"""
Reads doc_service_config.json from the shared config volume.
30-second TTL cache + env var overrides.

Env var overrides (all optional):
  DOC_MAX_PDF_MB   — max upload size in megabytes (e.g. "50")
"""
import asyncio
import json
import os
import time
from copy import deepcopy
from pathlib import Path

from app.core.config import settings

_DEFAULT_CONFIG: dict = {
    "documents": {"max_pdf_bytes": 20 * 1024 * 1024},
}

_cache: dict | None = None
_cache_at: float = 0.0
_CACHE_TTL = 30.0


def _read_config_sync() -> dict:
    path = Path(settings.CONFIG_PATH)
    if not path.exists():
        base = deepcopy(_DEFAULT_CONFIG)
    else:
        with open(path) as f:
            base = json.load(f)
    return _apply_env_overrides(base)


def _apply_env_overrides(config: dict) -> dict:
    cfg = deepcopy(config)
    docs = cfg.setdefault("documents", {})
    if v := os.environ.get("DOC_MAX_PDF_MB"):
        try:
            docs["max_pdf_bytes"] = int(v) * 1024 * 1024
        except ValueError:
            pass
    return cfg


async def load_doc_config() -> dict:
    global _cache, _cache_at
    now = time.monotonic()
    if _cache is not None and (now - _cache_at) < _CACHE_TTL:
        return _cache
    data = await asyncio.to_thread(_read_config_sync)
    _cache = data
    _cache_at = now
    return data