from __future__ import annotations

from typing import ClassVar

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


@register
class SmaCross(Strategy):
    """Classic moving-average crossover, long-only."""

    key: ClassVar[str] = "sma_cross"
    name: ClassVar[str] = "SMA Crossover"
    description: ClassVar[str] = (
        "Open a long position when the fast SMA crosses above the slow SMA, "
        "close it when the fast SMA crosses back below."
    )
    default_params: ClassVar[dict] = {"fast": 10, "slow": 30, "size": 1.0}
    param_help: ClassVar[dict] = {
        "fast": "Fast SMA period",
        "slow": "Slow SMA period",
        "size": "Fraction of equity to allocate per trade",
    }
    param_bounds: ClassVar[dict] = {"fast": (2, 200), "slow": (3, 400), "size": (0.01, 1.0)}

    def on_candle(self, ctx: StrategyContext) -> None:
        fast_period = int(self.params["fast"])
        slow_period = int(self.params["slow"])
        closes = ctx.closes
        if len(closes) < slow_period + 2:
            return

        fast = sma(closes, fast_period)
        slow = sma(closes, slow_period)
        f_prev, f_now = fast[-2], fast[-1]
        s_prev, s_now = slow[-2], slow[-1]
        if None in (f_prev, f_now, s_prev, s_now):
            return

        crossed_up = f_prev <= s_prev and f_now > s_now
        crossed_down = f_prev >= s_prev and f_now < s_now

        if ctx.is_flat and crossed_up:
            ctx.enter_long(size=float(self.params["size"]), reason="fast SMA crossed above slow")
        elif ctx.side == PositionSide.LONG and crossed_down:
            ctx.close(reason="fast SMA crossed below slow")