from __future__ import annotations

from typing import ClassVar

from app.engine.strategies.base import Strategy, StrategyContext, register
from app.models import PositionSide


@register
class WilliamsR(Strategy):
    """Williams %R mean reversion, long-only."""

    key: ClassVar[str] = "williams_r"
    name: ClassVar[str] = "Williams %R"
    description: ClassVar[str] = (
        "Enter long when Williams %R is oversold (at or below the oversold "
        "level) and exit when it becomes overbought. Optional ATR stop."
    )
    default_params: ClassVar[dict] = {
        "period": 14,
        "oversold": -80.0,
        "overbought": -20.0,
        "atr_period": 14,
        "atr_stop_mult": 2.0,
        "size": 1.0,
    }
    param_help: ClassVar[dict] = {
        "period": "Williams %R lookback",
        "oversold": "Oversold level (e.g. -80)",
        "overbought": "Overbought level (e.g. -20)",
        "atr_period": "ATR lookback for the stop",
        "atr_stop_mult": "Stop distance in ATRs (0 disables)",
        "size": "Fraction of equity per trade",
    }
    param_bounds: ClassVar[dict] = {
        "period": (2, 100),
        "oversold": (-100.0, -50.0),
        "overbought": (-50.0, 0.0),
        "atr_stop_mult": (0.0, 10.0),
        "size": (0.01, 1.0),
    }

    def on_candle(self, ctx: StrategyContext) -> None:
        value = ctx.williams_r(int(self.params["period"]))
        if value is None:
            return

        if ctx.is_flat and value <= float(self.params["oversold"]):
            stop = None
            mult = float(self.params["atr_stop_mult"])
            if mult > 0:
                atr_value = ctx.atr(int(self.params["atr_period"]))
                if atr_value:
                    stop = ctx.price - mult * atr_value
            ctx.enter_long(
                size=float(self.params["size"]),
                stop_loss=stop,
                reason=f"Williams %R {value:.1f} oversold",
            )
        elif ctx.side == PositionSide.LONG and value >= float(self.params["overbought"]):
            ctx.close(reason=f"Williams %R {value:.1f} overbought")