"""Persisted user defaults (ports, scope IP, save directory).

One flat JSON file, one dataclass.  ``save()`` always writes every field, so
a partial UI update can never silently drop another field's saved value
(which is exactly what the old dict-based writer did to helios_port).
"""
from __future__ import annotations

import json
import logging
from dataclasses import asdict, dataclass, fields
from pathlib import Path

logger = logging.getLogger(__name__)

DEFAULTS_PATH = Path(__file__).resolve().parent.parent / "aui_defaults.json"


@dataclass
class ScanDefaults:
    t3r_port: str = "/dev/ttyUSB0"
    bbd_port: str = "/dev/ttyUSB1"
    oscope_ip: str = "192.168.0.1"
    save_dir: str = str(DEFAULTS_PATH.parent / "scans")
    helios_port: str = "/dev/ttyUSB2"
    burst_mode: bool = False
    strict_rows: bool = False

    @classmethod
    def load(cls, path: Path = DEFAULTS_PATH) -> "ScanDefaults":
        """Load defaults, tolerating a missing/corrupt file and unknown keys."""
        if path.exists():
            try:
                with open(path) as f:
                    data = json.load(f)
                known = {f.name for f in fields(cls)}
                return cls(**{k: v for k, v in data.items() if k in known})
            except (OSError, ValueError, TypeError) as e:
                logger.warning("Could not load %s (%s); using fallback defaults", path, e)
        inst = cls()
        inst.save(path)
        return inst

    def save(self, path: Path = DEFAULTS_PATH) -> None:
        try:
            with open(path, "w") as f:
                json.dump(asdict(self), f, indent=2)
        except OSError as e:
            logger.warning("Could not save defaults to %s: %s", path, e)