from __future__ import annotations

from typing import ClassVar

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


@register
class Momentum(Strategy):
    """Rate-of-change momentum, long-only."""

    key: ClassVar[str] = "momentum"
    name: ClassVar[str] = "Momentum (ROC)"
    description: ClassVar[str] = (
        "Open long when the rate of change over the lookback exceeds the entry "
        "threshold; exit when momentum turns negative."
    )
    default_params: ClassVar[dict] = {
        "period": 10,
        "entry_threshold": 0.01,
        "atr_period": 14,
        "atr_stop_mult": 2.0,
        "trailing_stop_pct": 0.0,
        "size": 1.0,
    }
    param_help: ClassVar[dict] = {
        "period": "ROC lookback in bars",
        "entry_threshold": "Minimum ROC to enter (0.01 = 1%)",
        "atr_period": "ATR lookback for the initial stop",
        "atr_stop_mult": "Stop distance in ATRs (0 disables)",
        "trailing_stop_pct": "Trailing stop distance as a fraction of price (0 disables)",
        "size": "Fraction of equity per trade",
    }
    param_bounds: ClassVar[dict] = {
        "period": (2, 200),
        "entry_threshold": (0.0, 1.0),
        "atr_stop_mult": (0.0, 10.0),
        "trailing_stop_pct": (0.0, 0.5),
        "size": (0.01, 1.0),
    }

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

        if ctx.is_flat and value > float(self.params["entry_threshold"]):
            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,
                trailing_stop_pct=float(self.params["trailing_stop_pct"]),
                reason=f"ROC {value:.2%} above threshold",
            )
        elif ctx.side == PositionSide.LONG and value < 0:
            ctx.close(reason=f"ROC {value:.2%} turned negative")