"""Content-addressed blob store (SPEC §4 "Blob store", §6.4).

Layout: ``${BLOB_ROOT}/{user_id}/{sha256[:2]}/{sha256}`` (filesystem default).
Content-addressed, so identical payloads dedupe. Postgres holds metadata only;
deleting a user removes their blob subtree.
"""

from __future__ import annotations

import hashlib
import uuid
from pathlib import Path

from app.config import get_settings


def _root() -> Path:
    return Path(get_settings().blob_root)


def sha256_hex(data: bytes) -> str:
    """Return the hex sha256 digest of ``data``."""
    return hashlib.sha256(data).hexdigest()


def blob_path(user_id: uuid.UUID, sha: str) -> Path:
    """Return the on-disk path for a user's blob (does not create it)."""
    return _root() / str(user_id) / sha[:2] / sha


def store(user_id: uuid.UUID, data: bytes) -> str:
    """Store ``data`` content-addressed; return its sha256. Idempotent (dedupes)."""
    sha = sha256_hex(data)
    path = blob_path(user_id, sha)
    if not path.exists():
        path.parent.mkdir(parents=True, exist_ok=True)
        tmp = path.with_suffix(".tmp")
        tmp.write_bytes(data)
        tmp.replace(path)  # atomic within the same directory
    return sha


def load(user_id: uuid.UUID, sha: str) -> bytes:
    """Load a blob by sha256. Raises FileNotFoundError if absent."""
    return blob_path(user_id, sha).read_bytes()


def exists(user_id: uuid.UUID, sha: str) -> bool:
    """Return True if the blob is present."""
    return blob_path(user_id, sha).exists()


def remove(user_id: uuid.UUID, sha: str) -> None:
    """Delete a blob if present (used by account/user deletion). Idempotent."""
    blob_path(user_id, sha).unlink(missing_ok=True)