import os
import dgl
import numpy as np
import torch as th
import torch.nn as nn
import torch.nn.functional as F
import torch.optim as optim
import dgl.multiprocessing as mp
import dgl.function as fn
import dgl.nn.pytorch as dglnn
import time
import argparse
from torch.nn.parallel import DistributedDataParallel
import tqdm

from model import SAGE, compute_acc_unsupervised as compute_acc
from negative_sampler import NegativeSampler
from load_graph import load_reddit, load_ogb

class CrossEntropyLoss(nn.Module):
    def forward(self, block_outputs, pos_graph, neg_graph):
        with pos_graph.local_scope():
            pos_graph.ndata['h'] = block_outputs
            pos_graph.apply_edges(fn.u_dot_v('h', 'h', 'score'))
            pos_score = pos_graph.edata['score']
        with neg_graph.local_scope():
            neg_graph.ndata['h'] = block_outputs
            neg_graph.apply_edges(fn.u_dot_v('h', 'h', 'score'))
            neg_score = neg_graph.edata['score']

        score = th.cat([pos_score, neg_score])
        label = th.cat([th.ones_like(pos_score), th.zeros_like(neg_score)]).long()
        loss = F.binary_cross_entropy_with_logits(score, label.float())
        return loss

def evaluate(model, g, nfeat, labels, train_nids, val_nids, test_nids, device):
    """
    Evaluate the model on the validation set specified by ``val_mask``.
    g : The entire graph.
    inputs : The features of all the nodes.
    labels : The labels of all the nodes.
    val_mask : A 0-1 mask indicating which nodes do we actually compute the accuracy for.
    device : The GPU device to evaluate on.
    """
    model.eval()
    with th.no_grad():
        # single gpu
        if isinstance(model, SAGE):
            pred = model.inference(g, nfeat, device, args.batch_size, args.num_workers)
        # multi gpu
        else:
            pred = model.module.inference(g, nfeat, device, args.batch_size, args.num_workers)
    model.train()
    return compute_acc(pred, labels, train_nids, val_nids, test_nids)

#### Entry point
def run(proc_id, n_gpus, args, devices, data):
    # Unpack data
    device = th.device(devices[proc_id])
    if n_gpus > 0:
        th.cuda.set_device(device)
    if n_gpus > 1:
        dist_init_method = 'tcp://{master_ip}:{master_port}'.format(
            master_ip='127.0.0.1', master_port='12345')
        world_size = n_gpus
        th.distributed.init_process_group(backend="nccl",
                                          init_method=dist_init_method,
                                          world_size=world_size,
                                          rank=proc_id)
    train_nid, val_nid, test_nid, n_classes, g, nfeat, labels = data

    if args.data_device == 'gpu':
        nfeat = nfeat.to(device)
        labels = labels.to(device)
    elif args.data_device == 'uva':
        nfeat = dgl.contrib.UnifiedTensor(nfeat, device=device)
        labels = dgl.contrib.UnifiedTensor(labels, device=device)
    in_feats = nfeat.shape[1]

    # Create PyTorch DataLoader for constructing blocks
    n_edges = g.num_edges()
    train_seeds = th.arange(n_edges)

    if args.graph_device == 'gpu':
        train_seeds = train_seeds.to(device)
        g = g.to(device)
        args.num_workers = 0
    elif args.graph_device == 'uva':
        train_seeds = train_seeds.to(device)
        g.pin_memory_()
        args.num_workers = 0

    # Create sampler
    sampler = dgl.dataloading.MultiLayerNeighborSampler(
        [int(fanout) for fanout in args.fan_out.split(',')])
    dataloader = dgl.dataloading.EdgeDataLoader(
        g, train_seeds, sampler, exclude='reverse_id',
        # For each edge with ID e in Reddit dataset, the reverse edge is e ± |E|/2.
        reverse_eids=th.cat([
            th.arange(n_edges // 2, n_edges),
            th.arange(0, n_edges // 2)]).to(train_seeds),
        negative_sampler=NegativeSampler(g, args.num_negs, args.neg_share,
                                         device if args.graph_device == 'uva' else None),
        device=device,
        use_ddp=n_gpus > 1,
        batch_size=args.batch_size,
        shuffle=True,
        drop_last=False,
        num_workers=args.num_workers)

