"""Torch Module for Relational graph convolution layer"""
# pylint: disable= no-member, arguments-differ, invalid-name
import torch as th
from torch import nn

from .... import function as fn
from ..linear import TypedLinear

class RelGraphConv(nn.Module):
    r"""Relational graph convolution layer.

    Relational graph convolution is introduced in "`Modeling Relational Data with Graph
    Convolutional Networks <https://arxiv.org/abs/1703.06103>`__"
    and can be described in DGL as below:

    .. math::

       h_i^{(l+1)} = \sigma(\sum_{r\in\mathcal{R}}
       \sum_{j\in\mathcal{N}^r(i)}e_{j,i}W_r^{(l)}h_j^{(l)}+W_0^{(l)}h_i^{(l)})

    where :math:`\mathcal{N}^r(i)` is the neighbor set of node :math:`i` w.r.t. relation
    :math:`r`. :math:`e_{j,i}` is the normalizer. :math:`\sigma` is an activation
    function. :math:`W_0` is the self-loop weight.

    The basis regularization decomposes :math:`W_r` by:

    .. math::

       W_r^{(l)} = \sum_{b=1}^B a_{rb}^{(l)}V_b^{(l)}

    where :math:`B` is the number of bases, :math:`V_b^{(l)}` are linearly combined
    with coefficients :math:`a_{rb}^{(l)}`.

    The block-diagonal-decomposition regularization decomposes :math:`W_r` into :math:`B`
    number of block diagonal matrices. We refer :math:`B` as the number of bases.

    The block regularization decomposes :math:`W_r` by:

    .. math::

       W_r^{(l)} = \oplus_{b=1}^B Q_{rb}^{(l)}

    where :math:`B` is the number of bases, :math:`Q_{rb}^{(l)}` are block
    bases with shape :math:`R^{(d^{(l+1)}/B)*(d^{l}/B)}`.

    Parameters
    ----------
    in_feat : int
        Input feature size; i.e, the number of dimensions of :math:`h_j^{(l)}`.
    out_feat : int
        Output feature size; i.e., the number of dimensions of :math:`h_i^{(l+1)}`.
    num_rels : int
        Number of relations. .
    regularizer : str, optional
        Which weight regularizer to use "basis" or "bdd":

         - "basis" is short for basis-decomposition.
         - "bdd" is short for block-diagonal-decomposition.

        Default applies no regularization.
    num_bases : int, optional
        Number of bases. Needed when ``regularizer`` is specified. Default: ``None``.
    bias : bool, optional
        True if bias is added. Default: ``True``.
    activation : callable, optional
        Activation function. Default: ``None``.
    self_loop : bool, optional
        True to include self loop message. Default: ``True``.
    dropout : float, optional
        Dropout rate. Default: ``0.0``
    layer_norm: float, optional
        Add layer norm. Default: ``False``

    Examples
    --------
    >>> import dgl
    >>> import numpy as np
    >>> import torch as th
    >>> from dgl.nn import RelGraphConv
    >>>
    >>> g = dgl.graph(([0,1,2,3,2,5], [1,2,3,4,0,3]))
    >>> feat = th.ones(6, 10)
    >>> conv = RelGraphConv(10, 2, 3, regularizer='basis', num_bases=2)
    >>> etype = th.tensor([0,1,2,0,1,2])
    >>> res = conv(g, feat, etype)
    >>> res
    tensor([[ 0.3996, -2.3303],
            [-0.4323, -0.1440],
            [ 0.3996, -2.3303],
            [ 2.1046, -2.8654],
            [-0.4323, -0.1440],
            [-0.1309, -1.0000]], grad_fn=<AddBackward0>)
    """
    def __init__(self,
                 in_feat,
                 out_feat,
                 num_rels,
                 regularizer=None,
                 num_bases=None,
                 bias=True,
                 activation=None,
                 self_loop=True,
                 dropout=0.0,
                 layer_norm=False):
        super().__init__()
        self.linear_r = TypedLinear(in_feat, out_feat, num_rels, regularizer, num_bases)
        self.bias = bias
        self.activation = activation
        self.self_loop = self_loop
        self.layer_norm = layer_norm

        # bias
        if self.bias:
            self.h_bias = nn.Parameter(th.Tensor(out_feat))
            nn.init.zeros_(self.h_bias)

        # TODO(minjie): consider remove those options in the future to make
        #   the module only about graph convolution.
        # layer norm
        if self.layer_norm:
            self.layer_norm_weight = nn.LayerNorm(out_feat, elementwise_affine=True)

        # weight for self loop
        if self.self_loop:
            self.loop_weight = nn.Parameter(th.Tensor(in_feat, out_feat))
            nn.init.xavier_uniform_(self.loop_weight, gain=nn.init.calculate_gain('relu'))

        self.dropout = nn.Dropout(dropout)

    def message(self, edges):
        """Message function."""
        m = self.linear_r(edges.src['h'], edges.data['etype'], self.presorted)
        if 'norm' in edges.data:
            m = m * edges.data['norm']
        return {'m' : m}

    def forward(self, g, feat, etypes, norm=None, *, presorted=False):
        """Forward computation.

        Parameters
        ----------
        g : DGLGraph
            The graph.
        feat : torch.Tensor
            A 2D tensor of node features. Shape: :math:`(|V|, D_{in})`.
        etypes : torch.Tensor or list[int]
            An 1D integer tensor of edge types. Shape: :math:`(|E|,)`.
        norm : torch.Tensor, optional
            An 1D tensor of edge norm value.  Shape: :math:`(|E|,)`.
        presorted : bool, optional
            Whether the edges of the input graph have been sorted by their types.
            Forward on pre-sorted graph may be faster. Graphs created
            by :func:`~dgl.to_homogeneous` automatically satisfy the condition.
            Also see :func:`~dgl.reorder_graph` for sorting edges manually.

        Returns
        -------
        torch.Tensor
            New node features. Shape: :math:`(|V|, D_{out})`.
        """
        self.presorted = presorted
        with g.local_scope():
            g.srcdata['h'] = feat
            if norm is not None:
                g.edata['norm'] = norm
            g.edata['etype'] = etypes
            # message passing
            g.update_all(self.message, fn.sum('m', 'h'))
            # apply bias and activation
            h = g.dstdata['h']
            if self.layer_norm:
                h = self.layer_norm_weight(h)
            if self.bias:
                h = h + self.h_bias
            if self.self_loop:
                h = h + feat[:g.num_dst_nodes()] @ self.loop_weight
            if self.activation:
                h = self.activation(h)
            h = self.dropout(h)
            return h
