# Authors: Lars Buitinck
#          Dan Blanchard <dblanchard@ets.org>
# License: BSD 3 clause

from array import array
from collections.abc import Mapping
from operator import itemgetter

import numpy as np
import scipy.sparse as sp

from ..base import BaseEstimator, TransformerMixin
from ..utils import check_array, tosequence
from ..utils.validation import _deprecate_positional_args


def _tosequence(X):
    """Turn X into a sequence or ndarray, avoiding a copy if possible."""
    if isinstance(X, Mapping):  # single sample
        return [X]
    else:
        return tosequence(X)


class DictVectorizer(TransformerMixin, BaseEstimator):
    """Transforms lists of feature-value mappings to vectors.

    This transformer turns lists of mappings (dict-like objects) of feature
    names to feature values into Numpy arrays or scipy.sparse matrices for use
    with scikit-learn estimators.

    When feature values are strings, this transformer will do a binary one-hot
    (aka one-of-K) coding: one boolean-valued feature is constructed for each
    of the possible string values that the feature can take on. For instance,
    a feature "f" that can take on the values "ham" and "spam" will become two
    features in the output, one signifying "f=ham", the other "f=spam".

    However, note that this transformer will only do a binary one-hot encoding
    when feature values are of type string. If categorical features are
    represented as numeric values such as int, the DictVectorizer can be
    followed by :class:`sklearn.preprocessing.OneHotEncoder` to complete
    binary one-hot encoding.

    Features that do not occur in a sample (mapping) will have a zero value
    in the resulting array/matrix.

    Read more in the :ref:`User Guide <dict_feature_extraction>`.

    Parameters
    ----------
    dtype : dtype, default=np.float64
        The type of feature values. Passed to Numpy array/scipy.sparse matrix
        constructors as the dtype argument.
    separator : str, default="="
        Separator string used when constructing new features for one-hot
        coding.
    sparse : bool, default=True
        Whether transform should produce scipy.sparse matrices.
    sort : bool, default=True
        Whether ``feature_names_`` and ``vocabulary_`` should be
        sorted when fitting.

    Attributes
    ----------
    vocabulary_ : dict
        A dictionary mapping feature names to feature indices.

    feature_names_ : list
        A list of length n_features containing the feature names (e.g., "f=ham"
        and "f=spam").

    Examples
    --------
    >>> from sklearn.feature_extraction import DictVectorizer
    >>> v = DictVectorizer(sparse=False)
    >>> D = [{'foo': 1, 'bar': 2}, {'foo': 3, 'baz': 1}]
    >>> X = v.fit_transform(D)
    >>> X
    array([[2., 0., 1.],
           [0., 1., 3.]])
    >>> v.inverse_transform(X) == \
        [{'bar': 2.0, 'foo': 1.0}, {'baz': 1.0, 'foo': 3.0}]
    True
    >>> v.transform({'foo': 4, 'unseen_feature': 3})
    array([[0., 0., 4.]])

    See also
    --------
    FeatureHasher : performs vectorization using only a hash function.
    sklearn.preprocessing.OrdinalEncoder : handles nominal/categorical
      features encoded as columns of arbitrary data types.
    """
    @_deprecate_positional_args
    def __init__(self, *, dtype=np.float64, separator="=", sparse=True,
                 sort=True):
        self.dtype = dtype
        self.separator = separator
        self.sparse = sparse
        self.sort = sort

    def fit(self, X, y=None):
        """Learn a list of feature name -> indices mappings.

        Parameters
        ----------
        X : Mapping or iterable over Mappings
            Dict(s) or Mapping(s) from feature names (arbitrary Python
            objects) to feature values (strings or convertible to dtype).
        y : (ignored)

        Returns
        -------
        self
        """
        feature_names = []
        vocab = {}

        for x in X:
            for f, v in x.items():
                if isinstance(v, str):
                    f = "%s%s%s" % (f, self.separator, v)
                if f not in vocab:
                    feature_names.append(f)
                    vocab[f] = len(vocab)

        if self.sort:
            feature_names.sort()
            vocab = {f: i for i, f in enumerate(feature_names)}

        self.feature_names_ = feature_names
        self.vocabulary_ = vocab

        return self

    def _transform(self, X, fitting):
        # Sanity check: Python's array has no way of explicitly requesting the
        # signed 32-bit integers that scipy.sparse needs, so we use the next
        # best thing: typecode "i" (int). However, if that gives larger or
        # smaller integers than 32-bit ones, np.frombuffer screws up.
        assert array("i").itemsize == 4, (
            "sizeof(int) != 4 on your platform; please report this at"
            " https://github.com/scikit-learn/scikit-learn/issues and"
            " include the output from platform.platform() in your bug report")

        dtype = self.dtype
        if fitting:
            feature_names = []
            vocab = {}
        else:
            feature_names = self.feature_names_
            vocab = self.vocabulary_

        # Process everything as sparse regardless of setting
        X = [X] if isinstance(X, Mapping) else X

        indices = array("i")
        indptr = [0]
        # XXX we could change values to an array.array as well, but it
        # would require (heuristic) conversion of dtype to typecode...
        values = []

        # collect all the possible feature names and build sparse matrix at
        # same time
        for x in X:
            for f, v in x.items():
                if isinstance(v, str):
                    f = "%s%s%s" % (f, self.separator, v)
                    v = 1
                if f in vocab:
                    indices.append(vocab[f])
                    values.append(dtype(v))
                else:
                    if fitting:
                        feature_names.append(f)
                        vocab[f] = len(vocab)
                        indices.append(vocab[f])
                        values.append(dtype(v))

            indptr.append(len(indices))

        if len(indptr) == 1:
            raise ValueError("Sample sequence X is empty.")