    # Define model and optimizer
    model = SAGE(in_feats, args.num_hidden, args.num_hidden, args.num_layers, F.relu, args.dropout)
    model = model.to(device)
    if n_gpus > 1:
        model = DistributedDataParallel(model, device_ids=[device], output_device=device)
    loss_fcn = CrossEntropyLoss()
    optimizer = optim.Adam(model.parameters(), lr=args.lr)

    # Training loop
    avg = 0
    iter_pos = []
    iter_neg = []
    iter_d = []
    iter_t = []
    best_eval_acc = 0
    best_test_acc = 0
    for epoch in range(args.num_epochs):
        tic = time.time()

        # Loop over the dataloader to sample the computation dependency graph as a list of
        # blocks.
        tic_step = time.time()
        for step, (input_nodes, pos_graph, neg_graph, blocks) in enumerate(dataloader):
            batch_inputs = nfeat[input_nodes].to(device)
            pos_graph = pos_graph.to(device)
            neg_graph = neg_graph.to(device)
            blocks = [block.int().to(device) for block in blocks]
            d_step = time.time()

            # Compute loss and prediction
            batch_pred = model(blocks, batch_inputs)
            loss = loss_fcn(batch_pred, pos_graph, neg_graph)
            optimizer.zero_grad()
            loss.backward()
            optimizer.step()

            t = time.time()
            pos_edges = pos_graph.num_edges()
            neg_edges = neg_graph.num_edges()
            iter_pos.append(pos_edges / (t - tic_step))
            iter_neg.append(neg_edges / (t - tic_step))
            iter_d.append(d_step - tic_step)
            iter_t.append(t - d_step)
            if step % args.log_every == 0 and proc_id == 0:
                gpu_mem_alloc = th.cuda.max_memory_allocated() / 1000000 if th.cuda.is_available() else 0
                print('[{}]Epoch {:05d} | Step {:05d} | Loss {:.4f} | Speed (samples/sec) {:.4f}|{:.4f} | Load {:.4f}| train {:.4f} | GPU {:.1f} MB'.format(
                    proc_id, epoch, step, loss.item(), np.mean(iter_pos[3:]), np.mean(iter_neg[3:]), np.mean(iter_d[3:]), np.mean(iter_t[3:]), gpu_mem_alloc))
            tic_step = time.time()

            if step % args.eval_every == 0 and proc_id == 0:
                eval_acc, test_acc = evaluate(model, g, nfeat, labels, train_nid, val_nid, test_nid, device)
                print('Eval Acc {:.4f} Test Acc {:.4f}'.format(eval_acc, test_acc))
                if eval_acc > best_eval_acc:
                    best_eval_acc = eval_acc
                    best_test_acc = test_acc
                print('Best Eval Acc {:.4f} Test Acc {:.4f}'.format(best_eval_acc, best_test_acc))
        toc = time.time()
        if proc_id == 0:
            print('Epoch Time(s): {:.4f}'.format(toc - tic))
        if epoch >= 5:
            avg += toc - tic
        if n_gpus > 1:
            th.distributed.barrier()

    if proc_id == 0:
        print('Avg epoch time: {}'.format(avg / (epoch - 4)))

def main(args):
    devices = list(map(int, args.gpu.split(',')))
    n_gpus = len(devices)

