; end
end

return mcSerial