from __future__ import annotations

import copy
import hashlib
import hmac
import json
import os
from datetime import UTC, datetime
from pathlib import Path
from typing import Any


INTEGRITY_VERSION = 1
INTEGRITY_KEY_ENV = "PACKING_INTEGRITY_SECRET"
INTEGRITY_FIELD = "integrity"
PRIVATE_PREFIX = "_"


def canonical_json(payload: Any) -> str:
    return json.dumps(payload, ensure_ascii=False, sort_keys=True, separators=(",", ":"))


def sha256_text(text: str) -> str:
    return hashlib.sha256(text.encode("utf-8")).hexdigest()


def sha256_file(path: Path) -> str:
    digest = hashlib.sha256()
    with path.open("rb") as handle:
        for chunk in iter(lambda: handle.read(1024 * 1024), b""):
            digest.update(chunk)
    return digest.hexdigest()


def integrity_secret() -> str:
    return os.environ.get(INTEGRITY_KEY_ENV, "")


def record_payload(record: dict[str, Any]) -> dict[str, Any]:
    payload = copy.deepcopy(record)
    payload.pop(INTEGRITY_FIELD, None)
    for key in list(payload):
        if key.startswith(PRIVATE_PREFIX) or key == "sync_status":
            payload.pop(key, None)
    return payload


def record_sha256(record: dict[str, Any]) -> str:
    return sha256_text(canonical_json(record_payload(record)))


def _abs_data_path(data_root: Path, path: str | Path) -> Path:
    p = Path(path)
    return p if p.is_absolute() else data_root.parent / p


def solution_sha256(record: dict[str, Any], data_root: Path) -> str:
    path = record.get("solution_path")
    if not path:
        return ""
    target = _abs_data_path(data_root, str(path))
    if not target.exists():
        return ""
    return sha256_file(target)


def sign_record_digest(record_digest: str, solution_digest: str) -> str:
    secret = integrity_secret()
    if not secret:
        return ""
    message = f"{record_digest}:{solution_digest}".encode("utf-8")
    return hmac.new(secret.encode("utf-8"), message, hashlib.sha256).hexdigest()


def seal_record(record: dict[str, Any], data_root: Path, *, signed_at: str | None = None) -> dict[str, Any]:
    out = copy.deepcopy(record)
    previous = out.get(INTEGRITY_FIELD)
    record_digest = record_sha256(out)
    solution_digest = solution_sha256(out, data_root)
    signature = sign_record_digest(record_digest, solution_digest)
    if not signature and isinstance(previous, dict) and previous.get("record_sha256") == record_digest:
        signature = str(previous.get("signature") or "")
    out[INTEGRITY_FIELD] = {
        "version": INTEGRITY_VERSION,
        "record_sha256": record_digest,
        "solution_sha256": solution_digest,
        "signature": signature,
        "signed_at": signed_at or datetime.now(UTC).isoformat(timespec="seconds"),
    }
    return out


def verify_record_integrity(record: dict[str, Any], data_root: Path) -> list[str]:
    integrity = record.get(INTEGRITY_FIELD)
    if not isinstance(integrity, dict):
        return ["missing integrity stamp"]

    errors: list[str] = []
    expected_record = record_sha256(record)
    stored_record = str(integrity.get("record_sha256") or "")
    if stored_record != expected_record:
        errors.append("record hash mismatch")

    expected_solution = solution_sha256(record, data_root)
    stored_solution = str(integrity.get("solution_sha256") or "")
    if expected_solution != stored_solution:
        errors.append("solution file hash mismatch")

    secret = integrity_secret()
    stored_signature = str(integrity.get("signature") or "")
    if secret:
        expected_signature = sign_record_digest(stored_record, stored_solution)
        if not stored_signature or not hmac.compare_digest(stored_signature, expected_signature):
            errors.append("record signature mismatch")
    return errors


def attach_integrity_status(record: dict[str, Any], data_root: Path) -> dict[str, Any]:
    out = dict(record)
    errors = verify_record_integrity(out, data_root)
    out["_integrity_errors"] = errors
    out["_integrity_ok"] = not errors
    return out