from __future__ import annotations

from typing import ClassVar

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


@register
class MacdTrend(Strategy):
    """MACD crossover trend following, long-only."""

    key: ClassVar[str] = "macd_trend"
    name: ClassVar[str] = "MACD Trend"
    description: ClassVar[str] = (
        "Open long when the MACD line crosses above its signal line and close when "
        "it crosses back below."
    )
    default_params: ClassVar[dict] = {"fast": 12, "slow": 26, "signal": 9, "size": 1.0}
    param_help: ClassVar[dict] = {
        "fast": "Fast EMA period",
        "slow": "Slow EMA period",
        "signal": "Signal EMA period",
        "size": "Fraction of equity per trade",
    }
    param_bounds: ClassVar[dict] = {"fast": (2, 100), "slow": (3, 200), "signal": (2, 100)}

    def on_candle(self, ctx: StrategyContext) -> None:
        closes = ctx.closes
        if len(closes) < int(self.params["slow"]) + int(self.params["signal"]) + 2:
            return
        macd_line, signal_line, _ = macd(
            closes,
            int(self.params["fast"]),
            int(self.params["slow"]),
            int(self.params["signal"]),
        )
        m_prev, m_now = macd_line[-2], macd_line[-1]
        s_prev, s_now = signal_line[-2], signal_line[-1]
        if None in (m_prev, m_now, s_prev, s_now):
            return

        crossed_up = m_prev <= s_prev and m_now > s_now
        crossed_down = m_prev >= s_prev and m_now < s_now

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