'''Convert an arbitrary frequency in the AM broadcast band to the frequency
of the nearest radio station frequency.

Mike Markowski, mike.ab3ap@gmail.com
Feb 2021
'''

import numpy as np
from gnuradio import gr
import pmt

class snapBlock(gr.basic_block):

	def __init__(self):
		gr.basic_block.__init__(
			self,
			name="Snap to Station",
			in_sig=None,
			out_sig=None)

		# User input that is only somewhere near a station frequency.
		self.message_port_register_in(pmt.intern('raw_Hz_in'))
		self.set_msg_handler(pmt.intern('raw_Hz_in'), self.stationSnap)

		# Output in Hz and kHz that is exactly a station frequency.
		self.message_port_register_out(pmt.intern('snapped_Hz_out'))
		self.message_port_register_out(pmt.intern('snapped_kHz_out'))

	def stationSnap(self, msg):

		'''Accept a pmt pair with user selected frequency information and
		adjust it to the nearest broadcast AM frequency.

		Inputs:
		  msg (dictionary) : assumed to contain only: (freq . <float>)

		Outputs:
		  freq_Hz_out (pmt.dict) : (freq . snappedFreq) where snappedFreq
		    is input frequency in Hz moved to nearest broadcast frequency.
		  freq_kHz_out (pmt.dict) : (freq . snappedFreq) where snappedFreq
		    is input frequency in kHz moved to nearest broadcast frequency.
		'''

		# Disassemble pmt pair.
		cmd = pmt.car(msg)
		freq = pmt.cdr(msg)
		freqRaw_kHz = pmt.to_python(freq) / 1e3 # Easier to work in kHz.

		# Snap user-clicked freq to nearest AM station.
		spacing = 10 # N. American broadcast AM spacing in kHz.
		freq_kHz = float(round(freqRaw_kHz / spacing) * spacing)
		freq_Hz = freq_kHz * 1e3

		# Generate output message, (freq . freq_Hz).
		pair = pmt.cons(cmd, pmt.to_pmt(freq_Hz))
		self.message_port_pub(pmt.intern('snapped_Hz_out'), pair)

		# Generate output message, (freq . freq_kHz).
		pair2 = pmt.cons(cmd, pmt.to_pmt(freq_kHz))
		self.message_port_pub(pmt.intern('snapped_kHz_out'), pair2)