from dataclasses import dataclass
from pathlib import Path
from typing import Any, Dict, Optional

from .utils import read_yaml

class ConfigError(ValueError):
    """Raised when Nutfile contents are invalid."""

@dataclass(frozen=True)
class BuildConfig:
    name: str
    build_folder: str
    entry: str

    @property
    def buildFolder(self) -> str:
        # Compatibility alias for existing camelCase references.
        return self.build_folder

@dataclass(frozen=True)
class Config:
    path: Path
    raw: Dict[str, Any]
    build: BuildConfig

    @property
    def buildFolder(self) -> str:
        # Compatibility alias for older call-sites.
        return self.build.build_folder

def _ensure_dict(value: Any, context: str) -> Dict[str, Any]:
    if not isinstance(value, dict):
        raise ConfigError(f"{context} must be a mapping")
    return value

def _read_string(mapping: Dict[str, Any], key: str, default: str) -> str:
    value = mapping.get(key, default)
    if not isinstance(value, str) or not value.strip():
        raise ConfigError(f"build.{key} must be a non-empty string")
    return value

def load_config(path: str = "Nutfile") -> Config:
    config_path = Path(path)
    raw_data: Optional[Dict[str, Any]] = read_yaml(str(config_path))

    if raw_data is None:
        raw_data = {}
    raw_dict = _ensure_dict(raw_data, "Nutfile root")

    build_section = raw_dict.get("build", {})
    build_dict = _ensure_dict(build_section, "build section")

    build = BuildConfig(
        name=_read_string(build_dict, "name", "Example Build"),
        build_folder=_read_string(build_dict, "buildFolder", "build"),
        entry=_read_string(build_dict, "entry", "src/main.nut"),
    )

    return Config(
        path=config_path,
        raw=raw_dict,
        build=build,
    )