"""
validation/transition_validator.py — Validates regime stability.

Tests: Transition matrix, average duration, flip rate, state entropy.
Answers: "Does the regime design produce stable, persistent states?"

Hard requirements:
  - avg_duration > 5 days
  - flip_rate < 15%
  - Fails → regime definition needs redesign.
"""

from typing import Optional
import sqlite3
import logging

import numpy as np
import pandas as pd

from config import config
from .metrics import transition_matrix, regime_duration_stats

logger = logging.getLogger(__name__)


class TransitionReport:
    """Structured report for regime stability validation."""

    def __init__(self):
        self.avg_duration: float = 0.0
        self.flip_rate: float = 0.0
        self.state_entropy: float = 0.0
        self.n_days: int = 0
        self.transition_matrix: Optional[pd.DataFrame] = None
        self.persistence_score: float = 0.0
        self.is_stable: bool = False
        self.conclusion: str = ""
        self.warnings: list[str] = []

    def summary(self) -> str:
        lines = [
            f"Regime Stability (N={self.n_days} days)",
            f"  Avg Duration: {self.avg_duration:.1f} days (need > {config.regime_min_avg_duration})",
            f"  Flip Rate: {self.flip_rate:.1%} (need < {config.regime_max_flip_rate:.0%})",
            f"  State Entropy: {self.state_entropy:.3f}",
            f"  Persistence Score: {self.persistence_score:.2f}",
            f"  Stable: {'YES' if self.is_stable else 'NO — redesign needed'}",
        ]
        if self.warnings:
            lines.append(f"  Warnings: {'; '.join(self.warnings)}")
        if self.transition_matrix is not None:
            lines.append(f"  Transition Matrix:\n{self.transition_matrix.to_string()}")
        lines.append(f"  → {self.conclusion}")
        return "\n".join(lines)


class TransitionValidator:
    """
    Validates regime temporal stability.

    Regime must persist — not flip daily.
    If flip_rate > 20% or avg_duration < 3 days → regime definition failed.
    """

    def __init__(self, db_path: Optional[str] = None):
        self.db_path = db_path or config.db_path

    def validate(self, regime_labels: pd.Series) -> TransitionReport:
        """Validate a regime sequence for stability."""
        report = TransitionReport()
        report.n_days = len(regime_labels)

        if len(regime_labels) < 30:
            report.conclusion = "INSUFFICIENT DATA (< 30 days)"
            return report

        # Duration stats
        stats = regime_duration_stats(regime_labels)
        report.avg_duration = stats["avg_duration"]
        report.flip_rate = stats["flip_rate"]
        report.state_entropy = stats["state_entropy"]

        # Transition matrix
        report.transition_matrix = transition_matrix(regime_labels)

        # Persistence: how often does regime stay the same?
        diag = np.diag(report.transition_matrix.values)
        report.persistence_score = round(float(np.mean(diag)), 2)

        # Stability check
        report.is_stable = (
            report.avg_duration >= config.regime_min_avg_duration and
            report.flip_rate <= config.regime_max_flip_rate
        )

        # Warnings
        if report.avg_duration < 3:
            report.warnings.append(f"CRITICAL: avg duration={report.avg_duration:.1f}d — regime flips too fast")
        elif report.avg_duration < config.regime_min_avg_duration:
            report.warnings.append(f"WARNING: avg duration={report.avg_duration:.1f}d < {config.regime_min_avg_duration}")

        if report.flip_rate > 0.20:
            report.warnings.append(f"CRITICAL: flip rate={report.flip_rate:.1%} — regime unstable")
        elif report.flip_rate > config.regime_max_flip_rate:
            report.warnings.append(f"WARNING: flip rate={report.flip_rate:.1%} > {config.regime_max_flip_rate:.0%}")

        if report.state_entropy > 2.0:
            report.warnings.append(f"NOTE: high state entropy={report.state_entropy:.2f}, regimes may be too fine-grained")

        if report.is_stable:
            report.conclusion = "PASS: regime design is stable"
        else:
            report.conclusion = "FAIL: regime definition needs adjustment"

        return report

    def validate_from_db(self) -> TransitionReport:
        """Load regime history from DB and validate stability."""
        conn = sqlite3.connect(self.db_path)
        df = pd.read_sql_query(
            "SELECT date, regime FROM regime_history ORDER BY date", conn
        )
        conn.close()

        if df.empty:
            r = TransitionReport()
            r.conclusion = "NO DATA"
            return r

        regimes = df.set_index("date")["regime"]
        return self.validate(regimes)