import httpx
import asyncio
from fastapi import FastAPI, Request, Response
from fastapi.middleware.cors import CORSMiddleware
from fastapi.responses import StreamingResponse
import urllib.parse

app = FastAPI(title="Universal CORS Proxy", version="1.0.0")

# ─── CORS — sab domains allow ───────────────────────────────────────────────
app.add_middleware(
    CORSMiddleware,
    allow_origins=["*"],
    allow_credentials=True,
    allow_methods=["*"],
    allow_headers=["*"],
    expose_headers=["*"],
)

# ─── Headers jo proxy nahi karega ────────────────────────────────────────────
HOP_BY_HOP_HEADERS = {
    "connection", "keep-alive", "proxy-authenticate", "proxy-authorization",
    "te", "trailers", "transfer-encoding", "upgrade",
    "host",        # host hum khud set karenge
    "content-length",  # FastAPI khud recalculate karega — mismatch error fix
}

TIMEOUT = httpx.Timeout(30.0, connect=10.0)


def extract_target_url(path: str, query_string: str) -> str:
    """
    Path se target URL nikalo.
    Formats supported:
      /https://api.example.com/v1/users
      /http://localhost:3000/data
    """
    # leading slash hata do
    raw = path.lstrip("/")

    # agar URL encoded hai toh decode karo
    decoded = urllib.parse.unquote(raw)

    # scheme verify karo
    if not (decoded.startswith("http://") or decoded.startswith("https://")):
        return None

    # query string attach karo agar hai
    if query_string:
        decoded = f"{decoded}?{query_string}"

    return decoded


def filter_headers(headers: dict, skip: set = HOP_BY_HOP_HEADERS) -> dict:
    """Hop-by-hop headers remove karo, baaki forward karo."""
    return {k: v for k, v in headers.items() if k.lower() not in skip}


@app.get("/")
async def root():
    return {
        "service": "Universal CORS Proxy",
        "usage": "/{target_url}",
        "example": "/https://api.github.com/users/octocat",
        "methods": ["GET", "POST", "PUT", "PATCH", "DELETE", "HEAD", "OPTIONS"],
    }


@app.api_route("/{full_path:path}", methods=["GET", "POST", "PUT", "PATCH", "DELETE", "HEAD", "OPTIONS"])
async def proxy(full_path: str, request: Request):
    # ── 1. Target URL extract karo ──────────────────────────────────────────
    query_string = request.url.query
    target_url = extract_target_url(full_path, query_string)

    if not target_url:
        return Response(
            content='{"error": "Invalid URL. Use: /{full_url} e.g. /https://api.example.com/endpoint"}',
            status_code=400,
            media_type="application/json",
        )

    # ── 2. Request body lo ──────────────────────────────────────────────────
    body = await request.body()

    # ── 3. Headers filter karo ──────────────────────────────────────────────
    forward_headers = filter_headers(dict(request.headers))

    # ── 4. Actual request bhejo ─────────────────────────────────────────────
    async with httpx.AsyncClient(
        timeout=TIMEOUT,
        follow_redirects=True,
        verify=True,  # SSL verify on — production ke liye
    ) as client:
        try:
            upstream_response = await client.request(
                method=request.method,
                url=target_url,
                headers=forward_headers,
                content=body if body else None,
            )
        except httpx.ConnectError as e:
            return Response(
                content=f'{{"error": "Could not connect to target", "detail": "{str(e)}"}}',
                status_code=502,
                media_type="application/json",
            )
        except httpx.TimeoutException:
            return Response(
                content='{"error": "Request to target timed out"}',
                status_code=504,
                media_type="application/json",
            )
        except Exception as e:
            return Response(
                content=f'{{"error": "Proxy error", "detail": "{str(e)}"}}',
                status_code=500,
                media_type="application/json",
            )

    # ── 5. Response headers filter karo + CORS inject karo ──────────────────
    response_headers = filter_headers(dict(upstream_response.headers))
    response_headers["Access-Control-Allow-Origin"] = "*"
    response_headers["Access-Control-Allow-Methods"] = "GET, POST, PUT, PATCH, DELETE, HEAD, OPTIONS"
    response_headers["Access-Control-Allow-Headers"] = "*"
    response_headers["X-Proxied-By"] = "universal-cors-proxy"
    response_headers["X-Original-URL"] = target_url.split("?")[0]  # query strip for safety

    # ── 6. Response return karo ─────────────────────────────────────────────
    return Response(
        content=upstream_response.content,
        status_code=upstream_response.status_code,
        headers=response_headers,
        media_type=upstream_response.headers.get("content-type", "application/octet-stream"),
    )


# ─── Run ─────────────────────────────────────────────────────────────────────
if __name__ == "__main__":
    import uvicorn
    uvicorn.run("app:app", host="0.0.0.0", port=7860, reload=True)