"""Tools for parsing a ROE file."""

from os import SEEK_CUR, SEEK_SET
from os.path import basename, splitext
from struct import unpack

from .exceptions import InvalidROEFileError
from .utils import nibble_flip


class Roe:
    """The DNA of an electronic fish with an embedded icon."""
    def __init__(self, name: str = "", author: str | None = None) -> None:
        self.name: str = name
        self.author: str | None = author
        self.is_mutant: bool = False
        self.unknowns: dict[str, bytes] = {}

    @classmethod
    def from_file(cls, filename: str) -> "Roe":
        """Factory for importing roe from a .ROE file."""

        # Unlike .FSH files, the name comes from the filename itself. Since
        # DOS was limited to the 8.3 naming convention, a fish's name has a
        # forced limit of only eight characters.
        name = splitext(basename(filename))[0][0:8]
        roe = cls(name)

        with open(filename, "rb") as rfile:
            # First byte of file determines mutant status. Non-zero = mutant.
            # Second byte is padding.
            roe.is_mutant = unpack("?x", rfile.read(2))[0]

            # Next two bytes are unknown.
            roe.unknowns["00000002"] = unpack("2s", rfile.read(2))[0]

            # Next sixteen bytes is a nibble-flipped encoding of the original
            # author with a zero null termination byte.
            author = ""
            flipped_author = unpack("16s", rfile.read(16))[0]
            for letter in flipped_author:
                code = nibble_flip(letter)
                if code == 0:
                    break
                author += chr(code)
            roe.author = author.upper()

        return roe