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"""Regressor utilities for MySQL Connector/Python.

Provides a scikit-learn compatible regressor backed by HeatWave ML.
"""
from typing import Optional, Union

import numpy as np
import pandas as pd
from sklearn.base import RegressorMixin

from mysql.ai.ml.base import MyBaseMLModel
from mysql.ai.ml.model import ML_TASK
from mysql.ai.utils import copy_dict

from mysql.connector.abstracts import MySQLConnectionAbstract


class MyRegressor(MyBaseMLModel, RegressorMixin):
    """
    MySQL HeatWave scikit-learn compatible regressor estimator.

    Provides prediction output from a regression model deployed in MySQL,
    and manages fit, explain, and prediction options as per HeatWave ML interface.

    Attributes:
        predict_extra_options (dict): Optional parameter dict passed to the backend for prediction.
        _model (MyModel): Underlying interface for database model operations.
        fit_extra_options (dict): See MyBaseMLModel.
        explain_extra_options (dict): See MyBaseMLModel.

    Args:
        db_connection (MySQLConnectionAbstract): Active MySQL connector DB connection.
        model_name (str, optional): Custom name for the model.
        fit_extra_options (dict, optional): Extra options for fitting.
        explain_extra_options (dict, optional): Extra options for explanations.
        predict_extra_options (dict, optional): Extra options for predictions.

    Methods:
        predict(X): Predict regression target.
    """

    def __init__(
        self,
        db_connection: MySQLConnectionAbstract,
        model_name: Optional[str] = None,
        fit_extra_options: Optional[dict] = None,
        explain_extra_options: Optional[dict] = None,
        predict_extra_options: Optional[dict] = None,
    ):
        """
        Initialize a MyRegressor.

        Args:
            db_connection: Active MySQL connector database connection.
            model_name: Optional, custom model name.
            fit_extra_options: Optional fit options.
            explain_extra_options: Optional explain options.
            predict_extra_options: Optional prediction options.

        Raises:
            DatabaseError:
                If a database connection issue occurs.
                If an operational error occurs during execution.
        """
        MyBaseMLModel.__init__(
            self,
            db_connection,
            ML_TASK.REGRESSION,
            model_name=model_name,
            fit_extra_options=fit_extra_options,
        )

        self.predict_extra_options = copy_dict(predict_extra_options)
        self.explain_extra_options = copy_dict(explain_extra_options)

    def predict(
        self, X: Union[pd.DataFrame, np.ndarray]
    ) -> np.ndarray:  # pylint: disable=invalid-name
        """
        Predict a continuous target for the input features using the MySQL model.

        Args:
            X: Input samples as a numpy array or pandas DataFrame.

        Returns:
            ndarray: Array of predicted target values, shape (n_samples,).

        Raises:
            DatabaseError:
                If provided options are invalid or unsupported,
                or if the model is not initialized, i.e., fit or import has not
                been called
                If a database connection issue occurs.
                If an operational error occurs during execution.
        """
        result = self._model.predict(X, options=self.predict_extra_options)
        return result["Prediction"].to_numpy()

    def explain_predictions(
        self, X: Union[pd.DataFrame, np.ndarray]
    ) -> pd.DataFrame:  # pylint: disable=invalid-name
        """
        Explain model predictions using provided data.

        References:
            https://dev.mysql.com/doc/heatwave/en/mys-hwaml-ml-explain-table.html
                A full list of supported options can be found under "ML_EXPLAIN_TABLE Options"

        Args:
            X: DataFrame for which predictions should be explained.

        Returns:
            DataFrame containing explanation details (feature attributions, etc.)

        Raises:
            DatabaseError:
                If provided options are invalid or unsupported,
                or if the model is not initialized, i.e., fit or import has not
                been called
                If a database connection issue occurs.
                If an operational error occurs during execution.

        Notes:
            Temporary input/output tables are cleaned up after explanation.
        """
        self._model.explain_predictions(X, options=self.explain_extra_options)
