from __future__ import annotations

import base64
import gzip
import hashlib
import os
import pickle
from pathlib import Path
from typing import Any

from .contracts import NodePayload


ENCODING = "pickle+gzip+base64"
FILE_ENCODING = "pickle+gzip+file"


def _encode_bytes(raw: bytes) -> str:
    return base64.b64encode(gzip.compress(raw)).decode("ascii")


def _decode_bytes(payload: str) -> bytes:
    return gzip.decompress(base64.b64decode(payload.encode("ascii")))


def _farm_root() -> Path:
    return Path(os.environ.get("KEY_FARM_ROOT", "/data/farm"))


def _decode_file_payload(payload: str) -> bytes:
    path = Path(payload)
    if not path.is_absolute():
        path = _farm_root() / path
    return gzip.decompress(path.read_bytes())


def pack_object(obj: Any) -> tuple[str, str]:
    raw = pickle.dumps(obj, protocol=pickle.HIGHEST_PROTOCOL)
    return _encode_bytes(raw), hashlib.sha256(raw).hexdigest()


def unpack_object(payload: str, sha256: str | None = None) -> Any:
    raw = _decode_bytes(payload)
    digest = hashlib.sha256(raw).hexdigest()
    if sha256 and digest != sha256:
        raise ValueError(f"payload digest mismatch: {digest} != {sha256}")
    return pickle.loads(raw)


def pack_node(node: Any) -> NodePayload:
    node_id = str(getattr(node, "id", ""))
    if not node_id:
        raise ValueError("node must expose a stable id before KEY generation dispatch")
    return pack_item(node, node_id)


def pack_item(item: Any, item_id: str | None = None) -> NodePayload:
    payload, digest = pack_object(item)
    stable_id = item_id or str(getattr(item, "id", "")) or digest[:16]
    return NodePayload(node_id=stable_id, encoding=ENCODING, payload=payload, sha256=digest)


def unpack_node(node_payload: NodePayload) -> Any:
    if node_payload.encoding == ENCODING:
        return unpack_object(node_payload.payload, node_payload.sha256)
    if node_payload.encoding == FILE_ENCODING:
        raw = _decode_file_payload(node_payload.payload)
        digest = hashlib.sha256(raw).hexdigest()
        if node_payload.sha256 and digest != node_payload.sha256:
            raise ValueError(f"payload digest mismatch: {digest} != {node_payload.sha256}")
        return pickle.loads(raw)
    else:
        raise ValueError(f"unsupported node encoding: {node_payload.encoding}")