import os
from collections.abc import Awaitable, Callable

from .blobs import BlobCache
from .metadata import FileMetadataCache

def _env_int(name: str, default: int) -> int:
  try:
    return int(os.getenv(name, str(default)))
  except (TypeError, ValueError):
    return default

class FileCache:
  """Facade over the metadata cache (shared) and the blob cache (process-local)."""

  def __init__(self, metadata: FileMetadataCache, blobs: BlobCache, blob_max_age: int, edge_max_age: int):
    self.metadata = metadata
    self.blobs = blobs
    self.blob_max_age = blob_max_age
    self.edge_max_age = edge_max_age

  async def get_metadata(self, file_id: str, loader: Callable[[], Awaitable[dict | None]]):
    return await self.metadata.get(file_id, loader)

  async def get_blob(self, storage_key: str, loader: Callable[[], Awaitable[bytes]]) -> bytes:
    cached = self.blobs.get(storage_key)
    if cached is not None:
      return cached

    data = await loader()
    self.blobs.set(storage_key, data)
    return data

  async def invalidate(self, file_id: str, storage_key: str | None = None) -> None:
    await self.metadata.invalidate(file_id)
    if storage_key:
      self.blobs.invalidate(storage_key)

  def stats(self) -> dict:
    return {
      'metadata_hits': self.metadata.hits,
      'metadata_misses': self.metadata.misses,
      'blob_hits': self.blobs.hits,
      'blob_misses': self.blobs.misses,
      'blob_bytes': self.blobs.current_bytes,
    }

def build_file_cache(cache) -> FileCache:
  """Build the cache stack from FILE_CACHE_* environment settings."""
  return FileCache(
    metadata=FileMetadataCache(cache, ttl=_env_int('FILE_CACHE_METADATA_TTL', 60)),
    blobs=BlobCache(
      max_total_bytes=_env_int('FILE_CACHE_BLOB_TOTAL_BYTES', 64 * 1024 * 1024),
      max_item_bytes=_env_int('FILE_CACHE_BLOB_ITEM_BYTES', 2 * 1024 * 1024),
      ttl=_env_int('FILE_CACHE_BLOB_TTL', 300),
    ),
    blob_max_age=_env_int('FILE_CACHE_BROWSER_MAX_AGE', 86400),
    # Cloudflare keeps serving deleted files, so the edge window stays short.
    edge_max_age=_env_int('FILE_CACHE_EDGE_MAX_AGE', 1800),
  )