# Author: James Chapman
# This code heavily leans on the scikit-learn original
# Original Authors:
#         Alexandre Gramfort <alexandre.gramfort@inria.fr>,
#         Gael Varoquaux <gael.varoquaux@normalesup.org>
#         Andreas Mueller <amueller@ais.uni-bonn.de>
#         Olivier Grisel <olivier.grisel@ensta.org>
#         Raghav RV <rvraghav93@gmail.com>

import itertools
import numbers
import time
from collections import defaultdict
from itertools import product
from typing import Mapping, Iterable

import numpy as np
from joblib import Parallel
from mvlearn.compose import SimpleSplitter
from mvlearn.utils import check_Xs
from sklearn import clone
from sklearn.base import is_classifier
from sklearn.metrics import check_scoring
from sklearn.metrics._scorer import _check_multimetric_scoring
from sklearn.model_selection import check_cv
from sklearn.model_selection._search import (
    BaseSearchCV as SKBaseSearchCV,
    ParameterGrid,
    _check_param_grid,
)
from sklearn.model_selection._validation import _fit_and_score, _insert_error_scores
from sklearn.pipeline import Pipeline
from sklearn.utils import indexable
from sklearn.utils.fixes import delayed
from sklearn.utils.validation import _check_fit_params, check_random_state


def param2grid(params):
    """
    Converts parameters with a list for each view into a scikit-learn friendly form

    Parameters
    ----------
    params : a dictionary of parameters where some parameters may contain a list of lists (one list for each 'view')

    Returns : a parameter grid in the form expected by scikit-learn where each element is a single candidate
    (a single value or a list with one value for each view)
    -------

    Examples
    ---------
    >>> params = {'regs': [[1, 2], [3, 4]]}
    >>> param2grid(params)
    [[1,3], [1,4], [2,3], [2,4]]
    """
    for k, v in params.items():
        if any([isinstance(v_, list) for v_ in v]):
            # itertools expects all lists to perform product
            v = [[v_] if not isinstance(v_, list) else v_ for v_ in v]
            params[k] = list(map(list, itertools.product(*v)))
    return params


class ParameterSampler:
    """Generator on parameters sampled from given distributions.
    Non-deterministic iterable over random candidate combinations for hyper-
    parameter search. If all parameters are presented as a list,
    sampling without replacement is performed. If at least one parameter
    is given as a distribution, sampling with replacement is used.
    It is highly recommended to use continuous distributions for continuous
    parameters.
    Parameters
    ----------
    param_distributions : dict
        Dictionary with parameters names (`str`) as keys and distributions
        or lists of parameters to try. Distributions must provide a ``rvs``
        method for sampling (such as those from scipy.stats.distributions).
        If a list is given, it is sampled uniformly.
        If a list of dicts is given, first a dict is sampled uniformly, and
        then a parameter is sampled using that dict as above.
    n_iter : int
        Number of parameter settings that are produced.
    random_state : int, RandomState instance or None, default=None
        Pseudo random number generator state used for random uniform sampling
        from lists of possible values instead of scipy.stats distributions.
        Pass an int for reproducible output across multiple
        function calls.
    Returns
    -------
    params : dict of str to any
        **Yields** dictionaries mapping each estimator parameter to
        as sampled value.
    """

    def __init__(self, param_distributions, n_iter, *, random_state=None):
        if not isinstance(param_distributions, (Mapping, Iterable)):
            raise TypeError(
                "Parameter distribution is not a dict or a list ({!r})".format(
                    param_distributions
                )
            )

        if isinstance(param_distributions, Mapping):
            # wrap dictionary in a singleton list to support either dict
            # or list of dicts
            param_distributions = [param_distributions]

        for dist in param_distributions:
            if not isinstance(dist, dict):
                raise TypeError(
                    "Parameter distribution is not a dict ({!r})".format(dist)
                )
            for key in dist:
                if isinstance(dist[key], Iterable):
                    if any(
                            [
                                not isinstance(view_param, Iterable)
                                and not hasattr(view_param, "rvs")
                                for view_param in dist[key]
                            ]
                    ):
                        raise TypeError(
                            "Parameter value for at least one view is not iterable "
                            "or distribution (key={!r}, value={!r})".format(
                                key, dist[key]
                            )
                        )
                elif not hasattr(dist[key], "rvs"):
                    raise TypeError(
                        "Parameter value is not iterable "
                        "or distribution (key={!r}, value={!r})".format(key, dist[key])
                    )
        self.n_iter = n_iter
        self.random_state = random_state
        self.param_distributions = param_distributions

