import asyncio
import concurrent
import concurrent.futures
import inspect
import logging
import os
import signal
import sys
import threading
import time
from abc import ABC, abstractmethod
from contextlib import asynccontextmanager
from functools import update_wrapper
from typing import (
    Any,
    Awaitable,
    Callable,
    Concatenate,
    Coroutine,
    Optional,
    ParamSpec,
    Tuple,
    Type,
    TypeVar,
    cast,
)

import httpx
import uvicorn
from fastapi import FastAPI, Request, responses
from prisma.errors import DataError, UniqueViolationError
from pydantic import BaseModel, TypeAdapter, create_model

import backend.util.exceptions as exceptions
from backend.monitoring.instrumentation import instrument_fastapi
from backend.util.json import to_dict
from backend.util.metrics import sentry_init
from backend.util.process import AppProcess
from backend.util.retry import conn_retry, create_retry_decorator
from backend.util.settings import Config, get_service_name

logger = logging.getLogger(__name__)
T = TypeVar("T")
C = TypeVar("C", bound=Callable)

config = Config()
api_host = config.pyro_host
api_comm_retry = config.pyro_client_comm_retry
api_comm_timeout = config.pyro_client_comm_timeout
api_call_timeout = config.rpc_client_call_timeout
api_comm_max_wait = config.pyro_client_max_wait


def _validate_no_prisma_objects(obj: Any, path: str = "result") -> None:
    """
    Recursively validate that no Prisma objects are being returned from service methods.
    This enforces proper separation of layers - only application models should cross service boundaries.
    """
    if obj is None:
        return

    # Check if it's a Prisma model object
    if hasattr(obj, "__class__") and hasattr(obj.__class__, "__module__"):
        module_name = obj.__class__.__module__
        if module_name and "prisma.models" in module_name:
            raise ValueError(
                f"Prisma object {obj.__class__.__name__} found in {path}. "
                "Service methods must return application models, not Prisma objects. "
                f"Use {obj.__class__.__name__}.from_db() to convert to application model."
            )

    # Recursively check collections
    if isinstance(obj, (list, tuple)):
        for i, item in enumerate(obj):
            _validate_no_prisma_objects(item, f"{path}[{i}]")
    elif isinstance(obj, dict):
        for key, value in obj.items():
            _validate_no_prisma_objects(value, f"{path}['{key}']")


P = ParamSpec("P")
R = TypeVar("R")
EXPOSED_FLAG = "__exposed__"


def expose(func: C) -> C:
    func = getattr(func, "__func__", func)
    setattr(func, EXPOSED_FLAG, True)
    return func


# --------------------------------------------------
# AppService for IPC service based on HTTP request through FastAPI
# --------------------------------------------------
class BaseAppService(AppProcess, ABC):
    shared_event_loop: asyncio.AbstractEventLoop

    @classmethod
    @abstractmethod
    def get_port(cls) -> int:
        pass

    @classmethod
    def get_host(cls) -> str:
        source_host = os.environ.get(f"{get_service_name().upper()}_HOST", api_host)
        target_host = os.environ.get(f"{cls.__name__.upper()}_HOST", api_host)

        if source_host == target_host and source_host != api_host:
            logger.warning(
                f"Service {cls.__name__} is the same host as the source service."
                f"Use the localhost of {api_host} instead."
            )
            return api_host

        return target_host

    def run_service(self) -> None:
        # HACK: run the main event loop outside the main thread to disable Uvicorn's
        # internal signal handlers, since there is no config option for this :(
        shared_asyncio_thread = threading.Thread(
            target=self._run_shared_event_loop,
            daemon=True,
            name=f"{self.service_name}-shared-event-loop",
        )
        shared_asyncio_thread.start()
        shared_asyncio_thread.join()

    def _run_shared_event_loop(self) -> None:
        try:
            self.shared_event_loop.run_forever()
        finally:
            logger.info(f"[{self.service_name}] 🛑 Shared event loop stopped")
            self.shared_event_loop.close()  # ensure held resources are released

    def run_and_wait(self, coro: Coroutine[Any, Any, T]) -> T:
        return asyncio.run_coroutine_threadsafe(coro, self.shared_event_loop).result()

    def run(self):
        self.shared_event_loop = asyncio.new_event_loop()
        asyncio.set_event_loop(self.shared_event_loop)

    def cleanup(self):
        """
        **💡 Overriding `AppService.lifespan` may be a more convenient option.**

        Implement this method on a subclass to do post-execution cleanup,
        e.g. disconnecting from a database or terminating child processes.

