"""
Proxy all /api/documents/* requests to doc-service:8001/documents/*.

Uses a module-level AsyncClient for connection pooling.
Strips hop-by-hop headers that must not be forwarded.
"""
import os

import httpx
from fastapi import APIRouter, Depends, HTTPException, Request
from fastapi.responses import Response

from app.deps import get_current_user
from app.models.user import User

DOC_SERVICE_URL = os.environ.get("DOC_SERVICE_URL", "http://doc-service:8001")

_client = httpx.AsyncClient(base_url=DOC_SERVICE_URL, timeout=120.0)

router = APIRouter()

# Headers that must not be forwarded in either direction.
# Also strip accept-encoding so doc-service never compresses responses —
# httpx decompresses transparently but the content-encoding header would
# then mismatch the already-decompressed body we forward to the browser.
_HOP_BY_HOP = frozenset([
    "connection",
    "keep-alive",
    "proxy-authenticate",
    "proxy-authorization",
    "te",
    "trailers",
    "transfer-encoding",
    "upgrade",
    "host",
    "accept-encoding",
])

# Additional response headers we let FastAPI recalculate rather than forward.
# content-length is set automatically from the response body size.
# content-type is set via the media_type argument, so strip it from headers
# to avoid duplicates.
_STRIP_RESPONSE = frozenset([*_HOP_BY_HOP, "content-length", "content-type"])


def _forward_headers(request: Request, user_id: str) -> dict:
    headers = {
        k: v
        for k, v in request.headers.items()
        if k.lower() not in _HOP_BY_HOP
    }
    headers["x-user-id"] = user_id
    return headers


@router.api_route("", methods=["GET", "POST"])
@router.api_route("/{path:path}", methods=["GET", "POST", "PUT", "PATCH", "DELETE"])
async def proxy_documents(
    request: Request,
    current_user: User = Depends(get_current_user),
    path: str = "",
) -> Response:
    url = f"/documents/{path}" if path else "/documents"
    headers = _forward_headers(request, str(current_user.id))
    body = await request.body()

    try:
        response = await _client.request(
            method=request.method,
            url=url,
            headers=headers,
            content=body,
            params=dict(request.query_params),
        )
    except httpx.RequestError as exc:
        raise HTTPException(status_code=502, detail=f"doc-service unreachable: {exc}")

    resp_headers = {
        k: v
        for k, v in response.headers.items()
        if k.lower() not in _STRIP_RESPONSE
    }

    return Response(
        content=response.content,
        status_code=response.status_code,
        headers=resp_headers,
        media_type=response.headers.get("content-type"),
    )