"""Proxy ``FastMCP`` servers for user-declared external MCPs (``stdio``/``http``).

Built via ``fastmcp.server.create_proxy``; the proxy lazily opens its
transport on first request, so unused MCPs cost nothing until routed to.
"""

from __future__ import annotations

from typing import TYPE_CHECKING

from fastmcp import Client
from fastmcp.client.transports import StdioTransport, StreamableHttpTransport
from fastmcp.server import create_proxy

from beaver_gateway.mcp.lenient import LenientStdioTransport

if TYPE_CHECKING:
    from fastmcp import FastMCP
    from fastmcp.client.transports.base import ClientTransport

    from beaver_gateway.mcp.types import HttpMcp, StdioMcp


def build_stdio_proxy(spec: StdioMcp) -> FastMCP:
    """Wrap a stdio subprocess MCP into a mountable ``FastMCPProxy``.

    ``spec.command`` is a non-empty tuple; the first element is the
    executable and the rest are CLI args. ``StdioTransport`` keeps the
    subprocess alive across calls. When ``spec.lenient`` is set we
    swap in :class:`LenientStdioTransport`, which silently drops
    non-JSON-RPC stdout lines instead of forwarding them as exceptions
    (lets us ingest MCPs that print ``Processing...`` chatter on stdout
    without leaking warnings to downstream UIs).
    """
    if not spec.command:
        msg = f"stdio MCP {spec.name!r} has empty command"
        raise ValueError(msg)
    command, *args = spec.command
    cwd = str(spec.cwd) if spec.cwd is not None else None
    transport: ClientTransport
    if spec.lenient:
        transport = LenientStdioTransport(
            command=command, args=list(args), env=spec.env, cwd=cwd
        )
    else:
        transport = StdioTransport(
            command=command, args=list(args), env=spec.env, cwd=cwd
        )
    return create_proxy(Client(transport, name=spec.name))


def build_http_proxy(spec: HttpMcp) -> FastMCP:
    """Wrap a remote streamable-HTTP MCP into a mountable ``FastMCPProxy``.

    ``spec.headers`` are folded into the upstream client; pass per-call
    auth (e.g. ``X-Api-Key``) here rather than as ``auth`` when the
    upstream rejects Bearer headers.
    """
    transport = StreamableHttpTransport(
        url=spec.url, auth=spec.auth, headers=spec.headers
    )
    return create_proxy(Client(transport, name=spec.name))