periphery = require('periphery')

Serial 	  = periphery.Serial

Scheduler = require('scheduler')

local T1				=   100  --300
local T2				=   2000 --1000
local T3		    	=   5000 --3000

local ASCII_EOT   		= "\x04"        -- end of transmission
local ASCII_ENQ   		= "\x05"        -- enquiary
local ASCII_ACK   		= "\x06"	    -- acknowledge
local ASCII_NAK   		= "\x15"	    -- negative acknowledge

local pending 			= false
local reading 			= false
local writing 			= false

local serial

local onProcessRequest;

-----------------------------------------------------------------------
local function hexDumpString(buf)
	if buf then
		for i=1,math.ceil(#buf/16) * 16 do
			if (i-1) % 16 == 0 then io.stderr:write(string.format('%06X  ', i-1)) end
			io.stderr:write( i > #buf and '   ' or string.format('%02X ', buf:byte(i)) )
			if i %  8 == 0 then io.stderr:write(' ') end
			if i % 16 == 0 then io.stderr:write( buf:sub(i-16+1, i):gsub('[^%g]','.'), '\n' ) end
		end
	io.stderr:write("\n");
	end
end
-----------------------------------------------------------------------

function begin(device, baud)
	serial 			 = Serial(device,baud)
	transactionTimer = Scheduler.Timer(T3)
end

local function discardInput() 
	hexDumpString(buf);
	io.stderr:write("SECS I:\t Discard input: ")
    while serial:poll(100) do
    	c = serial:read(1)
    	io.stderr:write(string.format('%02X ',c:byte(1)));
    end
    io.stderr:write("\n")
end

local function sendMsg(buf) 
  
--  hexDumpString(buf)
 	
 	writing = true 
    serial:write(ASCII_ENQ)
    
    if serial:poll(T1) then
    	c = serial:read(1)
    
		if c == ASCII_EOT then
	    	serial:write(string.char(#buf))
	
	    	local chksum = 0    -- 0 normal, 1 force error
	
	    	for i=1, #buf do
	        	serial:write(string.char(buf:byte(i)))
	        	chksum = chksum + buf:byte(i);
--          	io.stderr:write(string.format('%02X ',buf:byte(i)));
	    	end
	
	    	serial:write(string.char(math.floor(chksum / 256)))
	    	serial:write(string.char(chksum % 256))
			
			if serial:poll(T1) then
	    		c = serial:read(1)
	    		if not (c == ASCII_ACK) then
	        		io.stderr:write("SECS I:\t NAK Received\n")
	        		--discardInput()
	    		end
	    	else
	    		io.stderr:write("SECS I:\t AKN Timeout\n")
	    		discardInput()
	    	end
	    	writing = false
	    end
	else 
		io.stderr:write("SECS I:\t EOT Timeout\n")
		discardInput()
		writing = false
	end
	
end

local function receiveMsg()
    serial:write(ASCII_EOT)
    
    reading = true
    if serial:poll(T1) then
	    local cnt = string.byte(serial:read(1))
    	io.stderr:write("SECS I:\t receiveMsg count:  "..cnt.."\n")
		    
		local buf = serial:read(cnt+2,10*T1)
	    
		local chksum = 0    -- 0 normal, 1 force error
		for i=1,  #buf-2 do
			chksum = chksum + buf:byte(i)
		end
		
		local msgChksum = buf:byte(#buf-1)*256 + buf:byte(#buf) 
		
		if msgChksum == chksum then
			serial:write(ASCII_ACK)  
			return buf
		else
			io.stderr:write("SECS I:\t Checksum Error\n")
			hexDumpString(buf)
			serial:write(ASCII_NAK)  
			discardInput()
			--io.stderr:write(string.format("SECS I:\t Checksum: %04X %04X\n",chksum,msgChksum))
			io.stderr:write(string.format("SECS I:\t Bytes: %d Checksum: %04X %04X\n",#buf,chksum,msgChksum))
			return ""
		end
		reading = false
	else
	    io.stderr:write("SECS I:\t Countbyte Timeout\n")
	    discardInput()
	    reading = false
	    return ""
	end
end

local function poll()
	  
	if ( serial:poll(T1) ) then
	    c = serial:read(1)
--	    io.stderr:write(string.format("C: %02X\n",c:byte()));  
		if c == ASCII_ENQ then
			local buf=receiveMsg()
			if #buf >= 11 then 
		    	onProcessRequest(buf)
		    else
		    	io.stderr:write("SECS I:\t Poll error bytes: "..#buf.."\n")		    	
		    	discardInput(buf)
		    	serial:write(ASCII_NAK) 
		    end     
        elseif c == ASCII_NAK then
            io.stderr:write("SECS I:\t Poll NAK received\n")
            --discardInput()
            pending = false
        else
        	---- TODO: Illegal byte, skip input send NAK ----
            io.stderr:write(string.format("SECS I:\t Poll error byte = %02X\n",string.byte(c)))
            discardInput()
            serial:write(ASCII_NAK)  
            pending = false
		end
	else
		if pending and transactionTimer.elapsed() then
			---- TODO: Timeout, skip input send NAK ----
			io.stderr:write("SECS I:\t Poll transaction timeout\n")
			discardInput(buf)
			serial:write(ASCII_NAK)
	    	pending = false;
		end
	end
	
	io.stderr:flush();
end

return {
	begin				= begin;
	poll				= poll;
	sendMsg				= sendMsg;
	receiveMsg			= receiveMsg;
	isReading			= function()   	return reading 								end;
	isWriting			= function()   	return writing 								end;
	isPending			= function()   	return pending 								end;
	onProcessRequest	= function(cb) 	onProcessRequest = cb 						end;
	startTransaction	= function() 	transactionTimer.restart(); pending = true 	end;
	stopTransaction		= function() 	pending = false 							end;
}