"""
Apollo PM Demodulator — extracts phase modulation from complex baseband.

The spacecraft transmitter phase-modulates a 76.25 MHz carrier at 0.133 rad
peak deviation (7.6 degrees). After frequency multiplication (×30) to 2287.5 MHz
and downconversion to complex baseband at the receiver, this block recovers the
composite modulating signal containing all subcarriers.

At 0.133 rad, the small-angle approximation holds (sin(0.133) ≈ 0.1327,
<0.3% error), so the demodulated output is essentially linear with the
modulating signal.

Signal chain: complex baseband → carrier PLL → phase extraction → float output

Reference: IMPLEMENTATION_SPEC.md section 2.3
"""

from gnuradio import analog, blocks, gr


class pm_demod(gr.hier_block2):
    """Phase modulation demodulator with carrier recovery.

    Inputs:
        complex baseband (e.g., from SDR or usb_signal_gen)

    Outputs:
        float — demodulated composite signal containing all subcarriers
    """

    def __init__(self, carrier_pll_bw: float = 0.02, sample_rate: float = 5_120_000):
        gr.hier_block2.__init__(
            self,
            "apollo_pm_demod",
            gr.io_signature(1, 1, gr.sizeof_gr_complex),
            gr.io_signature(1, 1, gr.sizeof_float),
        )

        # Carrier tracking PLL — locks to the residual carrier in the PM signal.
        # The PLL bandwidth needs to be narrow enough to track carrier drift
        # but wide enough for acquisition. 0.02 rad/sample is a good default
        # for the 5.12 MHz sample rate.
        #
        # PLL freq range: ±carrier_pll_bw * sample_rate / (2*pi) Hz
        max_freq = carrier_pll_bw * 2.0
        min_freq = -max_freq
        self.pll = analog.pll_carriertracking_cc(carrier_pll_bw, max_freq, min_freq)

        # Extract instantaneous phase: atan2(Im, Re)
        self.phase = blocks.complex_to_arg(1)

        # Connect: input → PLL → phase extraction → output
        self.connect(self, self.pll, self.phase, self)

    def get_carrier_pll_bw(self) -> float:
        return self.pll.get_loop_bandwidth()

    def set_carrier_pll_bw(self, bw: float):
        self.pll.set_loop_bandwidth(bw)