"""
This module provides an interface to build torch_geometric.data.Data objects.
"""

import torch
from torch_geometric.data import Data
from torch_geometric.utils import to_undirected
from . import LabelTensor
from .utils import check_consistency, is_function


class Graph(Data):
    """
    A class to build torch_geometric.data.Data objects.
    """

    def __new__(
        cls,
        **kwargs,
    ):
        """
        :param kwargs: Parameters to construct the Graph object.
        :return: A new instance of the Graph class.
        :rtype: Graph
        """
        # create class instance
        instance = Data.__new__(cls)

        # check the consistency of types defined in __init__, the others are not
        # checked (as in pyg Data object)
        instance._check_type_consistency(**kwargs)

        return instance

    def __init__(
        self,
        x=None,
        edge_index=None,
        pos=None,
        edge_attr=None,
        undirected=False,
        **kwargs,
    ):
        """
        Initialize the Graph object.

        :param x: Optional tensor of node features (N, F) where F is the number
            of features per node.
        :type x: torch.Tensor, LabelTensor
        :param torch.Tensor edge_index: A tensor of shape (2, E) representing
            the indices of the graph's edges.
        :param pos: A tensor of shape (N, D) representing the positions of N
            points in D-dimensional space.
        :type pos: torch.Tensor | LabelTensor
        :param edge_attr: Optional tensor of edge_featured (E, F') where F' is
            the number of edge features
        :param bool undirected: Whether to make the graph undirected
        :param kwargs: Additional keyword arguments passed to the
            `torch_geometric.data.Data` class constructor. If the argument
            is a `torch.Tensor` or `LabelTensor`, it is included in the Data
            object as a graph parameter.
        """
        # preprocessing
        self._preprocess_edge_index(edge_index, undirected)

        # calling init
        super().__init__(
            x=x, edge_index=edge_index, edge_attr=edge_attr, pos=pos, **kwargs
        )

    def _check_type_consistency(self, **kwargs):
        # default types, specified in cls.__new__, by default they are Nont
        # if specified in **kwargs they get override
        x, pos, edge_index, edge_attr = None, None, None, None
        if "pos" in kwargs:
            pos = kwargs["pos"]
            self._check_pos_consistency(pos)
        if "edge_index" in kwargs:
            edge_index = kwargs["edge_index"]
            self._check_edge_index_consistency(edge_index)
        if "x" in kwargs:
            x = kwargs["x"]
            self._check_x_consistency(x, pos)
        if "edge_attr" in kwargs:
            edge_attr = kwargs["edge_attr"]
            self._check_edge_attr_consistency(edge_attr, edge_index)
        if "undirected" in kwargs:
            undirected = kwargs["undirected"]
            check_consistency(undirected, bool)

    @staticmethod
    def _check_pos_consistency(pos):
        """
        Check if the position tensor is consistent.
        :param torch.Tensor pos: The position tensor.
        """
        if pos is not None:
            check_consistency(pos, (torch.Tensor, LabelTensor))
            if pos.ndim != 2:
                raise ValueError("pos must be a 2D tensor.")

    @staticmethod
    def _check_edge_index_consistency(edge_index):
        """
        Check if the edge index is consistent.
        :param torch.Tensor edge_index: The edge index tensor.
        """
        check_consistency(edge_index, (torch.Tensor, LabelTensor))
        if edge_index.ndim != 2:
            raise ValueError("edge_index must be a 2D tensor.")
        if edge_index.size(0) != 2:
            raise ValueError("edge_index must have shape [2, num_edges].")

    @staticmethod
    def _check_edge_attr_consistency(edge_attr, edge_index):
        """
        Check if the edge attr is consistent.
        :param torch.Tensor edge_attr: The edge attribute tensor.

        :param torch.Tensor edge_index: The edge index tensor.
        """
        if edge_attr is not None:
            check_consistency(edge_attr, (torch.Tensor, LabelTensor))
            if edge_attr.ndim != 2:
                raise ValueError("edge_attr must be a 2D tensor.")
            if edge_attr.size(0) != edge_index.size(1):
                raise ValueError(
                    "edge_attr must have shape "
                    "[num_edges, num_edge_features], expected "
                    f"num_edges {edge_index.size(1)} "
                    f"got {edge_attr.size(0)}."
                )

    @staticmethod
    def _check_x_consistency(x, pos=None):
        """
        Check if the input tensor x is consistent with the position tensor pos.
        :param torch.Tensor x: The input tensor.
        :param torch.Tensor pos: The position tensor.
        """
        if x is not None:
            check_consistency(x, (torch.Tensor, LabelTensor))
            if x.ndim != 2:
                raise ValueError("x must be a 2D tensor.")
            if pos is not None:
                if x.size(0) != pos.size(0):
                    raise ValueError("Inconsistent number of nodes.")
            if pos is not None:
                if x.size(0) != pos.size(0):
                    raise ValueError("Inconsistent number of nodes.")