    def __iter__(self):
        rng = check_random_state(self.random_state)
        for _ in range(self.n_iter):
            dist = rng.choice(self.param_distributions)
            # Always sort the keys of a dictionary, for reproducibility
            items = sorted(dist.items())
            params = dict()
            for k, v in items:
                # if value is an iterable then either the elements are the distribution or each element is a distribution
                # for each view.
                if isinstance(v, Iterable):
                    # if each element is a distribution for each view (i.e. it is a non-string Iterable) then call return_param for each view
                    if any(
                            [
                                (isinstance(v_, Iterable) and not isinstance(v_, str))
                                or hasattr(v_, "rvs")
                                for v_ in v
                            ]
                    ):
                        params[k] = [self.return_param(v_) for v_ in v]
                    # if the parameter is shared across views then the list will just contain non-iterable values
                    else:
                        params[k] = self.return_param(v)
                # if value is not iterable then it is either a distribution or a value in which case call return param on it.
                else:
                    params[k] = self.return_param(v)
            yield params

    def return_param(self, v):
        rng = check_random_state(self.random_state)
        if hasattr(v, "rvs"):
            param = v.rvs(random_state=rng)
        elif isinstance(v, Iterable) and not isinstance(v, str):
            param = v[rng.randint(len(v))]
        else:
            param = v
        return param

    def __len__(self):
        """Number of points that will be sampled."""
        return self.n_iter


class BaseSearchCV(SKBaseSearchCV):
    def __init__(
            self,
            estimator,
            *,
            scoring=None,
            n_jobs=None,
            refit=True,
            cv=None,
            verbose=0,
            pre_dispatch="2*n_jobs",
            error_score=np.nan,
            return_train_score=True,
    ):
        super().__init__(
            estimator=estimator,
            scoring=scoring,
            n_jobs=n_jobs,
            refit=refit,
            cv=cv,
            verbose=verbose,
            pre_dispatch=pre_dispatch,
            error_score=error_score,
            return_train_score=return_train_score,
        )

    def fit(self, Xs, y=None, *, groups=None, **fit_params):
        """Run fit with all sets of parameters.
        Parameters
        ----------
        Xs : array-like of shape (n_samples, n_features)
            Training vector, where `n_samples` is the number of samples and
            `n_features` is the number of features.
        y : array-like of shape (n_samples, n_output) \
            or (n_samples,), default=None
            Target relative to X for classification or regression;
            None for unsupervised learning.
        groups : array-like of shape (n_samples,), default=None
            Group labels for the samples used while splitting the dataset into
            train/test set. Only used in conjunction with a "Group" :term:`cv`
            instance (e.g., :class:`~sklearn.model_selection.GroupKFold`).
        **fit_params : dict of str -> object
            Parameters passed to the ``fit`` method of the estimator.
        Returns
        -------
        self : object
            Instance of fitted estimator.
        """
        estimator = self.estimator
        refit_metric = "score"

        if callable(self.scoring):
            scorers = self.scoring
        elif self.scoring is None or isinstance(self.scoring, str):
            scorers = check_scoring(self.estimator, self.scoring)
        else:
            scorers = _check_multimetric_scoring(self.estimator, self.scoring)
            self._check_refit_for_multimetric(scorers)
            refit_metric = self.refit

        Xs[0], y, groups = indexable(Xs[0], y, groups)
        fit_params = _check_fit_params(Xs[0], fit_params)

        cv_orig = check_cv(self.cv, y, classifier=is_classifier(estimator))
        n_splits = cv_orig.get_n_splits(Xs[0], y, groups)

        base_estimator = clone(self.estimator)

        parallel = Parallel(n_jobs=self.n_jobs, pre_dispatch=self.pre_dispatch)

        fit_and_score_kwargs = dict(
            scorer=scorers,
            fit_params=fit_params,
            return_train_score=self.return_train_score,
            return_n_test_samples=True,
            return_times=True,
            return_parameters=False,
            error_score=self.error_score,
            verbose=self.verbose,
        )
        results = {}
        with parallel:
            all_candidate_params = []
            all_out = []
            all_more_results = defaultdict(list)

            def evaluate_candidates(candidate_params, cv=None, more_results=None):
                cv = cv or cv_orig
                candidate_params = list(candidate_params)
                n_candidates = len(candidate_params)

                if self.verbose > 0:
                    print(
                        "Fitting {0} folds for each of {1} candidates,"
                        " totalling {2} fits".format(
                            n_splits, n_candidates, n_candidates * n_splits
                        )
                    )

