"""Secrets and package bundling for Agent distribution.

Two independent secrets guard the distribution flow, both random(256 bits),
single-use and short-TTL, both stored only as SHA-256 hashes:

- the *download* token: embedded in the shareable link an operator hands to
  whoever installs the Agent (or clicked directly, authenticated, from the
  panel);
- the *enrollment* token: embedded inside the downloaded bundle as
  `enrollment.json`, consumed exactly once by `POST /v1/agents/enroll`.

Neither token is ever the Agent's own permanent Bearer token (issued only
after a successful enrollment) and neither is ever logged or audited in
plaintext.
"""
from __future__ import annotations

import hashlib
import hmac
import io
import json
import re
import secrets
import zipfile
from dataclasses import dataclass


class EnrollmentRejected(Exception):
    def __init__(self, reason: str):
        super().__init__(reason)
        self.reason = reason


def new_token() -> str:
    """256 bits of randomness, URL-safe — usable directly in a link or a JSON field."""
    return secrets.token_urlsafe(32)


def token_digest(token: str) -> str:
    return hashlib.sha256(token.encode()).hexdigest()


def token_matches(token: str | None, stored_hash: str | None) -> bool:
    if not token or not stored_hash:
        return False
    return hmac.compare_digest(token_digest(token), stored_hash)


ENROLLMENT_UUID_RE = re.compile(r"^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$")


def valid_uuid(value: str | None) -> bool:
    return bool(value) and bool(ENROLLMENT_UUID_RE.match(value))


@dataclass(frozen=True)
class BundlePlan:
    hub_url: str
    enrollment_uuid: str
    enrollment_token: str
    enroll_path: str = "/v1/agents/enroll"


def build_bundle(release_zip_bytes: bytes, plan: BundlePlan) -> bytes:
    """Return a new zip = the release zip's entries plus one
    `<package-root>/enrollment.json` holding only temporary, single-use data.
    Never a permanent credential — that is issued only once enrollment succeeds."""
    with zipfile.ZipFile(io.BytesIO(release_zip_bytes)) as source:
        names = source.namelist()
        if not names:
            raise EnrollmentRejected("EMPTY_RELEASE_PACKAGE")
        root = names[0].split("/", 1)[0]
        out = io.BytesIO()
        with zipfile.ZipFile(out, "w", zipfile.ZIP_DEFLATED) as dest:
            for name in names:
                dest.writestr(name, source.read(name))
            payload = {
                "installation_id": plan.enrollment_uuid,
                "enrollment_token": plan.enrollment_token,
                "hub_url": plan.hub_url,
                "enroll_path": plan.enroll_path,
            }
            dest.writestr(f"{root}/enrollment.json", json.dumps(payload, indent=1))
    return out.getvalue()