#   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 InputPages
from ..util import assert_has_imagemagick

from PIL import Image

import io
import subprocess
import sys
from typing import Generator, List

def xcf_get_pages(input_file: str) -> InputPages:
	# Check ImageMagick support
	assert_has_imagemagick('XCF support requires ImageMagick')
	
	# Init metadata
	num_layers = 0
	dpi = None
	width = None
	height = None
	
	# Read metadata
	proc = subprocess.run(['magick', 'identify', '-verbose', input_file], capture_output=True, encoding='utf-8', check=True)
	for line in proc.stdout.splitlines():
		if line == 'Image:':
			num_layers += 1
		elif line.startswith('  Geometry: '):
			layer_width = float(line[len('  Geometry: '):line.index('x')])
			layer_height = float(line[line.index('x')+1:line.index('+')])
			if (width is not None and layer_width != width) or (height is not None and layer_height != height):
				print('Error: Image with variable-dimension layers is not supported ({}x{} vs {}x{})'.format(layer_width, layer_height, width, height))
				sys.exit(1)
			width = layer_width
			height = layer_height
		elif line.startswith('  Resolution: '):
			resolution_x = float(line[len('  Resolution: '):line.index('x')])
			resolution_y = float(line[line.index('x')+1:])
			if resolution_x != resolution_y:
				raise Exception('Unexpected non-square DPI ({}x{})'.format(resolution_x, resolution_y))
			if dpi is not None and resolution_x != dpi:
				raise Exception('Unexpected variable DPI image ({} vs {})'.format(resolution_x, dpi))
			dpi = resolution_x
		elif line.startswith('  Units: '):
			if line != '  Units: PixelsPerInch':
				raise Exception('Unexpected Units (expected PixelsPerInch, got {})'.format(line[len('  Units: '):]))
	
	if num_layers == 0:
		raise Exception('Unexpected 0 layers')
	if dpi is None:
		raise Exception('Unexpected no DPI information')
	if width is None:
		raise Exception('Unexpected no width information')
	if height is None:
		raise Exception('Unexpected no height information')
	
	return InputPages(
		file_name=input_file,
		num_pages=num_layers,
		width=width,
		height=height,
		dpi=dpi,
		pages=_do_get_pages(input_file, num_layers)
	)

def _do_get_pages(input_file: str, num_layers: int) -> Generator[Image]:
	for layer_num in range(num_layers):
		# Extract layer as PNG (to proc.stdout)
		proc = subprocess.run(['magick', '{}[{}]'.format(input_file, layer_num), 'png:-'], capture_output=True)
		
		if proc.returncode != 0:
			raise Exception('ImageMagick error')
		
		# Read into PIL Image
		png_data = io.BytesIO(proc.stdout)
		image = Image.open(png_data)
		
		yield image