# template tile for Lab #7, Task #5
import numpy
import waveforms as w
import lab7

# transmission rate
bits_per_second = 20000

# Uses lab7.sync to determine if message received correctly
# return None if received message does *not* contain lab7.sync
def am_receive(samples,fc,samples_per_bit,channel_bw):
    #### your code here
    return None

if __name__ == '__main__':
    # a random binary message with zeros at both ends to
    # ensure periodicity
    message_size = 30
    message = numpy.zeros(message_size+2,dtype=numpy.int)
    message[1:-1] = numpy.random.randint(2,size=message_size)

    # message with sync
    message = lab7.sync + list(message)
    
    # send it through transmitter, modulate to legal freq near 125 kHz
    samples_per_bit = lab7.samples_per_bit(lab7.sample_rate,
                                           bits_per_second)
    fc = lab7.quantize_frequency(500e3,lab7.sample_rate,
                                 len(message)*samples_per_bit)
    xmit_out = lab7.am_transmit(message,samples_per_bit,lab7.sample_rate,
                           fc,lab7.channel_bw)

    #######################################################
    ## ADDED FOR TASK #5: try different transmission delays
    #######################################################
    for delay in xrange(8):
        print "%d-sample delay:" % delay
        delayed_xmit_out = xmit_out.delay(nsamples=delay)
        delayed_xmit_out = delayed_xmit_out.noise(amplitude=0.1)
        
        # run receiver
        received = am_receive(delayed_xmit_out,fc,
                              samples_per_bit,lab7.channel_bw)

        # report results
        print '    message: ',message
        print '    received:',received
        if not numpy.array_equal(message,received):
            print '    => differences'
        else:
            print '    => message received okay'

    # when ready for checkoff, enable the following line.
    #lab7.checkoff(am_receive,'L7_5')