"""Regime detector for market regime classification.

Classifies the current market regime for each ticker based on
EMA trend indicators and volatility ratios. Adjusts scoring
thresholds and contradiction penalties per regime.

Requirements: 7.1, 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.9
"""
from __future__ import annotations

import math
import statistics
from dataclasses import dataclass
from enum import Enum


class MarketRegime(str, Enum):
    """Market regime classification categories."""

    TREND_FOLLOWING = "trend_following"
    PANIC = "panic"
    MEAN_REVERSION = "mean_reversion"
    UNCERTAINTY = "uncertainty"


@dataclass(frozen=True)
class RegimeClassification:
    """Result of regime detection for a ticker."""

    regime: MarketRegime
    trend_indicator: float  # R = sign(EMA_20 - EMA_100)
    volatility_ratio: float  # V_r = σ_20 / σ_100
    bullish_threshold: float  # Adjusted ±threshold for direction
    bearish_threshold: float
    contradiction_penalty_multiplier: float  # 0.4 default, 0.6 for uncertainty


@dataclass(frozen=True)
class RegimeConfig:
    """Configuration parameters for regime detection."""

    ema_short_period: int = 20
    ema_long_period: int = 100
    vol_short_period: int = 20
    vol_long_period: int = 100
    panic_vol_ratio: float = 1.5
    trend_vol_ratio: float = 1.2
    mean_reversion_vol_ratio: float = 1.0
    default_threshold: float = 0.15
    panic_threshold: float = 0.10
    mean_reversion_threshold: float = 0.20
    uncertainty_contradiction_multiplier: float = 0.6


# Default uncertainty classification used when data is insufficient
_DEFAULT_UNCERTAINTY = RegimeClassification(
    regime=MarketRegime.UNCERTAINTY,
    trend_indicator=0.0,
    volatility_ratio=1.0,
    bullish_threshold=0.15,
    bearish_threshold=-0.15,
    contradiction_penalty_multiplier=0.6,
)


def compute_ema(values: list[float], period: int) -> float:
    """Compute exponential moving average over the last ``period`` values.

    Uses the standard EMA formula with multiplier = 2 / (period + 1).
    Iterates through the values, seeding the EMA with the first value.

    Raises ``ValueError`` when *values* is empty or *period* < 1.
    """
    if not values or period < 1:
        raise ValueError("values must be non-empty and period must be >= 1")

    # Use only the last `period` values (or all if fewer)
    data = values[-period:] if len(values) >= period else values

    multiplier = 2.0 / (period + 1)
    ema = data[0]
    for value in data[1:]:
        ema = (value - ema) * multiplier + ema
    return ema


def _sign(x: float) -> float:
    """Return -1.0, 0.0, or 1.0 for the sign of *x*."""
    if x > 0.0:
        return 1.0
    if x < 0.0:
        return -1.0
    return 0.0


def classify_regime(
    closing_prices: list[float],
    returns: list[float],
    config: RegimeConfig = RegimeConfig(),
) -> RegimeClassification:
    """Classify market regime from price and return history.

    Requires at least ``config.ema_long_period`` days of price history
    for EMA_100.  Falls back to UNCERTAINTY when data is insufficient
    or standard deviations are zero.

    Requirements: 7.1, 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.9
    """
    # Insufficient price data → uncertainty
    if len(closing_prices) < config.ema_long_period:
        return _DEFAULT_UNCERTAINTY

    # Insufficient return data → uncertainty
    if len(returns) < config.vol_long_period:
        return _DEFAULT_UNCERTAINTY

    # --- Trend indicator: R = sign(EMA_short - EMA_long) ---
    ema_short = compute_ema(closing_prices, config.ema_short_period)
    ema_long = compute_ema(closing_prices, config.ema_long_period)
    trend_indicator = _sign(ema_short - ema_long)

    # --- Volatility ratio: V_r = σ_short / σ_long ---
    short_returns = returns[-config.vol_short_period:]
    long_returns = returns[-config.vol_long_period:]

    # Guard against zero or near-zero standard deviations
    if len(short_returns) < 2 or len(long_returns) < 2:
        return _DEFAULT_UNCERTAINTY

    sigma_short = statistics.stdev(short_returns)
    sigma_long = statistics.stdev(long_returns)

    if sigma_long == 0.0 or sigma_short == 0.0:
        return _DEFAULT_UNCERTAINTY

    if math.isnan(sigma_short) or math.isnan(sigma_long):
        return _DEFAULT_UNCERTAINTY

    volatility_ratio = sigma_short / sigma_long

    # --- Classification rules (Req 7.3) ---
    # Panic takes priority: V_r > 1.5
    if volatility_ratio > config.panic_vol_ratio:
        regime = MarketRegime.PANIC
        threshold = config.panic_threshold  # ±0.10
        contradiction_mult = 0.4
    # Trend-following: R ≠ 0 AND V_r < 1.2
    elif trend_indicator != 0.0 and volatility_ratio < config.trend_vol_ratio:
        regime = MarketRegime.TREND_FOLLOWING
        threshold = config.default_threshold  # ±0.15
        contradiction_mult = 0.4
    # Mean-reversion: R = 0 AND V_r < 1.0
    elif trend_indicator == 0.0 and volatility_ratio < config.mean_reversion_vol_ratio:
        regime = MarketRegime.MEAN_REVERSION
        threshold = config.mean_reversion_threshold  # ±0.20
        contradiction_mult = 0.4
    # Uncertainty: all other cases
    else:
        regime = MarketRegime.UNCERTAINTY
        threshold = config.default_threshold  # ±0.15
        contradiction_mult = config.uncertainty_contradiction_multiplier  # 0.6

    return RegimeClassification(
        regime=regime,
        trend_indicator=trend_indicator,
        volatility_ratio=volatility_ratio,
        bullish_threshold=threshold,
        bearish_threshold=-threshold,
        contradiction_penalty_multiplier=contradiction_mult,
    )