"""Task status watchers for docling-serve client jobs."""

from __future__ import annotations

import asyncio
import logging
import time
from collections.abc import AsyncIterator, Awaitable, Callable, Iterator
from typing import Protocol

from websockets.asyncio.client import connect as async_ws_connect
from websockets.exceptions import ConnectionClosedError, ConnectionClosedOK
from websockets.sync.client import connect

from docling.datamodel.service.responses import (
    MessageKind,
    TaskStatusResponse,
    WebsocketMessage,
)
from docling.service_client.exceptions import (
    ServiceUnavailableError,
    TaskNotFoundError,
    TaskTimeoutError,
)

_logger = logging.getLogger(__name__)

TERMINAL_TASK_STATUSES: set[str] = {"success", "failure"}
WS_MAX_RECONNECT_ATTEMPTS = 3
WS_RECONNECT_BACKOFF_BASE_SECONDS = 1.0


def is_terminal_task_status(status: TaskStatusResponse) -> bool:
    return status.task_status in TERMINAL_TASK_STATUSES


def _poll_sleep_duration(
    poll_started: float, poll_interval: float, deadline: float
) -> float:
    elapsed = time.monotonic() - poll_started
    remaining = deadline - time.monotonic()
    if remaining <= 0:
        return 0.0
    return max(0.0, min(poll_interval, remaining) - elapsed)


def _process_ws_envelope(
    envelope: WebsocketMessage,
    task_id: str,
) -> TaskStatusResponse | None:
    """Return the TaskStatusResponse from an envelope, or None for CONNECTION frames.

    Raises TaskNotFoundError or ServiceUnavailableError on error frames.
    """
    if envelope.error:
        if envelope.error == "Task not found.":
            raise TaskNotFoundError(f"Task {task_id} was not found.")
        raise ServiceUnavailableError(
            "WebSocket status stream failed.",
            detail=envelope.error,
        )
    return envelope.task


class StatusWatcher(Protocol):
    """Protocol for job status watchers."""

    def iter_updates(
        self, task_id: str, timeout: float | None
    ) -> Iterator[TaskStatusResponse]: ...

    def wait_for_terminal(
        self, task_id: str, timeout: float | None
    ) -> TaskStatusResponse: ...


class AsyncStatusWatcher(Protocol):
    """Protocol for async job status watchers."""

    def iter_updates(
        self, task_id: str, timeout: float | None
    ) -> AsyncIterator[TaskStatusResponse]: ...

    async def wait_for_terminal(
        self, task_id: str, timeout: float | None
    ) -> TaskStatusResponse: ...


class PollingWatcher:
    """Status watcher using `GET /v1/status/poll/{task_id}` with server-side wait."""

    def __init__(
        self,
        poll_status: Callable[[str, float], TaskStatusResponse],
        poll_server_wait: float,
        poll_client_interval: float | None,
        default_timeout: float,
    ) -> None:
        self._poll_status = poll_status
        self._poll_server_wait = poll_server_wait
        self._poll_client_interval = (
            poll_server_wait if poll_client_interval is None else poll_client_interval
        )
        self._default_timeout = default_timeout

    def iter_updates(
        self, task_id: str, timeout: float | None = None
    ) -> Iterator[TaskStatusResponse]:
        wait_timeout = self._default_timeout if timeout is None else timeout
        deadline = time.monotonic() + wait_timeout
        while True:
            remaining = deadline - time.monotonic()
            if remaining <= 0:
                raise TaskTimeoutError(
                    f"Timed out waiting for task {task_id} after {wait_timeout:.2f}s."
                )

            poll_wait = min(self._poll_server_wait, remaining)
            poll_started = time.monotonic()
            update = self._poll_status(task_id, poll_wait)
            yield update
            if is_terminal_task_status(update):
                return

            # Keep a minimum client-side poll cadence when server-side wait is ignored.
            sleep_for = _poll_sleep_duration(
                poll_started=poll_started,
                poll_interval=self._poll_client_interval,
                deadline=deadline,
            )
            if sleep_for > 0:
                time.sleep(sleep_for)

    def wait_for_terminal(
        self, task_id: str, timeout: float | None = None
    ) -> TaskStatusResponse:
        final_status: TaskStatusResponse | None = None
        for update in self.iter_updates(task_id=task_id, timeout=timeout):
            final_status = update

        if final_status is None:
            raise TaskTimeoutError(
                f"Timed out waiting for task {task_id} to emit status updates."
            )
        return final_status


class WebSocketWatcher:
    """Status watcher using `WS /v1/status/ws/{task_id}` with poll fallback."""

