"""Brightness and colour of screenshots (U5.3), without external libraries.

Prints for each PNG (8-bit RGB/RGBA, every 4th pixel in both directions):
  luma   mean Rec. 709 luma of the sRGB values (0 black … 1 white)
  sat    mean HSV saturation
  green  share of pixels with a green hue (saturation > .15, hue 61°–162°)
  blue   share of pixels with a blue hue (saturation > .15, hue 180°–259°)
Usage: python3 tools/port/png_stats.py file.png [file.png …] [--crop x0 y0 x1 y1]
"""
import colorsys
import struct
import sys
import zlib


def read_png(path):
    data = open(path, 'rb').read()
    if data[:8] != b'\x89PNG\r\n\x1a\n':
        raise ValueError(path + ': not a PNG')
    pos, idat = 8, []
    while pos < len(data):
        length, kind = struct.unpack('>I4s', data[pos:pos + 8])
        body = data[pos + 8:pos + 8 + length]
        if kind == b'IHDR':
            width, height, depth, color, _, _, interlace = struct.unpack('>IIBBBBB', body)
        elif kind == b'IDAT':
            idat.append(body)
        pos += 12 + length
    if depth != 8 or interlace != 0 or color not in (2, 6):
        raise ValueError('%s: needs 8-bit RGB/RGBA without interlace' % path)
    bpp = 3 if color == 2 else 4
    raw = zlib.decompress(b''.join(idat))
    stride = width * bpp
    rows, prev, i = [], bytearray(stride), 0
    for _ in range(height):
        kind, line = raw[i], bytearray(raw[i + 1:i + 1 + stride])
        i += 1 + stride
        for x in range(stride):
            a = line[x - bpp] if x >= bpp else 0
            b = prev[x]
            c = prev[x - bpp] if x >= bpp else 0
            if kind == 1:
                line[x] = (line[x] + a) & 255
            elif kind == 2:
                line[x] = (line[x] + b) & 255
            elif kind == 3:
                line[x] = (line[x] + ((a + b) >> 1)) & 255
            elif kind == 4:
                p = a + b - c
                pa, pb, pc = abs(p - a), abs(p - b), abs(p - c)
                line[x] = (line[x] + (a if pa <= pb and pa <= pc else b if pb <= pc else c)) & 255
        rows.append(bytes(line))
        prev = line
    return width, height, bpp, rows


def stats(path, crop=None):
    width, height, bpp, rows = read_png(path)
    x0, y0, x1, y1 = crop if crop else (0, 0, width, height)
    luma = sat = green = blue = n = 0
    for y in range(y0, y1, 4):
        row = rows[y]
        for x in range(x0, x1, 4):
            r, g, b = row[x * bpp] / 255, row[x * bpp + 1] / 255, row[x * bpp + 2] / 255
            hue = colorsys.rgb_to_hls(r, g, b)[0]
            top = max(r, g, b)
            s = 0 if top == 0 else (top - min(r, g, b)) / top
            luma += 0.2126 * r + 0.7152 * g + 0.0722 * b
            sat += s
            n += 1
            if s > .15 and .17 < hue < .45:
                green += 1
            if s > .15 and .5 < hue < .72:
                blue += 1
    return luma / n, sat / n, green / n, blue / n


def main(argv):
    crop = None
    if '--crop' in argv:
        at = argv.index('--crop')
        crop = tuple(int(v) for v in argv[at + 1:at + 5])
        argv = argv[:at] + argv[at + 5:]
    for path in argv:
        luma, sat, green, blue = stats(path, crop)
        print('%-48s luma %.3f  sat %.3f  green %.2f  blue %.2f' % (path.split('/')[-1], luma, sat, green, blue))


if __name__ == '__main__':
    main(sys.argv[1:])