from __future__ import annotations

import os
import re
from pathlib import Path
from typing import Any

import yaml

from app.models import AppConfig

_ENV_PATTERN = re.compile(r"\$\{([A-Z0-9_]+)\}")


def _expand_env(value):
    if isinstance(value, str):
        return _ENV_PATTERN.sub(lambda m: os.getenv(m.group(1), ""), value)
    if isinstance(value, list):
        return [_expand_env(v) for v in value]
    if isinstance(value, dict):
        return {k: _expand_env(v) for k, v in value.items()}
    return value


def _load_yaml(path: Path) -> dict[str, Any]:
    if not path.is_file():
        return {}
    raw = yaml.safe_load(path.read_text(encoding="utf-8")) or {}
    if not isinstance(raw, dict):
        raise ValueError(f"Config file must contain a top-level mapping: {path}")
    return raw


def _section_value(raw: dict[str, Any], section: str) -> Any:
    if section in raw:
        return raw[section]
    return raw


def _load_split_config(path: Path) -> dict[str, Any]:
    config_dir = path if path.is_dir() else path.parent
    legacy_raw = _load_yaml(path) if path.is_file() else {}

    app_raw = _load_yaml(config_dir / "app.yaml")
    sources_raw = _load_yaml(config_dir / "sources.yaml")
    regions_raw = _load_yaml(config_dir / "regions.yaml")
    groups_raw = _load_yaml(config_dir / "policy-groups.yaml")
    rules_raw = _load_yaml(config_dir / "rules.yaml")
    clients_raw = _load_yaml(config_dir / "clients.yaml")

    merged: dict[str, Any] = {}
    merged.update({key: value for key, value in legacy_raw.items() if key not in AppConfig.model_fields})
    merged["public_path"] = app_raw.get("public_path", legacy_raw.get("public_path"))
    merged["sources"] = _section_value(sources_raw, "sources") if sources_raw else legacy_raw.get("sources", {})
    merged["regions"] = _section_value(regions_raw, "regions") if regions_raw else legacy_raw.get("regions", {})
    merged["selector_groups"] = groups_raw.get("selector_groups", legacy_raw.get("selector_groups", []))
    merged["policy_groups"] = groups_raw.get("policy_groups", legacy_raw.get("policy_groups", []))
    merged["rules"] = _section_value(rules_raw, "rules") if rules_raw else legacy_raw.get("rules", {})
    merged["clients"] = _section_value(clients_raw, "clients") if clients_raw else legacy_raw.get("clients", {})
    return merged


def load_app_config(path: Path) -> AppConfig:
    expanded = _expand_env(_load_split_config(path))
    return AppConfig.model_validate(expanded)