"""Storage abstraction — MinIO (production) or LocalStorage (dev fallback).

Usage:
    from app.core.storage import get_storage
    storage = get_storage()
    key = storage.upload(local_path, "uploads/step_files/my.step")
    local_path = storage.download("uploads/step_files/my.step", tmp_dir / "my.step")

Environment variables (set in docker-compose.yml):
    MINIO_URL       — S3 endpoint URL (e.g. http://minio:9000)
    MINIO_USER      — Access key (default: minioadmin)
    MINIO_PASSWORD  — Secret key (default: minioadmin)
    MINIO_BUCKET    — Bucket name (default: uploads)

If MINIO_URL is not set, falls back to LocalStorage (reads/writes to UPLOAD_DIR).
"""
import logging
import os
from pathlib import Path

logger = logging.getLogger(__name__)


class MinIOStorage:
    """S3-compatible object storage via boto3 (MinIO backend)."""

    def __init__(
        self,
        url: str,
        user: str,
        password: str,
        bucket: str = "uploads",
    ):
        import boto3
        from botocore.config import Config

        self._bucket = bucket
        self._client = boto3.client(
            "s3",
            endpoint_url=url,
            aws_access_key_id=user,
            aws_secret_access_key=password,
            config=Config(signature_version="s3v4"),
        )
        self._ensure_bucket()

    def _ensure_bucket(self):
        """Create the bucket if it does not exist."""
        try:
            self._client.head_bucket(Bucket=self._bucket)
        except Exception:
            try:
                self._client.create_bucket(Bucket=self._bucket)
                logger.info("Created MinIO bucket: %s", self._bucket)
            except Exception as exc:
                logger.warning("Could not create MinIO bucket %s: %s", self._bucket, exc)

    def upload(self, local_path: Path, object_key: str) -> str:
        """Upload a local file to MinIO. Returns the object_key."""
        self._client.upload_file(str(local_path), self._bucket, object_key)
        logger.debug("Uploaded %s → minio://%s/%s", local_path.name, self._bucket, object_key)
        return object_key

    def download(self, object_key: str, local_path: Path) -> Path:
        """Download object from MinIO to local_path. Returns local_path."""
        local_path.parent.mkdir(parents=True, exist_ok=True)
        self._client.download_file(self._bucket, object_key, str(local_path))
        logger.debug("Downloaded minio://%s/%s → %s", self._bucket, object_key, local_path.name)
        return local_path

    def exists(self, object_key: str) -> bool:
        """Return True if the object exists in MinIO."""
        try:
            self._client.head_object(Bucket=self._bucket, Key=object_key)
            return True
        except Exception:
            return False

    def delete(self, object_key: str) -> None:
        """Delete an object from MinIO (best-effort)."""
        try:
            self._client.delete_object(Bucket=self._bucket, Key=object_key)
        except Exception as exc:
            logger.warning("MinIO delete failed for %s: %s", object_key, exc)

    def get_url(self, object_key: str, expires_in: int = 3600) -> str:
        """Generate a presigned URL for direct download (valid for expires_in seconds)."""
        return self._client.generate_presigned_url(
            "get_object",
            Params={"Bucket": self._bucket, "Key": object_key},
            ExpiresIn=expires_in,
        )

    @property
    def backend(self) -> str:
        return "minio"


class LocalStorage:
    """Fallback: reads/writes to the local UPLOAD_DIR filesystem.

    Object keys are treated as relative paths under UPLOAD_DIR.
    This preserves backward compatibility with the existing uploads/ volume.
    """

    def __init__(self, upload_dir: str):
        self._root = Path(upload_dir)

    def _resolve(self, object_key: str) -> Path:
        return self._root / object_key

    def upload(self, local_path: Path, object_key: str) -> str:
        """Copy local_path to the local storage path for object_key."""
        import shutil
        dest = self._resolve(object_key)
        dest.parent.mkdir(parents=True, exist_ok=True)
        if str(local_path) != str(dest):
            shutil.copy2(str(local_path), str(dest))
        return object_key

    def download(self, object_key: str, local_path: Path) -> Path:
        """'Download' by returning the existing local path."""
        src = self._resolve(object_key)
        if src == local_path:
            return local_path
        import shutil
        local_path.parent.mkdir(parents=True, exist_ok=True)
        shutil.copy2(str(src), str(local_path))
        return local_path

    def exists(self, object_key: str) -> bool:
        return self._resolve(object_key).exists()

    def delete(self, object_key: str) -> None:
        path = self._resolve(object_key)
        path.unlink(missing_ok=True)

    def get_url(self, object_key: str, expires_in: int = 3600) -> str:
        return f"/api/files/{object_key}"

    @property
    def backend(self) -> str:
        return "local"


_storage_instance: MinIOStorage | LocalStorage | None = None


def get_storage() -> MinIOStorage | LocalStorage:
    """Return the configured storage backend (singleton)."""
    global _storage_instance
    if _storage_instance is not None:
        return _storage_instance

    minio_url = os.environ.get("MINIO_URL", "")
    if minio_url:
        user = os.environ.get("MINIO_USER", "minioadmin")
        password = os.environ.get("MINIO_PASSWORD", "minioadmin")
        bucket = os.environ.get("MINIO_BUCKET", "uploads")
        try:
            _storage_instance = MinIOStorage(url=minio_url, user=user, password=password, bucket=bucket)
            logger.info("Storage backend: MinIO (%s, bucket=%s)", minio_url, bucket)
        except Exception as exc:
            logger.warning("MinIO init failed (%s) — falling back to LocalStorage: %s", minio_url, exc)
            _storage_instance = LocalStorage(os.environ.get("UPLOAD_DIR", "/app/uploads"))
    else:
        upload_dir = os.environ.get("UPLOAD_DIR", "/app/uploads")
        _storage_instance = LocalStorage(upload_dir)
        logger.info("Storage backend: local filesystem (%s)", upload_dir)

    return _storage_instance