"""Provider 凭据解析及本地加密存储。"""

import json
import os
import re
import threading
from pathlib import Path
from typing import Protocol

from cryptography.fernet import Fernet, InvalidToken

from app.config import get_settings


_CREDENTIAL_ID = re.compile(r"^[A-Za-z0-9][A-Za-z0-9._-]{0,127}$")


class CredentialStoreError(RuntimeError):
    pass


class CredentialResolver(Protocol):
    def resolve(self, credential_id: str | None) -> str | None: ...


class EnvironmentCredentialResolver:
    """解析由桌面 Host 注入 Sidecar 进程的临时凭证上下文。"""

    _development_aliases = {
        "openai": "OPENAI_API_KEY",
        "deepseek": "DEEPSEEK_API_KEY",
    }

    def resolve(self, credential_id: str | None) -> str | None:
        if not credential_id:
            return None
        normalized = re.sub(r"[^A-Za-z0-9]", "_", credential_id).upper()
        injected = os.getenv(f"AINOTE_CREDENTIAL_{normalized}")
        if injected:
            return injected
        alias = self._development_aliases.get(credential_id.lower())
        return os.getenv(alias) if alias else None


class EncryptedCredentialStore:
    """将本地开发凭据作为 Fernet 密文存储，Provider 使用时按 ID 解密。"""

    # TODO(security): 桌面 Host 接入后将主密钥迁移到系统钥匙串/凭据保险库。

    def __init__(self) -> None:
        self._lock = threading.RLock()

    @staticmethod
    def _validate_id(credential_id: str) -> None:
        if not _CREDENTIAL_ID.fullmatch(credential_id):
            raise CredentialStoreError("Credential ID contains unsupported characters.")

    @staticmethod
    def _paths() -> tuple[Path, Path]:
        directory = get_settings().data_dir / "credentials"
        return directory / "master.key", directory / "credentials.json"

    @staticmethod
    def _restrict(path: Path, mode: int) -> None:
        try:
            path.chmod(mode)
        except OSError:
            pass

    def _fernet(self) -> Fernet:
        key_path, _ = self._paths()
        environment_key = os.getenv("APP_CREDENTIAL_MASTER_KEY")
        if environment_key:
            try:
                return Fernet(environment_key.encode("ascii"))
            except (ValueError, UnicodeEncodeError) as exc:
                raise CredentialStoreError("APP_CREDENTIAL_MASTER_KEY is invalid.") from exc

        key_path.parent.mkdir(parents=True, exist_ok=True)
        self._restrict(key_path.parent, 0o700)
        if not key_path.exists():
            # 先写临时文件再原子替换，避免异常退出留下半截主密钥。
            temporary = key_path.with_suffix(".tmp")
            temporary.write_bytes(Fernet.generate_key())
            self._restrict(temporary, 0o600)
            try:
                temporary.replace(key_path)
            except FileExistsError:
                temporary.unlink(missing_ok=True)
        self._restrict(key_path, 0o600)
        try:
            return Fernet(key_path.read_bytes().strip())
        except (OSError, ValueError) as exc:
            raise CredentialStoreError("Credential master key cannot be loaded.") from exc

    def _read_tokens(self) -> dict[str, str]:
        _, store_path = self._paths()
        if not store_path.exists():
            return {}
        try:
            data = json.loads(store_path.read_text(encoding="utf-8"))
        except (OSError, json.JSONDecodeError) as exc:
            raise CredentialStoreError("Encrypted credential store cannot be loaded.") from exc
        if not isinstance(data, dict) or not all(
            isinstance(key, str) and isinstance(value, str) for key, value in data.items()
        ):
            raise CredentialStoreError("Encrypted credential store has an invalid format.")
        return data

    def _write_tokens(self, tokens: dict[str, str]) -> None:
        _, store_path = self._paths()
        store_path.parent.mkdir(parents=True, exist_ok=True)
        self._restrict(store_path.parent, 0o700)
        temporary = store_path.with_suffix(".tmp")
        temporary.write_text(
            json.dumps(tokens, ensure_ascii=True, sort_keys=True),
            encoding="utf-8",
        )
        self._restrict(temporary, 0o600)
        # 凭据表同样使用原子替换，确保并发读取只会看到完整 JSON。
        temporary.replace(store_path)
        self._restrict(store_path, 0o600)

    def put(self, credential_id: str, secret: str) -> None:
        self._validate_id(credential_id)
        if not secret:
            raise CredentialStoreError("Credential secret cannot be empty.")
        with self._lock:
            tokens = self._read_tokens()
            token = self._fernet().encrypt(secret.encode("utf-8")).decode("ascii")
            tokens[credential_id] = token
            self._write_tokens(tokens)

    def resolve(self, credential_id: str | None) -> str | None:
        if not credential_id:
            return None
        self._validate_id(credential_id)
        with self._lock:
            token = self._read_tokens().get(credential_id)
            if token is None:
                return None
            try:
                return self._fernet().decrypt(token.encode("ascii")).decode("utf-8")
            except (InvalidToken, UnicodeDecodeError) as exc:
                raise CredentialStoreError("Credential cannot be decrypted.") from exc

    def has(self, credential_id: str) -> bool:
        self._validate_id(credential_id)
        with self._lock:
            return credential_id in self._read_tokens()

    def delete(self, credential_id: str) -> bool:
        self._validate_id(credential_id)
        with self._lock:
            tokens = self._read_tokens()
            removed = tokens.pop(credential_id, None) is not None
            if removed:
                self._write_tokens(tokens)
            return removed


class ChainedCredentialResolver:
    def __init__(self, *resolvers: CredentialResolver) -> None:
        self._resolvers = resolvers

    def resolve(self, credential_id: str | None) -> str | None:
        # 顺序即优先级：调用方可让 Host 注入值覆盖本地开发凭据。
        for resolver in self._resolvers:
            value = resolver.resolve(credential_id)
            if value:
                return value
        return None