"""Pixel-diff two screenshot dirs (matching filenames). Usage:
python3 audit/appshell_pixdiff.py DIR_A DIR_B [label_a label_b]
Prints per-file diff pixel counts + max channel delta; PIXDIFF-ZERO if every shared
file matches bit-for-bit. Also flags size mismatches."""
import os, sys
from PIL import Image, ImageChops

A, B = sys.argv[1], sys.argv[2]
la, lb = (sys.argv[3:5] or ['A', 'B'])
fa = sorted(f for f in os.listdir(A) if f.endswith('.png'))
fb = sorted(f for f in os.listdir(B) if f.endswith('.png'))
missing = set(fa) - set(fb)
if missing:
    print('FILES MISSING IN', lb, ':', sorted(missing))
zero, n = True, 0
for f in fa:
    if f not in fb:
        continue
    n += 1
    ia, ib = Image.open(os.path.join(A, f)), Image.open(os.path.join(B, f))
    if ia.size != ib.size:
        print(f'{f}: SIZE DIFF {ia.size} vs {ib.size}')
        zero = False
        continue
    d = ImageChops.difference(ia.convert('RGB'), ib.convert('RGB'))
    bbox = d.getbbox()
    if bbox is None:
        print(f'{f}: 0 px diff (identical)')
    else:
        hist = d.convert('L').histogram()
        ndiff = sum(hist[1:])
        mx = max(i for i, c in enumerate(hist) if c)
        pct = ndiff / (ia.size[0] * ia.size[1]) * 100
        print(f'{f}: {ndiff} px diff ({pct:.4f}%), bbox {bbox}, maxdelta {mx}')
        zero = False
if n == 0:
    print('no shared files!')
    zero = False
print('PIXTDIFF-ZERO' if zero else 'PIXTDIFF-NONZERO')
sys.exit(0 if zero else 1)