"""Read-write utility functions."""

import struct
import typing


class LittleEndianTypes:
    UCHAR = struct.Struct(b'<b')
    USHORT = struct.Struct(b'<H')
    USHORT2 = struct.Struct(b'<HH')  # two shorts in a row
    SSHORT = struct.Struct(b'<h')
    UINT = struct.Struct(b'<I')
    SINT = struct.Struct(b'<i')
    FLOAT = struct.Struct(b'<f')
    ULONG = struct.Struct(b'<Q')

    @classmethod
    def _read(cls, fileobj: typing.BinaryIO, typestruct: struct.Struct):
        data = fileobj.read(typestruct.size)
        return typestruct.unpack(data)[0]

    @classmethod
    def read_char(cls, fileobj: typing.BinaryIO):
        return cls._read(fileobj, cls.UCHAR)

    @classmethod
    def read_ushort(cls, fileobj: typing.BinaryIO):
        return cls._read(fileobj, cls.USHORT)

    @classmethod
    def read_short(cls, fileobj: typing.BinaryIO):
        return cls._read(fileobj, cls.SSHORT)

    @classmethod
    def read_uint(cls, fileobj: typing.BinaryIO):
        return cls._read(fileobj, cls.UINT)

    @classmethod
    def read_int(cls, fileobj: typing.BinaryIO):
        return cls._read(fileobj, cls.SINT)

    @classmethod
    def read_float(cls, fileobj: typing.BinaryIO):
        return cls._read(fileobj, cls.FLOAT)

    @classmethod
    def read_ulong(cls, fileobj: typing.BinaryIO):
        return cls._read(fileobj, cls.ULONG)

    @classmethod
    def read_pointer(cls, fileobj: typing.BinaryIO, fileheader):
        """Read a pointer from a file.

        The pointer size is given by the header (BlendFileHeader).
        """

        if fileheader.pointer_size == 4:
            return cls.read_uint(fileobj)
        if fileheader.pointer_size == 8:
            return cls.read_ulong(fileobj)
        raise ValueError('unsupported pointer size %d' % fileheader.pointer_size)


class BigEndianTypes(LittleEndianTypes):
    UCHAR = struct.Struct(b'>b')
    USHORT = struct.Struct(b'>H')
    USHORT2 = struct.Struct(b'>HH')  # two shorts in a row
    SSHORT = struct.Struct(b'>h')
    UINT = struct.Struct(b'>I')
    SINT = struct.Struct(b'>i')
    FLOAT = struct.Struct(b'>f')
    ULONG = struct.Struct(b'>Q')


def write_string(fileobj: typing.BinaryIO, astring: str, fieldlen: int):
    assert isinstance(astring, str)
    write_bytes(fileobj, astring.encode('utf-8'), fieldlen)


def write_bytes(fileobj: typing.BinaryIO, data: bytes, fieldlen: int):
    assert isinstance(data, (bytes, bytearray))
    if len(data) >= fieldlen:
        to_write = data[0:fieldlen]
    else:
        to_write = data + b'\0'

    fileobj.write(to_write)


def read_bytes0(fileobj, length):
    data = fileobj.read(length)
    return read_data0(data)


def read_string(fileobj, length):
    return fileobj.read(length).decode('utf-8')


def read_string0(fileobj, length):
    return read_bytes0(fileobj, length).decode('utf-8')


def read_data0_offset(data, offset):
    add = data.find(b'\0', offset) - offset
    return data[offset:offset + add]


def read_data0(data):
    add = data.find(b'\0')
    return data[:add]