    def __init__(
        self,
        ws_url_for_task: Callable[[str], str],
        poll_fallback: PollingWatcher | None,
        fallback_to_poll: bool,
        connect_timeout: float,
        default_timeout: float,
        additional_headers: dict[str, str] | None = None,
    ) -> None:
        self._ws_url_for_task = ws_url_for_task
        self._poll_fallback = poll_fallback
        self._fallback_to_poll = fallback_to_poll
        self._connect_timeout = connect_timeout
        self._default_timeout = default_timeout
        self._additional_headers = additional_headers or {}

    def iter_updates(
        self, task_id: str, timeout: float | None = None
    ) -> Iterator[TaskStatusResponse]:
        wait_timeout = self._default_timeout if timeout is None else timeout
        try:
            yield from self._iter_ws_updates(task_id=task_id, timeout=wait_timeout)
        except ServiceUnavailableError:
            if self._fallback_to_poll and self._poll_fallback is not None:
                yield from self._poll_fallback.iter_updates(
                    task_id=task_id, timeout=wait_timeout
                )
                return
            raise

    def wait_for_terminal(
        self, task_id: str, timeout: float | None = None
    ) -> TaskStatusResponse:
        final_status: TaskStatusResponse | None = None
        for update in self.iter_updates(task_id=task_id, timeout=timeout):
            final_status = update

        if final_status is None:
            raise TaskTimeoutError(
                f"Timed out waiting for task {task_id} to emit status updates."
            )
        return final_status

    def _iter_ws_updates(
        self, task_id: str, timeout: float
    ) -> Iterator[TaskStatusResponse]:
        ws_url = self._ws_url_for_task(task_id)
        deadline = time.monotonic() + timeout

        for attempt in range(WS_MAX_RECONNECT_ATTEMPTS + 1):
            try:
                yield from self._iter_ws_connection(ws_url, task_id, deadline, timeout)
                return
            except (ConnectionClosedError, OSError) as exc:
                remaining = deadline - time.monotonic()
                if attempt >= WS_MAX_RECONNECT_ATTEMPTS or remaining <= 0:
                    raise ServiceUnavailableError(
                        "WebSocket status stream is unavailable.", detail=str(exc)
                    ) from exc
                delay = min(WS_RECONNECT_BACKOFF_BASE_SECONDS * (2**attempt), remaining)
                _logger.warning(
                    "WebSocket connection dropped for task %s: %s — reconnecting in %.1fs",
                    task_id,
                    exc,
                    delay,
                )
                time.sleep(delay)
            except (TaskTimeoutError, TaskNotFoundError, ServiceUnavailableError):
                raise
            except Exception as exc:
                raise ServiceUnavailableError(
                    "WebSocket status stream is unavailable.", detail=str(exc)
                ) from exc

    def _iter_ws_connection(
        self, ws_url: str, task_id: str, deadline: float, timeout: float
    ) -> Iterator[TaskStatusResponse]:
        with connect(
            ws_url,
            open_timeout=self._connect_timeout,
            close_timeout=self._connect_timeout,
            additional_headers=self._additional_headers,
        ) as websocket:
            while True:
                remaining = deadline - time.monotonic()
                if remaining <= 0:
                    raise TaskTimeoutError(
                        f"Timed out waiting for task {task_id} after {timeout:.2f}s."
                    )

                raw_message = websocket.recv(timeout=remaining)
                envelope = WebsocketMessage.model_validate_json(raw_message)
                status = _process_ws_envelope(envelope, task_id)

                if status is None:
                    continue

                yield status
                if is_terminal_task_status(status):
                    return

                # Only send "next" for UPDATE messages.  The server sends
                # CONNECTION once before the update loop begins; sending
                # "next" in response to it would queue an extra token that
                # the server later consumes as a request for a post-terminal
                # UPDATE, causing a send-after-close RuntimeError.
                if envelope.message == MessageKind.UPDATE:
                    try:
                        websocket.send("next")
                    except ConnectionClosedOK:
                        # The current server contract mixes request/response
                        # "next" handshakes with async notifier-driven closes.
                        # Under that contract, the socket may close cleanly
                        # after an UPDATE but before the client can ask for
                        # the next one. Treat that as normal end-of-stream.
                        #
                        # Once the server websocket contract is simplified to
                        # a pure push stream, remove the "next" handshake
                        # entirely instead of keeping this special case.
                        return


class AsyncPollingWatcher:
    """Async status watcher using `GET /v1/status/poll/{task_id}` with server-side wait."""

    def __init__(
        self,
        poll_status: Callable[[str, float], Awaitable[TaskStatusResponse]],
        poll_server_wait: float,
        poll_client_interval: float | None,
        default_timeout: float,
    ) -> None:
        self._poll_status = poll_status
        self._poll_server_wait = poll_server_wait
        self._poll_client_interval = (
            poll_server_wait if poll_client_interval is None else poll_client_interval
        )
        self._default_timeout = default_timeout

    async def iter_updates(
        self, task_id: str, timeout: float | None = None
    ) -> AsyncIterator[TaskStatusResponse]:  # type: ignore[override]
        wait_timeout = self._default_timeout if timeout is None else timeout
        deadline = time.monotonic() + wait_timeout
        while True:
            remaining = deadline - time.monotonic()
            if remaining <= 0:
                raise TaskTimeoutError(
                    f"Timed out waiting for task {task_id} after {wait_timeout:.2f}s."
                )

            poll_wait = min(self._poll_server_wait, remaining)
            poll_started = time.monotonic()
            update = await self._poll_status(task_id, poll_wait)
            yield update
            if is_terminal_task_status(update):
                return

