#!/usr/bin/env python3
"""
Apollo Test Signal Generator Demo — pure Python, no GNU Radio needed.

Generates synthetic USB baseband signals and analyzes them spectrally.
Useful for verifying the signal generator and understanding the signal structure.

Usage:
    uv run python examples/test_signal_gen_demo.py
"""

import numpy as np

from apollo.constants import (
    PCM_HIGH_BIT_RATE,
    PCM_HIGH_WORDS_PER_FRAME,
    PCM_SUBCARRIER_HZ,
    PCM_WORD_LENGTH,
    SAMPLE_RATE_BASEBAND,
    VOICE_SUBCARRIER_HZ,
)
from apollo.usb_signal_gen import generate_usb_baseband


def main():
    print("Apollo USB Signal Generator Demo")
    print("=" * 50)

    # Generate a clean signal (no noise)
    print("\n1. Clean PCM-only signal (3 frames):")
    signal, bits = generate_usb_baseband(frames=3, snr_db=None)
    frame_bits = PCM_HIGH_WORDS_PER_FRAME * PCM_WORD_LENGTH
    expected_samples = 3 * int(frame_bits * SAMPLE_RATE_BASEBAND / PCM_HIGH_BIT_RATE)
    print(f"   Samples: {len(signal)} (expected {expected_samples})")
    print(f"   Duration: {len(signal)/SAMPLE_RATE_BASEBAND*1000:.1f} ms")
    print(f"   Envelope std: {np.std(np.abs(signal)):.4f} (PM = near-constant)")

    # Analyze spectrum
    print("\n2. Spectral analysis:")
    fft = np.fft.fft(signal[:50000])
    freqs = np.fft.fftfreq(50000, 1.0 / SAMPLE_RATE_BASEBAND)
    power = np.abs(fft) ** 2

    # Check PCM subcarrier band
    pcm_mask = (np.abs(freqs) > 950_000) & (np.abs(freqs) < 1_100_000)
    pcm_power = np.mean(power[pcm_mask])
    total_power = np.mean(power)
    print(f"   PCM band (950-1100 kHz): {10*np.log10(pcm_power/total_power):.1f} dB re total")

    # Generate with voice
    print("\n3. Signal with voice subcarrier:")
    signal_v, _ = generate_usb_baseband(frames=3, voice_enabled=True, snr_db=None)
    fft_v = np.fft.fft(signal_v[:50000])
    voice_mask = (np.abs(freqs) > 1_200_000) & (np.abs(freqs) < 1_300_000)
    voice_power = np.mean(np.abs(fft_v[voice_mask]) ** 2)
    print(f"   Voice band (1.2-1.3 MHz): {10*np.log10(voice_power/total_power):.1f} dB re total")

    # Generate with noise
    print("\n4. Signal with 20 dB SNR noise:")
    signal_n, _ = generate_usb_baseband(frames=3, snr_db=20.0)
    print(f"   Envelope std: {np.std(np.abs(signal_n)):.4f} (noisy = higher variance)")

    print("\nKey frequencies:")
    print(f"   Sample rate:       {SAMPLE_RATE_BASEBAND/1e6:.2f} MHz")
    print(f"   PCM subcarrier:    {PCM_SUBCARRIER_HZ/1e6:.3f} MHz")
    print(f"   Voice subcarrier:  {VOICE_SUBCARRIER_HZ/1e6:.3f} MHz")
    print(f"   PCM bit rate:      {PCM_HIGH_BIT_RATE/1000:.1f} kbps")


if __name__ == "__main__":
    main()