        **Note:** if you override this method in a subclass, it must call
        `super().cleanup()` *at the end*!
        """
        # Stop the shared event loop to allow resource clean-up
        self.shared_event_loop.call_soon_threadsafe(self.shared_event_loop.stop)

        super().cleanup()


class RemoteCallError(BaseModel):
    type: str = "RemoteCallError"
    args: Optional[Tuple[Any, ...]] = None


class UnhealthyServiceError(ValueError):
    def __init__(
        self, message: str = "Service is unhealthy or not ready", log: bool = True
    ):
        msg = f"[{get_service_name()}] - {message}"
        super().__init__(msg)
        self.message = msg
        if log:
            logger.error(self.message)

    def __str__(self):
        return self.message


class HTTPClientError(Exception):
    """Exception for HTTP client errors (4xx status codes) that should not be retried."""

    def __init__(self, status_code: int, message: str):
        self.status_code = status_code
        super().__init__(f"HTTP {status_code}: {message}")


class HTTPServerError(Exception):
    """Exception for HTTP server errors (5xx status codes) that can be retried."""

    def __init__(self, status_code: int, message: str):
        self.status_code = status_code
        super().__init__(f"HTTP {status_code}: {message}")


EXCEPTION_MAPPING = {
    e.__name__: e
    for e in [
        ValueError,
        DataError,
        RuntimeError,
        TimeoutError,
        ConnectionError,
        UnhealthyServiceError,
        HTTPClientError,
        HTTPServerError,
        UniqueViolationError,
        *[
            ErrorType
            for _, ErrorType in inspect.getmembers(exceptions)
            if inspect.isclass(ErrorType)
            and issubclass(ErrorType, Exception)
            and ErrorType.__module__ == exceptions.__name__
        ],
    ]
}


class AppService(BaseAppService, ABC):
    fastapi_app: FastAPI
    http_server: uvicorn.Server | None = None
    log_level: str = "info"

    def set_log_level(self, log_level: str):
        """Set the uvicorn log level. Returns self for chaining."""
        self.log_level = log_level
        return self

    @staticmethod
    def _handle_internal_http_error(status_code: int = 500, log_error: bool = True):
        def handler(request: Request, exc: Exception):
            if log_error:
                if status_code >= 500:
                    logger.error(
                        f"{request.method} {request.url.path} failed: {exc}",
                        exc_info=exc,
                    )
                else:
                    logger.warning(
                        f"{request.method} {request.url.path} failed: {exc}",
                        exc_info=exc,
                    )
            return responses.JSONResponse(
                status_code=status_code,
                content=RemoteCallError(
                    type=str(exc.__class__.__name__),
                    args=exc.args or (str(exc),),
                ).model_dump(),
            )

        return handler

    def _create_fastapi_endpoint(self, func: Callable) -> Callable:
        """
        Generates a FastAPI endpoint for the given function, handling default and optional parameters.

        :param func: The original function (sync/async, bound or unbound)
        :return: A FastAPI endpoint function.
        """
        sig = inspect.signature(func)
        fields = {}

        is_bound_method = False
        for name, param in sig.parameters.items():
            if name in ("self", "cls"):
                is_bound_method = True
                continue

            # Use the provided annotation or fallback to str if not specified
            annotation = (
                param.annotation if param.annotation != inspect.Parameter.empty else str
            )

            # If a default value is provided, use it; otherwise, mark the field as required with '...'
            default = param.default if param.default != inspect.Parameter.empty else ...

            fields[name] = (annotation, default)