        indices = np.frombuffer(indices, dtype=np.intc)
        shape = (len(indptr) - 1, len(vocab))

        result_matrix = sp.csr_matrix((values, indices, indptr),
                                      shape=shape, dtype=dtype)

        # Sort everything if asked
        if fitting and self.sort:
            feature_names.sort()
            map_index = np.empty(len(feature_names), dtype=np.int32)
            for new_val, f in enumerate(feature_names):
                map_index[new_val] = vocab[f]
                vocab[f] = new_val
            result_matrix = result_matrix[:, map_index]

        if self.sparse:
            result_matrix.sort_indices()
        else:
            result_matrix = result_matrix.toarray()

        if fitting:
            self.feature_names_ = feature_names
            self.vocabulary_ = vocab

        return result_matrix

    def fit_transform(self, X, y=None):
        """Learn a list of feature name -> indices mappings and transform X.

        Like fit(X) followed by transform(X), but does not require
        materializing X in memory.

        Parameters
        ----------
        X : Mapping or iterable over Mappings
            Dict(s) or Mapping(s) from feature names (arbitrary Python
            objects) to feature values (strings or convertible to dtype).
        y : (ignored)

        Returns
        -------
        Xa : {array, sparse matrix}
            Feature vectors; always 2-d.
        """
        return self._transform(X, fitting=True)

    def inverse_transform(self, X, dict_type=dict):
        """Transform array or sparse matrix X back to feature mappings.

        X must have been produced by this DictVectorizer's transform or
        fit_transform method; it may only have passed through transformers
        that preserve the number of features and their order.

        In the case of one-hot/one-of-K coding, the constructed feature
        names and values are returned rather than the original ones.

        Parameters
        ----------
        X : {array-like, sparse matrix} of shape (n_samples, n_features)
            Sample matrix.
        dict_type : type, default=dict
            Constructor for feature mappings. Must conform to the
            collections.Mapping API.

        Returns
        -------
        D : list of dict_type objects of shape (n_samples,)
            Feature mappings for the samples in X.
        """
        # COO matrix is not subscriptable
        X = check_array(X, accept_sparse=['csr', 'csc'])
        n_samples = X.shape[0]

        names = self.feature_names_
        dicts = [dict_type() for _ in range(n_samples)]

        if sp.issparse(X):
            for i, j in zip(*X.nonzero()):
                dicts[i][names[j]] = X[i, j]
        else:
            for i, d in enumerate(dicts):
                for j, v in enumerate(X[i, :]):
                    if v != 0:
                        d[names[j]] = X[i, j]

        return dicts

    def transform(self, X):
        """Transform feature->value dicts to array or sparse matrix.

        Named features not encountered during fit or fit_transform will be
        silently ignored.

        Parameters
        ----------
        X : Mapping or iterable over Mappings of shape (n_samples,)
            Dict(s) or Mapping(s) from feature names (arbitrary Python
            objects) to feature values (strings or convertible to dtype).

        Returns
        -------
        Xa : {array, sparse matrix}
            Feature vectors; always 2-d.
        """
        if self.sparse:
            return self._transform(X, fitting=False)

        else:
            dtype = self.dtype
            vocab = self.vocabulary_
            X = _tosequence(X)
            Xa = np.zeros((len(X), len(vocab)), dtype=dtype)

            for i, x in enumerate(X):
                for f, v in x.items():
                    if isinstance(v, str):
                        f = "%s%s%s" % (f, self.separator, v)
                        v = 1
                    try:
                        Xa[i, vocab[f]] = dtype(v)
                    except KeyError:
                        pass

            return Xa

    def get_feature_names(self):
        """Returns a list of feature names, ordered by their indices.

        If one-of-K coding is applied to categorical features, this will
        include the constructed feature names but not the original ones.
        """
        return self.feature_names_

    def restrict(self, support, indices=False):
        """Restrict the features to those in support using feature selection.

        This function modifies the estimator in-place.

        Parameters
        ----------
        support : array-like
            Boolean mask or list of indices (as returned by the get_support
            member of feature selectors).
        indices : bool, default=False
            Whether support is a list of indices.

        Returns
        -------
        self

        Examples
        --------
        >>> from sklearn.feature_extraction import DictVectorizer
        >>> from sklearn.feature_selection import SelectKBest, chi2
        >>> v = DictVectorizer()
        >>> D = [{'foo': 1, 'bar': 2}, {'foo': 3, 'baz': 1}]
        >>> X = v.fit_transform(D)
        >>> support = SelectKBest(chi2, k=2).fit(X, [0, 1])
        >>> v.get_feature_names()
        ['bar', 'baz', 'foo']
        >>> v.restrict(support.get_support())
        DictVectorizer()
        >>> v.get_feature_names()
        ['bar', 'foo']
        """
        if not indices:
            support = np.where(support)[0]

        names = self.feature_names_
        new_vocab = {}
        for i in support:
            new_vocab[names[i]] = len(new_vocab)

        self.vocabulary_ = new_vocab
        self.feature_names_ = [f for f, i in sorted(new_vocab.items(),
                                                    key=itemgetter(1))]

        return self

    def _more_tags(self):
        return {'X_types': ["dict"]}