'''Convert an arbitrary frequency in the FM 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 MHz that is exactly a station frequency.
		self.message_port_register_out(pmt.intern('snapped_Hz_out'))
		self.message_port_register_out(pmt.intern('snapped_MHz_out'))

	def stationSnap(self, msg):

		'''Accept a pmt pair with user selected frequency information and
		adjust it to the nearest broadcast FM 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_MHz_out (pmt.dict) : (freq . snappedFreq) where snappedFreq
		    is input frequency in MHz moved to nearest broadcast frequency.
		'''

		# Disassemble pmt pair.
		cmd = pmt.car(msg)
		freq = pmt.cdr(msg)
		freqRaw_MHz = pmt.to_python(freq) / 1e6 # Easier to work in MHz.

		# Snap user-clicked freq to nearest FM station.
		spacing = 0.2 # N. American broadcast FM spacing in MHz.
		nearest = 0.1 # Round to nearest odd tenth of MHz.
		freq_MHz = nearest + round((freqRaw_MHz - nearest)/spacing) * spacing
		freq_Hz = freq_MHz * 1e6

		# 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_MHz).
		pair = pmt.cons(cmd, pmt.to_pmt(freq_MHz))
		self.message_port_pub(pmt.intern('snapped_MHz_out'), pair)