"""DNS-01 authenticator plugin for Certbot using the yeil dns-server RPC.

Talks to the dns-server (ShakeStation fork) over HTTP Basic auth. The RPC
shape is `{ method, params }` POST, returning `{ result } | { result: null,
error: { message } }`. Same protocol the yeil DNS web app uses; see
yeil/dns/src/lib/rpc.ts.
"""

import base64
import json
import logging
from urllib.error import HTTPError, URLError
from urllib.request import Request, urlopen

from certbot import errors, interfaces
from certbot.plugins import dns_common
from zope.interface import implementer

logger = logging.getLogger(__name__)


@implementer(interfaces.IAuthenticator)
@implementer(interfaces.IPluginFactory)
class Authenticator(dns_common.DNSAuthenticator):
    description = "Obtain certificates via DNS-01 using the yeil dns-server RPC."

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.credentials = None
        # (domain, validation_name, validation) -> (zone_id, record_id)
        self._records = {}

    @classmethod
    def add_parser_arguments(cls, add):
        super(Authenticator, cls).add_parser_arguments(
            add, default_propagation_seconds=20
        )
        add("credentials", help="Path to your yeil credentials INI file.")

    def more_info(self):
        return (
            "Configures Certbot to perform DNS-01 challenges by adding TXT "
            "records via the yeil dns-server RPC."
        )

    def _setup_credentials(self):
        self.credentials = self._configure_credentials(
            "credentials",
            "yeil dns-server credentials INI file",
            {
                "rpc_url": "Base URL of the dns-server RPC (e.g. http://100.123.x.x:6969)",
                "rpc_key": "Shared RPC key (config.rpc.key on the dns-server)",
            },
        )

    # ── RPC ────────────────────────────────────────────────────────────

    def _rpc(self, method, params=None):
        """POST {method, params} to the dns-server RPC and return result.

        Raises errors.PluginError on transport or RPC error.
        """
        url = self.credentials.conf("rpc_url")
        key = self.credentials.conf("rpc_key")
        token = base64.b64encode(f"x:{key}".encode("utf-8")).decode("ascii")
        body = json.dumps({"method": method, "params": params or {}}).encode("utf-8")

        req = Request(url, data=body, method="POST")
        req.add_header("Content-Type", "application/json")
        req.add_header("Content-Length", str(len(body)))
        req.add_header("Authorization", f"Basic {token}")

        try:
            with urlopen(req, timeout=30) as resp:
                data = json.loads(resp.read().decode("utf-8"))
        except HTTPError as e:
            try:
                err_body = json.loads(e.read().decode("utf-8"))
                msg = err_body.get("error", {}).get("message") or e.reason
            except Exception:
                msg = e.reason
            raise errors.PluginError(f"yeil dns-server error ({e.code}): {msg}")
        except URLError as e:
            raise errors.PluginError(f"yeil dns-server unreachable: {e}")

        if isinstance(data, dict) and data.get("error"):
            err = data["error"]
            msg = err.get("message") if isinstance(err, dict) else str(err)
            raise errors.PluginError(f"yeil dns-server error: {msg}")
        return data.get("result") if isinstance(data, dict) else None

    # ── Zone resolution ────────────────────────────────────────────────

    def _find_zone_id(self, fqdn):
        """Walk up the labels of fqdn, calling findzone, until one matches.

        Returns (zone_id, zone_name). Raises PluginError if nothing found.
        """
        labels = fqdn.rstrip(".").split(".")
        # Need at least a domain.tld pair to be a candidate zone.
        while len(labels) >= 2:
            candidate = ".".join(labels)
            try:
                result = self._rpc("findzone", {"domain": candidate})
            except errors.PluginError as e:
                # A "zone not found" response surfaces as a PluginError; that's
                # the signal to walk up. Anything else (auth, network) we'd
                # rather re-raise after exhausting candidates, so swallow here.
                logger.debug("findzone(%s) miss: %s", candidate, e)
                result = None
            if isinstance(result, dict) and result.get("id"):
                return result["id"], candidate
            labels = labels[1:]
        raise errors.PluginError(
            f"No registered zone found in dns-server for any suffix of {fqdn}"
        )

    @staticmethod
    def _relative_name(validation_name, zone_name):
        """`_acme-challenge.smtp.yeil.org` in zone `yeil.org` -> `_acme-challenge.smtp`.

        If validation_name equals the zone, returns "@" (the apex).
        """
        v = validation_name.rstrip(".")
        z = zone_name.rstrip(".")
        if v == z:
            return "@"
        suffix = "." + z
        if v.endswith(suffix):
            return v[: -len(suffix)]
        # Shouldn't happen if _find_zone_id picked the zone from this fqdn.
        raise errors.PluginError(
            f"validation_name {v} is not within zone {z}"
        )

    # ── certbot hooks ──────────────────────────────────────────────────

    def _perform(self, domain, validation_name, validation):
        zone_id, zone_name = self._find_zone_id(validation_name)
        rel_name = self._relative_name(validation_name, zone_name)
        result = self._rpc(
            "addrecord",
            {
                "zone": zone_id,
                "name": rel_name,
                "type": "TXT",
                "content": validation,
                "ttl": 60,
            },
        )
        record_id = (
            result.get("id") if isinstance(result, dict) else None
        )
        if not record_id:
            raise errors.PluginError(
                "dns-server addrecord did not return a record id"
            )
        self._records[(domain, validation_name, validation)] = (zone_id, record_id)

    def _cleanup(self, domain, validation_name, validation):
        entry = self._records.pop((domain, validation_name, validation), None)
        if not entry:
            logger.warning(
                "No stored record for %s; skipping cleanup", validation_name
            )
            return
        zone_id, record_id = entry
        try:
            self._rpc(
                "deleterecord",
                {"zone": zone_id, "record": record_id},
            )
        except errors.PluginError as e:
            # Don't fail the renewal because of a stale TXT we couldn't
            # delete; log and move on. Operator can prune by hand.
            logger.warning(
                "Failed to clean up TXT record %s (zone=%s record=%s): %s",
                validation_name, zone_id, record_id, e,
            )