        # Dynamically create a Pydantic model for the request body
        RequestBodyModel = create_model("RequestBodyModel", **fields)
        f = func.__get__(self) if is_bound_method else func

        if asyncio.iscoroutinefunction(f):

            async def async_endpoint(body: RequestBodyModel):  # type: ignore #RequestBodyModel being variable
                result = await f(
                    **{name: getattr(body, name) for name in type(body).model_fields}
                )
                _validate_no_prisma_objects(result, f"{func.__name__} result")
                return result

            return async_endpoint
        else:

            def sync_endpoint(body: RequestBodyModel):  # type: ignore #RequestBodyModel being variable
                result = f(
                    **{name: getattr(body, name) for name in type(body).model_fields}
                )
                _validate_no_prisma_objects(result, f"{func.__name__} result")
                return result

            return sync_endpoint

    @conn_retry("FastAPI server", "Running FastAPI server")
    def __start_fastapi(self):
        logger.info(
            f"[{self.service_name}] Starting RPC server at http://{api_host}:{self.get_port()}"
        )

        self.http_server = uvicorn.Server(
            uvicorn.Config(
                self.fastapi_app,
                host=api_host,
                port=self.get_port(),
                log_config=None,  # Explicitly None to avoid uvicorn replacing the logger.
                log_level=self.log_level,
            )
        )
        self.run_and_wait(self.http_server.serve())

        # Perform clean-up when the server exits
        if not self._cleaned_up:
            self._cleaned_up = True
            logger.info(f"[{self.service_name}] 🧹 Running cleanup")
            self.cleanup()
            logger.info(f"[{self.service_name}] ✅ Cleanup done")

    def _self_terminate(self, signum: int, frame):
        """Pass SIGTERM to Uvicorn so it can shut down gracefully"""
        signame = signal.Signals(signum).name
        if not self._shutting_down:
            self._shutting_down = True
            if self.http_server:
                logger.info(
                    f"[{self.service_name}] 🛑 Received {signame} ({signum}) - "
                    "Entering RPC server graceful shutdown"
                )
                self.http_server.handle_exit(signum, frame)  # stop accepting requests

                # NOTE: Actually stopping the process is triggered by:
                # 1. The call to self.cleanup() at the end of __start_fastapi() 👆🏼
                # 2. BaseAppService.cleanup() stopping the shared event loop
            else:
                logger.warning(
                    f"[{self.service_name}] {signame} received before HTTP server init."
                    " Terminating..."
                )
                sys.exit(0)

        else:
            # Expedite shutdown on second SIGTERM
            logger.info(
                f"[{self.service_name}] 🛑🛑 Received {signame} ({signum}), "
                "but shutdown is already underway. Terminating..."
            )
            sys.exit(0)

    @asynccontextmanager
    async def lifespan(self, app: FastAPI):
        """
        The FastAPI/Uvicorn server's lifespan manager, used for setup and shutdown.

        You can extend and use this in a subclass like:
        ```
        @asynccontextmanager
        async def lifespan(self, app: FastAPI):
            async with super().lifespan(app):
                await db.connect()
                yield
                await db.disconnect()
        ```
        """
        # Startup - this runs before Uvicorn starts accepting connections

        yield

        # Shutdown - this runs when FastAPI/Uvicorn shuts down
        logger.info(f"[{self.service_name}] ✅ FastAPI has finished")

    async def health_check(self) -> str:
        """A method to check the health of the process."""
        return "OK"

    def run(self):
        sentry_init()
        super().run()

        self.fastapi_app = FastAPI(lifespan=self.lifespan)

        # Add Prometheus instrumentation to all services
        try:
            instrument_fastapi(
                self.fastapi_app,
                service_name=self.service_name,
                expose_endpoint=True,
                endpoint="/metrics",
                include_in_schema=False,
            )
        except ImportError:
            logger.warning(
                f"Prometheus instrumentation not available for {self.service_name}"
            )
        except Exception as e:
            logger.error(
                f"Failed to instrument {self.service_name} with Prometheus: {e}"
            )

