"""
Training Parallelism — parallel evaluation across scenarios.

CMA-ES evaluates sequentially. This module parallelizes evaluation
across scenarios for 4-8x faster convergence.
"""
from __future__ import annotations

import concurrent.futures
import time
from dataclasses import dataclass
from typing import Any, Callable, List, Optional, Sequence

from malkhut.state import FulfilmentPolicyParams, MarketWorldState
from malkhut.training.cma_trainer import PolicyEvaluator, Scenario


class ParallelEvaluator:
    """
    Parallel evaluation of strategies across scenarios.

    Uses ThreadPoolExecutor for I/O-bound scenarios.
    Uses ProcessPoolExecutor for CPU-bound scenarios.
    """

    def __init__(
        self,
        evaluator: PolicyEvaluator,
        max_workers: int = 4,
    ) -> None:
        self.evaluator = evaluator
        self._max_workers = max_workers

    def evaluate_candidate(
        self,
        params: FulfilmentPolicyParams,
        scenarios: Sequence[Scenario],
        rng_seed: int = 0,
    ) -> tuple[float, list]:
        """Evaluate candidate with parallel scenario execution."""
        if len(scenarios) <= 1 or self._max_workers <= 1:
            return self.evaluator.evaluate_candidate(params, scenarios, rng_seed)

        # Split scenarios across workers
        chunk_size = max(1, len(scenarios) // self._max_workers)
        chunks = []
        for i in range(0, len(scenarios), chunk_size):
            chunks.append(scenarios[i:i + chunk_size])

        # Parallel evaluation
        all_results = []
        with concurrent.futures.ThreadPoolExecutor(max_workers=self._max_workers) as executor:
            futures = []
            for i, chunk in enumerate(chunks):
                future = executor.submit(
                    self.evaluator.evaluate_candidate,
                    params, chunk, rng_seed + i,
                )
                futures.append(future)

            for future in concurrent.futures.as_completed(futures):
                score, results = future.result()
                all_results.extend(results)

        # Aggregate scores
        if all_results:
            scores = [r.pnl_bps for r in all_results]
            avg_score = sum(scores) / len(scores)
        else:
            avg_score = 0.0

        return avg_score, all_results


@dataclass(frozen=True, slots=True)
class TrainingMetrics:
    """Metrics for a training run."""
    total_time_s: float
    generations: int
    total_evals: int
    best_score: float
    avg_score: float
    score_improvement: float
    convergence_gen: int


class TrainingMonitor:
    """
    Monitor training progress and convergence.

    Tracks metrics, detects convergence, logs progress.
    """

    def __init__(self) -> None:
        self._scores: list[float] = []
        self._times: list[float] = []
        self._start_time = time.time()

    def record_generation(self, score: float) -> None:
        self._scores.append(score)
        self._times.append(time.time())

    @property
    def best_score(self) -> float:
        return max(self._scores) if self._scores else 0.0

    @property
    def avg_score(self) -> float:
        return sum(self._scores) / len(self._scores) if self._scores else 0.0

    @property
    def improvement(self) -> float:
        if len(self._scores) < 2:
            return 0.0
        return self._scores[-1] - self._scores[0]

    @property
    def converged(self) -> bool:
        if len(self._scores) < 5:
            return False
        recent = self._scores[-5:]
        variance = sum((s - self.avg_score) ** 2 for s in recent) / len(recent)
        return variance < 0.01  # low variance = converged

    def metrics(self) -> TrainingMetrics:
        return TrainingMetrics(
            total_time_s=time.time() - self._start_time,
            generations=len(self._scores),
            total_evals=0,
            best_score=self.best_score,
            avg_score=self.avg_score,
            score_improvement=self.improvement,
            convergence_gen=len(self._scores) if self.converged else -1,
        )