"""Background model trainer with MLflow tracking."""
import os
import time
import uuid
import threading
import numpy as np
from datetime import datetime

# Allow override via env var so Airflow tasks (different CWD) hit the same DB
_MLFLOW_URI = os.environ.get("MLFLOW_TRACKING_URI", "sqlite:///mlflow.db")

import mlflow
import mlflow.sklearn
from sklearn.preprocessing import StandardScaler, LabelEncoder
from sklearn.metrics import (
    accuracy_score, f1_score, precision_score, recall_score,
    r2_score, mean_absolute_error, mean_squared_error,
    confusion_matrix, classification_report,
)

from mlops.datasets import load_dataset
from mlops.algorithms import get_algorithm, ALGORITHMS

# ── Shared job state ──────────────────────────────────────────────────────────
training_jobs: dict = {}
automl_jobs: dict = {}
_lock = threading.Lock()


# ── Internal helpers ──────────────────────────────────────────────────────────

def _get_or_create_experiment(name: str) -> str:
    mlflow.set_tracking_uri(_MLFLOW_URI)
    exp = mlflow.get_experiment_by_name(name)
    if exp is None:
        return mlflow.create_experiment(name)
    return exp.experiment_id


def _update_job(store: dict, job_id: str, **kwargs):
    with _lock:
        store[job_id].update(kwargs)


def _classification_metrics(y_test, y_pred) -> dict:
    return {
        "accuracy":  round(float(accuracy_score(y_test, y_pred)), 4),
        "f1_score":  round(float(f1_score(y_test, y_pred, average="weighted", zero_division=0)), 4),
        "precision": round(float(precision_score(y_test, y_pred, average="weighted", zero_division=0)), 4),
        "recall":    round(float(recall_score(y_test, y_pred, average="weighted", zero_division=0)), 4),
    }


def _regression_metrics(y_test, y_pred) -> dict:
    mse = float(mean_squared_error(y_test, y_pred))
    return {
        "r2_score": round(float(r2_score(y_test, y_pred)), 4),
        "mae":      round(float(mean_absolute_error(y_test, y_pred)), 4),
        "mse":      round(mse, 4),
        "rmse":     round(float(np.sqrt(mse)), 4),
    }


# ── Single training run ───────────────────────────────────────────────────────

def _do_train(job_id: str, dataset_name: str, algorithm_name: str,
              algorithm_category: str, task_type: str, custom_params: dict | None):
    """Executed in a daemon thread; updates training_jobs[job_id] in place."""
    start_time = time.time()
    try:
        _update_job(training_jobs, job_id, status="running", progress=5)
        mlflow.set_tracking_uri(_MLFLOW_URI)

        # 1. Load data
        X_train, X_test, y_train, y_test, meta = load_dataset(dataset_name)
        _update_job(training_jobs, job_id, progress=20, dataset_meta=meta)

        # 2. Algorithm config
        algo_cfg = get_algorithm(task_type, algorithm_category, algorithm_name)
        params = {**algo_cfg["params"], **(custom_params or {})}

        # 3. Pre-process
        scaler = StandardScaler()
        X_train_s = scaler.fit_transform(X_train)
        X_test_s  = scaler.transform(X_test)

        # Handle NB algorithms that can't take negative inputs
        if "Naive Bayes" in algorithm_name or "Complement" in algorithm_name:
            from sklearn.preprocessing import MinMaxScaler
            mms = MinMaxScaler()
            X_train_s = mms.fit_transform(X_train)
            X_test_s  = mms.transform(X_test)

        _update_job(training_jobs, job_id, progress=35)

        # 4. Train inside an MLflow run
        exp_id = _get_or_create_experiment(dataset_name)
        with mlflow.start_run(experiment_id=exp_id,
                              run_name=f"{algorithm_name} — {dataset_name}") as run:
            run_id = run.info.run_id
            _update_job(training_jobs, job_id, mlflow_run_id=run_id, progress=40)

            mlflow.set_tags({
                "algorithm":  algorithm_name,
                "category":   algorithm_category,
                "dataset":    dataset_name,
                "task_type":  task_type,
                "job_id":     job_id,
            })
            mlflow.log_params({"algorithm": algorithm_name,
                               "category": algorithm_category,
                               "dataset": dataset_name,
                               **{k: str(v) for k, v in params.items()}})