        # Register the exposed API routes.
        for attr_name, attr in vars(type(self)).items():
            if getattr(attr, EXPOSED_FLAG, False):
                route_path = f"/{attr_name}"
                self.fastapi_app.add_api_route(
                    route_path,
                    self._create_fastapi_endpoint(attr),
                    methods=["POST"],
                )
        self.fastapi_app.add_api_route(
            "/health_check", self.health_check, methods=["POST", "GET"]
        )
        self.fastapi_app.add_api_route(
            "/health_check_async", self.health_check, methods=["POST", "GET"]
        )
        self.fastapi_app.add_exception_handler(
            ValueError, self._handle_internal_http_error(400)
        )
        self.fastapi_app.add_exception_handler(
            DataError, self._handle_internal_http_error(400)
        )
        self.fastapi_app.add_exception_handler(
            UniqueViolationError, self._handle_internal_http_error(400)
        )
        self.fastapi_app.add_exception_handler(
            Exception, self._handle_internal_http_error(500)
        )

        # Start the FastAPI server in a separate thread.
        api_thread = threading.Thread(
            target=self.__start_fastapi,
            daemon=True,
            name=f"{self.service_name}-http-server",
        )
        api_thread.start()

        # Run the main service loop (blocking).
        self.run_service()


# --------------------------------------------------
# HTTP Client utilities for dynamic service client abstraction
# --------------------------------------------------
AS = TypeVar("AS", bound=AppService)


class AppServiceClient(ABC):
    @classmethod
    @abstractmethod
    def get_service_type(cls) -> Type[AppService]:
        pass

    def health_check(self):
        pass

    async def health_check_async(self):
        pass

    def close(self):
        pass


ASC = TypeVar("ASC", bound=AppServiceClient)


@conn_retry("AppService client", "Creating service client", max_retry=api_comm_retry)
def get_service_client(
    service_client_type: Type[ASC],
    call_timeout: int | None = api_call_timeout,
    request_retry: bool = False,
) -> ASC:

    def _maybe_retry(fn: Callable[..., R]) -> Callable[..., R]:
        """Decorate *fn* with tenacity retry when enabled."""
        if not request_retry:
            return fn

        # Use preconfigured retry decorator for service communication
        return create_retry_decorator(
            max_attempts=api_comm_retry,
            max_wait=api_comm_max_wait,
            context="Service communication",
            exclude_exceptions=(
                # Don't retry these specific exceptions that won't be fixed by retrying
                ValueError,  # Invalid input/parameters
                DataError,  # Prisma data integrity errors (foreign key, unique constraints)
                UniqueViolationError,  # Unique constraint violations
                KeyError,  # Missing required data
                TypeError,  # Wrong data types
                AttributeError,  # Missing attributes
                asyncio.CancelledError,  # Task was cancelled
                concurrent.futures.CancelledError,  # Future was cancelled
                HTTPClientError,  # HTTP 4xx client errors - don't retry
            ),
        )(fn)

    class DynamicClient:
        def __init__(self) -> None:
            service_type = service_client_type.get_service_type()
            host = service_type.get_host()
            port = service_type.get_port()
            self.base_url = f"http://{host}:{port}".rstrip("/")
            self._connection_failure_count = 0
            self._last_client_reset = 0
            self._async_clients = {}  # None key for default async client
            self._sync_clients = {}  # For sync clients (no event loop concept)

        def _create_sync_client(self) -> httpx.Client:
            return httpx.Client(
                base_url=self.base_url,
                timeout=call_timeout,
                limits=httpx.Limits(
                    max_keepalive_connections=200,  # 10x default for async concurrent calls
                    max_connections=500,  # High limit for burst handling
                    keepalive_expiry=30.0,  # Keep connections alive longer
                ),
            )

        def _create_async_client(self) -> httpx.AsyncClient:
            return httpx.AsyncClient(
                base_url=self.base_url,
                timeout=call_timeout,
                limits=httpx.Limits(
                    max_keepalive_connections=200,  # 10x default for async concurrent calls
                    max_connections=500,  # High limit for burst handling
                    keepalive_expiry=30.0,  # Keep connections alive longer
                ),
            )

        @property
        def sync_client(self) -> httpx.Client:
            """Get the sync client (thread-safe singleton)."""
            # Use service name as key for better identification
            service_name = service_client_type.get_service_type().__name__
            if client := self._sync_clients.get(service_name):
                return client
            return self._sync_clients.setdefault(
                service_name, self._create_sync_client()
            )

        @property
        def async_client(self) -> httpx.AsyncClient:
            """Get the appropriate async client for the current context.

