"""Client connection options for the async Python wrapper."""

from __future__ import annotations

import ssl
from collections.abc import Sequence
from dataclasses import dataclass, field
from pathlib import Path

import grpc

from .auth import REDACTED, ApiKey
from .errors import MxGatewayTransportError


@dataclass(frozen=True)
class ClientOptions:
    """Connection settings for `GatewayClient.connect`."""

    endpoint: str
    api_key: str | ApiKey | None = None
    plaintext: bool = False
    ca_file: str | None = None
    require_certificate_validation: bool = False
    server_name_override: str | None = None
    call_timeout: float | None = 30.0
    stream_timeout: float | None = None
    max_grpc_message_bytes: int = 16 * 1024 * 1024

    def __post_init__(self) -> None:
        """Validate options; raise `ValueError` for invalid combinations."""
        if not self.endpoint:
            raise ValueError("endpoint must not be empty")

        if self.plaintext and self.ca_file:
            raise ValueError("ca_file cannot be used with plaintext connections")
        if self.call_timeout is not None and self.call_timeout <= 0:
            raise ValueError("call_timeout must be greater than zero")
        if self.stream_timeout is not None and self.stream_timeout <= 0:
            raise ValueError("stream_timeout must be greater than zero")
        if self.max_grpc_message_bytes <= 0:
            raise ValueError("max_grpc_message_bytes must be greater than zero")

    def __repr__(self) -> str:
        """Return a repr that redacts the API key value."""
        api_key = REDACTED if self.api_key else None
        return (
            f"{type(self).__name__}(endpoint={self.endpoint!r}, "
            f"api_key={api_key!r}, plaintext={self.plaintext!r}, "
            f"ca_file={self.ca_file!r}, "
            f"require_certificate_validation={self.require_certificate_validation!r}, "
            f"server_name_override={self.server_name_override!r}, "
            f"call_timeout={self.call_timeout!r}, "
            f"stream_timeout={self.stream_timeout!r}, "
            f"max_grpc_message_bytes={self.max_grpc_message_bytes!r})"
        )


@dataclass(frozen=True)
class BrowseChildrenOptions:
    """Filters and shape options for ``GalaxyRepositoryClient.browse``.

    Mirrors the AND-combined filter set on ``BrowseChildrenRequest`` so a
    single instance can be re-used across an entire lazy browse session
    (the filter set is part of the page-token contract).
    """

    category_ids: Sequence[int] = field(default_factory=tuple)
    template_chain_contains: Sequence[str] = field(default_factory=tuple)
    tag_name_glob: str | None = None
    include_attributes: bool | None = None
    alarm_bearing_only: bool = False
    historized_only: bool = False


def _split_authority(endpoint: str) -> tuple[str, int]:
    """Split a gRPC target (optionally scheme-prefixed) into (host, port).

    Handles bracketed IPv6 literals (e.g. ``[::1]:5120`` or bare ``[::1]``),
    returning the host without brackets so it is safe to pass to
    ``ssl.get_server_certificate``.
    """
    target = endpoint.split("://", 1)[-1]
    if target.startswith("["):
        # Bracketed IPv6: "[::1]:5120" or "[::1]"
        bracket_end = target.find("]")
        host = target[1:bracket_end]  # strip surrounding brackets
        remainder = target[bracket_end + 1 :]  # ":5120" or ""
        port_str = remainder.lstrip(":")
        return (host, int(port_str) if port_str else 443)
    host, _, port = target.rpartition(":")
    return (host or "localhost", int(port) if port else 443)


def create_channel(options: ClientOptions) -> grpc.aio.Channel:
    """Create a plaintext or TLS `grpc.aio` channel from client options.

    The TLS default is lenient: grpc-python has no per-channel skip-verify, so
    the server's presented certificate is fetched once (unverified) and pinned
    as the channel's only trust root (trust-on-first-use). Set
    `require_certificate_validation=True` to force system-trust verification, or
    pass `ca_file` to verify against a specific CA — both bypass the TOFU path.
    """

    channel_options: list[tuple[str, str | int]] = [
        ("grpc.max_receive_message_length", options.max_grpc_message_bytes),
        ("grpc.max_send_message_length", options.max_grpc_message_bytes),
    ]
    if options.server_name_override:
        channel_options.append(("grpc.ssl_target_name_override", options.server_name_override))

    if options.plaintext:
        return grpc.aio.insecure_channel(options.endpoint, options=channel_options)

    if options.ca_file:
        root_certificates = Path(options.ca_file).read_bytes()
        credentials = grpc.ssl_channel_credentials(root_certificates=root_certificates)
    elif options.require_certificate_validation:
        credentials = grpc.ssl_channel_credentials()
    else:
        # Lenient default: grpc-python has no per-channel skip-verify, so fetch the
        # server's certificate (unverified) and pin it for this channel (TOFU).
        host, port = _split_authority(options.endpoint)
        try:
            presented = ssl.get_server_certificate((host, port))
        except OSError as error:
            raise MxGatewayTransportError(
                f"failed to fetch TLS certificate from {options.endpoint}: {error}"
            ) from error
        credentials = grpc.ssl_channel_credentials(root_certificates=presented.encode("ascii"))
        # The gateway self-signed cert always carries a "localhost" SAN, so default
        # the SNI/target-name override to it when none was supplied, tolerating
        # dial-by-IP or hostname mismatch.
        if not options.server_name_override:
            channel_options.append(("grpc.ssl_target_name_override", "localhost"))

    return grpc.aio.secure_channel(
        options.endpoint,
        credentials,
        options=channel_options,
    )