#   pdf-segmented: Generate PDFs using separate compression for foreground and background
#   Copyright (C) 2025  Lee Yingtong Li
#
#   This program is free software: you can redistribute it and/or modify
#   it under the terms of the GNU Affero General Public License as published by
#   the Free Software Foundation, either version 3 of the License, or
#   (at your option) any later version.
#
#   This program is distributed in the hope that it will be useful,
#   but WITHOUT ANY WARRANTY; without even the implied warranty of
#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#   GNU Affero General Public License for more details.
#
#   You should have received a copy of the GNU Affero General Public License
#   along with this program.  If not, see <https://www.gnu.org/licenses/>.

from . import CompressedLayer

from PIL import Image

from dataclasses import dataclass
import io
import struct

@dataclass
class PNGLayer(CompressedLayer):
	data: bytes
	
	def get_flate_data(self):
		# Parse PNG data to get the IDAT chunks
		bytesio = io.BytesIO(self.data)
		bytesio.read(8)  # Read PNG header
		
		flate_data = bytearray()
		
		while True:
			# Read PNG chunks
			length_bytes = bytesio.read(4)
			if length_bytes == b'':  # EOF
				break
			length = struct.unpack('>I', length_bytes)[0]
			cid = bytesio.read(4)
			data = bytesio.read(length)
			crc = bytesio.read(4)
			
			# IDAT chunk contains DEFLATE data
			if cid == b'IDAT':
				flate_data.extend(data)
		
		return bytes(flate_data)

def png_compress_layer(layer: Image, is_foreground: bool) -> PNGLayer:
	if is_foreground:
		# Foreground is 1bpp
		layer = layer.convert('1')
	
	# Save image to PNG
	bytesio = io.BytesIO()
	layer.save(bytesio, format='png', optimize=True)
	
	return PNGLayer(data=bytesio.getvalue())