            _update_job(training_jobs, job_id, progress=50)

            model = algo_cfg["class"](**params)
            model.fit(X_train_s, y_train)
            _update_job(training_jobs, job_id, progress=75)

            y_pred = model.predict(X_test_s)

            if task_type == "classification":
                metrics = _classification_metrics(y_test, y_pred)
                cm = confusion_matrix(y_test, y_pred).tolist()
                extra = {"confusion_matrix": cm,
                         "report": classification_report(y_test, y_pred, output_dict=True,
                                                          zero_division=0)}
            else:
                metrics = _regression_metrics(y_test, y_pred)
                extra = {"y_test_sample": y_test[:50].tolist(),
                         "y_pred_sample": y_pred[:50].tolist()}

            mlflow.log_metrics(metrics)
            mlflow.sklearn.log_model(model, "model")
            _update_job(training_jobs, job_id, progress=90)

        duration = round(time.time() - start_time, 2)
        _update_job(training_jobs, job_id,
                    status="completed", progress=100,
                    metrics=metrics, extra=extra,
                    duration=duration,
                    completed_at=datetime.utcnow().isoformat())

    except Exception as exc:
        _update_job(training_jobs, job_id,
                    status="failed", error=str(exc), progress=0)


def start_training(dataset_name: str, algorithm_name: str,
                   algorithm_category: str, task_type: str,
                   custom_params: dict | None = None) -> str:
    """Kick off a background training job and return its job_id."""
    job_id = str(uuid.uuid4())[:8]
    with _lock:
        training_jobs[job_id] = {
            "job_id":    job_id,
            "status":    "queued",
            "progress":  0,
            "dataset":   dataset_name,
            "algorithm": algorithm_name,
            "category":  algorithm_category,
            "task_type": task_type,
            "created_at": datetime.utcnow().isoformat(),
        }
    t = threading.Thread(
        target=_do_train,
        args=(job_id, dataset_name, algorithm_name,
              algorithm_category, task_type, custom_params),
        daemon=True,
    )
    t.start()
    return job_id


# ── AutoML: exhaustive search across all algorithms ───────────────────────────

def _do_automl(job_id: str, dataset_name: str, task_type: str,
               optimize_metric: str, max_runs: int):
    """Run every algorithm for the chosen task and log the best."""
    try:
        _update_job(automl_jobs, job_id, status="running", progress=2)
        mlflow.set_tracking_uri(_MLFLOW_URI)

        X_train, X_test, y_train, y_test, meta = load_dataset(dataset_name)
        _update_job(automl_jobs, job_id, dataset_meta=meta, progress=5)

        scaler = StandardScaler()
        X_train_s = scaler.fit_transform(X_train)
        X_test_s  = scaler.transform(X_test)

        exp_id = _get_or_create_experiment(f"AutoML — {dataset_name}")

        # Collect all algorithms for this task
        all_algos = []
        for cat_name, cat in ALGORITHMS[task_type].items():
            for alg_name, alg_cfg in cat.items():
                all_algos.append((cat_name, alg_name, alg_cfg))

        if max_runs < len(all_algos):
            import random
            random.seed(42)
            all_algos = random.sample(all_algos, max_runs)

        results = []
        total = len(all_algos)

        for idx, (cat_name, alg_name, alg_cfg) in enumerate(all_algos):
            _update_job(automl_jobs, job_id,
                        progress=int(5 + 90 * idx / total),
                        current_algo=alg_name)
            try:
                with mlflow.start_run(experiment_id=exp_id,
                                      run_name=f"AutoML: {alg_name}") as run:
                    mlflow.set_tags({"algorithm": alg_name, "category": cat_name,
                                     "automl_job": job_id, "task_type": task_type})

