"""Negative samplers."""

from _collections_abc import Mapping

from torch.utils.data import functional_datapipe
from torchdata.datapipes.iter import Mapper


@functional_datapipe("sample_negative")
class NegativeSampler(Mapper):
    """
    A negative sampler used to generate negative samples and return
    a mix of positive and negative samples.
    """

    def __init__(
        self,
        datapipe,
        negative_ratio,
    ):
        """
        Initlization for a negative sampler.

        Parameters
        ----------
        datapipe : DataPipe
            The datapipe.
        negative_ratio : int
            The proportion of negative samples to positive samples.
        """
        super().__init__(datapipe, self._sample)
        assert negative_ratio > 0, "Negative_ratio should be positive Integer."
        self.negative_ratio = negative_ratio

    def _sample(self, minibatch):
        """
        Generate a mix of positive and negative samples.

        Parameters
        ----------
        minibatch : MiniBatch
            An instance of 'MiniBatch' class requires the 'node_pairs' field.
            This function is responsible for generating negative edges
            corresponding to the positive edges defined by the 'node_pairs'. In
            cases where negative edges already exist, this function will
            overwrite them.

        Returns
        -------
        MiniBatch
            An instance of 'MiniBatch' encompasses both positive and negative
            samples.
        """
        node_pairs = minibatch.node_pairs
        assert node_pairs is not None
        if isinstance(node_pairs, Mapping):
            minibatch.negative_srcs, minibatch.negative_dsts = {}, {}
            for etype, pos_pairs in node_pairs.items():
                self._collate(
                    minibatch, self._sample_with_etype(pos_pairs, etype), etype
                )
        else:
            self._collate(minibatch, self._sample_with_etype(node_pairs))
        return minibatch

    def _sample_with_etype(self, node_pairs, etype=None):
        """Generate negative pairs for a given etype form positive pairs
        for a given etype.

        Parameters
        ----------
        node_pairs : Tuple[Tensor, Tensor]
            A tuple of tensors that represent source-destination node pairs of
            positive edges, where positive means the edge must exist in the
            graph.
        etype : str
            Canonical edge type.

        Returns
        -------
        Tuple[Tensor, Tensor]
            A collection of negative node pairs.
        """
        raise NotImplementedError

    def _collate(self, minibatch, neg_pairs, etype=None):
        """Collates positive and negative samples into minibatch.

        Parameters
        ----------
        minibatch : MiniBatch
            The input minibatch, which contains positive node pairs, will be filled
            with negative information in this function.
        neg_pairs : Tuple[Tensor, Tensor]
            A tuple of tensors represents source-destination node pairs of
            negative edges, where negative means the edge may not exist in
            the graph.
        etype : str
            Canonical edge type.
        """
        neg_src, neg_dst = neg_pairs
        if neg_src is not None:
            neg_src = neg_src.view(-1, self.negative_ratio)
        if neg_dst is not None:
            neg_dst = neg_dst.view(-1, self.negative_ratio)
        if etype is not None:
            minibatch.negative_srcs[etype] = neg_src
            minibatch.negative_dsts[etype] = neg_dst
        else:
            minibatch.negative_srcs = neg_src
            minibatch.negative_dsts = neg_dst
