# Read from Arduino's serial interface.
# Requires pySerial (http://pyserial.sourceforge.net/)
# David Elworthy, January 2 2015. http://www.friendlymoose.com/.

import serial
import struct
import time

PORT='COM5'
TIMEOUT=1

class SerialFetcher:
    OK = 0
    CHECKSUM_ERROR = 1

    def __init__(self, port=PORT, timeout=TIMEOUT):
        self.serial_port = None
        self.port = port
        self.timeout = timeout

    def WaitForPort(self):
        """Wait until serial port connects, if necessary."""
        # The dtr settings prevent the initial serial connection from resetting the Arduino.
        if self.serial_port == None or not self.serial_port.isOpen():
            # print "Wait for port"
            while True:
                try:
                    self.serial_port = serial.Serial(port=self.port, baudrate=9600, timeout=self.timeout, dsrdtr=True)
                except serial.serialutil.SerialException:
                    self.serial_port = None
                if self.serial_port:
                    self.serial_port.setDTR(False)
                    # print "Port ready"
                    return

    def GetFromPort(self):
        """Get all the data that is available on the serial port (blocking)."""
        self.WaitForPort()

        # Read value, expected to be the size
        buffer = self.serial_port.read(1)
        if len(buffer) != 1:
            # Bad size field
            return None
        size = struct.unpack("B", buffer)[0]
        print "Size %s" % size

        # Read the checksum
        buffer = self.serial_port.read(1)
        if len(buffer) != 1:
            return None
        expected_checksum = struct.unpack('B', buffer)[0]

        # Read the data
        data = self.serial_port.read(size)
        actual_checksum = 0
        for b in data:
            actual_checksum += ord(b)
        actual_checksum = actual_checksum % 256
        #print "Check expected %s actual %s" % (expected_checksum, actual_checksum)

        # Send the response
        if expected_checksum == actual_checksum:
            self.serial_port.write([SerialFetcher.OK, actual_checksum])
        else:
            print "Check expected %s actual %s" % (expected_checksum, actual_checksum)
            self.serial_port.write([SerialFetcher.CHECKSUM_ERROR, actual_checksum])
            data = []

        self.serial_port.close()
        return data


fetcher = SerialFetcher()
s = struct.Struct('hhh')
try:
    while True:
        data = fetcher.GetFromPort()
        if data:
            print "Data:"
            datalen = len(data)
            offset = 0
            while offset < datalen:
                values = s.unpack_from(data, offset)
                offset += s.size
                print " %s" % repr(values)
except KeyboardInterrupt:
    if fetcher != None and fetcher.serial_port != None:
        fetcher.serial_port.close()
    print "Done"