"""Node and edge featurization for molecular graphs."""
# pylint: disable= no-member, arguments-differ, invalid-name
import itertools
from collections import defaultdict
import dgl.backend as F
import numpy as np

from rdkit import Chem

__all__ = ['one_hot_encoding',
           'atom_type_one_hot',
           'atomic_number_one_hot',
           'atomic_number',
           'atom_degree_one_hot',
           'atom_degree',
           'atom_total_degree_one_hot',
           'atom_total_degree',
           'atom_explicit_valence_one_hot',
           'atom_explicit_valence',
           'atom_implicit_valence_one_hot',
           'atom_implicit_valence',
           'atom_hybridization_one_hot',
           'atom_total_num_H_one_hot',
           'atom_total_num_H',
           'atom_formal_charge_one_hot',
           'atom_formal_charge',
           'atom_num_radical_electrons_one_hot',
           'atom_num_radical_electrons',
           'atom_is_aromatic_one_hot',
           'atom_is_aromatic',
           'atom_is_in_ring_one_hot',
           'atom_is_in_ring',
           'atom_chiral_tag_one_hot',
           'atom_mass',
           'ConcatFeaturizer',
           'BaseAtomFeaturizer',
           'CanonicalAtomFeaturizer',
           'bond_type_one_hot',
           'bond_is_conjugated_one_hot',
           'bond_is_conjugated',
           'bond_is_in_ring_one_hot',
           'bond_is_in_ring',
           'bond_stereo_one_hot',
           'BaseBondFeaturizer',
           'CanonicalBondFeaturizer']

def one_hot_encoding(x, allowable_set, encode_unknown=False):
    """One-hot encoding.

    Parameters
    ----------
    x
        Value to encode.
    allowable_set : list
        The elements of the allowable_set should be of the
        same type as x.
    encode_unknown : bool
        If True, map inputs not in the allowable set to the
        additional last element.

    Returns
    -------
    list
        List of boolean values where at most one value is True.
        The list is of length ``len(allowable_set)`` if ``encode_unknown=False``
        and ``len(allowable_set) + 1`` otherwise.
    """
    if encode_unknown and (allowable_set[-1] is not None):
        allowable_set.append(None)

    if encode_unknown and (x not in allowable_set):
        x = None

    return list(map(lambda s: x == s, allowable_set))

#################################################################
# Atom featurization
#################################################################

def atom_type_one_hot(atom, allowable_set=None, encode_unknown=False):
    """One hot encoding for the type of an atom.

    Parameters
    ----------
    atom : rdkit.Chem.rdchem.Atom
        RDKit atom instance.
    allowable_set : list of str
        Atom types to consider. Default: ``C``, ``N``, ``O``, ``S``, ``F``, ``Si``, ``P``,
        ``Cl``, ``Br``, ``Mg``, ``Na``, ``Ca``, ``Fe``, ``As``, ``Al``, ``I``, ``B``, ``V``,
        ``K``, ``Tl``, ``Yb``, ``Sb``, ``Sn``, ``Ag``, ``Pd``, ``Co``, ``Se``, ``Ti``, ``Zn``,
        ``H``, ``Li``, ``Ge``, ``Cu``, ``Au``, ``Ni``, ``Cd``, ``In``, ``Mn``, ``Zr``, ``Cr``,
        ``Pt``, ``Hg``, ``Pb``.
    encode_unknown : bool
        If True, map inputs not in the allowable set to the
        additional last element. (Default: False)

    Returns
    -------
    list
        List of boolean values where at most one value is True.
    """
    if allowable_set is None:
        allowable_set = ['C', 'N', 'O', 'S', 'F', 'Si', 'P', 'Cl', 'Br', 'Mg', 'Na', 'Ca',
                         'Fe', 'As', 'Al', 'I', 'B', 'V', 'K', 'Tl', 'Yb', 'Sb', 'Sn',
                         'Ag', 'Pd', 'Co', 'Se', 'Ti', 'Zn', 'H', 'Li', 'Ge', 'Cu', 'Au',
                         'Ni', 'Cd', 'In', 'Mn', 'Zr', 'Cr', 'Pt', 'Hg', 'Pb']
    return one_hot_encoding(atom.GetSymbol(), allowable_set, encode_unknown)

def atomic_number_one_hot(atom, allowable_set=None, encode_unknown=False):
    """One hot encoding for the atomic number of an atom.

