from __future__ import annotations

from typing import ClassVar

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


@register
class BollingerReversion(Strategy):
    """Buy the lower Bollinger band, exit at the middle band."""

    key: ClassVar[str] = "bollinger_reversion"
    name: ClassVar[str] = "Bollinger Reversion"
    description: ClassVar[str] = (
        "Enter long when the close falls below the lower Bollinger band and exit "
        "when it returns to the middle band (SMA). Optional ATR stop."
    )
    default_params: ClassVar[dict] = {
        "period": 20,
        "num_std": 2.0,
        "atr_period": 14,
        "atr_stop_mult": 0.0,
        "size": 1.0,
    }
    param_help: ClassVar[dict] = {
        "period": "Bollinger lookback",
        "num_std": "Band width in standard deviations",
        "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": (5, 100),
        "num_std": (0.5, 4.0),
        "atr_stop_mult": (0.0, 10.0),
        "size": (0.01, 1.0),
    }

    def on_candle(self, ctx: StrategyContext) -> None:
        period = int(self.params["period"])
        if len(ctx.closes) < period:
            return
        middle = ctx.sma(period)
        deviation = ctx.std(period)
        if middle is None or deviation is None:
            return
        lower = middle - float(self.params["num_std"]) * deviation

        if ctx.is_flat and ctx.price < lower:
            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="close below lower band",
            )
        elif ctx.side == PositionSide.LONG and ctx.price >= middle:
            ctx.close(reason="close back at middle band")