"""
Order-book consumer for the opportunity engine.

Connects to fh_ob's Unix-domain socket and receives JSON-serialized top-5
order-book snapshots.  On each update the registered on_update callback is
invoked, which triggers triangle evaluation in OpportunityEngine.

The consumer maintains an in-memory snapshot of the last seen book for each
symbol, accessible via get_book().
"""
import asyncio
import json
from dataclasses import dataclass, field
from pathlib import Path
from typing import Callable, Optional, Awaitable

import structlog

logger = structlog.get_logger().bind(component="book_consumer")


@dataclass
class BookLevel:
    """
    A single price level in an order book.

    Attributes
    ----------
    price, size : float
        Price and available size at this level.
    """

    price: float
    size: float

    @classmethod
    def from_dict(cls, data: dict) -> "BookLevel":
        return cls(
            price=float(data["price"]),
            size=float(data["size"]),
        )


@dataclass
class OrderBookTop5:
    """
    Top-5 bid/ask snapshot for a single symbol.

    Attributes
    ----------
    symbol : str
        KuCoin symbol e.g. "BTC-USDT".
    bids : list[BookLevel]
        Best bids, most aggressive first.
    asks : list[BookLevel]
        Best asks, most aggressive first.
    ts_ms : int
        Timestamp (ms) of the snapshot from fh_ob.
    """

    symbol: str
    bids: list[BookLevel] = field(default_factory=list)
    asks: list[BookLevel] = field(default_factory=list)
    ts_ms: int = 0

    @classmethod
    def from_json(cls, data: dict) -> "OrderBookTop5":
        bids = [BookLevel.from_dict(b) for b in data.get("bids", [])]
        asks = [BookLevel.from_dict(a) for a in data.get("asks", [])]
        return cls(
            symbol=data.get("symbol", ""),
            bids=bids,
            asks=asks,
            ts_ms=data.get("ts_ms", 0),
        )


class BookConsumer:
    """
    Consumes order-book snapshots from fh_ob and dispatches them to OpportunityEngine.

    Maintains a socket connection until EOF or error, then reconnects
    automatically.  Book updates are pushed to an internal queue; a dedicated
    worker drains the queue and calls on_update, keeping the reader loop
    non-blocking.
    """

    def __init__(
        self,
        socket_path: Path,
        on_update: Callable[[str, OrderBookTop5], None | Awaitable[None]],
    ) -> None:
        self._socket_path = socket_path
        self._on_update = on_update
        self._running = False
        self._books: dict[str, OrderBookTop5] = {}
        self._log = logger
        self._queue: asyncio.Queue[str] = asyncio.Queue(maxsize=2048)
        self._queued: set[str] = set()
        self._worker_task: Optional[asyncio.Task] = None

    def get_book(self, symbol: str) -> Optional[OrderBookTop5]:
        """Return the last known book for a symbol, or None if not yet received."""
        return self._books.get(symbol)

    def set_on_update(self, callback: Callable[[str, OrderBookTop5], None]) -> None:
        """Replace the on_update callback.  Used when the callback needs a
        reference to an object that does not yet exist at construction time."""
        self._on_update = callback

    async def start(self) -> None:
        """
        Connect to fh_ob and run the consume loop until stop() is called.

        On unexpected disconnection a 1-second backoff is applied before
        reconnecting.  Interrupted cleanly by CancelledError.
        """
        self._running = True
        self._worker_task = asyncio.create_task(self._worker())
        while self._running:
            try:
                await self._connect()
            except asyncio.CancelledError:
                break
            except Exception as e:
                self._log.warning("connection_error", error=str(e))
                await asyncio.sleep(1.0)
        if self._worker_task:
            self._worker_task.cancel()
            try:
                await self._worker_task
            except asyncio.CancelledError:
                pass

    async def stop(self) -> None:
        """Request the consume loop to exit on the next iteration."""
        self._running = False

    async def _worker(self) -> None:
        """Drain the update queue and call on_update for each symbol."""
        while self._running:
            try:
                symbol = await asyncio.wait_for(self._queue.get(), timeout=0.5)
            except asyncio.TimeoutError:
                continue
            except asyncio.CancelledError:
                break
            self._queued.discard(symbol)
            book = self._books.get(symbol)
            if not book:
                continue
            try:
                result = self._on_update(symbol, book)
                if asyncio.iscoroutine(result):
                    await result
            except Exception as e:
                self._log.error("on_update_error", symbol=symbol, error=str(e))

    async def _connect(self) -> None:
        """
        Open the Unix socket, read and queue messages until EOF or error.

        Each JSON line is parsed into an OrderBookTop5, stored in self._books,
        and the symbol is pushed to the queue for the worker to evaluate.
        The reader never blocks on evaluation.
        """
        reader, writer = await asyncio.open_unix_connection(path=str(self._socket_path))
        self._log.info("connected", path=str(self._socket_path))

        try:
            while self._running:
                try:
                    line = await reader.readline()
                except asyncio.CancelledError:
                    raise
                except Exception as e:
                    self._log.error("socket_read_error", error=str(e))
                    break

                if not line:
                    self._log.warning("socket_eof")
                    break

                try:
                    data = json.loads(line.decode())
                except (json.JSONDecodeError, UnicodeDecodeError) as e:
                    self._log.warning("invalid_json", line=line[:50], error=str(e))
                    continue

                book = OrderBookTop5.from_json(data)
                if not book.symbol:
                    continue

                self._books[book.symbol] = book
                if book.symbol not in self._queued:
                    self._queued.add(book.symbol)
                    try:
                        self._queue.put_nowait(book.symbol)
                    except asyncio.QueueFull:
                        self._queued.discard(book.symbol)

        finally:
            writer.close()
            await writer.wait_closed()
            self._log.info("disconnected")