# Copyright 2021 The Android Open Source Project
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#
import struct


class PackedStruct(object):
    """Class representing a C style packed structure

    Derived classes need to provide a dictionary with key will be the attributes and the values are
    the format characters for each field. e.g.

    class Foo(PackedStruct):
        _FIELDS = {
            x: 'I',
            name: '64s',
        }

    In this case Foo.x will represent an "unsigned int" C value, while Foo.name will be a "char[64]"
    C value

    """

    def __init__(self, *args, **kwargs):
        self._fmt = '<' + ''.join(fmt for fmt in self._FIELDS.values())
        for name in self._FIELDS:
            setattr(self, name, None)

        for name, val in zip(self._FIELDS.keys(), args):
            setattr(self, name, val)
        for name, val in kwargs.items():
            setattr(self, name, val)

    def __repr__(self):
        return '{} {{\n'.format(self.__class__.__name__) + ',\n'.join(
            '    {!r}: {!r}'.format(k, getattr(self, k)) for k in self._FIELDS) + '\n}'

    def __str__(self):
        return struct.pack(self._fmt, *(getattr(self, x) for x in self._FIELDS))

    def __bytes__(self):
        return struct.pack(self._fmt, *(getattr(self, x) for x in self._FIELDS))

    def __len__(self):
        return struct.calcsize(self._fmt)

    @classmethod
    def from_bytes(cls, data):
        fmt_str = '<' + ''.join(fmt for fmt in cls._FIELDS.values())
        return cls(*struct.unpack(fmt_str, data))