"""对象存储适配器（交付报告 P0-2）。

设计：统一接口 save/read/delete/exists，两个实现：
- local（默认）：磁盘目录，行为与现状一致；
- s3（可选）：通过环境变量启用（YAWEN_STORAGE_BACKEND=s3 + endpoint/key/secret/bucket），
  依赖 boto3（未安装时导入报错并回退 local，错误信息可读）。

产物路径统一用 "local://相对路径" / "s3://bucket/key" 形式存库，
读取时由 resolve_path 还原为可读的绝对路径或 s3 引用。
"""
from __future__ import annotations

import os
import shutil
from pathlib import Path
from urllib.parse import urlparse

from .config import DATA_DIR


class StorageBackend:
    def save(self, key: str, data: bytes) -> str: ...
    def read(self, key: str) -> bytes: ...
    def delete(self, key: str) -> None: ...
    def exists(self, key: str) -> bool: ...


class LocalStorage(StorageBackend):
    """磁盘实现：key 是相对 DATA_DIR/storage 的路径。"""

    def __init__(self, root: Path | None = None):
        self.root = Path(root) if root else DATA_DIR / "storage"
        self.root.mkdir(parents=True, exist_ok=True)

    def _path(self, key: str) -> Path:
        clean = key.lstrip("/").replace("..", "_")
        return self.root / clean

    def save(self, key: str, data: bytes) -> str:
        path = self._path(key)
        path.parent.mkdir(parents=True, exist_ok=True)
        tmp = path.with_suffix(path.suffix + ".tmp")
        tmp.write_bytes(data)
        tmp.replace(path)
        # 引用里不回传原始 key 的 ..，写库引用使用净化后的路径
        clean_key = str(path.relative_to(self.root))
        return f"local://{clean_key}"

    def read(self, key: str) -> bytes:
        return self._path(key).read_bytes()

    def delete(self, key: str) -> None:
        path = self._path(key)
        if path.exists():
            path.unlink()

    def exists(self, key: str) -> bool:
        return self._path(key).exists()

    def read_text(self, key: str) -> str:
        return self.read(key).decode("utf-8", errors="ignore")


class S3Storage(StorageBackend):
    """S3/MinIO/COS 实现：懒加载 boto3，未配置时抛可读错误。"""

    def __init__(self):
        try:
            import boto3  # noqa: F401
        except ImportError as exc:
            raise RuntimeError(
                "S3 存储后端需要 boto3：请在 server 环境执行 pip install boto3") from exc
        self.bucket = os.environ.get("YAWEN_S3_BUCKET", "")
        if not self.bucket:
            raise RuntimeError("S3 存储后端需要环境变量 YAWEN_S3_BUCKET")
        self.client = boto3.client(
            "s3",
            endpoint_url=os.environ.get("YAWEN_S3_ENDPOINT") or None,
            aws_access_key_id=os.environ.get("YAWEN_S3_ACCESS_KEY") or None,
            aws_secret_access_key=os.environ.get("YAWEN_S3_SECRET_KEY") or None,
            region_name=os.environ.get("YAWEN_S3_REGION") or None,
        )

    def save(self, key: str, data: bytes) -> str:
        self.client.put_object(Bucket=self.bucket, Key=key, Body=data)
        return f"s3://{self.bucket}/{key}"

    def read(self, key: str) -> bytes:
        return self.client.get_object(Bucket=self.bucket, Key=key)["Body"].read()

    def delete(self, key: str) -> None:
        self.client.delete_object(Bucket=self.bucket, Key=key)

    def exists(self, key: str) -> bool:
        try:
            self.client.head_object(Bucket=self.bucket, Key=key)
            return True
        except Exception:
            return False


_backend: StorageBackend | None = None


def get_storage() -> StorageBackend:
    global _backend
    if _backend is None:
        backend_name = os.environ.get("YAWEN_STORAGE_BACKEND", "local").lower()
        if backend_name == "s3":
            _backend = S3Storage()
        else:
            _backend = LocalStorage()
    return _backend


def reset_storage() -> None:
    """测试用：清空缓存的 backend 单例。"""
    global _backend
    _backend = None


def parse_ref(ref: str) -> tuple[str, str]:
    """'s3://bucket/key' → ('s3', 'bucket/key')；'local://a/b' → ('local', 'a/b')；
    裸路径视为 local。"""
    ref = str(ref or "")
    if "://" in ref:
        scheme, rest = ref.split("://", 1)
        return scheme, rest
    return "local", ref


def resolve_display_path(ref: str) -> str:
    """把存库引用转成可展示/下载用的路径。"""
    scheme, key = parse_ref(ref)
    if scheme == "s3":
        return ref
    return str(DATA_DIR / "storage" / key.lstrip("/").replace("..", "_"))


__all__ = ["StorageBackend", "LocalStorage", "S3Storage", "get_storage",
           "reset_storage", "parse_ref", "resolve_display_path"]