"""
Unified domain events for market data.

All providers normalize raw messages into these canonical types.
Timestamps are always UTC. ts_exchange may be None if the source
doesn't provide exchange timestamps.
"""
from __future__ import annotations

import time
from datetime import datetime, timezone
from enum import Enum
from typing import Optional

from pydantic import BaseModel, Field


class EventType(str, Enum):
    TRADE = "trade"
    QUOTE = "quote"
    BOOK_L2 = "book_l2"
    HEARTBEAT = "heartbeat"


def _utc_now() -> datetime:
    return datetime.now(timezone.utc)


def _mono_ns() -> int:
    """Monotonic nanoseconds for internal latency measurement."""
    return time.monotonic_ns()


class BaseEvent(BaseModel):
    """Common fields for every market-data event."""

    event_type: EventType
    provider: str
    ts_recv: datetime = Field(default_factory=_utc_now)
    ts_recv_mono_ns: int = Field(default_factory=_mono_ns)


class TradeEvent(BaseEvent):
    """A single matched trade (fill)."""

    event_type: EventType = EventType.TRADE
    symbol: str
    price: float
    size: float
    ts_exchange: Optional[datetime] = None
    side: Optional[str] = None  # "buy" | "sell" | None
    trade_id: Optional[str] = None


class QuoteEvent(BaseEvent):
    """Best bid/ask (top-of-book)."""

    event_type: EventType = EventType.QUOTE
    symbol: str
    bid: float
    ask: float
    bid_size: float
    ask_size: float
    ts_exchange: Optional[datetime] = None


class BookLevel(BaseModel):
    price: float
    size: float


class BookL2Event(BaseEvent):
    """L2 order-book snapshot (partial depth)."""

    event_type: EventType = EventType.BOOK_L2
    symbol: str
    bids: list[BookLevel] = Field(default_factory=list)
    asks: list[BookLevel] = Field(default_factory=list)
    ts_exchange: Optional[datetime] = None


class HeartbeatEvent(BaseEvent):
    """Provider heartbeat / keep-alive signal."""

    event_type: EventType = EventType.HEARTBEAT


# Union type for type-safe consumers
Event = TradeEvent | QuoteEvent | BookL2Event | HeartbeatEvent