    Parameters
    ----------
    atom : rdkit.Chem.rdchem.Atom
        RDKit atom instance.
    allowable_set : list of int
        Atomic numbers to consider. Default: ``1`` - ``100``.
    encode_unknown : bool
        If True, map inputs not in the allowable set to the
        additional last element. (Default: False)

    Returns
    -------
    list
        List of boolean values where at most one value is True.
    """
    if allowable_set is None:
        allowable_set = list(range(1, 101))
    return one_hot_encoding(atom.GetAtomicNum(), allowable_set, encode_unknown)

def atomic_number(atom):
    """Get the atomic number for an atom.

    Parameters
    ----------
    atom : rdkit.Chem.rdchem.Atom
        RDKit atom instance.

    Returns
    -------
    list
       List containing one int only.
    """
    return [atom.GetAtomicNum()]

def atom_degree_one_hot(atom, allowable_set=None, encode_unknown=False):
    """One hot encoding for the degree of an atom.

    Note that the result will be different depending on whether the Hs are
    explicitly modeled in the graph.

    Parameters
    ----------
    atom : rdkit.Chem.rdchem.Atom
        RDKit atom instance.
    allowable_set : list of int
        Atom degrees to consider. Default: ``0`` - ``10``.
    encode_unknown : bool
        If True, map inputs not in the allowable set to the
        additional last element. (Default: False)

    Returns
    -------
    list
        List of boolean values where at most one value is True.

    See Also
    --------
    atom_total_degree_one_hot
    """
    if allowable_set is None:
        allowable_set = list(range(11))
    return one_hot_encoding(atom.GetDegree(), allowable_set, encode_unknown)

def atom_degree(atom):
    """Get the degree of an atom.

    Note that the result will be different depending on whether the Hs are
    explicitly modeled in the graph.

    Parameters
    ----------
    atom : rdkit.Chem.rdchem.Atom
        RDKit atom instance.

    Returns
    -------
    list
        List containing one int only.

    See Also
    --------
    atom_total_degree
    """
    return [atom.GetDegree()]

def atom_total_degree_one_hot(atom, allowable_set=None, encode_unknown=False):
    """One hot encoding for the degree of an atom including Hs.

    Parameters
    ----------
    atom : rdkit.Chem.rdchem.Atom
        RDKit atom instance.
    allowable_set : list
        Total degrees to consider. Default: ``0`` - ``5``.
    encode_unknown : bool
        If True, map inputs not in the allowable set to the
        additional last element. (Default: False)

    See Also
    --------
    atom_degree_one_hot
    """
    if allowable_set is None:
        allowable_set = list(range(6))
    return one_hot_encoding(atom.GetTotalDegree(), allowable_set, encode_unknown)

def atom_total_degree(atom):
    """The degree of an atom including Hs.

    See Also
    --------
    atom_degree

    Returns
    -------
    list
        List containing one int only.
    """
    return [atom.GetTotalDegree()]

def atom_explicit_valence_one_hot(atom, allowable_set=None, encode_unknown=False):
    """One hot encoding for the explicit valence of an aotm.

    Parameters
    ----------
    atom : rdkit.Chem.rdchem.Atom
        RDKit atom instance.
    allowable_set : list of int
        Atom explicit valences to consider. Default: ``1`` - ``6``.
    encode_unknown : bool
        If True, map inputs not in the allowable set to the
        additional last element. (Default: False)

    Returns
    -------
    list
        List of boolean values where at most one value is True.
    """
    if allowable_set is None:
        allowable_set = list(range(1, 7))
    return one_hot_encoding(atom.GetExplicitValence(), allowable_set, encode_unknown)

def atom_explicit_valence(atom):
    """Get the explicit valence of an atom.

