"""Signal cluster classification and within-cluster correlation penalty.

Groups signals into four clusters — momentum, structure, volatility,
fundamentals — and applies exponential decay within each cluster to prevent
likelihood ratio stacking inflation in the Bayesian pipeline.

Within a cluster the strongest signal (by ``|log_lr|``) contributes at full
weight; subsequent signals contribute at ``0.5^(n-1)`` decay.  Signals in
different clusters are treated as independent (no penalty).  Single-signal
clusters receive no penalty.

Requirements: 7.1, 7.2, 7.3, 7.4
"""

from __future__ import annotations

import logging
from collections import defaultdict
from enum import Enum

from services.signal_engine.models import LikelihoodRatio

logger = logging.getLogger(__name__)

# ---------------------------------------------------------------------------
# Signal cluster enum
# ---------------------------------------------------------------------------


class SignalCluster(str, Enum):
    """Correlation cluster for grouping related signals."""

    MOMENTUM = "momentum"  # MA stack, RSI
    STRUCTURE = "structure"  # Fibonacci, Elliott Wave, Cup & Handle
    VOLATILITY = "volatility"  # ATR-based, Bollinger-derived
    FUNDAMENTALS = "fundamentals"  # valuation, earnings, macro


# ---------------------------------------------------------------------------
# Signal type → cluster mapping
# ---------------------------------------------------------------------------

_SIGNAL_CLUSTER_MAP: dict[str, SignalCluster] = {
    # Momentum
    "ma_stack": SignalCluster.MOMENTUM,
    "rsi": SignalCluster.MOMENTUM,
    # Structure
    "fibonacci": SignalCluster.STRUCTURE,
    "elliott_wave": SignalCluster.STRUCTURE,
    "cup_handle": SignalCluster.STRUCTURE,
    # Volatility
    "atr": SignalCluster.VOLATILITY,
    "bollinger": SignalCluster.VOLATILITY,
    # Fundamentals
    "valuation": SignalCluster.FUNDAMENTALS,
    "earnings": SignalCluster.FUNDAMENTALS,
    "macro": SignalCluster.FUNDAMENTALS,
}

# Decay factor applied to successive signals within the same cluster.
_WITHIN_CLUSTER_DECAY = 0.5


# ---------------------------------------------------------------------------
# Public API
# ---------------------------------------------------------------------------


def classify_signal(signal_type: str) -> SignalCluster:
    """Map a signal type string to its correlation cluster.

    Falls back to :pyattr:`SignalCluster.FUNDAMENTALS` for unknown signal
    types so that unrecognised signals still participate in the penalty
    system rather than silently bypassing it.
    """
    cluster = _SIGNAL_CLUSTER_MAP.get(signal_type)
    if cluster is None:
        logger.warning(
            "Unknown signal type %r — defaulting to FUNDAMENTALS cluster",
            signal_type,
        )
        return SignalCluster.FUNDAMENTALS
    return cluster


def apply_correlation_penalty(
    likelihood_ratios: list[LikelihoodRatio],
) -> list[LikelihoodRatio]:
    """Apply within-cluster decay penalty to correlated signals.

    Algorithm:
    1. Group LRs by cluster.
    2. Within each cluster, sort by ``abs(log_lr)`` descending (strongest
       first).
    3. The strongest signal keeps its full ``log_lr`` as
       ``penalized_log_lr``.
    4. The *n*-th signal (1-indexed) receives
       ``penalized_log_lr = log_lr * 0.5^(n-1)``.
    5. Single-signal clusters are untouched (``penalized_log_lr = log_lr``).
    6. Cross-cluster signals are independent — no penalty applied across
       clusters.

    Returns a **new** list of :class:`LikelihoodRatio` instances with
    updated ``penalized_log_lr`` values.  The original objects are not
    mutated.
    """
    if not likelihood_ratios:
        return []

    # Group by cluster
    clusters: dict[str, list[tuple[int, LikelihoodRatio]]] = defaultdict(list)
    for idx, lr in enumerate(likelihood_ratios):
        clusters[lr.cluster].append((idx, lr))

    # Build result list preserving original order
    result: list[LikelihoodRatio | None] = [None] * len(likelihood_ratios)

    for cluster_name, members in clusters.items():
        # Sort by abs(log_lr) descending — strongest first
        sorted_members = sorted(members, key=lambda t: abs(t[1].log_lr), reverse=True)

        for rank, (orig_idx, lr) in enumerate(sorted_members):
            decay = _WITHIN_CLUSTER_DECAY ** rank  # 0.5^0=1, 0.5^1=0.5, ...
            penalized = lr.log_lr * decay

            result[orig_idx] = LikelihoodRatio(
                signal_type=lr.signal_type,
                cluster=lr.cluster,
                lr=lr.lr,
                log_lr=lr.log_lr,
                penalized_log_lr=penalized,
                hit_rate=lr.hit_rate,
                strength=lr.strength,
            )

    # Safety: should never happen, but guard against it
    return [r for r in result if r is not None]