"""
core/confidence_scorer.py
Calculates signal freshness, staleness decay, and multi-platform confidence.
Enforces zero-imputation rules across timestamps and verification confidence.
"""

from datetime import datetime, timezone
from typing import Optional
import numpy as np
import pandas as pd


class FreshnessConfidenceScorer:
    """
    Evaluates signal age and applies confidence penalties for stale data.
    Decays confidence by 10% if signal exceeds 14 days old.
    """

    @staticmethod
    def calculate_signal_age_days(collected_at: Optional[str]) -> Optional[float]:
        """Calculates difference in days between current UTC timestamp and collection date."""
        if not collected_at or pd.isna(collected_at) or str(collected_at).strip().lower() in ("nan", "none", ""):
            return None
        try:
            # Parse ISO or standard timestamp format
            dt = pd.to_datetime(collected_at, utc=True)
            now = datetime.now(timezone.utc)
            delta = now - dt.to_pydatetime()
            return round(max(0.0, delta.total_seconds() / 86400.0), 2)
        except Exception:
            return None

    @classmethod
    def apply_staleness_decay(
        cls, 
        base_confidence: float, 
        signal_age_days: Optional[float]
    ) -> float:
        """Decays confidence by 10% if age > 14 days; missing age leaves confidence unadjusted."""
        if signal_age_days is None or pd.isna(signal_age_days):
            return base_confidence
        if signal_age_days > 14.0:
            return round(max(0.0, base_confidence * 0.90), 2)
        return round(base_confidence, 2)

    @classmethod
    def enrich_cohort_freshness(cls, df: pd.DataFrame) -> pd.DataFrame:
        """Adds signal_age_days and updates confidence scores for cohort records."""
        out = df.copy()
        if "collected_at" in out.columns:
            out["signal_age_days"] = out["collected_at"].apply(cls.calculate_signal_age_days)
        else:
            out["signal_age_days"] = np.nan

        # Decay instagram_confidence_score where applicable
        if "instagram_confidence_score" in out.columns:
            out["instagram_confidence_score"] = out.apply(
                lambda row: cls.apply_staleness_decay(
                    row.get("instagram_confidence_score", 0.0), 
                    row.get("signal_age_days")
                ),
                axis=1
            )
        return out