    Parameters
    ----------
    atom : rdkit.Chem.rdchem.Atom
        RDKit atom instance.

    Returns
    -------
    list
        List containing one int only.
    """
    return [atom.GetExplicitValence()]

def atom_implicit_valence_one_hot(atom, allowable_set=None, encode_unknown=False):
    """One hot encoding for the implicit valence of an atom.

    Parameters
    ----------
    atom : rdkit.Chem.rdchem.Atom
        RDKit atom instance.
    allowable_set : list of int
        Atom implicit valences to consider. Default: ``0`` - ``6``.
    encode_unknown : bool
        If True, map inputs not in the allowable set to the
        additional last element. (Default: False)

    Returns
    -------
    list
        List of boolean values where at most one value is True.
    """
    if allowable_set is None:
        allowable_set = list(range(7))
    return one_hot_encoding(atom.GetImplicitValence(), allowable_set, encode_unknown)

def atom_implicit_valence(atom):
    """Get the implicit valence of an atom.

    Parameters
    ----------
    atom : rdkit.Chem.rdchem.Atom
        RDKit atom instance.

    Reurns
    ------
    list
        List containing one int only.
    """
    return [atom.GetImplicitValence()]

# pylint: disable=I1101
def atom_hybridization_one_hot(atom, allowable_set=None, encode_unknown=False):
    """One hot encoding for the hybridization of an atom.

    Parameters
    ----------
    atom : rdkit.Chem.rdchem.Atom
        RDKit atom instance.
    allowable_set : list of rdkit.Chem.rdchem.HybridizationType
        Atom hybridizations to consider. Default: ``Chem.rdchem.HybridizationType.SP``,
        ``Chem.rdchem.HybridizationType.SP2``, ``Chem.rdchem.HybridizationType.SP3``,
        ``Chem.rdchem.HybridizationType.SP3D``, ``Chem.rdchem.HybridizationType.SP3D2``.
    encode_unknown : bool
        If True, map inputs not in the allowable set to the
        additional last element. (Default: False)

    Returns
    -------
    list
        List of boolean values where at most one value is True.
    """
    if allowable_set is None:
        allowable_set = [Chem.rdchem.HybridizationType.SP,
                         Chem.rdchem.HybridizationType.SP2,
                         Chem.rdchem.HybridizationType.SP3,
                         Chem.rdchem.HybridizationType.SP3D,
                         Chem.rdchem.HybridizationType.SP3D2]
    return one_hot_encoding(atom.GetHybridization(), allowable_set, encode_unknown)

def atom_total_num_H_one_hot(atom, allowable_set=None, encode_unknown=False):
    """One hot encoding for the total number of Hs of an atom.

    Parameters
    ----------
    atom : rdkit.Chem.rdchem.Atom
        RDKit atom instance.
    allowable_set : list of int
        Total number of Hs to consider. Default: ``0`` - ``4``.
    encode_unknown : bool
        If True, map inputs not in the allowable set to the
        additional last element. (Default: False)

    Returns
    -------
    list
        List of boolean values where at most one value is True.
    """
    if allowable_set is None:
        allowable_set = list(range(5))
    return one_hot_encoding(atom.GetTotalNumHs(), allowable_set, encode_unknown)

def atom_total_num_H(atom):
    """Get the total number of Hs of an atom.

    Parameters
    ----------
    atom : rdkit.Chem.rdchem.Atom
        RDKit atom instance.

    Returns
    -------
    list
        List containing one int only.
    """
    return [atom.GetTotalNumHs()]

def atom_formal_charge_one_hot(atom, allowable_set=None, encode_unknown=False):
    """One hot encoding for the formal charge of an atom.

    Parameters
    ----------
    atom : rdkit.Chem.rdchem.Atom
        RDKit atom instance.
    allowable_set : list of int
        Formal charges to consider. Default: ``-2`` - ``2``.
    encode_unknown : bool
        If True, map inputs not in the allowable set to the
        additional last element. (Default: False)

    Returns
    -------
    list
        List of boolean values where at most one value is True.
    """
    if allowable_set is None:
        allowable_set = list(range(-2, 3))
    return one_hot_encoding(atom.GetFormalCharge(), allowable_set, encode_unknown)

def atom_formal_charge(atom):
    """Get formal charge for an atom.