                X_transformed, _, _, n_features = check_Xs(
                    Xs, copy=True, return_dimensions=True
                )
                pipeline = Pipeline(
                    [
                        ("splitter", SimpleSplitter(n_features)),
                        ("estimator", clone(base_estimator)),
                    ]
                )

                out = parallel(
                    delayed(_fit_and_score)(
                        pipeline,
                        np.hstack(Xs),
                        y,
                        train=train,
                        test=test,
                        parameters={
                            f"estimator__{k}": v for k, v in parameters.items()
                        },
                        split_progress=(split_idx, n_splits),
                        candidate_progress=(cand_idx, n_candidates),
                        **fit_and_score_kwargs,
                    )
                    for (cand_idx, parameters), (split_idx, (train, test)) in product(
                        enumerate(candidate_params),
                        enumerate(cv.split(Xs[0], y, groups)),
                    )
                )

                if len(out) < 1:
                    raise ValueError(
                        "No fits were performed. "
                        "Was the CV iterator empty? "
                        "Were there no candidates?"
                    )
                elif len(out) != n_candidates * n_splits:
                    raise ValueError(
                        "cv.split and cv.get_n_splits returned "
                        "inconsistent results. Expected {} "
                        "splits, got {}".format(n_splits, len(out) // n_candidates)
                    )

                # For callable self.scoring, the return type is only know after
                # calling. If the return type is a dictionary, the error scores
                # can now be inserted with the correct key. The type checking
                # of out will be done in `_insert_error_scores`.
                if callable(self.scoring):
                    _insert_error_scores(out, self.error_score)

                all_candidate_params.extend(candidate_params)
                all_out.extend(out)

                if more_results is not None:
                    for key, value in more_results.items():
                        all_more_results[key].extend(value)

                nonlocal results
                results = self._format_results(
                    all_candidate_params, n_splits, all_out, all_more_results
                )

                return results

            self._run_search(evaluate_candidates)

            # multimetric is determined here because in the case of a callable
            # self.scoring the return type is only known after calling
            first_test_score = all_out[0]["test_scores"]
            self.multimetric_ = isinstance(first_test_score, dict)

            # check refit_metric now for a callabe scorer that is multimetric
            if callable(self.scoring) and self.multimetric_:
                self._check_refit_for_multimetric(first_test_score)
                refit_metric = self.refit

        # For multi-metric evaluation, store the best_index_, best_params_ and
        # best_score_ iff refit is one of the scorer names
        # In single metric evaluation, refit_metric is "score"
        if self.refit or not self.multimetric_:
            self.best_index_ = self._select_best_index(
                self.refit, refit_metric, results
            )
            if not callable(self.refit):
                # With a non-custom callable, we can select the best score
                # based on the best index
                self.best_score_ = results[f"mean_test_{refit_metric}"][
                    self.best_index_
                ]
            self.best_params_ = results["params"][self.best_index_]

        if self.refit:
            # we clone again after setting params in case some
            # of the params are estimators as well.
            self.best_estimator_ = clone(
                clone(base_estimator).set_params(**self.best_params_)
            )
            refit_start_time = time.time()
            if y is not None:
                self.best_estimator_.fit(Xs, y, **fit_params)
            else:
                self.best_estimator_.fit(Xs, **fit_params)
            refit_end_time = time.time()
            self.refit_time_ = refit_end_time - refit_start_time

            if hasattr(self.best_estimator_, "feature_names_in_"):
                self.feature_names_in_ = self.best_estimator_.feature_names_in_

        # Store the only scorer not as a dict for single metric evaluation
        self.scorer_ = scorers

        self.cv_results_ = results
        self.n_splits_ = n_splits
        return self

    @staticmethod
    def _select_best_index(refit, refit_metric, results):
        """Select index of the best combination of hyperparemeters."""
        if callable(refit):
            # If callable, refit is expected to return the index of the best
            # parameter set.
            best_index = refit(results)
            if not isinstance(best_index, numbers.Integral):
                raise TypeError("best_index_ returned is not an integer")
            if best_index < 0 or best_index >= len(results["params"]):
                raise IndexError("best_index_ index out of range")
        else:
            best_index = results[f"rank_test_{refit_metric}"].argmin()
        return best_index


