#!/usr/bin/env python3
#   ev-to-dicom
#   Copyright © 2023  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/>.

import msgpack

from collections import OrderedDict

def read_ev_tlv(data: bytes):
	"""Read an Enhanced Viewer tag-length-value image payload"""
	
	i = 0
	
	def read_u16():
		nonlocal i
		i += 2
		return (data[i - 2] << 8) | data[i - 1]
	
	def read_u32():
		nonlocal i
		i += 4
		return (data[i - 4] << 24) | (data[i - 3] << 16) | (data[i - 2] << 8) | data[i - 1]
	
	metadata = OrderedDict()
	pixel_data = None
	
	while i < len(data):
		typ = read_u16()
		if typ == 0x0101:
			length = read_u32()
			
			payload = msgpack.unpackb(data[i:i+length])
			metadata.update(payload)
			
			i += length
		elif typ == 0x0202:
			length = read_u32()
			
			payload = data[i:i+length]
			pixel_data = payload
			
			i += length
		else:
			raise Exception('Unknown type 0x{:04x}'.format(typ))
	
	return metadata, pixel_data