    Parameters
    ----------
    atom : rdkit.Chem.rdchem.Atom
        RDKit atom instance.

    Returns
    -------
    list
        List containing one int only.
    """
    return [atom.GetFormalCharge()]

def atom_num_radical_electrons_one_hot(atom, allowable_set=None, encode_unknown=False):
    """One hot encoding for the number of radical electrons of an atom.

    Parameters
    ----------
    atom : rdkit.Chem.rdchem.Atom
        RDKit atom instance.
    allowable_set : list of int
        Number of radical electrons to consider. Default: ``0`` - ``4``.
    encode_unknown : bool
        If True, map inputs not in the allowable set to the
        additional last element. (Default: False)

    Returns
    -------
    list
        List of boolean values where at most one value is True.
    """
    if allowable_set is None:
        allowable_set = list(range(5))
    return one_hot_encoding(atom.GetNumRadicalElectrons(), allowable_set, encode_unknown)

def atom_num_radical_electrons(atom):
    """Get the number of radical electrons for an atom.

    Parameters
    ----------
    atom : rdkit.Chem.rdchem.Atom
        RDKit atom instance.

    Returns
    -------
    list
        List containing one int only.
    """
    return [atom.GetNumRadicalElectrons()]

def atom_is_aromatic_one_hot(atom, allowable_set=None, encode_unknown=False):
    """One hot encoding for whether the atom is aromatic.

    Parameters
    ----------
    atom : rdkit.Chem.rdchem.Atom
        RDKit atom instance.
    allowable_set : list of bool
        Conditions to consider. Default: ``False`` and ``True``.
    encode_unknown : bool
        If True, map inputs not in the allowable set to the
        additional last element. (Default: False)

    Returns
    -------
    list
        List of boolean values where at most one value is True.
    """
    if allowable_set is None:
        allowable_set = [False, True]
    return one_hot_encoding(atom.GetIsAromatic(), allowable_set, encode_unknown)

def atom_is_aromatic(atom):
    """Get whether the atom is aromatic.

    Parameters
    ----------
    atom : rdkit.Chem.rdchem.Atom
        RDKit atom instance.

    Returns
    -------
    list
        List containing one bool only.
    """
    return [atom.GetIsAromatic()]

def atom_is_in_ring_one_hot(atom, allowable_set=None, encode_unknown=False):
    """One hot encoding for whether the atom is in ring.

    Parameters
    ----------
    atom : rdkit.Chem.rdchem.Atom
        RDKit atom instance.
    allowable_set : list of bool
        Conditions to consider. Default: ``False`` and ``True``.
    encode_unknown : bool
        If True, map inputs not in the allowable set to the
        additional last element. (Default: False)

    Returns
    -------
    list
        List of boolean values where at most one value is True.
    """
    if allowable_set is None:
        allowable_set = [False, True]
    return one_hot_encoding(atom.IsInRing(), allowable_set, encode_unknown)

def atom_is_in_ring(atom):
    """Get whether the atom is in ring.

    Parameters
    ----------
    atom : rdkit.Chem.rdchem.Atom
        RDKit atom instance.

    Returns
    -------
    list
        List containing one bool only.
    """
    return [atom.IsInRing()]

def atom_chiral_tag_one_hot(atom, allowable_set=None, encode_unknown=False):
    """One hot encoding for the chiral tag of an atom.

