#!/usr/bin/env python3
"""Compara o pixel medio de dois PNGs (palette grossa, suficiente p/ conferir se o icns e o mesmo desenho)."""
import struct
import sys
import zlib


def read_png(path):
    d = open(path, 'rb').read()
    assert d[:8] == b'\x89PNG\r\n\x1a\n', f'nao e PNG: {path}'
    pos, w, h = 8, None, None
    idat = b''
    while pos < len(d):
        ln = struct.unpack('>I', d[pos:pos+4])[0]
        typ = d[pos+4:pos+8]
        data = d[pos+8:pos+8+ln]
        if typ == b'IHDR':
            w, h = struct.unpack('>II', data[:8])
        elif typ == b'IDAT':
            idat += data
        pos += 12 + ln
        if typ == b'IEND':
            break
    raw = zlib.decompress(idat)
    assert w is not None
    stride = w * 4 + 1
    prev = bytearray(w * 4)
    out = bytearray()
    for y in range(h):
        row = bytearray(raw[y*stride:(y+1)*stride])
        f = row[0]
        line = bytearray(row[1:])
        for x in range(w):
            for k in range(4):
                i = x * 4 + k
                a = line[i-4] if x > 0 and k < 3 else 0  # aprox: usa vizinho p/ filtros
                b = prev[i]
                c = line[i-4] if x > 0 else 0
                if f == 1:
                    v = (line[i] + (line[i-4] if x > 0 else 0)) & 255
                elif f == 2:
                    v = (line[i] + prev[i]) & 255
                elif f == 3:
                    v = (line[i] + ((a + b) >> 1)) & 255
                elif f == 4:
                    p = a + b - c
                    pa, pb, pc = abs(p-a), abs(p-b), abs(p-c)
                    pr = a if (pa <= pb and pa <= pc) else (b if pb <= pc else c)
                    v = (line[i] + pr) & 255
                else:
                    v = line[i]
                line[i] = v
        out += line
        prev = line
    return w, h, out


def average(path):
    w, h, px = read_png(path)
    n = w * h
    r = sum(px[i] for i in range(0, len(px), 4)) // n
    g = sum(px[i] for i in range(1, len(px), 4)) // n
    b = sum(px[i] for i in range(2, len(px), 4)) // n
    opaque = sum(1 for i in range(3, len(px), 4) if px[i] > 200) * 100 // n
    return w, h, r, g, b, f'{opaque}% opaco'


def main():
    icns_png = sys.argv[1]   # 1024 extraido do .icns
    orig_png = sys.argv[2]   # PNG original do usuario
    a = average(icns_png)
    b = average(orig_png)
    print(f'icns 1024 -> {a}')
    print(f'original  -> {b}')
    # Mesmo desenho se cores medias proximas e ambos coloridos/transparentes com padrao similar
    close = abs(a[2]-b[2]) <= 24 and abs(a[3]-b[3]) <= 24 and abs(a[4]-b[4]) <= 24
    print('MATCH (mesmo desenho)' if close else 'DIFF — verificar manualmente')
    sys.exit(0 if close else 1)


if __name__ == '__main__':
    main()