from ...exceptions import ReadError, SizeError
from datetime import datetime, timedelta
from io import BytesIO
from struct import unpack


__all__ = [
    "read_element_id",
    "read_element_size",
    "read_element_integer",
    "read_element_uinteger",
    "read_element_float",
    "read_element_string",
    "read_element_unicode",
    "read_element_date",
    "read_element_binary",
]


def _read(stream, size):
    """Read the `stream` for *exactly* `size` bytes and raise an exception if
    less than `size` bytes are actually read

    :param stream: file-like object from which to read
    :param int size: number of bytes to read
    :raise ReadError: when less than `size` bytes are actually read
    :return: read data from the `stream`
    :rtype: bytes

    """
    data = stream.read(size)
    if len(data) < size:
        raise ReadError("Less than %d bytes read (%d)" % (size, len(data)))
    return data


def read_element_id(stream):
    """Read the Element ID

    :param stream: file-like object from which to read
    :raise ReadError: when not all the required bytes could be read
    :return: the id of the element
    :rtype: int

    """
    char = _read(stream, 1)
    byte = ord(char)
    if byte & 0x80:
        return byte
    elif byte & 0x40:
        return unpack(">H", char + _read(stream, 1))[0]
    elif byte & 0x20:
        b, h = unpack(">BH", char + _read(stream, 2))
        return b * 2**16 + h
    elif byte & 0x10:
        return unpack(">L", char + _read(stream, 3))[0]
    else:
        ValueError("Not an Element ID")


def read_element_size(stream):
    """Read the Element Size

    :param stream: file-like object from which to read
    :raise ReadError: when not all the required bytes could be read
    :return: the size of element's data
    :rtype: int

    """
    char = _read(stream, 1)
    byte = ord(char)
    if byte & 0x80:
        return unpack(">B", bytes((byte ^ 0x80,)))[0]
    elif byte & 0x40:
        return unpack(">H", bytes((byte ^ 0x40,)) + _read(stream, 1))[0]
    elif byte & 0x20:
        b, h = unpack(">BH", bytes((byte ^ 0x20,)) + _read(stream, 2))
        return b * 2**16 + h
    elif byte & 0x10:
        return unpack(">L", bytes((byte ^ 0x10,)) + _read(stream, 3))[0]
    elif byte & 0x08:
        b, l = unpack(">BL", bytes((byte ^ 0x08,)) + _read(stream, 4))
        return b * 2**32 + l
    elif byte & 0x04:
        h, l = unpack(">HL", bytes((byte ^ 0x04,)) + _read(stream, 5))
        return h * 2**32 + l
    elif byte & 0x02:
        b, h, l = unpack(">BHL", bytes((byte ^ 0x02,)) + _read(stream, 6))
        return b * 2**48 + h * 2**32 + l
    elif byte & 0x01:
        return unpack(">Q", bytes((byte ^ 0x01,)) + _read(stream, 7))[0]
    else:
        ValueError("Not an Element Size")


def read_element_integer(stream, size):
    """Read the Element Data of type :data:`INTEGER`

    :param stream: file-like object from which to read
    :param int size: size of element's data
    :raise ReadError: when not all the required bytes could be read
    :raise SizeError: if size is incorrect
    :return: the read integer
    :rtype: int

    """
    if size == 1:
        return unpack(">b", _read(stream, 1))[0]
    elif size == 2:
        return unpack(">h", _read(stream, 2))[0]
    elif size == 3:
        b, h = unpack(">bH", _read(stream, 3))
        return b * 2**16 + h
    elif size == 4:
        return unpack(">l", _read(stream, 4))[0]
    elif size == 5:
        b, l = unpack(">bL", _read(stream, 5))
        return b * 2**32 + l
    elif size == 6:
        h, l = unpack(">hL", _read(stream, 6))
        return h * 2**32 + l
    elif size == 7:
        b, h, l = unpack(">bHL", _read(stream, 7))
        return b * 2**48 + h * 2**32 + l
    elif size == 8:
        return unpack(">q", _read(stream, 8))[0]
    else:
        raise SizeError(size)


def read_element_uinteger(stream, size):
    """Read the Element Data of type :data:`UINTEGER`

    :param stream: file-like object from which to read
    :param int size: size of element's data
    :raise ReadError: when not all the required bytes could be read
    :raise SizeError: if size is incorrect
    :return: the read unsigned integer
    :rtype: int

    """
    if size == 1:
        return unpack(">B", _read(stream, 1))[0]
    elif size == 2:
        return unpack(">H", _read(stream, 2))[0]
    elif size == 3:
        b, h = unpack(">BH", _read(stream, 3))
        return b * 2**16 + h
    elif size == 4:
        return unpack(">L", _read(stream, 4))[0]
    elif size == 5:
        b, l = unpack(">BL", _read(stream, 5))
        return b * 2**32 + l
    elif size == 6:
        h, l = unpack(">HL", _read(stream, 6))
        return h * 2**32 + l
    elif size == 7:
        b, h, l = unpack(">BHL", _read(stream, 7))
        return b * 2**48 + h * 2**32 + l
    elif size == 8:
        return unpack(">Q", _read(stream, 8))[0]
    else:
        raise SizeError(size)


def read_element_float(stream, size):
    """Read the Element Data of type :data:`FLOAT`

    :param stream: file-like object from which to read
    :param int size: size of element's data
    :raise ReadError: when not all the required bytes could be read
    :raise SizeError: if size is incorrect
    :return: the read float
    :rtype: float

    """
    if size == 4:
        return unpack(">f", _read(stream, 4))[0]
    elif size == 8:
        return unpack(">d", _read(stream, 8))[0]
    else:
        raise SizeError(size)


def read_element_string(stream, size):
    """Read the Element Data of type :data:`STRING`

    :param stream: file-like object from which to read
    :param int size: size of element's data
    :raise ReadError: when not all the required bytes could be read
    :raise SizeError: if size is incorrect
    :return: the read ascii-decoded string
    :rtype: unicode

    """
    return _read(stream, size).decode("ascii")


def read_element_unicode(stream, size):
    """Read the Element Data of type :data:`UNICODE`

    :param stream: file-like object from which to read
    :param int size: size of element's data
    :raise ReadError: when not all the required bytes could be read
    :raise SizeError: if size is incorrect
    :return: the read utf-8-decoded string
    :rtype: unicode

    """
    return _read(stream, size).decode("utf-8")


def read_element_date(stream, size):
    """Read the Element Data of type :data:`DATE`

    :param stream: file-like object from which to read
    :param int size: size of element's data
    :raise ReadError: when not all the required bytes could be read
    :raise SizeError: if size is incorrect
    :return: the read date
    :rtype: datetime

    """
    if size != 8:
        raise SizeError(size)
    nanoseconds = unpack(">q", _read(stream, 8))[0]
    return datetime(2001, 1, 1, 0, 0, 0, 0, None) + timedelta(microseconds=nanoseconds // 1000)


def read_element_binary(stream, size):
    """Read the Element Data of type :data:`BINARY`

    :param stream: file-like object from which to read
    :param int size: size of element's data
    :raise ReadError: when not all the required bytes could be read
    :raise SizeError: if size is incorrect
    :return: raw binary data
    :rtype: bytes

    """
    return BytesIO(stream.read(size))