    Parameters
    ----------
    atom : rdkit.Chem.rdchem.Atom
        RDKit atom instance.
    allowable_set : list of rdkit.Chem.rdchem.ChiralType
        Chiral tags to consider. Default: ``rdkit.Chem.rdchem.ChiralType.CHI_UNSPECIFIED``,
        ``rdkit.Chem.rdchem.ChiralType.CHI_TETRAHEDRAL_CW``,
        ``rdkit.Chem.rdchem.ChiralType.CHI_TETRAHEDRAL_CCW``,
        ``rdkit.Chem.rdchem.ChiralType.CHI_OTHER``.
    """
    if allowable_set is None:
        allowable_set = [Chem.rdchem.ChiralType.CHI_UNSPECIFIED,
                         Chem.rdchem.ChiralType.CHI_TETRAHEDRAL_CW,
                         Chem.rdchem.ChiralType.CHI_TETRAHEDRAL_CCW,
                         Chem.rdchem.ChiralType.CHI_OTHER]
    return one_hot_encoding(atom.GetChiralTag(), allowable_set, encode_unknown)

def atom_mass(atom, coef=0.01):
    """Get the mass of an atom and scale it.

    Parameters
    ----------
    atom : rdkit.Chem.rdchem.Atom
        RDKit atom instance.
    coef : float
        The mass will be multiplied by ``coef``.

    Returns
    -------
    list
        List containing one float only.
    """
    return [atom.GetMass() * coef]

class ConcatFeaturizer(object):
    """Concatenate the evaluation results of multiple functions as a single feature.

    Parameters
    ----------
    func_list : list
        List of functions for computing molecular descriptors from objects of a same
        particular data type, e.g. ``rdkit.Chem.rdchem.Atom``. Each function is of signature
        ``func(data_type) -> list of float or bool or int``. The resulting order of
        the features will follow that of the functions in the list.
    """
    def __init__(self, func_list):
        self.func_list = func_list

    def __call__(self, x):
        """Featurize the input data.

        Parameters
        ----------
        x :
            Data to featurize.

        Returns
        -------
        list
            List of feature values, which can be of type bool, float or int.
        """
        return list(itertools.chain.from_iterable(
            [func(x) for func in self.func_list]))

class BaseAtomFeaturizer(object):
    """An abstract class for atom featurizers.

    Loop over all atoms in a molecule and featurize them with the ``featurizer_funcs``.

    **We assume the resulting DGLGraph will not contain any virtual nodes.**

    Parameters
    ----------
    featurizer_funcs : dict
        Mapping feature name to the featurization function.
        Each function is of signature ``func(rdkit.Chem.rdchem.Atom) -> list or 1D numpy array``.
    feat_sizes : dict
        Mapping feature name to the size of the corresponding feature. If None, they will be
        computed when needed. Default: None.

    Examples
    --------

    >>> from dgl.data.dgllife import BaseAtomFeaturizer, atom_mass, atom_degree_one_hot
    >>> from rdkit import Chem

    >>> mol = Chem.MolFromSmiles('CCO')
    >>> atom_featurizer = BaseAtomFeaturizer({'mass': atom_mass, 'degree': atom_degree_one_hot})
    >>> atom_featurizer(mol)
    {'mass': tensor([[0.1201],
                     [0.1201],
                     [0.1600]]),
     'degree': tensor([[0., 1., 0., 0., 0., 0., 0., 0., 0., 0., 0.],
                       [0., 0., 1., 0., 0., 0., 0., 0., 0., 0., 0.],
                       [0., 1., 0., 0., 0., 0., 0., 0., 0., 0., 0.]])}
    """
    def __init__(self, featurizer_funcs, feat_sizes=None):
        self.featurizer_funcs = featurizer_funcs
        if feat_sizes is None:
            feat_sizes = dict()
        self._feat_sizes = feat_sizes

    def feat_size(self, feat_name):
        """Get the feature size for ``feat_name``.

        Returns
        -------
        int
            Feature size for the feature with name ``feat_name``.
        """
        if feat_name not in self.featurizer_funcs:
            return ValueError('Expect feat_name to be in {}, got {}'.format(
                list(self.featurizer_funcs.keys()), feat_name))

        if feat_name not in self._feat_sizes:
            atom = Chem.MolFromSmiles('C').GetAtomWithIdx(0)
            self._feat_sizes[feat_name] = len(self.featurizer_funcs[feat_name](atom))

        return self._feat_sizes[feat_name]

    def __call__(self, mol):
        """Featurize all atoms in a molecule.

        Parameters
        ----------
        mol : rdkit.Chem.rdchem.Mol
            RDKit molecule instance.

