"""Shared yaml config path resolver — works for monorepo dev + flat container deploy.

【這個模組在做什麼？】
  ssrf_policy.py + pricing_config.py 都需要讀 monorepo 共用的 yaml
  （packages/ssrf-policy/policy.yaml、packages/pricing-config/*.yaml）。

  本機 dev 跑 Python 時 __file__ 在 apps/ml-service/src/，往上四層 (parents[3])
  正好是 monorepo root。但 HF Spaces / Render 部署是把 apps/ml-service/* 攤平
  當 repo root，container 內 __file__ = /app/src/X.py，parents[3] 直接 IndexError。

【這個 helper 的作法】
  - 先試 monorepo layout（parents[3] / packages/ 存在）
  - fallback 到 container 的 _shared/ 目錄（GitHub Actions sync 時 stage 進去
    的 yaml 副本，Dockerfile 把它 COPY 到 /app/_shared/）
  - 都找不到就 raise，避免 silent fallback 讓 SSRF policy 變空白規則

【為什麼不用 env var override】
  ssrf_policy.py 已有 SSRF_POLICY_PATH，但要 caller 自己拼路徑——HF Variables /
  Render env 容易設錯。這個 helper 走「資料隨 image 走」原則，少一個運維變數。
"""

from __future__ import annotations

from pathlib import Path


def shared_packages_dir() -> Path:
    """Return the directory that holds shared monorepo `packages/*` yaml configs.

    Resolution order:
      1. **Monorepo layout**: `<repo>/packages/` exists relative to this file
         (used for local `pnpm dev` / `uv run` workflows).
      2. **Flat container layout**: `<container_root>/_shared/` exists
         (sync-hf-space.yml stages monorepo packages here before upload;
         Dockerfile COPYs it into /app/_shared/).

    Raises:
      FileNotFoundError if neither layout has the expected directory.
    """
    here = Path(__file__).resolve()

    # Monorepo: apps/ml-service/src/_shared_paths.py → parents[3] = repo root
    # Path.resolve().parents is finite; container path /app/src/X.py only has 3
    # parents (/app/src, /app, /), so probe length first to avoid IndexError.
    if len(here.parents) > 3:
        candidate = here.parents[3] / "packages"
        if candidate.is_dir():
            return candidate

    # Container: /app/src/_shared_paths.py → parents[1] = /app
    container_candidate = here.parents[1] / "_shared"
    if container_candidate.is_dir():
        return container_candidate

    raise FileNotFoundError(
        "Cannot locate shared packages directory. Tried monorepo "
        f"({here.parents[3] / 'packages' if len(here.parents) > 3 else '<n/a>'}) "
        f"and container fallback ({container_candidate}). "
        "Ensure either the monorepo layout is intact or the deployment image "
        "has _shared/ populated by the sync workflow."
    )