"""
Apollo BPSK Subcarrier Modulator -- NRZ data onto 1.024 MHz subcarrier.

The transmit-side counterpart to bpsk_subcarrier_demod. Takes an NRZ baseband
waveform (+1/-1) and modulates it onto a 1.024 MHz cosine subcarrier via
simple multiplication: output(t) = nrz(t) * cos(2*pi*f_sc*t).

This is Bi-Phase Shift Keying (BPSK): the cosine phase flips 180 degrees
when the NRZ data changes sign.

On the real spacecraft, a 33522B AWG (or equivalent) generates this
BPSK-modulated subcarrier before summing with the voice subcarrier.

Reference: IMPLEMENTATION_SPEC.md section 4.2
"""

from gnuradio import analog, blocks, gr

from apollo.constants import PCM_SUBCARRIER_HZ, SAMPLE_RATE_BASEBAND


class bpsk_subcarrier_mod(gr.hier_block2):
    """BPSK modulator: NRZ float input -> BPSK subcarrier float output."""

    def __init__(
        self,
        subcarrier_freq: float = PCM_SUBCARRIER_HZ,
        sample_rate: float = SAMPLE_RATE_BASEBAND,
    ):
        gr.hier_block2.__init__(
            self,
            "apollo_bpsk_subcarrier_mod",
            gr.io_signature(1, 1, gr.sizeof_float),
            gr.io_signature(1, 1, gr.sizeof_float),
        )

        self._subcarrier_freq = subcarrier_freq
        self._sample_rate = sample_rate

        # 1.024 MHz cosine subcarrier (continuous phase, maintained by sig_source)
        self.carrier = analog.sig_source_f(
            sample_rate, analog.GR_COS_WAVE, subcarrier_freq, 1.0, 0,
        )

        # Multiply NRZ data by subcarrier
        self.mixer = blocks.multiply_ff(1)

        # Connect: input (NRZ) -> mixer port 0, carrier -> mixer port 1 -> output
        self.connect(self, (self.mixer, 0))
        self.connect(self.carrier, (self.mixer, 1))
        self.connect(self.mixer, self)

    @property
    def subcarrier_freq(self) -> float:
        return self._subcarrier_freq

    @property
    def sample_rate(self) -> float:
        return self._sample_rate