        Returns
        -------
        dict
            For each function in self.featurizer_funcs with the key ``k``, store the computed
            feature under the key ``k``. Each feature is a tensor of dtype float32 and shape
            (N, M), where N is the number of atoms in the molecule.
        """
        num_atoms = mol.GetNumAtoms()
        atom_features = defaultdict(list)

        # Compute features for each atom
        for i in range(num_atoms):
            atom = mol.GetAtomWithIdx(i)
            for feat_name, feat_func in self.featurizer_funcs.items():
                atom_features[feat_name].append(feat_func(atom))

        # Stack the features and convert them to float arrays
        processed_features = dict()
        for feat_name, feat_list in atom_features.items():
            feat = np.stack(feat_list)
            processed_features[feat_name] = F.zerocopy_from_numpy(feat.astype(np.float32))

        return processed_features

class CanonicalAtomFeaturizer(BaseAtomFeaturizer):
    """A default featurizer for atoms.

    The atom features include:

    * **One hot encoding of the atom type**. The supported atom types include
      ``C``, ``N``, ``O``, ``S``, ``F``, ``Si``, ``P``, ``Cl``, ``Br``, ``Mg``,
      ``Na``, ``Ca``, ``Fe``, ``As``, ``Al``, ``I``, ``B``, ``V``, ``K``, ``Tl``,
      ``Yb``, ``Sb``, ``Sn``, ``Ag``, ``Pd``, ``Co``, ``Se``, ``Ti``, ``Zn``,
      ``H``, ``Li``, ``Ge``, ``Cu``, ``Au``, ``Ni``, ``Cd``, ``In``, ``Mn``, ``Zr``,
      ``Cr``, ``Pt``, ``Hg``, ``Pb``.
    * **One hot encoding of the atom degree**. The supported possibilities
      include ``0 - 10``.
    * **One hot encoding of the number of implicit Hs on the atom**. The supported
      possibilities include ``0 - 6``.
    * **Formal charge of the atom**.
    * **Number of radical electrons of the atom**.
    * **One hot encoding of the atom hybridization**. The supported possibilities include
      ``SP``, ``SP2``, ``SP3``, ``SP3D``, ``SP3D2``.
    * **Whether the atom is aromatic**.
    * **One hot encoding of the number of total Hs on the atom**. The supported possibilities
      include ``0 - 4``.

    **We assume the resulting DGLGraph will not contain any virtual nodes.**

    Parameters
    ----------
    atom_data_field : str
        Name for storing atom features in DGLGraphs, default to be 'h'.
    """
    def __init__(self, atom_data_field='h'):
        super(CanonicalAtomFeaturizer, self).__init__(
            featurizer_funcs={atom_data_field: ConcatFeaturizer(
                [atom_type_one_hot,
                 atom_degree_one_hot,
                 atom_implicit_valence_one_hot,
                 atom_formal_charge,
                 atom_num_radical_electrons,
                 atom_hybridization_one_hot,
                 atom_is_aromatic,
                 atom_total_num_H_one_hot]
            )})

def bond_type_one_hot(bond, allowable_set=None, encode_unknown=False):
    """One hot encoding for the type of a bond.

    Parameters
    ----------
    bond : rdkit.Chem.rdchem.Bond
        RDKit bond instance.
    allowable_set : list of Chem.rdchem.BondType
        Bond types to consider. Default: ``Chem.rdchem.BondType.SINGLE``,
        ``Chem.rdchem.BondType.DOUBLE``, ``Chem.rdchem.BondType.TRIPLE``,
        ``Chem.rdchem.BondType.AROMATIC``.
    encode_unknown : bool
        If True, map inputs not in the allowable set to the
        additional last element. (Default: False)

