# lab1_2.py -- template for your Task #2 design file
import numpy
import matplotlib
import matplotlib.pyplot as p
import lab1

matplotlib.interactive(True)

def v_samples_to_d_samples(samples):
    """
    Convert an array of voltage samples into an array of
    digitized samples.
    """
    pass  # replace this with your commented code

def find_center_of_start_bit(d_samples,start,samples_per_bit):
    """
    Starting at d_samples[start] find the middle of the next
    START bit returning -1 if no start bit is found.
    """
    pass  # replace this with your commented code

def decode_data(d_samples,start,nbits,samples_per_bit):
    """
    Select specific data bits from digitized samples:
      start is the index of the first selected bit
      nbits is the number of bits to select
      samples_per_bit is the interval between selections
    Return selected bits as a list or array.
    """
    pass  # replace this with your commented code

def receive(samples):
    """
    Convert an array of voltage samples into a message string.
    """
    # digitize the voltage samples
    d_samples = v_samples_to_d_samples(samples)
    nsamples = len(d_samples)

    # search through the samples starting at the beginning
    message = []
    start = 0
    while True:
        # locate sample at middle of next START bit
        start = find_center_of_start_bit(d_samples,start,8)
        if start < 0 or start + 10*8 >= nsamples:
            break  # no START bit found or too near end of samples

        # grab the eight data bits which follow
        bits = decode_data(d_samples,start+8,8,8)

        # first convert bit sequence to an int
        # and then to a character, append to message
        message.append(chr(lab1.bits_to_int(bits)))

        # finally skip to the middle of the STOP bit
        # and start looking for the next START bit
        start += 9*8

    # join all the message characters into a single string
    return "".join(message)

# testing code.  Do it this way so we can import this file
# and use its functions without also running the test code.
if __name__ == '__main__':
    # see if we can decode the message
    lab1.task2_test(receive,'hi there')