"""MPNN"""
import torch.nn as nn
import torch.nn.functional as F

from dgl.nn.pytorch import NNConv

__all__ = ['MPNNGNN']

class MPNNGNN(nn.Module):
    """MPNN.

    MPNN is introduced in `Neural Message Passing for Quantum Chemistry
    <https://arxiv.org/abs/1704.01212>`__.

    This class performs message passing in MPNN and returns the updated node representations.

    Parameters
    ----------
    node_in_feats : int
        Size for the input node features.
    node_out_feats : int
        Size for the output node representations. Default to 64.
    edge_in_feats : int
        Size for the input edge features. Default to 128.
    edge_hidden_feats : int
        Size for the hidden edge representations.
    num_step_message_passing : int
        Number of message passing steps. Default to 6.
    """
    def __init__(self, node_in_feats, edge_in_feats, node_out_feats=64,
                 edge_hidden_feats=128, num_step_message_passing=6):
        super(MPNNGNN, self).__init__()

        self.project_node_feats = nn.Sequential(
            nn.Linear(node_in_feats, node_out_feats),
            nn.ReLU()
        )
        self.num_step_message_passing = num_step_message_passing
        edge_network = nn.Sequential(
            nn.Linear(edge_in_feats, edge_hidden_feats),
            nn.ReLU(),
            nn.Linear(edge_hidden_feats, node_out_feats * node_out_feats)
        )
        self.gnn_layer = NNConv(
            in_feats=node_out_feats,
            out_feats=node_out_feats,
            edge_func=edge_network,
            aggregator_type='sum'
        )
        self.gru = nn.GRU(node_out_feats, node_out_feats)

    def forward(self, g, node_feats, edge_feats):
        """Performs message passing and updates node representations.

        Parameters
        ----------
        g : DGLGraph
            DGLGraph for a batch of graphs.
        node_feats : float32 tensor of shape (V, node_in_feats)
            Input node features.
        edge_feats : float32 tensor of shape (E, edge_in_feats)
            Input edge features.

        Returns
        -------
        node_feats : float32 tensor of shape (V, node_out_feats)
            Output node representations.
        """
        node_feats = self.project_node_feats(node_feats) # (V, node_out_feats)
        hidden_feats = node_feats.unsqueeze(0)           # (1, V, node_out_feats)

        for i in range(self.num_step_message_passing):
            node_feats = F.relu(self.gnn_layer(g, node_feats, edge_feats))
            node_feats, hidden_feats = self.gru(node_feats.unsqueeze(0), hidden_feats)
            node_feats = node_feats.squeeze(0)

        return node_feats