class GridSearchCV(BaseSearchCV):
    """Exhaustive search over specified parameter values for an estimator.
    Important members are fit, predict.
    GridSearchCV implements a "fit" and a "score" method.
    It also implements "score_samples", "predict", "predict_proba",
    "decision_function", "transform" and "inverse_transform" if they are
    implemented in the estimator used.
    The parameters of the estimator used to apply these methods are optimized
    by cross-validated grid-search over a parameter grid.
    Parameters
    ----------
    estimator : estimator object
        This is assumed to implement the scikit-learn estimator interface.
        Either estimator needs to provide a ``score`` function,
        or ``scoring`` must be passed.
    param_grid : dict or list of dictionaries
        Dictionary with parameters names (`str`) as keys and lists of
        parameter settings to try as values, or a list of such
        dictionaries, in which case the grids spanned by each dictionary
        in the list are explored. This enables searching over any sequence
        of parameter settings.
    scoring : str, callable, list, tuple or dict, default=None
        Strategy to evaluate the performance of the cross-validated model on
        the test set.
        If `scoring` represents a single score, one can use:
        - a single string (see :ref:`scoring_parameter`);
        - a callable (see :ref:`scoring`) that returns a single value.
        If `scoring` represents multiple scores, one can use:
        - a list or tuple of unique strings;
        - a callable returning a dictionary where the keys are the metric
          names and the values are the metric scores;
        - a dictionary with metric names as keys and callables a values.
    n_jobs : int, default=None
        Number of jobs to run in parallel.
        ``None`` means 1 unless in a :obj:`joblib.parallel_backend` context.
        ``-1`` means using all processors.
    refit : bool, str, or callable, default=True
        Refit an estimator using the best found parameters on the whole
        dataset.
        For multiple metric evaluation, this needs to be a `str` denoting the
        scorer that would be used to find the best parameters for refitting
        the estimator at the end.
        Where there are considerations other than maximum score in
        choosing a best estimator, ``refit`` can be set to a function which
        returns the selected ``best_index_`` given ``cv_results_``. In that
        case, the ``best_estimator_`` and ``best_params_`` will be set
        according to the returned ``best_index_`` while the ``best_score_``
        attribute will not be available.
        The refitted estimator is made available at the ``best_estimator_``
        attribute and permits using ``predict`` directly on this
        ``GridSearchCV`` instance.
        Also for multiple metric evaluation, the attributes ``best_index_``,
        ``best_score_`` and ``best_params_`` will only be available if
        ``refit`` is set and all of them will be determined w.r.t this specific
        scorer.
        See ``scoring`` parameter to know more about multiple metric
        evaluation.
    cv : int, cross-validation generator or an iterable, default=None
        Determines the cross-validation splitting strategy.
        Possible inputs for cv are:
        - None, to use the default 5-fold cross validation,
        - integer, to specify the number of folds in a `(Stratified)KFold`,
        - :term:`CV splitter`,
        - An iterable yielding (train, test) splits as arrays of indices.
        For integer/None inputs, if the estimator is a classifier and ``y`` is
        either binary or multiclass, :class:`StratifiedKFold` is used. In all
        other cases, :class:`KFold` is used. These splitters are instantiated
        with `shuffle=False` so the splits will be the same across calls.
        Refer :ref:`User Guide <cross_validation>` for the various
        cross-validation strategies that can be used here.
    verbose : int
        Controls the verbosity: the higher, the more messages.
        - >1 : the computation time for each fold and parameter candidate is
          displayed;
        - >2 : the score is also displayed;
        - >3 : the fold and candidate parameter indexes are also displayed
          together with the starting time of the computation.
    pre_dispatch : int, or str, default='2*n_jobs'
        Controls the number of jobs that get dispatched during parallel
        execution. Reducing this number can be useful to avoid an
        explosion of memory consumption when more jobs get dispatched
        than CPUs can process. This parameter can be:
            - None, in which case all the jobs are immediately
              created and spawned. Use this for lightweight and
              fast-running jobs, to avoid delays due to on-demand
              spawning of the jobs
            - An int, giving the exact number of total jobs that are
              spawned
            - A str, giving an expression as a function of n_jobs,
              as in '2*n_jobs'
    error_score : 'raise' or numeric, default=np.nan
        Value to assign to the score if an error occurs in estimator fitting.
        If set to 'raise', the error is raised. If a numeric value is given,
