"""An interface for extending pandas with custom arrays.

.. warning::

   This is an experimental API and subject to breaking changes
   without warning.
"""
import operator

import numpy as np

from pandas.compat import PY3, set_function_name
from pandas.compat.numpy import function as nv
from pandas.errors import AbstractMethodError
from pandas.util._decorators import Appender, Substitution

from pandas.core.dtypes.common import is_list_like
from pandas.core.dtypes.generic import ABCIndexClass, ABCSeries
from pandas.core.dtypes.missing import isna

from pandas.core import ops

_not_implemented_message = "{} does not implement {}."

_extension_array_shared_docs = dict()


class ExtensionArray(object):
    """
    Abstract base class for custom 1-D array types.

    pandas will recognize instances of this class as proper arrays
    with a custom type and will not attempt to coerce them to objects. They
    may be stored directly inside a :class:`DataFrame` or :class:`Series`.

    .. versionadded:: 0.23.0

    Notes
    -----
    The interface includes the following abstract methods that must be
    implemented by subclasses:

    * _from_sequence
    * _from_factorized
    * __getitem__
    * __len__
    * dtype
    * nbytes
    * isna
    * take
    * copy
    * _concat_same_type

    A default repr displaying the type, (truncated) data, length,
    and dtype is provided. It can be customized or replaced by
    by overriding:

    * __repr__ : A default repr for the ExtensionArray.
    * _formatter : Print scalars inside a Series or DataFrame.

    Some methods require casting the ExtensionArray to an ndarray of Python
    objects with ``self.astype(object)``, which may be expensive. When
    performance is a concern, we highly recommend overriding the following
    methods:

    * fillna
    * dropna
    * unique
    * factorize / _values_for_factorize
    * argsort / _values_for_argsort
    * searchsorted

    The remaining methods implemented on this class should be performant,
    as they only compose abstract methods. Still, a more efficient
    implementation may be available, and these methods can be overridden.

    One can implement methods to handle array reductions.

    * _reduce

    One can implement methods to handle parsing from strings that will be used
    in methods such as ``pandas.io.parsers.read_csv``.

    * _from_sequence_of_strings

    This class does not inherit from 'abc.ABCMeta' for performance reasons.
    Methods and properties required by the interface raise
    ``pandas.errors.AbstractMethodError`` and no ``register`` method is
    provided for registering virtual subclasses.

    ExtensionArrays are limited to 1 dimension.

    They may be backed by none, one, or many NumPy arrays. For example,
    ``pandas.Categorical`` is an extension array backed by two arrays,
    one for codes and one for categories. An array of IPv6 address may
    be backed by a NumPy structured array with two fields, one for the
    lower 64 bits and one for the upper 64 bits. Or they may be backed
    by some other storage type, like Python lists. Pandas makes no
    assumptions on how the data are stored, just that it can be converted
    to a NumPy array.
    The ExtensionArray interface does not impose any rules on how this data
    is stored. However, currently, the backing data cannot be stored in
    attributes called ``.values`` or ``._values`` to ensure full compatibility
    with pandas internals. But other names as ``.data``, ``._data``,
    ``._items``, ... can be freely used.
    """
    # '_typ' is for pandas.core.dtypes.generic.ABCExtensionArray.
    # Don't override this.
    _typ = 'extension'

    # ------------------------------------------------------------------------
    # Constructors
    # ------------------------------------------------------------------------
    @classmethod
    def _from_sequence(cls, scalars, dtype=None, copy=False):
        """
        Construct a new ExtensionArray from a sequence of scalars.

        Parameters
        ----------
        scalars : Sequence
            Each element will be an instance of the scalar type for this
            array, ``cls.dtype.type``.
        dtype : dtype, optional
            Construct for this particular dtype. This should be a Dtype
            compatible with the ExtensionArray.
        copy : boolean, default False
            If True, copy the underlying data.

        Returns
        -------
        ExtensionArray
        """
        raise AbstractMethodError(cls)

    @classmethod
    def _from_sequence_of_strings(cls, strings, dtype=None, copy=False):
        """Construct a new ExtensionArray from a sequence of strings.

        .. versionadded:: 0.24.0

        Parameters
        ----------
        strings : Sequence
            Each element will be an instance of the scalar type for this
            array, ``cls.dtype.type``.
        dtype : dtype, optional
            Construct for this particular dtype. This should be a Dtype
            compatible with the ExtensionArray.
        copy : boolean, default False
            If True, copy the underlying data.

        Returns
        -------
        ExtensionArray

        """
        raise AbstractMethodError(cls)

    @classmethod
    def _from_factorized(cls, values, original):
        """
        Reconstruct an ExtensionArray after factorization.