    @staticmethod
    def _preprocess_edge_index(edge_index, undirected):
        """
        Preprocess the edge index.
        :param torch.Tensor edge_index: The edge index.
        :param bool undirected: Whether the graph is undirected.
        :return: The preprocessed edge index.
        :rtype: torch.Tensor
        """
        if undirected:
            edge_index = to_undirected(edge_index)
        return edge_index


class GraphBuilder:
    """
    A class that allows the simple definition of Graph instances.
    """

    def __new__(
        cls,
        pos,
        edge_index,
        x=None,
        edge_attr=False,
        custom_edge_func=None,
        **kwargs,
    ):
        """
        Creates a new instance of the Graph class.

        :param pos: A tensor of shape (N, D) representing the positions of N
            points in D-dimensional space.
        :type pos: torch.Tensor | LabelTensor
        :param edge_index: A tensor of shape (2, E) representing the indices of
            the graph's edges.
        :type edge_index: torch.Tensor
        :param x: Optional tensor of node features (N, F) where F is the number
            of features per node.
        :type x: torch.Tensor, LabelTensor
        :param bool edge_attr: Optional edge attributes (E, F) where F is the
            number of features per edge.
        :param callable custom_edge_func: A custom function to compute edge
            attributes.
        :param kwargs: Additional keyword arguments passed to the Graph class
            constructor.
        :return: A Graph instance constructed using the provided information.
        :rtype: Graph
        """
        edge_attr = cls._create_edge_attr(
            pos, edge_index, edge_attr, custom_edge_func or cls._build_edge_attr
        )
        return Graph(
            x=x,
            edge_index=edge_index,
            edge_attr=edge_attr,
            pos=pos,
            **kwargs,
        )

    @staticmethod
    def _create_edge_attr(pos, edge_index, edge_attr, func):
        check_consistency(edge_attr, bool)
        if edge_attr:
            if is_function(func):
                return func(pos, edge_index)
            raise ValueError("custom_edge_func must be a function.")
        return None

    @staticmethod
    def _build_edge_attr(pos, edge_index):
        return (
            (pos[edge_index[0]] - pos[edge_index[1]])
            .abs()
            .as_subclass(torch.Tensor)
        )


class RadiusGraph(GraphBuilder):
    """
    A class to build a radius graph.
    """

    def __new__(cls, pos, radius, **kwargs):
        """
        Creates a new instance of the Graph class using a radius-based graph
        construction.

        :param pos: A tensor of shape (N, D) representing the positions of N
            points in D-dimensional space.
        :type pos: torch.Tensor | LabelTensor
        :param float radius: The radius within which points are connected.
        :Keyword Arguments:
            The additional keyword arguments to be passed to GraphBuilder
            and Graph classes
        :return: Graph instance containg the information passed in input and
            the computed edge_index
        :rtype: Graph
        """
        edge_index = cls.compute_radius_graph(pos, radius)
        return super().__new__(cls, pos=pos, edge_index=edge_index, **kwargs)

    @staticmethod
    def compute_radius_graph(points, radius):
        """
        Computes a radius-based graph for a given set of points.

        :param points: A tensor of shape (N, D) representing the positions of
            N points in D-dimensional space.
        :type points: torch.Tensor | LabelTensor
        :param float radius: The number of nearest neighbors to find for each
            point.
        :rtype torch.Tensor: A tensor of shape (2, E), where E is the number of
            edges, representing the edge indices of the KNN graph.
        """
        dist = torch.cdist(points, points, p=2)
        return (
            torch.nonzero(dist <= radius, as_tuple=False)
            .t()
            .as_subclass(torch.Tensor)
        )


class KNNGraph(GraphBuilder):
    """
    A class to build a KNN graph.
    """

    def __new__(cls, pos, neighbours, **kwargs):
        """
        Creates a new instance of the Graph class using k-nearest neighbors
        to compute edge_index.

        :param pos: A tensor of shape (N, D) representing the positions of N
            points in D-dimensional space.
        :type pos: torch.Tensor | LabelTensor
        :param int neighbours: The number of nearest neighbors to consider when
            building the graph.
        :Keyword Arguments:
            The additional keyword arguments to be passed to GraphBuilder
            and Graph classes

        :return: Graph instance containg the information passed in input and
            the computed edge_index
        :rtype: Graph
        """

        edge_index = cls.compute_knn_graph(pos, neighbours)
        return super().__new__(cls, pos=pos, edge_index=edge_index, **kwargs)

    @staticmethod
    def compute_knn_graph(points, k):
        """
        Computes the edge_index based k-nearest neighbors graph algorithm

        :param points: A tensor of shape (N, D) representing the positions of
            N points in D-dimensional space.
        :type points: torch.Tensor | LabelTensor
        :param int k: The number of nearest neighbors to find for each point.
        :rtype torch.Tensor: A tensor of shape (2, E), where E is the number of
            edges, representing the edge indices of the KNN graph.
        """

        dist = torch.cdist(points, points, p=2)
        knn_indices = torch.topk(dist, k=k + 1, largest=False).indices[:, 1:]
        row = torch.arange(points.size(0)).repeat_interleave(k)
        col = knn_indices.flatten()
        return torch.stack([row, col], dim=0).as_subclass(torch.Tensor)