"""Synthesizes a seamless 9.5 s fire-crackle loop (SL sound uploads max out at 10 s) for the fire pit.
Layers: a low breathy roar (filtered noise with slow swells), soft ticks, and a few sharp pops/snaps with short
resonant tails. Built circularly so the loop point is inaudible. Writes crackle.wav (44.1 kHz mono 16-bit).
Run with local/hear-venv python (numpy). Claude Opus 5.5 (Tessel), 2026-10-10."""
import wave
import numpy as np

SR = 44100
DUR = 9.5
N = int(SR * DUR)
rng = np.random.default_rng(23)


def circ_lowpass(x, cutoff_hz):
    """Brick-ish lowpass in the frequency domain; circular, so the loop stays seamless."""
    X = np.fft.rfft(x)
    f = np.fft.rfftfreq(len(x), 1 / SR)
    X *= 1 / (1 + (f / cutoff_hz) ** 4)
    return np.fft.irfft(X, len(x))


def circ_bandpass(x, lo, hi):
    X = np.fft.rfft(x)
    f = np.fft.rfftfreq(len(x), 1 / SR)
    X *= (1 / (1 + (lo / np.maximum(f, 1)) ** 4)) * (1 / (1 + (f / hi) ** 4))
    return np.fft.irfft(X, len(x))


def add_circ(buf, sig, start):
    idx = (start + np.arange(len(sig))) % len(buf)
    np.add.at(buf, idx, sig)


# roar: low rumble, swelling slowly (periodic envelope = whole cycles over the loop)
roar = circ_lowpass(rng.standard_normal(N), 350)
t = np.arange(N) / SR
swell = 0.75 + 0.15 * np.sin(2 * np.pi * 2 * t / DUR) + 0.1 * np.sin(2 * np.pi * 5 * t / DUR + 1.3)
roar *= swell
roar /= np.abs(roar).max()
hiss = circ_bandpass(rng.standard_normal(N), 2500, 9000)
hiss /= np.abs(hiss).max()

crack = np.zeros(N)


def pop(amp, length_ms, bright):
    n = int(SR * length_ms / 1000)
    env = np.exp(-np.linspace(0, 7 + 6 * rng.random(), n))
    s = rng.standard_normal(n) * env
    if bright < 1:
        s = np.convolve(s, np.ones(int(2 + 8 * (1 - bright))) / (2 + 8 * (1 - bright)), mode="same")
    # a tiny resonant body: wood splitting has a pitch
    f0 = rng.uniform(900, 3200)
    s += 0.35 * np.sin(2 * np.pi * f0 * np.arange(n) / SR) * env ** 2
    return amp * s


# soft ticks: many, clustered (fires crackle in bursts)
pos = 0
while pos < N:
    pos += int(rng.exponential(0.09) * SR)
    burst = rng.random() < 0.25
    for _ in range(rng.integers(2, 6) if burst else 1):
        add_circ(crack, pop(rng.uniform(0.05, 0.22), rng.uniform(3, 12), rng.uniform(0.3, 1)), pos % N)
        pos += int(rng.uniform(0.008, 0.04) * SR)
# loud snaps: a handful
for _ in range(9):
    add_circ(crack, pop(rng.uniform(0.45, 0.8), rng.uniform(15, 45), 1.0), int(rng.uniform(0, N)))

mix = 0.32 * roar + 0.05 * hiss + crack
mix /= np.abs(mix).max()
mix *= 0.85
pcm = (mix * 32767).astype(np.int16)
with wave.open("crackle.wav", "wb") as w:
    w.setnchannels(1)
    w.setsampwidth(2)
    w.setframerate(SR)
    w.writeframes(pcm.tobytes())
print(f"crackle.wav: {DUR}s, peak {np.abs(mix).max():.2f}")