"""Portfolio tracking for the portfolio manager service."""

from decimal import Decimal

from shared.models import Order, OrderSide, Position


class _PositionState:
    """Internal state for tracking a single symbol's position."""

    def __init__(self) -> None:
        self.quantity: Decimal = Decimal("0")
        self.avg_entry: Decimal = Decimal("0")


class PortfolioTracker:
    """Tracks positions and updates them based on filled orders."""

    def __init__(self) -> None:
        self._positions: dict[str, _PositionState] = {}
        self._realized_pnl: Decimal = Decimal("0")

    @property
    def realized_pnl(self) -> Decimal:
        return self._realized_pnl

    def _get_or_create(self, symbol: str) -> _PositionState:
        if symbol not in self._positions:
            self._positions[symbol] = _PositionState()
        return self._positions[symbol]

    def apply_order(self, order: Order) -> None:
        """Update internal position state based on a filled order."""
        state = self._get_or_create(order.symbol)

        if order.side == OrderSide.BUY:
            # Weighted average entry price
            total_cost = state.avg_entry * state.quantity + order.price * order.quantity
            state.quantity += order.quantity
            if state.quantity > Decimal("0"):
                state.avg_entry = total_cost / state.quantity
        elif order.side == OrderSide.SELL:
            # Calculate realized PnL for this sell
            sell_quantity = min(order.quantity, state.quantity)
            if sell_quantity > 0 and state.avg_entry > 0:
                self._realized_pnl += sell_quantity * (order.price - state.avg_entry)

            state.quantity -= sell_quantity
            if state.quantity <= Decimal("0"):
                state.quantity = Decimal("0")
                state.avg_entry = Decimal("0")

    def get_position(self, symbol: str) -> Position | None:
        """Return a Position model for the symbol, or None if no/zero position."""
        state = self._positions.get(symbol)
        if state is None or state.quantity <= Decimal("0"):
            return None
        return Position(
            symbol=symbol,
            quantity=state.quantity,
            avg_entry_price=state.avg_entry,
            current_price=state.avg_entry,  # No live price here; caller can update
        )

    def get_all_positions(self) -> list[Position]:
        """Return all non-zero positions."""
        positions = []
        for symbol in self._positions:
            pos = self.get_position(symbol)
            if pos is not None:
                positions.append(pos)
        return positions