        Parameters
        ----------
        values : ndarray
            An integer ndarray with the factorized values.
        original : ExtensionArray
            The original ExtensionArray that factorize was called on.

        See Also
        --------
        pandas.factorize
        ExtensionArray.factorize
        """
        raise AbstractMethodError(cls)

    # ------------------------------------------------------------------------
    # Must be a Sequence
    # ------------------------------------------------------------------------

    def __getitem__(self, item):
        # type (Any) -> Any
        """
        Select a subset of self.

        Parameters
        ----------
        item : int, slice, or ndarray
            * int: The position in 'self' to get.

            * slice: A slice object, where 'start', 'stop', and 'step' are
              integers or None

            * ndarray: A 1-d boolean NumPy ndarray the same length as 'self'

        Returns
        -------
        item : scalar or ExtensionArray

        Notes
        -----
        For scalar ``item``, return a scalar value suitable for the array's
        type. This should be an instance of ``self.dtype.type``.

        For slice ``key``, return an instance of ``ExtensionArray``, even
        if the slice is length 0 or 1.

        For a boolean mask, return an instance of ``ExtensionArray``, filtered
        to the values where ``item`` is True.
        """
        raise AbstractMethodError(self)

    def __setitem__(self, key, value):
        # type: (Union[int, np.ndarray], Any) -> None
        """
        Set one or more values inplace.

        This method is not required to satisfy the pandas extension array
        interface.

        Parameters
        ----------
        key : int, ndarray, or slice
            When called from, e.g. ``Series.__setitem__``, ``key`` will be
            one of

            * scalar int
            * ndarray of integers.
            * boolean ndarray
            * slice object

        value : ExtensionDtype.type, Sequence[ExtensionDtype.type], or object
            value or values to be set of ``key``.

        Returns
        -------
        None
        """
        # Some notes to the ExtensionArray implementor who may have ended up
        # here. While this method is not required for the interface, if you
        # *do* choose to implement __setitem__, then some semantics should be
        # observed:
        #
        # * Setting multiple values : ExtensionArrays should support setting
        #   multiple values at once, 'key' will be a sequence of integers and
        #  'value' will be a same-length sequence.
        #
        # * Broadcasting : For a sequence 'key' and a scalar 'value',
        #   each position in 'key' should be set to 'value'.
        #
        # * Coercion : Most users will expect basic coercion to work. For
        #   example, a string like '2018-01-01' is coerced to a datetime
        #   when setting on a datetime64ns array. In general, if the
        #   __init__ method coerces that value, then so should __setitem__
        # Note, also, that Series/DataFrame.where internally use __setitem__
        # on a copy of the data.
        raise NotImplementedError(_not_implemented_message.format(
            type(self), '__setitem__')
        )

    def __len__(self):
        # type: () -> int
        """
        Length of this array

        Returns
        -------
        length : int
        """
        raise AbstractMethodError(self)

    def __iter__(self):
        """
        Iterate over elements of the array.
        """
        # This needs to be implemented so that pandas recognizes extension
        # arrays as list-like. The default implementation makes successive
        # calls to ``__getitem__``, which may be slower than necessary.
        for i in range(len(self)):
            yield self[i]

    # ------------------------------------------------------------------------
    # Required attributes
    # ------------------------------------------------------------------------
    @property
    def dtype(self):
        # type: () -> ExtensionDtype
        """
        An instance of 'ExtensionDtype'.
        """
        raise AbstractMethodError(self)

    @property
    def shape(self):
        # type: () -> Tuple[int, ...]
        """
        Return a tuple of the array dimensions.
        """
        return (len(self),)

    @property
    def ndim(self):
        # type: () -> int
        """
        Extension Arrays are only allowed to be 1-dimensional.
        """
        return 1

    @property
    def nbytes(self):
        # type: () -> int
        """
        The number of bytes needed to store this object in memory.
        """
        # If this is expensive to compute, return an approximate lower bound
        # on the number of bytes needed.
        raise AbstractMethodError(self)

    # ------------------------------------------------------------------------
    # Additional Methods
    # ------------------------------------------------------------------------
    def astype(self, dtype, copy=True):
        """
        Cast to a NumPy array with 'dtype'.

        Parameters
        ----------
        dtype : str or dtype
            Typecode or data-type to which the array is cast.
        copy : bool, default True
            Whether to copy the data, even if not necessary. If False,
            a copy is made only if the old dtype does not match the
            new dtype.

        Returns
        -------
        array : ndarray
            NumPy ndarray with 'dtype' for its dtype.
        """
        return np.array(self, dtype=dtype, copy=copy)

    def isna(self):
        # type: () -> Union[ExtensionArray, np.ndarray]