#!/usr/bin/env python3
from PIL import Image
import sys
import struct
import zlib

if len(sys.argv) < 2:
    print('Usage png2toi image.png')
    sys.exit(1)

ifn = sys.argv[1]

if not ifn.endswith('.png'):
    print('Must provide PNG file')
    sys.exit(2)

im = Image.open(ifn)
w, h = im.size
print('Opened  %s ... %d x %d @ %s' % (ifn, w, h, im.mode))

if not im.mode == 'RGB':
    print('PNG file must use RGB mode')
    sys.exit(3)

pix = im.load()

ofn = '%s.toi' % ifn[:-4]
with open(ofn, 'wb') as f:
    f.write(bytes('TOIa', 'ascii'))
    f.write(struct.pack('>HH', w, h))
    data = bytes()
    for j in range(h):
        for i in range(w):
            r, g, b = pix[i, j]
            c = ((r & 0xF8) << 8) | ((g & 0xFC) << 3) | ((b & 0xF8) >> 3)
            data += struct.pack('>H', c)
    z = zlib.compressobj(level=9, wbits=10)
    zdata = z.compress(data) + z.flush()
    zdata = zdata[2:-4] # strip header and checksum
    f.write(zdata)

print('Written %s ... %d bytes' % (ofn, 4 + 4 + len(zdata)))