"""Shared constants for the golden .sras fixtures.

These mirror the values tests/gen_goldens.py used when the fixtures were
generated against the pre-refactor code (commit d185676); they must never
change, or the byte-identical comparisons stop meaning anything.
"""
SPF = 8
SAMPLE_RATE = 6.25e9
CHANNELS = [1, 3, 4]
PREAMBLES = [f"WFMOUTPRE:CH{ch};SYNTHETIC;PT_FMT Y;XINCR 1.6E-10" for ch in CHANNELS]
BACKGROUND = bytes(range(SPF))

# build_plan inputs for the fixture geometry: 2 angles × 3 rows × 4 frames
TINY_PLAN_ARGS = dict(x_start=1.0, y_start=1.0, x_delta=0.02, y_delta=0.02,
                      num_angles=2, row_spacing=0.01)
LASER_FREQ_HZ = 20000.0
VELOCITY_MM_S = 100.0


def synthetic_frame(ai, ri, ci, fi):
    return bytes((ai * 7 + ri * 5 + ci * 3 + fi + s) % 256 for s in range(SPF))