        FitFailedWarning is raised. This parameter does not affect the refit
        step, which will always raise the error.
    return_train_score : bool, default=False
        If ``False``, the ``cv_results_`` attribute will not include training
        scores.
        Computing training scores is used to get insights on how different
        parameter settings impact the overfitting/underfitting trade-off.
        However computing the scores on the training set can be computationally
        expensive and is not strictly required to select the parameters that
        yield the best generalization performance.
    Attributes
    ----------
    cv_results_ : dict of numpy (masked) ndarrays
        A dict with keys as column headers and values as columns, that can be
        imported into a pandas ``DataFrame``
        will be represented by a ``cv_results_`` dict of::
            {
            'param_kernel': masked_array(data = ['poly', 'poly', 'rbf', 'rbf'],
                                         mask = [False False False False]...)
            'param_gamma': masked_array(data = [-- -- 0.1 0.2],
                                        mask = [ True  True False False]...),
            'param_degree': masked_array(data = [2.0 3.0 -- --],
                                         mask = [False False  True  True]...),
            'split0_test_score'  : [0.80, 0.70, 0.80, 0.93],
            'split1_test_score'  : [0.82, 0.50, 0.70, 0.78],
            'mean_test_score'    : [0.81, 0.60, 0.75, 0.85],
            'std_test_score'     : [0.01, 0.10, 0.05, 0.08],
            'rank_test_score'    : [2, 4, 3, 1],
            'split0_train_score' : [0.80, 0.92, 0.70, 0.93],
            'split1_train_score' : [0.82, 0.55, 0.70, 0.87],
            'mean_train_score'   : [0.81, 0.74, 0.70, 0.90],
            'std_train_score'    : [0.01, 0.19, 0.00, 0.03],
            'mean_fit_time'      : [0.73, 0.63, 0.43, 0.49],
            'std_fit_time'       : [0.01, 0.02, 0.01, 0.01],
            'mean_score_time'    : [0.01, 0.06, 0.04, 0.04],
            'std_score_time'     : [0.00, 0.00, 0.00, 0.01],
            'params'             : [{'kernel': 'poly', 'degree': 2}, ...],
            }
        NOTE
        The key ``'params'`` is used to store a list of parameter
        settings dicts for all the parameter candidates.
        The ``mean_fit_time``, ``std_fit_time``, ``mean_score_time`` and
        ``std_score_time`` are all in seconds.
        For multi-metric evaluation, the scores for all the scorers are
        available in the ``cv_results_`` dict at the keys ending with that
        scorer's name (``'_<scorer_name>'``) instead of ``'_score'`` shown
        above. ('split0_test_precision', 'mean_train_precision' etc.)
    best_estimator_ : estimator
        Estimator that was chosen by the search, i.e. estimator
        which gave highest score (or smallest loss if specified)
        on the left out data. Not available if ``refit=False``.
        See ``refit`` parameter for more information on allowed values.
    best_score_ : float
        Mean cross-validated score of the best_estimator
        For multi-metric evaluation, this is present only if ``refit`` is
        specified.
        This attribute is not available if ``refit`` is a function.
    best_params_ : dict
        Parameter setting that gave the best results on the hold out data.
        For multi-metric evaluation, this is present only if ``refit`` is
        specified.
    best_index_ : int
        The index (of the ``cv_results_`` arrays) which corresponds to the best
        candidate parameter setting.
        The dict at ``search.cv_results_['params'][search.best_index_]`` gives
        the parameter setting for the best model, that gives the highest
        mean score (``search.best_score_``).
        For multi-metric evaluation, this is present only if ``refit`` is
        specified.
    scorer_ : function or a dict
        Scorer function used on the held out data to choose the best
        parameters for the model.
        For multi-metric evaluation, this attribute holds the validated
        ``scoring`` dict which maps the scorer key to the scorer callable.
    n_splits_ : int
        The number of cross-validation splits (folds/iterations).
    refit_time_ : float
        Seconds used for refitting the best model on the whole dataset.
        This is present only if ``refit`` is not False.
    multimetric_ : bool
        Whether or not the scorers compute several metrics.
    classes_ : ndarray of shape (n_classes,)
        The classes labels. This is present only if ``refit`` is specified and
        the underlying estimator is a classifier.
    n_features_in_ : int
        Number of features seen during :term:`fit`. Only defined if
        `best_estimator_` is defined (see the documentation for the `refit`
        parameter for more details) and that `best_estimator_` exposes
        `n_features_in_` when fit.
    feature_names_in_ : ndarray of shape (`n_features_in_`,)
        Names of features seen during :term:`fit`. Only defined if
        `best_estimator_` is defined (see the documentation for the `refit`
        parameter for more details) and that `best_estimator_` exposes
        `feature_names_in_` when fit.

