"""Read-only access to Active Directory with ldap3: search with the service account, bind to verify a password.

Every operation opens its own connection and unbinds when done. A user's password is used for one bind and
never stored or logged.
"""

from __future__ import annotations

import contextlib
import logging
import ssl
import uuid
from collections.abc import Iterator
from dataclasses import dataclass, field
from typing import Any, Protocol

from ..settings import SecretFileError, Settings

log = logging.getLogger(__name__)

IN_CHAIN = "1.2.840.113556.1.4.1941"
USER_ATTRS = (
    "objectGUID",
    "sAMAccountName",
    "userPrincipalName",
    "displayName",
    "employeeID",
    "mail",
    "userAccountControl",
    "distinguishedName",
)
ACCOUNTDISABLE = 2
INVALID_CREDENTIALS = 49
PAGE_SIZE = 500


class LdapUnavailable(Exception):
    """No domain controller answered, TLS failed, or the service bind was refused. Never holds a password."""


@dataclass
class AdUser:
    guid: uuid.UUID
    dn: str
    sam_account: str
    upn: str | None
    display_name: str
    emp_no: str | None
    email: str | None
    disabled: bool
    groups: list[str] = field(default_factory=list)


class DirectoryProtocol(Protocol):
    """What the app needs from AD. `Directory` talks to a domain controller; tests use a fake."""

    def find_user(self, login: str) -> AdUser | None: ...
    def get_user_by_guid(self, guid: uuid.UUID) -> AdUser | None: ...
    def verify_password(self, dn: str, password: str) -> bool: ...
    def groups_of(self, dn: str) -> list[str]: ...
    def list_groups(self) -> list[str]: ...
    def members_of(self, group_cn: str) -> list[AdUser]: ...


# ---------------------------------------------------------------- attribute helpers


def parse_guid(value: Any) -> uuid.UUID:
    """objectGUID as ldap3 returns it: 16 raw bytes (little-endian fields) or a "{...}" string."""
    if isinstance(value, list | tuple):
        if not value:
            raise ValueError("empty objectGUID")
        value = value[0]
    if isinstance(value, bytes | bytearray):
        if len(value) != 16:
            raise ValueError("objectGUID must be 16 bytes")
        return uuid.UUID(bytes_le=bytes(value))
    if isinstance(value, uuid.UUID):
        return value
    return uuid.UUID(str(value).strip().strip("{}"))


def guid_filter(guid: uuid.UUID) -> str:
    """`(objectGUID=\\xx...)` with the bytes escaped for a search filter."""
    from ldap3.utils.conv import escape_bytes

    return f"(objectGUID={escape_bytes(guid.bytes_le)})"


def _first(attrs: dict[str, Any], name: str) -> Any:
    v = attrs.get(name)
    if isinstance(v, list | tuple):
        return v[0] if v else None
    return v


def _text(attrs: dict[str, Any], name: str) -> str | None:
    v = _first(attrs, name)
    if v is None:
        return None
    if isinstance(v, bytes | bytearray):
        v = bytes(v).decode("utf-8", "replace")
    text = str(v).strip()
    return text or None


def user_from_entry(entry: dict[str, Any]) -> AdUser:
    """An AdUser from one ldap3 search response entry (`attributes` plus `raw_attributes`)."""
    attrs = entry.get("attributes") or {}
    raw = entry.get("raw_attributes") or {}
    guid_raw = _first(raw, "objectGUID") or _first(attrs, "objectGUID")
    if guid_raw is None:
        raise ValueError("entry has no objectGUID")
    uac_text = _text(attrs, "userAccountControl") or "0"
    try:
        uac = int(uac_text)
    except ValueError:
        uac = 0
    sam = _text(attrs, "sAMAccountName") or ""
    return AdUser(
        guid=parse_guid(guid_raw),
        dn=_text(attrs, "distinguishedName") or str(entry.get("dn") or ""),
        sam_account=sam,
        upn=_text(attrs, "userPrincipalName"),
        display_name=_text(attrs, "displayName") or sam,
        emp_no=_text(attrs, "employeeID"),
        email=_text(attrs, "mail"),
        disabled=bool(uac & ACCOUNTDISABLE),
    )


def _entries(response: Any) -> list[dict[str, Any]]:
    return [e for e in (response or []) if e.get("type") == "searchResEntry"]


# ---------------------------------------------------------------- the real directory


class Directory:
    """AD over ldaps:// (or ldap:// with STARTTLS). Built from Settings; every method is synchronous."""

    def __init__(self, settings: Settings):
        self.settings = settings
        self._pool: Any = None

    # ------------------------------------------------ connections

    def _servers(self) -> Any:
        import ldap3

        if self._pool is not None:
            return self._pool
        s = self.settings
        urls = s.ldap_urls
        if not urls:
            raise LdapUnavailable("LDAP_URL is not set")
        servers = []
        for url in urls:
            ldaps = url.lower().startswith("ldaps://")
            if not ldaps and not s.ldap_starttls and not s.ldap_allow_insecure:
                raise LdapUnavailable(f"{url} is plain LDAP without STARTTLS; refused")
            tls = ldap3.Tls(
                validate=ssl.CERT_REQUIRED,
                version=ssl.PROTOCOL_TLS_CLIENT,
                ca_certs_file=str(s.ldap_ca_bundle) if s.ldap_ca_bundle else None,
            )
            servers.append(ldap3.Server(url, use_ssl=ldaps, tls=tls, get_info=ldap3.NONE, connect_timeout=10))
        # FIRST: the first healthy controller is used. active=1 tries the list once (True would loop
        # forever when every controller is down); exhaust=60 skips a dead controller for a minute.
        self._pool = ldap3.ServerPool(servers, ldap3.FIRST, active=1, exhaust=60)
        return self._pool

