#   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 .input import InputPages

import numpy
from PIL import Image

from dataclasses import dataclass
from typing import Generator, List

@dataclass
class SegmentedPage:
	fg: Image
	bg: Image

def segment_pages(input_pages: InputPages) -> Generator[SegmentedPage]:
	for page_num, input_page in enumerate(input_pages.pages):
		print('Page {} of {}'.format(page_num + 1, input_pages.num_pages))
		
		yield segment_page(input_page)

def segment_page(input_page: Image) -> SegmentedPage:
	# Segment the input page into foreground and background
	
	# Convert image to foreground/background
	image_rgb = input_page.convert('RGB')
	numpy_rgb = numpy.asarray(image_rgb)
	
	# Precompute black and white pixels
	black_pixels = (numpy_rgb[:,:,0] == 0) & (numpy_rgb[:,:,1] == 0) & (numpy_rgb[:,:,2] == 0)
	white_pixels = (numpy_rgb[:,:,0] == 255) & (numpy_rgb[:,:,1] == 255) & (numpy_rgb[:,:,2] == 255)
	black_or_white = black_pixels | white_pixels
	
	# Precompute pixels with all neighbours either black or white
	bw1 = numpy.roll(black_or_white, (1, 1), (0, 1))
	bw1[0,:] = True
	bw1[:,0] = True
	bw2 = numpy.roll(black_or_white, (1, 0), (0, 1))
	bw2[0,:] = True
	bw3 = numpy.roll(black_or_white, (1, -1), (0, 1))
	bw3[0,:] = True
	bw3[:,-1] = True
	bw4 = numpy.roll(black_or_white, (0, -1), (0, 1))
	bw4[:,-1] = True
	bw5 = numpy.roll(black_or_white, (-1, -1), (0, 1))
	bw5[-1,:] = True
	bw5[:,-1] = True
	bw6 = numpy.roll(black_or_white, (-1, 0), (0, 1))
	bw6[-1,:] = True
	bw7 = numpy.roll(black_or_white, (-1, 1), (0, 1))
	bw7[-1,:] = True
	bw7[:,0] = True
	bw8 = numpy.roll(black_or_white, (0, 1), (0, 1))
	bw8[:,0] = True
	bw_neighbours = bw1 & bw2 & bw3 & bw4 & bw5 & bw6 & bw7 & bw8
	
	# Foreground is only black pixels with all neighbours either black or white
	fg_pixels = black_pixels & bw_neighbours
	
	# Foreground - white out all non-foreground pixels
	numpy_fg = numpy_rgb.copy()
	numpy_fg[~fg_pixels,:] = [255, 255, 255]
	image_fg = Image.fromarray(numpy_fg, image_rgb.mode)
	
	# Background - white out all foreground pixels
	numpy_bg = numpy_rgb.copy()
	numpy_bg[fg_pixels,:] = [255, 255, 255]
	image_bg = Image.fromarray(numpy_bg, image_rgb.mode)
	
	# TODO: Handle case where empty background or foreground
	
	return SegmentedPage(fg=image_fg, bg=image_bg)