            Returns per-event-loop client when in async context,
            falls back to default client otherwise.
            """
            try:
                loop = asyncio.get_running_loop()
            except RuntimeError:
                # No event loop, use None as default key
                loop = None

            if client := self._async_clients.get(loop):
                return client
            return self._async_clients.setdefault(loop, self._create_async_client())

        def _handle_connection_error(self, error: Exception) -> None:
            """Handle connection errors and implement self-healing"""
            self._connection_failure_count += 1
            current_time = time.time()

            # If we've had 3+ failures, and it's been more than 30 seconds since last reset
            if (
                self._connection_failure_count >= 3
                and current_time - self._last_client_reset > 30
            ):
                logger.warning(
                    f"Connection failures detected ({self._connection_failure_count}), recreating HTTP clients"
                )

                # Clear cached clients to force recreation on next access
                # Only recreate when there's actually a problem
                self._sync_clients.clear()
                self._async_clients.clear()

                # Reset counters
                self._connection_failure_count = 0
                self._last_client_reset = current_time

        def _handle_call_method_response(
            self, *, response: httpx.Response, method_name: str
        ) -> Any:
            try:
                response.raise_for_status()
                # Reset failure count on successful response
                self._connection_failure_count = 0
                return response.json()
            except httpx.HTTPStatusError as e:
                status_code = e.response.status_code

                # Try to parse the error response as RemoteCallError for mapped exceptions
                error_response = None
                try:
                    error_response = RemoteCallError.model_validate(e.response.json())
                except Exception:
                    pass

                # If we successfully parsed a mapped exception type, re-raise it
                if error_response and error_response.type in EXCEPTION_MAPPING:
                    exception_class = EXCEPTION_MAPPING[error_response.type]
                    args = error_response.args or [str(e)]

                    # Prisma DataError subclasses expect a dict `data` arg,
                    # but RPC serialization only preserves the string message
                    # from exc.args.  Wrap it in the expected structure so
                    # the constructor doesn't crash on `.get()`.
                    if issubclass(exception_class, DataError):
                        msg = str(args[0]) if args else str(e)
                        raise exception_class({"user_facing_error": {"message": msg}})

                    raise exception_class(*args)

                # Otherwise categorize by HTTP status code
                if 400 <= status_code < 500:
                    # Client errors (4xx) - wrap to prevent retries
                    raise HTTPClientError(status_code, str(e))
                elif 500 <= status_code < 600:
                    # Server errors (5xx) - wrap but allow retries
                    raise HTTPServerError(status_code, str(e))
                else:
                    # Other status codes (1xx, 2xx, 3xx) - re-raise original error
                    raise e

        @_maybe_retry
        def _call_method_sync(self, method_name: str, **kwargs: Any) -> Any:
            try:
                return self._handle_call_method_response(
                    method_name=method_name,
                    response=self.sync_client.post(method_name, json=to_dict(kwargs)),
                )
            except (httpx.ConnectError, httpx.ConnectTimeout) as e:
                self._handle_connection_error(e)
                raise

        @_maybe_retry
        async def _call_method_async(self, method_name: str, **kwargs: Any) -> Any:
            try:
                return self._handle_call_method_response(
                    method_name=method_name,
                    response=await self.async_client.post(
                        method_name, json=to_dict(kwargs)
                    ),
                )
            except (httpx.ConnectError, httpx.ConnectTimeout) as e:
                self._handle_connection_error(e)
                raise

        async def aclose(self) -> None:
            # Close all sync clients
            for client in self._sync_clients.values():
                client.close()
            self._sync_clients.clear()