    # load dataset
    if args.dataset == 'reddit':
        g, n_classes = load_reddit(self_loop=False)
    elif args.dataset == 'ogbn-products':
        g, n_classes = load_ogb('ogbn-products')
    else:
        raise Exception('unknown dataset')

    train_nid = g.ndata.pop('train_mask').nonzero().squeeze()
    val_nid = g.ndata.pop('val_mask').nonzero().squeeze()
    test_nid = g.ndata.pop('test_mask').nonzero().squeeze()

    nfeat = g.ndata.pop('features')
    labels = g.ndata.pop('labels')

    # Create csr/coo/csc formats before launching training processes with multi-gpu.
    # This avoids creating certain formats in each sub-process, which saves memory and CPU.
    g.create_formats_()

    # this to avoid competition overhead on machines with many cores.
    # Change it to a proper number on your machine, especially for multi-GPU training.
    os.environ['OMP_NUM_THREADS'] = str(mp.cpu_count() // 2 // n_gpus)
    if n_gpus > 1:
        # Copy the graph to shared memory explicitly before pinning.
        # In other cases, we can just rely on fork's copy-on-write.
        # TODO: the original graph g is not freed.
        if args.graph_device == 'uva':
            g = g.shared_memory('g')
        if args.data_device == 'uva':
            nfeat = nfeat.share_memory_()
            labels = labels.share_memory_()
    # Pack data
    data = train_nid, val_nid, test_nid, n_classes, g, nfeat, labels

    if devices[0] == -1:
        assert args.graph_device == 'cpu', \
               f"Must have GPUs to enable {args.graph_device} sampling."
        assert args.data_device == 'cpu', \
               f"Must have GPUs to enable {args.data_device} feature storage."
        run(0, 0, args, ['cpu'], data)
    elif n_gpus == 1:
        run(0, n_gpus, args, devices, data)
    else:
        procs = []
        for proc_id in range(n_gpus):
            p = mp.Process(target=run, args=(proc_id, n_gpus, args, devices, data))
            p.start()
            procs.append(p)
        for p in procs:
            p.join()


if __name__ == '__main__':
    argparser = argparse.ArgumentParser("multi-gpu training")
    argparser.add_argument("--gpu", type=str, default='0',
                           help="GPU, can be a list of gpus for multi-gpu training,"
                                " e.g., 0,1,2,3; -1 for CPU")
    argparser.add_argument('--dataset', type=str, default='reddit',
                           choices=('reddit', 'ogbn-products'))
    argparser.add_argument('--num-epochs', type=int, default=20)
    argparser.add_argument('--num-hidden', type=int, default=16)
    argparser.add_argument('--num-layers', type=int, default=2)
    argparser.add_argument('--num-negs', type=int, default=1)
    argparser.add_argument('--neg-share', default=False, action='store_true',
                           help="sharing neg nodes for positive nodes")
    argparser.add_argument('--fan-out', type=str, default='10,25')
    argparser.add_argument('--batch-size', type=int, default=10000)
    argparser.add_argument('--log-every', type=int, default=20)
    argparser.add_argument('--eval-every', type=int, default=1000)
    argparser.add_argument('--lr', type=float, default=0.003)
    argparser.add_argument('--dropout', type=float, default=0.5)
    argparser.add_argument('--num-workers', type=int, default=0,
                           help="Number of sampling processes. Use 0 for no extra process.")
    argparser.add_argument('--graph-device', choices=('cpu', 'gpu', 'uva'), default='cpu',
                           help="Device to perform the sampling. "
                                "Must have 0 workers for 'gpu' and 'uva'")
    argparser.add_argument('--data-device', choices=('cpu', 'gpu', 'uva'), default='gpu',
                           help="By default the script puts all node features and labels "
                                "on GPU when using it to save time for data copy. This may "
                                "be undesired if they cannot fit in GPU memory at once. "
                                "Use 'cpu' to keep the features on host memory and "
                                "'uva' to enable UnifiedTensor (GPU zero-copy access on "
                                "pinned host memory).")
    args = argparser.parse_args()

    main(args)
