"""
domain/value_objects/device_info.py
────────────────────────────────────
DeviceInfo — immutable value object describing an IoT sensor device.

Value objects have no identity — two DeviceInfo objects with the same
field values are considered equal (enforced by ``frozen=True``).
"""
from __future__ import annotations

from dataclasses import dataclass
from typing import Optional


@dataclass(frozen=True)
class DeviceInfo:
    """
    Describes the IoT sensor/device that produced a PPG signal.

    Attributes:
        device_id:        Unique hardware identifier (MAC, serial, etc.).
        device_type:      Human-readable device category (e.g. ``"PPG Wristband"``).
        firmware_version: Firmware version string at time of recording.
        manufacturer:     Optional manufacturer name.
    """

    device_id: str
    device_type: str
    firmware_version: str
    manufacturer: Optional[str] = None

    def __post_init__(self) -> None:
        if not self.device_id or not self.device_id.strip():
            raise ValueError("DeviceInfo.device_id must be a non-empty string")
        if not self.device_type or not self.device_type.strip():
            raise ValueError("DeviceInfo.device_type must be a non-empty string")
        if not self.firmware_version or not self.firmware_version.strip():
            raise ValueError("DeviceInfo.firmware_version must be a non-empty string")

    def __str__(self) -> str:
        return (
            f"{self.device_type} [{self.device_id}] "
            f"fw={self.firmware_version}"
            + (f" by {self.manufacturer}" if self.manufacturer else "")
        )