"""
Market regime classification for strategy gating.

Classifies each bar into one of four regimes based on rolling returns,
volatility, and volume profile. Used to compute conditional strategy
performance — a strategy that only works in trending regimes must
KNOW when it's in a trending regime.
"""

from __future__ import annotations

from collections import deque
from typing import Optional

import numpy as np


def classify_regime(
    returns_20: float,
    vol_20: float,
    vol_ratio: float = 1.0,
    trend_threshold: float = 0.05,
    vol_threshold: float = 0.04,
) -> str:
    """Classify a single bar into a market regime.

    Args:
        returns_20: rolling 20-bar return (fraction, e.g. 0.15 = +15%)
        vol_20: rolling 20-bar realized volatility (annualized or period)
        vol_ratio: current volume / rolling average volume
        trend_threshold: minimum abs return to classify as trending
        vol_threshold: volatility above which market is "volatile"

    Returns one of: trending_up, trending_down, ranging, volatile
    """
    if vol_20 > vol_threshold or vol_ratio > 2.0:
        return "volatile"

    if returns_20 > trend_threshold:
        return "trending_up"
    elif returns_20 < -trend_threshold:
        return "trending_down"
    else:
        return "ranging"


class RegimeClassifier:
    """Stateful regime classifier using rolling windows.

    Usage:
        rc = RegimeClassifier(window=20)
        for bar in bars:
            rc.feed(mid_px=bar.close, close=bar.close,
                     open_px=bar.open, vol=bar.volume)
            regime = rc.current_regime
    """

    def __init__(
        self,
        window: int = 20,
        trend_threshold: float = 0.05,
        vol_threshold: float = 0.04,
    ):
        self._window = window
        self._trend_threshold = trend_threshold
        self._vol_threshold = vol_threshold

        self._prices: deque[float] = deque(maxlen=window + 1)
        self._volumes: deque[float] = deque(maxlen=window)
        self._current_regime: str = "unknown"
        self._regime_counts: dict[str, int] = {"trending_up": 0, "trending_down": 0,
                                                 "ranging": 0, "volatile": 0, "unknown": 0}

    def feed(self, mid_px: float, close: float, open_px: float, vol: float):
        """Feed a new bar observation."""
        self._prices.append(mid_px)
        self._volumes.append(vol)

        if len(self._prices) < self._window + 1:
            return

        # Rolling return
        returns_20 = (self._prices[-1] - self._prices[0]) / self._prices[0] if self._prices[0] > 0 else 0

        # Rolling volatility
        price_list = list(self._prices)
        rets = [(price_list[i] - price_list[i - 1]) / price_list[i - 1]
                for i in range(1, len(price_list)) if price_list[i - 1] > 0]
        vol_20 = np.std(rets) if rets else 0.0

        # Volume ratio
        avg_vol = sum(self._volumes) / max(len(self._volumes), 1)
        vol_ratio = vol / avg_vol if avg_vol > 0 else 1.0

        self._current_regime = classify_regime(
            returns_20, vol_20, vol_ratio,
            self._trend_threshold, self._vol_threshold,
        )
        self._regime_counts[self._current_regime] += 1

    @property
    def current_regime(self) -> str:
        return self._current_regime

    def regime_counts(self) -> dict[str, int]:
        return dict(self._regime_counts)

    def dominant_regime(self) -> str:
        """Most frequent regime observed so far."""
        return max(self._regime_counts, key=self._regime_counts.get)


def conditional_performance(
    trades: list[dict],
    regime_trade_counts: dict[str, int],
) -> dict:
    """Compute per-regime strategy performance from trade records.

    Args:
        trades: list of trade dicts with pnl_net, pnl_gross, time
        regime_trade_counts: {regime_name: count_of_trades}

    Returns:
        dict with per-regime stats (avg_pnl, win_rate, total_pnl, count)
        and best_regime / worst_regime classification.
    """
    # For simplicity, assume all trades belong to the regime
    # In production, each trade would be timestamp-matched to regime at entry
    all_pnls = [float(t.get("pnl_net", t.get("pnl", 0))) for t in trades]

    result = {"regimes": {}, "overall": {"count": len(trades), "total_pnl": round(sum(all_pnls), 2)}}

    for regime, count in regime_trade_counts.items():
        if count == 0:
            result["regimes"][regime] = {"count": 0, "total_pnl": 0, "avg_pnl": 0, "win_rate": 0}
            continue

        # Take the next batch of trades for this regime
        # (simplified — real impl would match by timestamp)
        regime_pnls = all_pnls[:count]
        wins = sum(1 for p in regime_pnls if p > 0)

        result["regimes"][regime] = {
            "count": count,
            "total_pnl": round(sum(regime_pnls), 2),
            "avg_pnl": round(sum(regime_pnls) / count, 2) if count else 0,
            "win_rate": round(wins / count, 3) if count else 0,
        }

    # Best and worst regime
    scored = [(r, info["avg_pnl"]) for r, info in result["regimes"].items() if info["count"] > 0]
    if scored:
        result["best_regime"] = max(scored, key=lambda x: x[1])[0]
        result["worst_regime"] = min(scored, key=lambda x: x[1])[0]

    return result