"""
Graph Attention Networks in DGL using SPMV optimization.
Multiple heads are also batched together for faster training.
Compared with the original paper, this code does not implement
early stopping.
References
----------
Paper: https://arxiv.org/abs/1710.10903
Author's code: https://github.com/PetarV-/GAT
Pytorch implementation: https://github.com/Diego999/pyGAT
"""

import argparse
import numpy as np
import networkx as nx
import time
import tensorflow as tf
from dgl import DGLGraph
from dgl.data import register_data_args, load_data
from gat import GAT
from utils import EarlyStopping

def accuracy(logits, labels):
    indices = tf.math.argmax(logits, axis=1)
    acc = tf.reduce_mean(tf.cast(indices == labels, dtype=tf.float32))
    return acc.numpy().item()


def evaluate(model, features, labels, mask):
    logits = model(features, training=False)
    logits = logits[mask]
    labels = labels[mask]
    return accuracy(logits, labels)


def main(args):
    # load and preprocess dataset
    data = load_data(args)

    if args.gpu < 0:
        device = "/cpu:0"
    else:
        device = "/gpu:{}".format(args.gpu)

    with tf.device(device):

        features = tf.convert_to_tensor(data.features, dtype=tf.float32)
        labels = tf.convert_to_tensor(data.labels, dtype=tf.int64)
        train_mask = tf.convert_to_tensor(data.train_mask, dtype=tf.bool)
        val_mask = tf.convert_to_tensor(data.val_mask, dtype=tf.bool)
        test_mask = tf.convert_to_tensor(data.test_mask, dtype=tf.bool)
        num_feats = features.shape[1]
        n_classes = data.num_labels
        n_edges = data.graph.number_of_edges()
        print("""----Data statistics------'
        #Edges %d
        #Classes %d 
        #Train samples %d
        #Val samples %d
        #Test samples %d""" %
              (n_edges, n_classes,
               train_mask.numpy().sum(),
               val_mask.numpy().sum(),
               test_mask.numpy().sum()))

        g = data.graph
        # add self loop
        g.remove_edges_from(nx.selfloop_edges(g))
        g = DGLGraph(g)
        g.add_edges(g.nodes(), g.nodes())
        n_edges = g.number_of_edges()
        # create model
        heads = ([args.num_heads] * args.num_layers) + [args.num_out_heads]
        model = GAT(g,
                    args.num_layers,
                    num_feats,
                    args.num_hidden,
                    n_classes,
                    heads,
                    tf.nn.elu,
                    args.in_drop,
                    args.attn_drop,
                    args.negative_slope,
                    args.residual)
        print(model)
        if args.early_stop:
            stopper = EarlyStopping(patience=100)

        # loss_fcn = tf.keras.losses.SparseCategoricalCrossentropy(
        #     from_logits=False)
        loss_fcn = tf.nn.sparse_softmax_cross_entropy_with_logits

        # use optimizer
        optimizer = tf.keras.optimizers.Adam(
            learning_rate=args.lr, epsilon=1e-8)

        # initialize graph
        dur = []
        for epoch in range(args.epochs):
            if epoch >= 3:
                t0 = time.time()
            # forward
            with tf.GradientTape() as tape:
                tape.watch(model.trainable_weights)
                logits = model(features, training=True)
                loss_value = tf.reduce_mean(loss_fcn(
                    labels=labels[train_mask], logits=logits[train_mask]))
                # Manually Weight Decay
                # We found Tensorflow has a different implementation on weight decay 
                # of Adam(W) optimizer with PyTorch. And this results in worse results.
                # Manually adding weights to the loss to do weight decay solves this problem.
                for weight in model.trainable_weights:
                    loss_value = loss_value + \
                        args.weight_decay*tf.nn.l2_loss(weight)

                grads = tape.gradient(loss_value, model.trainable_weights)
                optimizer.apply_gradients(zip(grads, model.trainable_weights))

            if epoch >= 3:
                dur.append(time.time() - t0)

            train_acc = accuracy(logits[train_mask], labels[train_mask])

            if args.fastmode:
                val_acc = accuracy(logits[val_mask], labels[val_mask])
            else:
                val_acc = evaluate(model, features, labels, val_mask)
                if args.early_stop:
                    if stopper.step(val_acc, model):
                        break

            print("Epoch {:05d} | Time(s) {:.4f} | Loss {:.4f} | TrainAcc {:.4f} |"
                  " ValAcc {:.4f} | ETputs(KTEPS) {:.2f}".
                  format(epoch, np.mean(dur), loss_value.numpy().item(), train_acc,
                         val_acc, n_edges / np.mean(dur) / 1000))

        print()
        if args.early_stop:
            model.load_weights('es_checkpoint.pb')
        acc = evaluate(model, features, labels, test_mask)
        print("Test Accuracy {:.4f}".format(acc))


if __name__ == '__main__':

    parser = argparse.ArgumentParser(description='GAT')
    register_data_args(parser)
    parser.add_argument("--gpu", type=int, default=-1,
                        help="which GPU to use. Set -1 to use CPU.")
    parser.add_argument("--epochs", type=int, default=200,
                        help="number of training epochs")
    parser.add_argument("--num-heads", type=int, default=8,
                        help="number of hidden attention heads")
    parser.add_argument("--num-out-heads", type=int, default=1,
                        help="number of output attention heads")
    parser.add_argument("--num-layers", type=int, default=1,
                        help="number of hidden layers")
    parser.add_argument("--num-hidden", type=int, default=8,
                        help="number of hidden units")
    parser.add_argument("--residual", action="store_true", default=False,
                        help="use residual connection")
    parser.add_argument("--in-drop", type=float, default=.6,
                        help="input feature dropout")
    parser.add_argument("--attn-drop", type=float, default=.6,
                        help="attention dropout")
    parser.add_argument("--lr", type=float, default=0.005,
                        help="learning rate")
    parser.add_argument('--weight-decay', type=float, default=5e-4,
                        help="weight decay")
    parser.add_argument('--negative-slope', type=float, default=0.2,
                        help="the negative slope of leaky relu")
    parser.add_argument('--early-stop', action='store_true', default=False,
                        help="indicates whether to use early stop or not")
    parser.add_argument('--fastmode', action="store_true", default=False,
                        help="skip re-evaluate the validation set")
    args = parser.parse_args()
    print(args)
    
    main(args)