    Examples
    ---------
    >>> from cca_zoo.model_selection import GridSearchCV
    >>> from cca_zoo.models import MCCA
    >>> X1 = [[0, 0, 1], [1, 0, 0], [2, 2, 2], [3, 5, 4]]
    >>> X2 = [[0.1, -0.2], [0.9, 1.1], [6.2, 5.9], [11.9, 12.3]]
    >>> X3 = [[0, 1, 0], [1, 9, 0], [4, 3, 3,], [12, 8, 10]]
    >>> model = MCCA()
    >>> params = {'c': [[0.1, 0.2], [0.3, 0.4], 0.1]}
    >>> GridSearchCV(model,param_grid=params, cv=3).fit([X1,X2,X3]).best_estimator_.c
    [0.1, 0.3, 0.1]

    Notes
    -----
    The parameters selected are those that maximize the score of the left out
    data, unless an explicit score is passed in which case it is used instead.
    If `n_jobs` was set to a value higher than one, the data is copied for each
    point in the grid (and not `n_jobs` times). This is done for efficiency
    reasons if individual jobs take very little time, but may raise errors if
    the dataset is large and not enough memory is available.  A workaround in
    this case is to set `pre_dispatch`. Then, the memory is copied only
    `pre_dispatch` many times. A reasonable value for `pre_dispatch` is `2 *
    n_jobs`.

    """

    _required_parameters = ["estimator", "param_grid"]

    def __init__(
            self,
            estimator,
            param_grid,
            *,
            scoring=None,
            n_jobs=None,
            refit=True,
            cv=None,
            verbose=0,
            pre_dispatch="2*n_jobs",
            error_score=np.nan,
            return_train_score=False,
    ):
        super().__init__(
            estimator=estimator,
            scoring=scoring,
            n_jobs=n_jobs,
            refit=refit,
            cv=cv,
            verbose=verbose,
            pre_dispatch=pre_dispatch,
            error_score=error_score,
            return_train_score=return_train_score,
        )
        self.param_grid = param2grid(param_grid)
        _check_param_grid(param_grid)

    def _run_search(self, evaluate_candidates):
        """Search all candidates in param_grid"""
        evaluate_candidates(ParameterGrid(self.param_grid))


class RandomizedSearchCV(BaseSearchCV):
    """Randomized search on hyper parameters.
    RandomizedSearchCV implements a "fit" and a "score" method.
    It also implements "score_samples", "predict", "predict_proba",
    "decision_function", "transform" and "inverse_transform" if they are
    implemented in the estimator used.
    The parameters of the estimator used to apply these methods are optimized
    by cross-validated search over parameter settings.
    In contrast to GridSearchCV, not all parameter values are tried out, but
    rather a fixed number of parameter settings is sampled from the specified
    distributions. The number of parameter settings that are tried is
    given by n_iter.
    If all parameters are presented as a list,
    sampling without replacement is performed. If at least one parameter
    is given as a distribution, sampling with replacement is used.
    It is highly recommended to use continuous distributions for continuous
    parameters.

