from __future__ import annotations

import base64
import hashlib
import logging
from dataclasses import dataclass, field, asdict
from datetime import datetime
from typing import Optional

logger = logging.getLogger(__name__)


@dataclass
class ContentChunk:
    """
    Модель чанка зашифрованного контента.

    Все бинарные поля представлены в base64-строках для JSON-совместимости.
    - chunk_hash: HEX(SHA-256(raw_encrypted_chunk_bytes)) — для дедупликации
    - signature: base64-encoded Ed25519 подпись структуры чанка (детали в ChunkManager)
    """
    chunk_id: str
    content_id: str
    chunk_index: int
    chunk_hash: str  # hex sha256(raw encrypted data)
    encrypted_data: str  # base64
    signature: Optional[str] = None
    created_at: str = field(default_factory=lambda: datetime.utcnow().isoformat())

    def to_dict(self) -> dict:
        return asdict(self)

    @classmethod
    def from_dict(cls, data: dict) -> "ContentChunk":
        required = ["chunk_id", "content_id", "chunk_index", "chunk_hash", "encrypted_data"]
        for f in required:
            if f not in data:
                raise ValueError(f"Missing required field in ContentChunk: {f}")
        return cls(
            chunk_id=data["chunk_id"],
            content_id=data["content_id"],
            chunk_index=int(data["chunk_index"]),
            chunk_hash=data["chunk_hash"],
            encrypted_data=data["encrypted_data"],
            signature=data.get("signature"),
            created_at=data.get("created_at") or datetime.utcnow().isoformat(),
        )

    def encrypted_bytes(self) -> bytes:
        return base64.b64decode(self.encrypted_data)

    @staticmethod
    def compute_sha256_hex(buf: bytes) -> str:
        return hashlib.sha256(buf).hexdigest()