            # Close all async clients (including default with None key)
            for client in self._async_clients.values():
                await client.aclose()
            self._async_clients.clear()

        def close(self) -> None:
            # Close all sync clients
            for client in self._sync_clients.values():
                client.close()
            self._sync_clients.clear()
            # Note: Cannot close async clients synchronously
            # They will be cleaned up by garbage collection

        def __del__(self):
            """Cleanup HTTP clients on garbage collection to prevent resource leaks."""
            try:
                # Close any remaining sync clients
                for client in self._sync_clients.values():
                    client.close()

                # Warn if async clients weren't properly closed
                if self._async_clients:
                    import warnings

                    warnings.warn(
                        "DynamicClient async clients not explicitly closed. "
                        "Call aclose() before destroying the client.",
                        ResourceWarning,
                        stacklevel=2,
                    )
            except Exception:
                # Silently ignore cleanup errors in __del__
                pass

        async def __aenter__(self):
            """Async context manager entry."""
            return self

        async def __aexit__(self, exc_type, exc_val, exc_tb):
            """Async context manager exit."""
            await self.aclose()

        def _get_params(
            self, signature: inspect.Signature, *args: Any, **kwargs: Any
        ) -> dict[str, Any]:
            if args:
                arg_names = list(signature.parameters.keys())
                if arg_names and arg_names[0] in ("self", "cls"):
                    arg_names = arg_names[1:]
                kwargs.update(dict(zip(arg_names, args)))
            return kwargs

        def _get_return(self, expected_return: TypeAdapter | None, result: Any) -> Any:
            """Validate and coerce the RPC result to the expected return type.

            Falls back to the raw result with a warning if validation fails.
            """
            if expected_return:
                try:
                    return expected_return.validate_python(result)
                except Exception as e:
                    logger.warning(
                        "RPC return type validation failed, using raw result: %s",
                        type(e).__name__,
                    )
                    return result
            return result

        def __getattr__(self, name: str) -> Callable[..., Any]:
            original_func = getattr(service_client_type, name, None)
            if original_func is None:
                raise AttributeError(
                    f"Method {name} not found in {service_client_type}"
                )

            rpc_name = original_func.__name__
            sig = inspect.signature(original_func)
            ret_ann = sig.return_annotation
            expected_return = (
                None if ret_ann is inspect.Signature.empty else TypeAdapter(ret_ann)
            )

            if inspect.iscoroutinefunction(original_func):

                async def async_method(*args: P.args, **kwargs: P.kwargs):
                    params = self._get_params(sig, *args, **kwargs)
                    result = await self._call_method_async(rpc_name, **params)
                    return self._get_return(expected_return, result)

                return async_method

            else:

                def sync_method(*args: P.args, **kwargs: P.kwargs):
                    params = self._get_params(sig, *args, **kwargs)
                    result = self._call_method_sync(rpc_name, **params)
                    return self._get_return(expected_return, result)

                return sync_method

    client = cast(ASC, DynamicClient())

    return client


def endpoint_to_sync(
    func: Callable[Concatenate[Any, P], Awaitable[R]],
) -> Callable[Concatenate[Any, P], R]:
    """
    Produce a *typed* stub that **looks** synchronous to the type‑checker.
    """

    def _stub(*args: P.args, **kwargs: P.kwargs) -> R:  # pragma: no cover
        raise RuntimeError("should be intercepted by __getattr__")

    update_wrapper(_stub, func)
    return cast(Callable[Concatenate[Any, P], R], _stub)


def endpoint_to_async(
    func: Callable[Concatenate[Any, P], R],
) -> Callable[Concatenate[Any, P], Awaitable[R]]:
    """
    The async mirror of `to_sync`.
    """

    async def _stub(*args: P.args, **kwargs: P.kwargs) -> R:  # pragma: no cover
        raise RuntimeError("should be intercepted by __getattr__")

    update_wrapper(_stub, func)
    return cast(Callable[Concatenate[Any, P], Awaitable[R]], _stub)
