"""MitreId — validated MITRE ATT&CK technique identifier.

Immutable value object that ensures the identifier follows the ATT&CK
format: ``T`` followed by 4 digits, optionally a dot and 3 more digits
for sub-techniques (e.g. ``T1059``, ``T1059.001``).
"""

from __future__ import annotations

import re
from dataclasses import dataclass

_MITRE_ID_RE = re.compile(r"^T\d{4}(\.\d{3})?$")


@dataclass(frozen=True, slots=True)
class MitreId:
    """Validated MITRE ATT&CK technique identifier."""

    value: str

    def __post_init__(self) -> None:
        if not _MITRE_ID_RE.match(self.value):
            raise ValueError(
                f"Invalid MITRE ATT&CK ID '{self.value}'. "
                "Expected format: T1234 or T1234.001"
            )

    @property
    def is_subtechnique(self) -> bool:
        return "." in self.value

    @property
    def parent_id(self) -> str | None:
        """Return the parent technique ID (e.g. T1059 for T1059.001)."""
        if not self.is_subtechnique:
            return None
        return self.value.split(".")[0]

    def __str__(self) -> str:
        return self.value

    def __eq__(self, other: object) -> bool:
        if isinstance(other, MitreId):
            return self.value == other.value
        if isinstance(other, str):
            return self.value == other
        return NotImplemented

    def __hash__(self) -> int:
        return hash(self.value)