                    # NB needs non-negative values
                    X_tr = X_train_s
                    X_te = X_test_s
                    if "Naive Bayes" in alg_name or "Complement" in alg_name:
                        from sklearn.preprocessing import MinMaxScaler
                        mms = MinMaxScaler()
                        X_tr = mms.fit_transform(X_train)
                        X_te = mms.transform(X_test)

                    model = alg_cfg["class"](**alg_cfg["params"])
                    t0 = time.time()
                    model.fit(X_tr, y_train)
                    dur = round(time.time() - t0, 2)

                    y_pred = model.predict(X_te)
                    if task_type == "classification":
                        metrics = _classification_metrics(y_test, y_pred)
                    else:
                        metrics = _regression_metrics(y_test, y_pred)

                    mlflow.log_params({"algorithm": alg_name, "category": cat_name})
                    mlflow.log_metrics(metrics)
                    mlflow.sklearn.log_model(model, "model")

                    results.append({
                        "rank":       idx + 1,
                        "algorithm":  alg_name,
                        "category":   cat_name,
                        "metrics":    metrics,
                        "duration":   dur,
                        "run_id":     run.info.run_id,
                        "color":      alg_cfg.get("color", "#8b5cf6"),
                    })
            except Exception:
                pass  # skip failed algorithms silently

        # Sort by optimise metric
        higher_is_better = optimize_metric in ("accuracy", "f1_score", "precision",
                                               "recall", "r2_score")
        results.sort(key=lambda r: r["metrics"].get(optimize_metric, 0),
                     reverse=higher_is_better)
        for i, r in enumerate(results):
            r["rank"] = i + 1

        _update_job(automl_jobs, job_id,
                    status="completed", progress=100,
                    results=results,
                    best=results[0] if results else None,
                    completed_at=datetime.utcnow().isoformat())

    except Exception as exc:
        _update_job(automl_jobs, job_id, status="failed", error=str(exc))


def train_for_pipeline(dataset_name: str, task_type: str, category: str,
                       algorithm: str, experiment_name: str = "pipeline") -> dict:
    """
    Synchronous training helper used by Airflow pipeline tasks.
    Runs the full train/eval loop and returns a metrics dict.
    Raises RuntimeError if training fails.
    """
    from sklearn.preprocessing import StandardScaler, MinMaxScaler

    mlflow.set_tracking_uri(_MLFLOW_URI)
    X_train, X_test, y_train, y_test, _ = load_dataset(dataset_name)
    algo_cfg = get_algorithm(task_type, category, algorithm)
    params   = algo_cfg["params"]

    if "Naive Bayes" in algorithm or "Complement" in algorithm:
        scaler = MinMaxScaler()
    else:
        scaler = StandardScaler()

    X_tr = scaler.fit_transform(X_train)
    X_te = scaler.transform(X_test)

    exp_id = _get_or_create_experiment(experiment_name)
    with mlflow.start_run(experiment_id=exp_id,
                          run_name=f"{algorithm} — {dataset_name}") as run:
        mlflow.set_tags({
            "algorithm": algorithm, "category": category,
            "dataset": dataset_name, "source": "airflow_pipeline",
        })
        mlflow.log_params({"algorithm": algorithm, "category": category,
                           "dataset": dataset_name})
        model = algo_cfg["class"](**params)
        model.fit(X_tr, y_train)
        y_pred = model.predict(X_te)
        if task_type == "classification":
            metrics = _classification_metrics(y_test, y_pred)
        else:
            metrics = _regression_metrics(y_test, y_pred)
        mlflow.log_metrics(metrics)
        mlflow.sklearn.log_model(model, "model")

    return metrics


def start_automl(dataset_name: str, task_type: str,
                 optimize_metric: str = "accuracy",
                 max_runs: int = 20) -> str:
    """Kick off an AutoML sweep and return the job_id."""
    job_id = str(uuid.uuid4())[:8]
    with _lock:
        automl_jobs[job_id] = {
            "job_id":     job_id,
            "status":     "queued",
            "progress":   0,
            "dataset":    dataset_name,
            "task_type":  task_type,
            "metric":     optimize_metric,
            "results":    [],
            "created_at": datetime.utcnow().isoformat(),
        }
    t = threading.Thread(
        target=_do_automl,
        args=(job_id, dataset_name, task_type, optimize_metric, max_runs),
        daemon=True,
    )
    t.start()
    return job_id