"""A very strange "hash" that uses the magic module (python3-magic) to guess
the file type."""

import typing

import magic

# It changed API a few times...
try:
    _magic_identify = magic.from_buffer
except AttributeError:
    _magic_identify = magic.none_magic.buffer

class FileDigester:
    """A hashlib-like class to guess a filetype using the magic module."""
    FILE_BYTES_MAX = 1024 * 1024 # copied from file source

    def __init__(self) -> None:
        self.buff: typing.Optional[bytes] = b""
        self.identification: typing.Optional[str] = None

    def _compute_identification(self) -> str:
        assert self.buff is not None
        try:
            return _magic_identify(self.buff)
        except UnicodeDecodeError:
            return "magic identification is not valid UTF-8"

    def update(self, buff: bytes) -> None:
        if self.identification:
            return
        assert self.buff is not None
        self.buff += buff
        if len(self.buff) >= self.FILE_BYTES_MAX:
            self.identification = self._compute_identification()
            self.buff = None

    def identify(self) -> str:
        """Return the guessed file magic identification."""
        if self.identification:
            return self.identification
        return self._compute_identification()

    def hexdigest(self) -> str:
        """Compatibility with hashlib. An alias of identify. Doesn't return
        hex."""
        return self.identify()

    def copy(self) -> "FileDigester":
        new = FileDigester()
        new.buff = self.buff
        new.identification = self.identification
        return new