"""OmegaConf-based configuration loading, merging, and Pydantic validation.

Supports:

* A base YAML file (typically ``configs/default.yaml``).
* An optional user YAML file merged on top of the base.
* Dot-list CLI overrides (``key.subkey=value``), e.g. as produced by
  ``OmegaConf.from_dotlist(["placement.rotation_deg.min=-5"])``.

The merged structure is converted to a plain Python container and validated
against :class:`~src.config.schema.PipelineConfig`, so any typo or
out-of-range value fails fast with a clear error instead of silently being
ignored.
"""

from __future__ import annotations

from pathlib import Path

from omegaconf import OmegaConf

from src.config.schema import PipelineConfig


def _default_config_path() -> Path:
    return Path(__file__).resolve().parents[2] / "configs" / "default.yaml"


def load_config(
    config_path: "str | Path | None" = None,
    overrides: "list[str] | None" = None,
) -> PipelineConfig:
    """Load, merge, and validate the pipeline configuration.

    Args:
        config_path: Path to a user YAML config. If ``None``, only the
            built-in ``configs/default.yaml`` is used.
        overrides: Optional list of ``"dotted.key=value"`` CLI-style
            overrides, applied last (highest precedence).

    Returns:
        A fully validated :class:`~src.config.schema.PipelineConfig`.

    Raises:
        pydantic.ValidationError: If the merged configuration is invalid.
        FileNotFoundError: If ``config_path`` is given but does not exist.
    """
    base = OmegaConf.load(_default_config_path())

    merged = base
    if config_path is not None:
        config_path = Path(config_path)
        if not config_path.exists():
            raise FileNotFoundError(f"Config file not found: {config_path}")
        user_conf = OmegaConf.load(config_path)
        merged = OmegaConf.merge(base, user_conf)

    if overrides:
        cli_conf = OmegaConf.from_dotlist(overrides)
        merged = OmegaConf.merge(merged, cli_conf)

    resolved = OmegaConf.to_container(merged, resolve=True)
    return PipelineConfig.model_validate(resolved)


def save_resolved_config(config: PipelineConfig, path: "str | Path") -> None:
    """Write a fully-resolved configuration (as actually used) to YAML for provenance."""
    path = Path(path)
    path.parent.mkdir(parents=True, exist_ok=True)
    OmegaConf.save(OmegaConf.create(config.model_dump()), path)