    Parameters
    ----------
    estimator : estimator object.
        A object of that type is instantiated for each grid point.
        This is assumed to implement the scikit-learn estimator interface.
        Either estimator needs to provide a ``score`` function,
        or ``scoring`` must be passed.
    param_distributions : dict or list of dicts
        Dictionary with parameters names (`str`) as keys and distributions
        or lists of parameters to try. Distributions must provide a ``rvs``
        method for sampling (such as those from scipy.stats.distributions).
        If a list is given, it is sampled uniformly.
        If a list of dicts is given, first a dict is sampled uniformly, and
        then a parameter is sampled using that dict as above.
    n_iter : int, default=10
        Number of parameter settings that are sampled. n_iter trades
        off runtime vs quality of the solution.
    scoring : str, callable, list, tuple or dict, default=None
        Strategy to evaluate the performance of the cross-validated model on
        the test set.
        If `scoring` represents a single score, one can use:
        - a single string (see :ref:`scoring_parameter`);
        - a callable (see :ref:`scoring`) that returns a single value.
        If `scoring` represents multiple scores, one can use:
        - a list or tuple of unique strings;
        - a callable returning a dictionary where the keys are the metric
          names and the values are the metric scores;
        - a dictionary with metric names as keys and callables a values.
        If None, the estimator's score method is used.
    n_jobs : int, default=None
        Number of jobs to run in parallel.
        ``None`` means 1 unless in a :obj:`joblib.parallel_backend` context.
        ``-1`` means using all processors.
    refit : bool, str, or callable, default=True
        Refit an estimator using the best found parameters on the whole
        dataset.
        For multiple metric evaluation, this needs to be a `str` denoting the
        scorer that would be used to find the best parameters for refitting
        the estimator at the end.
        Where there are considerations other than maximum score in
        choosing a best estimator, ``refit`` can be set to a function which
        returns the selected ``best_index_`` given the ``cv_results``. In that
        case, the ``best_estimator_`` and ``best_params_`` will be set
        according to the returned ``best_index_`` while the ``best_score_``
        attribute will not be available.
        The refitted estimator is made available at the ``best_estimator_``
        attribute and permits using ``predict`` directly on this
        ``RandomizedSearchCV`` instance.
        Also for multiple metric evaluation, the attributes ``best_index_``,
        ``best_score_`` and ``best_params_`` will only be available if
        ``refit`` is set and all of them will be determined w.r.t this specific
        scorer.
        See ``scoring`` parameter to know more about multiple metric
        evaluation.
    cv : int, cross-validation generator or an iterable, default=None
        Determines the cross-validation splitting strategy.
        Possible inputs for cv are:
        - None, to use the default 5-fold cross validation,
        - integer, to specify the number of folds in a `(Stratified)KFold`,
        - :term:`CV splitter`,
        - An iterable yielding (train, test) splits as arrays of indices.
        For integer/None inputs, if the estimator is a classifier and ``y`` is
        either binary or multiclass, :class:`StratifiedKFold` is used. In all
        other cases, :class:`KFold` is used. These splitters are instantiated
        with `shuffle=False` so the splits will be the same across calls.
        Refer :ref:`User Guide <cross_validation>` for the various
        cross-validation strategies that can be used here.
    verbose : int
        Controls the verbosity: the higher, the more messages.
    pre_dispatch : int, or str, default='2*n_jobs'
        Controls the number of jobs that get dispatched during parallel
        execution. Reducing this number can be useful to avoid an
        explosion of memory consumption when more jobs get dispatched
        than CPUs can process. This parameter can be:
            - None, in which case all the jobs are immediately
              created and spawned. Use this for lightweight and
              fast-running jobs, to avoid delays due to on-demand
              spawning of the jobs
            - An int, giving the exact number of total jobs that are
              spawned
            - A str, giving an expression as a function of n_jobs,
              as in '2*n_jobs'
    random_state : int, RandomState instance or None, default=None
        Pseudo random number generator state used for random uniform sampling
        from lists of possible values instead of scipy.stats distributions.
        Pass an int for reproducible output across multiple
        function calls.
    error_score : 'raise' or numeric, default=np.nan
        Value to assign to the score if an error occurs in estimator fitting.
        If set to 'raise', the error is raised. If a numeric value is given,
        FitFailedWarning is raised. This parameter does not affect the refit
        step, which will always raise the error.
    return_train_score : bool, default=False
        If ``False``, the ``cv_results_`` attribute will not include training
        scores.
        Computing training scores is used to get insights on how different
        parameter settings impact the overfitting/underfitting trade-off.
        However computing the scores on the training set can be computationally
        expensive and is not strictly required to select the parameters that
        yield the best generalization performance.
    Attributes
    ----------
    cv_results_ : dict of numpy (masked) ndarrays
        A dict with keys as column headers and values as columns, that can be
        imported into a pandas ``DataFrame``.
        will be represented by a ``cv_results_`` dict of::
            {
            'param_kernel' : masked_array(data = ['rbf', 'rbf', 'rbf'],
                                          mask = False),
            'param_gamma'  : masked_array(data = [0.1 0.2 0.3], mask = False),
            'split0_test_score'  : [0.80, 0.84, 0.70],
            'split1_test_score'  : [0.82, 0.50, 0.70],
            'mean_test_score'    : [0.81, 0.67, 0.70],
            'std_test_score'     : [0.01, 0.24, 0.00],
            'rank_test_score'    : [1, 3, 2],
            'split0_train_score' : [0.80, 0.92, 0.70],
            'split1_train_score' : [0.82, 0.55, 0.70],
            'mean_train_score'   : [0.81, 0.74, 0.70],
            'std_train_score'    : [0.01, 0.19, 0.00],
            'mean_fit_time'      : [0.73, 0.63, 0.43],
            'std_fit_time'       : [0.01, 0.02, 0.01],
            'mean_score_time'    : [0.01, 0.06, 0.04],
            'std_score_time'     : [0.00, 0.00, 0.00],
            'params'             : [{'kernel' : 'rbf', 'gamma' : 0.1}, ...],
            }
        NOTE
        The key ``'params'`` is used to store a list of parameter
        settings dicts for all the parameter candidates.
        The ``mean_fit_time``, ``std_fit_time``, ``mean_score_time`` and
        ``std_score_time`` are all in seconds.
        For multi-metric evaluation, the scores for all the scorers are
        available in the ``cv_results_`` dict at the keys ending with that
        scorer's name (``'_<scorer_name>'``) instead of ``'_score'`` shown
        above. ('split0_test_precision', 'mean_train_precision' etc.)
    best_estimator_ : estimator
        Estimator that was chosen by the search, i.e. estimator
        which gave highest score (or smallest loss if specified)
        on the left out data. Not available if ``refit=False``.
        For multi-metric evaluation, this attribute is present only if
        ``refit`` is specified.
        See ``refit`` parameter for more information on allowed values.
    best_score_ : float
        Mean cross-validated score of the best_estimator.
        For multi-metric evaluation, this is not available if ``refit`` is
        ``False``. See ``refit`` parameter for more information.
        This attribute is not available if ``refit`` is a function.
    best_params_ : dict
        Parameter setting that gave the best results on the hold out data.
        For multi-metric evaluation, this is not available if ``refit`` is
        ``False``. See ``refit`` parameter for more information.
    best_index_ : int
        The index (of the ``cv_results_`` arrays) which corresponds to the best
        candidate parameter setting.
        The dict at ``search.cv_results_['params'][search.best_index_]`` gives
        the parameter setting for the best model, that gives the highest
        mean score (``search.best_score_``).
        For multi-metric evaluation, this is not available if ``refit`` is
        ``False``. See ``refit`` parameter for more information.
    scorer_ : function or a dict
        Scorer function used on the held out data to choose the best
        parameters for the model.
        For multi-metric evaluation, this attribute holds the validated
        ``scoring`` dict which maps the scorer key to the scorer callable.
    n_splits_ : int
        The number of cross-validation splits (folds/iterations).
    refit_time_ : float
        Seconds used for refitting the best model on the whole dataset.
        This is present only if ``refit`` is not False.
    multimetric_ : bool
        Whether or not the scorers compute several metrics.
    classes_ : ndarray of shape (n_classes,)
        The classes labels. This is present only if ``refit`` is specified and
        the underlying estimator is a classifier.
    n_features_in_ : int
        Number of features seen during :term:`fit`. Only defined if
        `best_estimator_` is defined and that `best_estimator_` exposes
        `n_features_in_` when fit.
    feature_names_in_ : ndarray of shape (`n_features_in_`,)
        Names of features seen during :term:`fit`. Only defined if
        `best_estimator_` is defined and that `best_estimator_` exposes
        `feature_names_in_` when fit.

