#!/usr/bin/env python3
"""Regression check for the display path (FINDINGS 22).

Compares a MAME snapshot of GVRAM against what the X68000's 15-bit+I palette
MUST produce for the same source frame. This is an exact test, not a threshold:
if the palette packing, the line stride, or the monitor-contrast setting drifts,
`exact` goes False. Do not soften it into a PSNR threshold -- the whole point of
FINDINGS 22 is that the render is bit-for-bit predictable.

  python3 tools/bench/verify_frame.py tmp/frame_ref.png tmp/snap_verify/x68000/0000.png
"""
import sys, numpy as np
from PIL import Image

ref_path = sys.argv[1] if len(sys.argv) > 1 else "tmp/frame_ref.png"
snap_path = sys.argv[2] if len(sys.argv) > 2 else "tmp/snap_verify/x68000/0000.png"

ref = np.asarray(Image.open(ref_path).convert("RGB")).astype(int)
snap = np.asarray(Image.open(snap_path).convert("RGB")).astype(int)
H, W = ref.shape[:2]
got = snap[0:H, 0:W]

# MAME x68k_v.cpp: GGGGGRRRRRBBBBBI, expanded via pal6bit((field << 1) | I)
pal6bit = lambda v: (v << 2) | (v >> 4)
pred = pal6bit(((ref >> 3) << 1) | 1)

exact = bool((pred == got).all())
mse = ((ref - got) ** 2).mean()
psnr = 99.0 if mse == 0 else 10 * np.log10(255 * 255 / mse)

print(f"exact match vs 15-bit+I prediction : {exact}")
print(f"display quantisation cost          : {psnr:.2f} dB  (expected 38.88 on 00020 f0001)")
if not exact:
    bad = np.argwhere((pred != got).any(axis=2))
    print(f"  {len(bad)} differing pixels; first at {tuple(bad[0])}"
          f" pred={tuple(pred[tuple(bad[0])])} got={tuple(got[tuple(bad[0])])}")
    print("  check: CRTC R20 bit 11 clear, R20 bits 9-8 = 0x0100, $E8E001 contrast = 15")
sys.exit(0 if exact else 1)