            # Keep a minimum client-side poll cadence when server-side wait is ignored.
            sleep_for = _poll_sleep_duration(
                poll_started=poll_started,
                poll_interval=self._poll_client_interval,
                deadline=deadline,
            )
            if sleep_for > 0:
                await asyncio.sleep(sleep_for)

    async def wait_for_terminal(
        self, task_id: str, timeout: float | None = None
    ) -> TaskStatusResponse:
        final_status: TaskStatusResponse | None = None
        async for update in self.iter_updates(task_id=task_id, timeout=timeout):
            final_status = update

        if final_status is None:
            raise TaskTimeoutError(
                f"Timed out waiting for task {task_id} to emit status updates."
            )
        return final_status


class AsyncWebSocketWatcher:
    """Async status watcher using `WS /v1/status/ws/{task_id}` with poll fallback."""

    def __init__(
        self,
        ws_url_for_task: Callable[[str], str],
        poll_fallback: AsyncPollingWatcher | None,
        fallback_to_poll: bool,
        connect_timeout: float,
        default_timeout: float,
        additional_headers: dict[str, str] | None = None,
    ) -> None:
        self._ws_url_for_task = ws_url_for_task
        self._poll_fallback = poll_fallback
        self._fallback_to_poll = fallback_to_poll
        self._connect_timeout = connect_timeout
        self._default_timeout = default_timeout
        self._additional_headers = additional_headers or {}

    async def iter_updates(
        self, task_id: str, timeout: float | None = None
    ) -> AsyncIterator[TaskStatusResponse]:  # type: ignore[override]
        wait_timeout = self._default_timeout if timeout is None else timeout
        try:
            async for update in self._iter_ws_updates(
                task_id=task_id, timeout=wait_timeout
            ):
                yield update
        except ServiceUnavailableError:
            if self._fallback_to_poll and self._poll_fallback is not None:
                async for update in self._poll_fallback.iter_updates(
                    task_id=task_id, timeout=wait_timeout
                ):
                    yield update
                return
            raise

    async def wait_for_terminal(
        self, task_id: str, timeout: float | None = None
    ) -> TaskStatusResponse:
        final_status: TaskStatusResponse | None = None
        async for update in self.iter_updates(task_id=task_id, timeout=timeout):
            final_status = update

        if final_status is None:
            raise TaskTimeoutError(
                f"Timed out waiting for task {task_id} to emit status updates."
            )
        return final_status

    async def _iter_ws_updates(
        self, task_id: str, timeout: float
    ) -> AsyncIterator[TaskStatusResponse]:  # type: ignore[override]
        ws_url = self._ws_url_for_task(task_id)
        deadline = time.monotonic() + timeout

        for attempt in range(WS_MAX_RECONNECT_ATTEMPTS + 1):
            try:
                async for update in self._iter_ws_connection(
                    ws_url, task_id, deadline, timeout
                ):
                    yield update
                return
            except (ConnectionClosedError, OSError) as exc:
                remaining = deadline - time.monotonic()
                if attempt >= WS_MAX_RECONNECT_ATTEMPTS or remaining <= 0:
                    raise ServiceUnavailableError(
                        "WebSocket status stream is unavailable.", detail=str(exc)
                    ) from exc
                delay = min(WS_RECONNECT_BACKOFF_BASE_SECONDS * (2**attempt), remaining)
                _logger.warning(
                    "WebSocket connection dropped for task %s: %s — reconnecting in %.1fs",
                    task_id,
                    exc,
                    delay,
                )
                await asyncio.sleep(delay)
            except (TaskTimeoutError, TaskNotFoundError, ServiceUnavailableError):
                raise
            except Exception as exc:
                raise ServiceUnavailableError(
                    "WebSocket status stream is unavailable.", detail=str(exc)
                ) from exc

    async def _iter_ws_connection(
        self, ws_url: str, task_id: str, deadline: float, timeout: float
    ) -> AsyncIterator[TaskStatusResponse]:  # type: ignore[override]
        async with async_ws_connect(
            ws_url,
            open_timeout=self._connect_timeout,
            close_timeout=self._connect_timeout,
            additional_headers=self._additional_headers,
        ) as websocket:
            while True:
                remaining = deadline - time.monotonic()
                if remaining <= 0:
                    raise TaskTimeoutError(
                        f"Timed out waiting for task {task_id} after {timeout:.2f}s."
                    )

                try:
                    raw_message = await asyncio.wait_for(
                        websocket.recv(), timeout=remaining
                    )
                except asyncio.TimeoutError:
                    raise TaskTimeoutError(
                        f"Timed out waiting for task {task_id} after {timeout:.2f}s."
                    )

                envelope = WebsocketMessage.model_validate_json(raw_message)
                status = _process_ws_envelope(envelope, task_id)

                if status is None:
                    continue

                yield status
                if is_terminal_task_status(status):
                    return

                if envelope.message == MessageKind.UPDATE:
                    try:
                        await websocket.send("next")
                    except ConnectionClosedOK:
                        return
