'''
PicoBoardReader module for reading values from the PicoBoard.

PicoBoard Web site: http://www.picocricket.com/picoboard.html

>>> sbr = PicoBoardReader()
>>> vals = sbr.getValues()
>>> sbr.displayValues(vals, skipChannels=(CH_SOUND,CH_LIGHT))
         Button: 1023
       Firmware: 4
   Resistance-A: 1023
   Resistance-B: 1023
   Resistance-C: 1023
   Resistance-D: 1023
         Slider: 1023
>>> sbr.close()
'''
__author__ = 'daveb@davebsoft.com (Dave Briccetti)'
 
import time
import serial # pySerial: http://pyserial.sourceforge.net

MAC_DEVICE = '/dev/cu.usbserial'
DATA_RATE = 38400
NUM_CHANNELS = 9
BYTES_PER_CHANNEL = 2
SEND_VALUES_CODE = chr(1)
PRESSED = 0 # Value for button pressed

CH_RESIST_A, CH_RESIST_B, CH_RESIST_C, CH_RESIST_D = 4, 2, 1, 0 
CH_BUTTON = 3
CH_LIGHT = 5
CH_SOUND = 6
CH_SLIDER = 7
CH_FIRMWARE = 15

CH_DESC = ('Resistance-D', 'Resistance-C', 'Resistance-B', 'Button', 
           'Resistance-A', 'Light', 'Sound', 'Slider', 
           '', '', '', '', '', '', '', 'Firmware')

class PicoBoardReader(object):
    '''Provide access to a PicoBoard.'''
    
    def __init__(self, device=MAC_DEVICE):
        self.ser = serial.Serial(device, DATA_RATE)
        self.oldVals = {}

    def close(self):
        '''Close the serial object.'''
        self.ser.close()
        
    def getValues(self, changesOnly=False):
        '''Return a dictionary of channel -> data mappings.
        
        If changesOnly is True, only include the channels with 
        changes since the last call.'''
        
        vals = {}
        self.ser.write(SEND_VALUES_CODE)    # Ask the Pico Board for its values
        resp = self.ser.read(NUM_CHANNELS * BYTES_PER_CHANNEL)  # Read the values
        for n in range(0, len(resp), BYTES_PER_CHANNEL):    # Process data for each channel
            chan, data = self._extractFields(ord(resp[n]), ord(resp[n+1]))
            vals[chan] = data
            
        result = PicoBoardReader.getChangedValues(self.oldVals, vals) \
            if changesOnly else vals
        self.oldVals = vals
        return result

    def _extractFields(self, hi, lo):
        '''Given the high- and low-order bytes of a channel's data, return the channel and data.'''
        chan = (hi & 0x78) >> 3         # Bits 6-3 in high-order byte
        datahigh = hi & 7               # Bits 2-0 in high-order byte
        datalow = lo & 0x7f             # Mask out the high-order bit (even though it's always 0)
        data = datahigh << 7 | datalow  # Join the 3 data bits from the high-order byte with the
                                        # 7 bits from the low-order byte 
        return chan, data
    
    @staticmethod
    def displayValues(vals, skipChannels=()):
        '''Display values for all the channels, sorted by channel description.
        
        skipChannels is a tuple of channels IDs to skip.'''
        
        for chanDesc, data in sorted([(CH_DESC[chan], data) for chan, data in vals.iteritems() if chan not in skipChannels]):
            print '%15s: %d' % (chanDesc, data)
            
    @staticmethod
    def getChangedValues(oldVals, newVals):
        '''Return a dictionary of the values in newVals not in oldVals.'''
        setOld = set(oldVals.iteritems())
        setNew = set(newVals.iteritems())
        return dict(setNew.difference(setOld))

def monitor():
    '''Poll periodically and show changes.'''
    sbr = PicoBoardReader()
    for n in range(10):
        vals = sbr.getValues(changesOnly=True)
        sbr.displayValues(vals, skipChannels=(CH_SOUND,CH_LIGHT))
        time.sleep(1)
    sbr.close()
    
if __name__ == '__main__':
    import doctest
    doctest.testmod()