    Examples
    ---------
    >>> from cca_zoo.model_selection import RandomizedSearchCV
    >>> from cca_zoo.models import MCCA
    >>> from sklearn.utils.fixes import loguniform
    >>> X1 = [[0, 0, 1], [1, 0, 0], [2, 2, 2], [3, 5, 4]]
    >>> X2 = [[0.1, -0.2], [0.9, 1.1], [6.2, 5.9], [11.9, 12.3]]
    >>> X3 = [[0, 1, 0], [1, 9, 0], [4, 3, 3,], [12, 8, 10]]
    >>> model = MCCA()
    >>> params = {'c': [loguniform(1e-4, 1e0), loguniform(1e-4, 1e0), [0.1]]}
    >>> def scorer(estimator, X):
    ...    scores = estimator.score(X)
    ...    return np.mean(scores)
    >>> RandomizedSearchCV(model,param_distributions=params, cv=3, scoring=scorer,n_iter=10).fit([X1,X2,X3]).n_iter
    10

    Notes
    -----
    The parameters selected are those that maximize the score of the held-out
    data, according to the scoring parameter.
    If `n_jobs` was set to a value higher than one, the data is copied for each
    parameter setting(and not `n_jobs` times). This is done for efficiency
    reasons if individual jobs take very little time, but may raise errors if
    the dataset is large and not enough memory is available.  A workaround in
    this case is to set `pre_dispatch`. Then, the memory is copied only
    `pre_dispatch` many times. A reasonable value for `pre_dispatch` is `2 *
    n_jobs`.
    """

    _required_parameters = ["estimator", "param_distributions"]

    def __init__(
            self,
            estimator,
            param_distributions,
            *,
            n_iter=10,
            scoring=None,
            n_jobs=None,
            refit=True,
            cv=None,
            verbose=0,
            pre_dispatch="2*n_jobs",
            random_state=None,
            error_score=np.nan,
            return_train_score=False,
    ):
        self.param_distributions = param_distributions
        self.n_iter = n_iter
        self.random_state = random_state
        super().__init__(
            estimator=estimator,
            scoring=scoring,
            n_jobs=n_jobs,
            refit=refit,
            cv=cv,
            verbose=verbose,
            pre_dispatch=pre_dispatch,
            error_score=error_score,
            return_train_score=return_train_score,
        )

    def _run_search(self, evaluate_candidates):
        """Search n_iter candidates from param_distributions"""
        evaluate_candidates(
            ParameterSampler(
                self.param_distributions, self.n_iter, random_state=self.random_state
            )
        )
