# Copyright (c) Meta Platforms, Inc. and affiliates.
# All rights reserved.
#
# This source code is licensed under the terms described in the LICENSE file in
# the root directory of this source tree.

import asyncio
import json
import signal
from collections.abc import (
    AsyncGenerator as AsyncGeneratorABC,
    AsyncIterator as AsyncIteratorABC,
)
from contextlib import asynccontextmanager
from typing import Any, AsyncGenerator, AsyncIterator, Dict, get_type_hints, Optional

import fire
import httpx
import yaml
from dotenv import load_dotenv

from fastapi import FastAPI, HTTPException, Request
from fastapi.exceptions import RequestValidationError
from fastapi.responses import JSONResponse, StreamingResponse
from fastapi.routing import APIRoute

from pydantic import BaseModel, ValidationError
from termcolor import cprint

from .datatypes import PassthroughApiAdapter
from .distribution import api_surface_endpoints
from .dynamic import instantiate_adapter

from .registry import resolve_distribution

load_dotenv()


def is_async_iterator_type(typ):
    if hasattr(typ, "__origin__"):
        origin = typ.__origin__
        if isinstance(origin, type):
            return issubclass(
                origin,
                (AsyncIterator, AsyncGenerator, AsyncIteratorABC, AsyncGeneratorABC),
            )
        return False
    return isinstance(
        typ, (AsyncIterator, AsyncGenerator, AsyncIteratorABC, AsyncGeneratorABC)
    )


def create_sse_event(data: Any) -> str:
    if isinstance(data, BaseModel):
        data = data.json()
    else:
        data = json.dumps(data)

    return f"data: {data}\n\n"


async def global_exception_handler(request: Request, exc: Exception):
    http_exc = translate_exception(exc)

    return JSONResponse(
        status_code=http_exc.status_code, content={"error": {"detail": http_exc.detail}}
    )


def translate_exception(exc: Exception) -> HTTPException:
    if isinstance(exc, ValidationError):
        return RequestValidationError(exc.raw_errors)

    # Add more custom exception translations here
    return HTTPException(status_code=500, detail="Internal server error")


async def passthrough(
    request: Request,
    downstream_url: str,
    downstream_headers: Optional[Dict[str, str]] = None,
):
    client = httpx.AsyncClient()

    headers = dict(request.headers)
    headers.pop("host", None)
    headers.update(downstream_headers or {})

    body = await request.body()

    try:
        response = await client.request(
            method=request.method,
            url=downstream_url,
            headers=headers,
            content=body,
            params=request.query_params,
        )
        return StreamingResponse(
            response.iter_bytes(),
            status_code=response.status_code,
            headers=dict(response.headers),
        )
    finally:
        await client.aclose()


def handle_sigint(*args, **kwargs):
    print("SIGINT or CTRL-C detected. Exiting gracefully", args)
    loop = asyncio.get_event_loop()
    for task in asyncio.all_tasks(loop):
        task.cancel()
    loop.stop()


@asynccontextmanager
async def lifespan(app: FastAPI):
    print("Starting up")
    yield
    print("Shutting down")


def create_dynamic_passthrough(
    downstream_url: str, downstream_headers: Optional[Dict[str, str]] = None
):
    async def endpoint(request: Request):
        return await passthrough(request, downstream_url, downstream_headers)

    return endpoint


def create_dynamic_typed_route(func: Any):
    hints = get_type_hints(func)
    request_model = next(iter(hints.values()))
    response_model = hints["return"]

    is_streaming = is_async_iterator_type(response_model)

    if is_streaming:

        async def endpoint(request: request_model):
            async def sse_generator(event_gen):
                try:
                    async for item in event_gen:
                        yield create_sse_event(item)
                        await asyncio.sleep(0.01)
                except asyncio.CancelledError:
                    print("Generator cancelled")
                    await event_gen.aclose()
                except Exception as e:
                    yield create_sse_event(
                        {
                            "error": {
                                "message": str(translate_exception(e)),
                            },
                        }
                    )

            return StreamingResponse(
                sse_generator(func(request2)), media_type="text/event-stream"
            )

    else:

        async def endpoint(request: request_model):
            try:
                return func(request)
            except Exception as e:
                raise translate_exception(e) from e

    return endpoint


def main(
    dist_name: str, yaml_config: str, port: int = 5000, disable_ipv6: bool = False
):
    dist = resolve_distribution(dist_name)
    if dist is None:
        raise ValueError(f"Could not find distribution {dist_name}")

    with open(yaml_config, "r") as fp:
        config = yaml.safe_load(fp)

    app = FastAPI()

    all_endpoints = api_surface_endpoints()

    adapter_configs = config["adapters"]
    for surface, adapter in dist.adapters.items():
        if surface.value not in adapter_configs:
            raise ValueError(
                f"Could not find adapter config for {surface}. Please add it to the config"
            )

        adapter_config = adapter_configs[surface.value]
        endpoints = all_endpoints[surface]
        if isinstance(adapter, PassthroughApiAdapter):
            for endpoint in endpoints:
                url = adapter.base_url.rstrip("/") + endpoint.route
                getattr(app, endpoint.method)(endpoint.route)(
                    create_dynamic_passthrough(url)
                )
        else:
            impl = instantiate_adapter(adapter, adapter_config)
            for endpoint in endpoints:
                if not hasattr(impl, endpoint.name):
                    # ideally this should be a typing violation already
                    raise ValueError(
                        f"Could not find method {endpoint.name} on {impl}!!"
                    )

                impl_method = getattr(impl, endpoint.name)
                getattr(app, endpoint.method)(endpoint.route, response_model=None)(
                    create_dynamic_typed_route(impl_method)
                )

    for route in app.routes:
        if isinstance(route, APIRoute):
            cprint(
                f"Serving {next(iter(route.methods))} {route.path}",
                "white",
                attrs=["bold"],
            )

    app.exception_handler(Exception)(global_exception_handler)
    signal.signal(signal.SIGINT, handle_sigint)

    import uvicorn

    # FYI this does not do hot-reloads
    listen_host = "::" if not disable_ipv6 else "0.0.0.0"
    print(f"Listening on {listen_host}:{port}")
    uvicorn.run(app, host=listen_host, port=port)


if __name__ == "__main__":
    fire.Fire(main)