"""Load YAML hyperparameters and resolve filesystem paths relative to the repository root."""
from __future__ import annotations

import os
from pathlib import Path
from typing import Any

import yaml

from flare.definitions import REPO_DIR

# Keys that may hold filesystem paths (relative paths are resolved against REPO_DIR).
_PATH_KEYS = frozenset(
    {
        "dataset_pth",
        "candidates_pth",
        "subformula_dir_pth",
        "split_pth",
        "checkpoint_pth",
        "df_test_path",
        "formula_to_smiles_pth",
    }
)


def resolve_repo_paths(params: dict[str, Any]) -> None:
    """In-place: turn repo-relative path strings into absolute paths."""
    root = REPO_DIR
    for key in _PATH_KEYS:
        val = params.get(key)
        if not val or not isinstance(val, str):
            continue
        p = Path(val)
        if not p.is_absolute():
            params[key] = str((root / p).resolve())
        else:
            params[key] = str(p.resolve())


def load_param_file(path: str | Path) -> dict[str, Any]:
    """Load a YAML parameter file and resolve path fields."""
    p = Path(path)
    if not p.is_file():
        raise FileNotFoundError(f"Parameter file not found: {p}")
    with open(p, encoding="utf-8") as f:
        params = yaml.load(f, Loader=yaml.FullLoader)
    if params is None:
        params = {}
    if not isinstance(params, dict):
        raise TypeError(f"Expected mapping at top level of {p}, got {type(params)}")
    resolve_repo_paths(params)
    return params


def default_param_path() -> Path:
    """Path to the default params file (overridable with FLARE_PARAMS)."""
    override = os.environ.get("FLARE_PARAMS")
    if override:
        return Path(override).expanduser()
    env_root = os.environ.get("FLARE_REPO_ROOT")
    if env_root:
        return Path(env_root).expanduser() / "params.yaml"
    return REPO_DIR / "params.yaml"