from __future__ import annotations

from typing import ClassVar

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


@register
class EmaCross(Strategy):
    """EMA crossover with an optional long-term trend filter."""

    key: ClassVar[str] = "ema_cross"
    name: ClassVar[str] = "EMA Crossover"
    description: ClassVar[str] = (
        "Open long when the fast EMA crosses above the slow EMA (and price is "
        "above the trend filter, if enabled); exit on the opposite cross."
    )
    default_params: ClassVar[dict] = {
        "fast": 9,
        "slow": 21,
        "trend_filter": 200,
        "size": 1.0,
    }
    param_help: ClassVar[dict] = {
        "fast": "Fast EMA period",
        "slow": "Slow EMA period",
        "trend_filter": "SMA trend filter period (0 disables)",
        "size": "Fraction of equity per trade",
    }
    param_bounds: ClassVar[dict] = {"fast": (2, 100), "slow": (3, 300), "size": (0.01, 1.0)}

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

        fast = ema(ctx.closes, fast_period)
        slow = ema(ctx.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

        trend_ok = True
        if trend_period > 0:
            trend = sma(ctx.closes, trend_period)[-1]
            trend_ok = trend is not None and ctx.price > trend

        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 and trend_ok:
            ctx.enter_long(size=float(self.params["size"]), reason="EMA cross up")
        elif ctx.side == PositionSide.LONG and crossed_down:
            ctx.close(reason="EMA cross down")