    def _open(self, user: str, password: str) -> Any:
        """An open, TLS-protected connection, not yet bound."""
        import ldap3

        conn = ldap3.Connection(
            self._servers(),
            user=user,
            password=password,
            authentication=ldap3.SIMPLE,
            receive_timeout=15,
            raise_exceptions=False,
            auto_referrals=False,
            read_only=True,
        )
        conn.open()
        url_is_ldaps = bool(getattr(conn.server, "ssl", False))
        if self.settings.ldap_starttls and not url_is_ldaps and not conn.start_tls():
            with contextlib.suppress(Exception):
                conn.unbind()
            raise LdapUnavailable(f"STARTTLS failed: {conn.result.get('description')}")
        return conn

    @contextlib.contextmanager
    def _service(self) -> Iterator[Any]:
        """A connection bound as the service account; always unbound afterwards."""
        from ldap3.core.exceptions import LDAPException

        s = self.settings
        if not s.ldap_bind_dn:
            raise LdapUnavailable("LDAP_BIND_DN is not set")
        try:
            password = s.ldap_password()
        except SecretFileError as e:
            raise LdapUnavailable(str(e)) from None
        conn = None
        try:
            conn = self._open(s.ldap_bind_dn, password)
            if not conn.bind():
                raise LdapUnavailable(f"service bind failed: {conn.result.get('description')}")
            yield conn
        except LDAPException as e:
            raise LdapUnavailable(f"{type(e).__name__}: {e}") from None
        finally:
            if conn is not None:
                with contextlib.suppress(Exception):
                    conn.unbind()

    def _search(self, conn: Any, base: str, flt: str, attrs: tuple[str, ...] | list[str]) -> list[dict[str, Any]]:
        import ldap3

        results = conn.extend.standard.paged_search(
            base, flt, ldap3.SUBTREE, attributes=list(attrs), paged_size=PAGE_SIZE, generator=False
        )
        desc = conn.result.get("description") if conn.result else "success"
        if desc not in ("success", None, "noSuchObject"):
            raise LdapUnavailable(f"search failed: {desc}")
        return _entries(results)

    # ------------------------------------------------ protocol

    def find_user(self, login: str) -> AdUser | None:
        from ldap3.utils.conv import escape_filter_chars

        login = login.strip()
        if not login:
            return None
        flt = self.settings.ldap_user_filter.replace("{0}", escape_filter_chars(login))
        with self._service() as conn:
            found = self._search(conn, self.settings.ldap_base_dn, flt, USER_ATTRS)
        users = [user_from_entry(e) for e in found]
        if len(users) != 1:
            if len(users) > 1:
                log.warning("LDAP_USER_FILTER matched %d entries for one login; refusing", len(users))
            return None
        return users[0]

    def get_user_by_guid(self, guid: uuid.UUID) -> AdUser | None:
        with self._service() as conn:
            found = self._search(conn, self.settings.ldap_base_dn, guid_filter(guid), USER_ATTRS)
        return user_from_entry(found[0]) if found else None

    def verify_password(self, dn: str, password: str) -> bool:
        """Simple bind as the user. An empty password is refused here: AD treats it as an anonymous bind."""
        from ldap3.core.exceptions import LDAPException

        if not password or not dn:
            return False
        conn = None
        try:
            conn = self._open(dn, password)
            if conn.bind():
                return True
            code = conn.result.get("result") if conn.result else None
            if code == INVALID_CREDENTIALS:
                return False
            raise LdapUnavailable(f"user bind failed: {conn.result.get('description')}")
        except LDAPException as e:
            raise LdapUnavailable(f"{type(e).__name__}") from None
        finally:
            if conn is not None:
                with contextlib.suppress(Exception):
                    conn.unbind()

    def groups_of(self, dn: str) -> list[str]:
        from ldap3.utils.conv import escape_filter_chars

        flt = f"(&(objectClass=group)(member:{IN_CHAIN}:={escape_filter_chars(dn)}))"
        with self._service() as conn:
            found = self._search(conn, self.settings.ldap_group_base_dn, flt, ["cn"])
        return sorted({cn for e in found if (cn := _text(e.get("attributes") or {}, "cn"))})

    def list_groups(self) -> list[str]:
        with self._service() as conn:
            found = self._search(conn, self.settings.ldap_group_base_dn, "(objectClass=group)", ["cn"])
        return sorted({cn for e in found if (cn := _text(e.get("attributes") or {}, "cn"))})

    def members_of(self, group_cn: str) -> list[AdUser]:
        from ldap3.utils.conv import escape_filter_chars

        with self._service() as conn:
            groups = self._search(
                conn,
                self.settings.ldap_group_base_dn,
                f"(&(objectClass=group)(cn={escape_filter_chars(group_cn)}))",
                ["cn", "distinguishedName"],
            )
            if not groups:
                return []
            gdn = _text(groups[0].get("attributes") or {}, "distinguishedName") or str(groups[0].get("dn") or "")
            flt = f"(&(objectClass=user)(objectCategory=person)(memberOf:{IN_CHAIN}:={escape_filter_chars(gdn)}))"
            found = self._search(conn, self.settings.ldap_base_dn, flt, USER_ATTRS)
        return [user_from_entry(e) for e in found]