    Returns
    -------
    list
        List of boolean values where at most one value is True.
    """
    if allowable_set is None:
        allowable_set = [Chem.rdchem.BondType.SINGLE,
                         Chem.rdchem.BondType.DOUBLE,
                         Chem.rdchem.BondType.TRIPLE,
                         Chem.rdchem.BondType.AROMATIC]
    return one_hot_encoding(bond.GetBondType(), allowable_set, encode_unknown)

def bond_is_conjugated_one_hot(bond, allowable_set=None, encode_unknown=False):
    """One hot encoding for whether the bond is conjugated.
    Parameters
    ----------
    bond : rdkit.Chem.rdchem.Bond
        RDKit bond instance.
    allowable_set : list of bool
        Conditions to consider. Default: ``False`` and ``True``.
    encode_unknown : bool
        If True, map inputs not in the allowable set to the
        additional last element. (Default: False)
    Returns
    -------
    list
        List of boolean values where at most one value is True.
    """
    if allowable_set is None:
        allowable_set = [False, True]
    return one_hot_encoding(bond.GetIsConjugated(), allowable_set, encode_unknown)

def bond_is_conjugated(bond):
    """Get whether the bond is conjugated.
    Parameters
    ----------
    bond : rdkit.Chem.rdchem.Bond
        RDKit bond instance.
    Returns
    -------
    list
        List containing one bool only.
    """
    return [bond.GetIsConjugated()]

def bond_is_in_ring_one_hot(bond, allowable_set=None, encode_unknown=False):
    """One hot encoding for whether the bond is in a ring of any size.
    Parameters
    ----------
    bond : rdkit.Chem.rdchem.Bond
        RDKit bond instance.
    allowable_set : list of bool
        Conditions to consider. Default: ``False`` and ``True``.
    encode_unknown : bool
        If True, map inputs not in the allowable set to the
        additional last element. (Default: False)
    Returns
    -------
    list
        List of boolean values where at most one value is True.
    """
    if allowable_set is None:
        allowable_set = [False, True]
    return one_hot_encoding(bond.IsInRing(), allowable_set, encode_unknown)

def bond_is_in_ring(bond):
    """Get whether the bond is in a ring of any size.
    Parameters
    ----------
    bond : rdkit.Chem.rdchem.Bond
        RDKit bond instance.
    Returns
    -------
    list
        List containing one bool only.
    """
    return [bond.IsInRing()]

def bond_stereo_one_hot(bond, allowable_set=None, encode_unknown=False):
    """One hot encoding for the stereo configuration of a bond.
    Parameters
    ----------
    bond : rdkit.Chem.rdchem.Bond
        RDKit bond instance.
    allowable_set : list of rdkit.Chem.rdchem.BondStereo
        Stereo configurations to consider. Default: ``rdkit.Chem.rdchem.BondStereo.STEREONONE``,
        ``rdkit.Chem.rdchem.BondStereo.STEREOANY``, ``rdkit.Chem.rdchem.BondStereo.STEREOZ``,
        ``rdkit.Chem.rdchem.BondStereo.STEREOE``, ``rdkit.Chem.rdchem.BondStereo.STEREOCIS``,
        ``rdkit.Chem.rdchem.BondStereo.STEREOTRANS``.
    encode_unknown : bool
        If True, map inputs not in the allowable set to the
        additional last element. (Default: False)
    Returns
    -------
    list
        List of boolean values where at most one value is True.
    """
    if allowable_set is None:
        allowable_set = [Chem.rdchem.BondStereo.STEREONONE,
                         Chem.rdchem.BondStereo.STEREOANY,
                         Chem.rdchem.BondStereo.STEREOZ,
                         Chem.rdchem.BondStereo.STEREOE,
                         Chem.rdchem.BondStereo.STEREOCIS,
                         Chem.rdchem.BondStereo.STEREOTRANS]
    return one_hot_encoding(bond.GetStereo(), allowable_set, encode_unknown)

class BaseBondFeaturizer(object):
    """An abstract class for bond featurizers.
    Loop over all bonds in a molecule and featurize them with the ``featurizer_funcs``.
    We assume the constructed ``DGLGraph`` is a bi-directed graph where the **i** th bond in the
    molecule, i.e. ``mol.GetBondWithIdx(i)``, corresponds to the **(2i)**-th and **(2i+1)**-th edges
    in the DGLGraph.

