"""Application settings with JSON persistence.

Provides runtime-configurable settings that persist across restarts.
Defaults come from environment variables; UI changes override them
and are saved to data/settings.json.
"""

import json
import logging
import os
from pathlib import Path
from typing import Any

logger = logging.getLogger(__name__)

SETTINGS_PATH = Path(__file__).resolve().parent.parent / "data" / "settings.json"

DEFAULTS: dict[str, Any] = {
    "detection_backend": os.environ.get("DETECTION_BACKEND", "yolos"),
}


def load_settings() -> dict[str, Any]:
    """Load settings from disk, merged with defaults."""
    settings = dict(DEFAULTS)
    if SETTINGS_PATH.exists():
        try:
            with open(SETTINGS_PATH, "r", encoding="utf-8") as f:
                saved = json.load(f)
            settings.update(saved)
        except (json.JSONDecodeError, IOError) as e:
            logger.warning("Failed to load settings: %s", e)
    return settings


def save_settings(settings: dict[str, Any]) -> None:
    """Write settings to disk."""
    SETTINGS_PATH.parent.mkdir(parents=True, exist_ok=True)
    with open(SETTINGS_PATH, "w", encoding="utf-8") as f:
        json.dump(settings, f, indent=2, ensure_ascii=False)


def get(key: str) -> Any:
    """Get a single setting value."""
    settings = load_settings()
    return settings.get(key, DEFAULTS.get(key))


def update(key: str, value: Any) -> None:
    """Update a single setting and persist."""
    settings = load_settings()
    settings[key] = value
    save_settings(settings)
    logger.info("Setting updated: %s = %s", key, value)