"""Small configuration loader with JSON fallback and dotted overrides."""

from __future__ import annotations

import json
from collections.abc import Iterable
from pathlib import Path
from typing import Any


def load_config(path: str | Path) -> dict[str, Any]:
    path = Path(path)
    text = path.read_text(encoding="utf-8")
    if path.suffix.lower() == ".json":
        loaded = json.loads(text)
    else:
        try:
            import yaml
        except ImportError as exc:
            raise ImportError(
                "YAML config requires PyYAML; alternatively pass a .json config"
            ) from exc
        loaded = yaml.safe_load(text)
    if not isinstance(loaded, dict):
        raise ValueError("top-level config must be a mapping")
    return loaded


def apply_overrides(config: dict[str, Any], overrides: Iterable[str]) -> dict[str, Any]:
    """Apply ``section.key=<JSON value>`` updates in place."""

    for override in overrides:
        if "=" not in override:
            raise ValueError(f"override must be KEY=VALUE, got {override!r}")
        dotted_key, raw_value = override.split("=", 1)
        try:
            value = json.loads(raw_value)
        except json.JSONDecodeError:
            value = raw_value
        keys = dotted_key.split(".")
        cursor: dict[str, Any] = config
        for key in keys[:-1]:
            child = cursor.setdefault(key, {})
            if not isinstance(child, dict):
                raise ValueError(f"cannot descend into non-mapping config key {key!r}")
            cursor = child
        cursor[keys[-1]] = value
    return config