    **We assume the resulting DGLGraph will be created with :func:`smiles_to_bigraph` without
    self loops.**

    Parameters
    ----------
    featurizer_funcs : dict
        Mapping feature name to the featurization function.
        Each function is of signature ``func(rdkit.Chem.rdchem.Bond) -> list or 1D numpy array``.
    feat_sizes : dict
        Mapping feature name to the size of the corresponding feature. If None, they will be
        computed when needed. Default: None.

    Examples
    --------

    >>> from dgl.data.dgllife import BaseBondFeaturizer, bond_type_one_hot, bond_is_in_ring
    >>> from rdkit import Chem

    >>> mol = Chem.MolFromSmiles('CCO')
    >>> bond_featurizer = BaseBondFeaturizer({'type': bond_type_one_hot, 'ring': bond_is_in_ring})
    >>> bond_featurizer(mol)
    {'type': tensor([[1., 0., 0., 0.],
                     [1., 0., 0., 0.],
                     [1., 0., 0., 0.],
                     [1., 0., 0., 0.]]),
     'ring': tensor([[0.], [0.], [0.], [0.]])}
    """
    def __init__(self, featurizer_funcs, feat_sizes=None):
        self.featurizer_funcs = featurizer_funcs
        if feat_sizes is None:
            feat_sizes = dict()
        self._feat_sizes = feat_sizes

    def feat_size(self, feat_name):
        """Get the feature size for ``feat_name``.

        Returns
        -------
        int
            Feature size for the feature with name ``feat_name``.
        """
        if feat_name not in self.featurizer_funcs:
            return ValueError('Expect feat_name to be in {}, got {}'.format(
                list(self.featurizer_funcs.keys()), feat_name))

        if feat_name not in self._feat_sizes:
            bond = Chem.MolFromSmiles('CO').GetBondWithIdx(0)
            self._feat_sizes[feat_name] = len(self.featurizer_funcs[feat_name](bond))

        return self._feat_sizes[feat_name]

    def __call__(self, mol):
        """Featurize all bonds in a molecule.

        Parameters
        ----------
        mol : rdkit.Chem.rdchem.Mol
            RDKit molecule instance.

        Returns
        -------
        dict
            For each function in self.featurizer_funcs with the key ``k``, store the computed
            feature under the key ``k``. Each feature is a tensor of dtype float32 and shape
            (N, M), where N is the number of atoms in the molecule.
        """
        num_bonds = mol.GetNumBonds()
        bond_features = defaultdict(list)

        # Compute features for each bond
        for i in range(num_bonds):
            bond = mol.GetBondWithIdx(i)
            for feat_name, feat_func in self.featurizer_funcs.items():
                feat = feat_func(bond)
                bond_features[feat_name].extend([feat, feat.copy()])

        # Stack the features and convert them to float arrays
        processed_features = dict()
        for feat_name, feat_list in bond_features.items():
            feat = np.stack(feat_list)
            processed_features[feat_name] = F.zerocopy_from_numpy(feat.astype(np.float32))

        return processed_features

class CanonicalBondFeaturizer(BaseBondFeaturizer):
    """A default featurizer for bonds.

    The bond features include:
    * **One hot encoding of the bond type**. The supported bond types include
      ``SINGLE``, ``DOUBLE``, ``TRIPLE``, ``AROMATIC``.
    * **Whether the bond is conjugated.**.
    * **Whether the bond is in a ring of any size.**
    * **One hot encoding of the stereo configuration of a bond**. The supported bond stereo
      configurations include ``STEREONONE``, ``STEREOANY``, ``STEREOZ``, ``STEREOE``,
      ``STEREOCIS``, ``STEREOTRANS``.

    **We assume the resulting DGLGraph will be created with :func:`smiles_to_bigraph` without
    self loops.**
    """
    def __init__(self, bond_data_field='e'):
        super(CanonicalBondFeaturizer, self).__init__(
            featurizer_funcs={bond_data_field: ConcatFeaturizer(
                [bond_type_one_hot,
                 bond_is_conjugated,
                 bond_is_in_ring,
                 bond_stereo_one_hot]
            )})
