from __future__ import annotations

import asyncio
import hashlib
from collections.abc import AsyncGenerator, Awaitable, Callable
from dataclasses import dataclass, field
from datetime import UTC, datetime, timedelta
from typing import Protocol

from datastar_py import ServerSentEventGenerator as SSE
from datastar_py.sse import DatastarEvent


class HtmlRenderable(Protocol):
    def __html__(self) -> str: ...


RenderResult = str | HtmlRenderable
RenderFunction = Callable[[], Awaitable[RenderResult]]
PageState = dict[str, object]
TabState = dict[str, PageState]


@dataclass
class _TabSession:
    data: TabState = field(default_factory=dict)
    created_at: datetime = field(default_factory=lambda: datetime.now(UTC))
    modified_at: datetime = field(default_factory=lambda: datetime.now(UTC))
    connections: int = 0


class TabStateStore:
    def __init__(self, *, clean_age_threshold: timedelta = timedelta(hours=24)) -> None:
        self._sessions: dict[str, _TabSession] = {}
        self.clean_age_threshold = clean_age_threshold

    def connect(self, tab_id: str, *, now: datetime | None = None) -> TabState:
        session = self._sessions.get(tab_id)
        current_time = _now(now)
        if session is None:
            session = _TabSession(created_at=current_time, modified_at=current_time)
            self._sessions[tab_id] = session
        session.connections += 1
        return session.data

    def disconnect(self, tab_id: str) -> None:
        session = self._sessions.get(tab_id)
        if session is None:
            return
        session.connections = max(0, session.connections - 1)
        if session.connections == 0:
            self._sessions.pop(tab_id, None)

    def get_tab_state(self, tab_id: str) -> TabState | None:
        session = self._sessions.get(tab_id)
        return None if session is None else session.data

    def get_page_state(self, tab_id: str | None, page_key: str) -> PageState:
        if tab_id is None:
            return {}
        session = self._sessions.get(tab_id)
        if session is None:
            return {}
        return session.data.get(page_key, {})

    def update_page_state(
        self,
        tab_id: str,
        page_key: str,
        update: Callable[[PageState], PageState],
        *,
        now: datetime | None = None,
    ) -> PageState:
        current_time = _now(now)
        session = self._sessions.get(tab_id)
        if session is None:
            session = _TabSession(created_at=current_time, modified_at=current_time)
            self._sessions[tab_id] = session

        page_state = dict(session.data.get(page_key, {}))
        session.data[page_key] = update(page_state)
        session.modified_at = current_time
        return session.data[page_key]

    def cleanup_stale(self, *, now: datetime | None = None) -> set[str]:
        current_time = _now(now)
        removed: set[str] = set()
        for tab_id, session in tuple(self._sessions.items()):
            if current_time - session.modified_at < self.clean_age_threshold:
                continue
            self._sessions.pop(tab_id, None)
            removed.add(tab_id)
        return removed


class RefreshBroker:
    def __init__(self) -> None:
        self._subscribers: dict[
            asyncio.Queue[object], tuple[asyncio.AbstractEventLoop, str | None]
        ] = {}

    def subscribe(self, *, tab_id: str | None = None) -> asyncio.Queue[object]:
        queue: asyncio.Queue[object] = asyncio.Queue(maxsize=1)
        self._subscribers[queue] = (asyncio.get_running_loop(), tab_id)
        return queue

    def unsubscribe(self, queue: asyncio.Queue[object]) -> None:
        self._subscribers.pop(queue, None)

    def publish(
        self, event: object = "refresh-event", *, tab_id: str | None = None
    ) -> None:
        for queue, (loop, subscriber_tab_id) in tuple(self._subscribers.items()):
            if tab_id is not None and subscriber_tab_id != tab_id:
                continue
            loop.call_soon_threadsafe(_publish_event, queue, event)


def _publish_event(queue: asyncio.Queue[object], event: object) -> None:
    if queue.full():
        try:
            queue.get_nowait()
        except asyncio.QueueEmpty:
            pass
    try:
        queue.put_nowait(event)
    except asyncio.QueueFull:
        return


async def render_sse_event(
    render: RenderFunction,
    *,
    last_event_id: str | None = None,
    use_view_transition: bool = False,
) -> tuple[str | None, DatastarEvent | None]:
    html = _coerce_html(await render())
    event_id = _render_hash(html)
    if event_id == last_event_id:
        return last_event_id, None
    return event_id, SSE.patch_elements(
        html,
        event_id=event_id,
        use_view_transition=use_view_transition,
    )


async def render_stream(
    queue: asyncio.Queue[object],
    render: RenderFunction,
    *,
    last_event_id: str | None = None,
    render_on_connect: bool = True,
) -> AsyncGenerator[DatastarEvent, None]:
    if render_on_connect:
        last_event_id, event = await render_sse_event(
            render, last_event_id=last_event_id
        )
        if event is not None:
            yield event

    while True:
        event_name = await queue.get()
        last_event_id, event = await render_sse_event(
            render,
            last_event_id=last_event_id,
            use_view_transition=event_name == "queue-reordered",
        )
        if event is not None:
            yield event


def _coerce_html(view: RenderResult) -> str:
    if isinstance(view, str):
        return view
    return view.__html__()


def _render_hash(html: str) -> str:
    return hashlib.blake2s(html.encode("utf-8"), digest_size=16).hexdigest()


def _now(now: datetime | None) -> datetime:
    return now or datetime.now(UTC)