from pathlib import Path
import argparse
import json
import os
import random
import sys
import time
import urllib

from torch import nn, optim
from torchvision import models, datasets, transforms
import torch
import torchvision

parser = argparse.ArgumentParser(description='Evaluate resnet50 features on ImageNet')
parser.add_argument('--data', type=Path, metavar='DIR',
                    help='path to dataset')
parser.add_argument('--pretrained', type=Path, metavar='FILE',
                    help='path to pretrained model')
parser.add_argument('--weights', default='freeze', type=str,
                    choices=('finetune', 'freeze'),
                    help='finetune or freeze resnet weights')
parser.add_argument('--train-percent', default=100, type=int,
                    choices=(100, 10, 1),
                    help='size of traing set in percent')
parser.add_argument('--workers', default=8, type=int, metavar='N',
                    help='number of data loader workers')
parser.add_argument('--epochs', default=100, type=int, metavar='N',
                    help='number of total epochs to run')
parser.add_argument('--batch-size', default=256, type=int, metavar='N',
                    help='mini-batch size')
parser.add_argument('--lr-backbone', default=0.0, type=float, metavar='LR',
                    help='backbone base learning rate')
parser.add_argument('--lr-classifier', default=1.0, type=float, metavar='LR',
                    help='classifier base learning rate')
parser.add_argument('--weight-decay', default=1e-6, type=float, metavar='W',
                    help='weight decay')
parser.add_argument('--print-freq', default=100, type=int, metavar='N',
                    help='print frequency')


def main():
    args = parser.parse_args()
    args.ngpus_per_node = torch.cuda.device_count()

    # single-node distributed training
    args.rank = 0
    args.dist_url = f'tcp://localhost:{random.randrange(49152, 65535)}'
    args.world_size = args.ngpus_per_node
    torch.multiprocessing.spawn(main_worker, (args,), args.ngpus_per_node)


def main_worker(gpu, args):
    args.rank += gpu
    torch.distributed.init_process_group(
        backend='nccl', init_method=args.dist_url,
        world_size=args.world_size, rank=args.rank)

    print(' '.join(sys.argv))

    torch.cuda.set_device(gpu)
    torch.backends.cudnn.benchmark = True

    model = models.resnet50().cuda(gpu)

    state_dict = torch.load(args.pretrained, map_location='cpu')
    missing_keys, unexpected_keys = model.load_state_dict(state_dict["backbone"], strict=False)
    assert missing_keys == ['fc.weight', 'fc.bias'] and unexpected_keys == []
    model.fc.weight.data.normal_(mean=0.0, std=0.01)
    model.fc.bias.data.zero_()
    if args.weights == 'freeze':
        model.requires_grad_(False)
        model.fc.requires_grad_(True)
    classifier_parameters, model_parameters = [], []
    for name, param in model.named_parameters():
        if name in {'fc.weight', 'fc.bias'}:
            classifier_parameters.append(param)
        else:
            model_parameters.append(param)
    model = torch.nn.parallel.DistributedDataParallel(model, device_ids=[gpu])

    criterion = nn.CrossEntropyLoss().cuda(gpu)

    param_groups = [dict(params=classifier_parameters, lr=args.lr_classifier)]
    if args.weights == 'finetune':
        param_groups.append(dict(params=model_parameters, lr=args.lr_backbone))
    optimizer = optim.SGD(param_groups, 0, momentum=0.9, weight_decay=args.weight_decay)
    scheduler = optim.lr_scheduler.CosineAnnealingLR(optimizer, args.epochs)

    start_epoch = 0
    best_acc = argparse.Namespace(top1=0, top5=0)

    # Data loading code
    traindir = args.data / 'train'
    valdir = args.data / 'val'
    normalize = transforms.Normalize(mean=[0.485, 0.456, 0.406],
                                     std=[0.229, 0.224, 0.225])

    train_dataset = datasets.ImageFolder(traindir, transforms.Compose([
            transforms.RandomResizedCrop(224),
            transforms.RandomHorizontalFlip(),
            transforms.ToTensor(),
            normalize,
        ]))
    val_dataset = datasets.ImageFolder(valdir, transforms.Compose([
            transforms.Resize(256),
            transforms.CenterCrop(224),
            transforms.ToTensor(),
            normalize,
        ]))

    if args.train_percent in {1, 10}:
        train_dataset.samples = []
        for fname in args.train_files:
            fname = fname.decode().strip()
            cls = fname.split('_')[0]
            train_dataset.samples.append(
                (traindir / cls / fname, train_dataset.class_to_idx[cls]))

    train_sampler = torch.utils.data.distributed.DistributedSampler(train_dataset)
    kwargs = dict(batch_size=args.batch_size // args.world_size, num_workers=args.workers, pin_memory=True)
    train_loader = torch.utils.data.DataLoader(train_dataset, sampler=train_sampler, **kwargs)
    val_loader = torch.utils.data.DataLoader(val_dataset, **kwargs)

    start_time = time.time()
    for epoch in range(start_epoch, args.epochs):
        # train
        if args.weights == 'finetune':
            model.train()
        elif args.weights == 'freeze':
            model.eval()
        else:
            assert False
        train_sampler.set_epoch(epoch)
        for step, (images, target) in enumerate(train_loader, start=epoch * len(train_loader)):
            output = model(images.cuda(gpu, non_blocking=True))
            loss = criterion(output, target.cuda(gpu, non_blocking=True))
            optimizer.zero_grad()
            loss.backward()
            optimizer.step()
            if step % args.print_freq == 0:
                torch.distributed.reduce(loss.div_(args.world_size), 0)
                if args.rank == 0:
                    pg = optimizer.param_groups
                    lr_classifier = pg[0]['lr']
                    lr_backbone = pg[1]['lr'] if len(pg) == 2 else 0
                    stats = dict(epoch=epoch, step=step, lr_backbone=lr_backbone,
                                 lr_classifier=lr_classifier, loss=loss.item(),
                                 time=int(time.time() - start_time))
                    print(json.dumps(stats))

        # evaluate
        model.eval()
        if args.rank == 0:
            top1 = AverageMeter('Acc@1')
            top5 = AverageMeter('Acc@5')
            with torch.no_grad():
                for images, target in val_loader:
                    output = model(images.cuda(gpu, non_blocking=True))
                    acc1, acc5 = accuracy(output, target.cuda(gpu, non_blocking=True), topk=(1, 5))
                    top1.update(acc1[0].item(), images.size(0))
                    top5.update(acc5[0].item(), images.size(0))
            best_acc.top1 = max(best_acc.top1, top1.avg)
            best_acc.top5 = max(best_acc.top5, top5.avg)
            stats = dict(epoch=epoch, acc1=top1.avg, acc5=top5.avg, best_acc1=best_acc.top1, best_acc5=best_acc.top5)
            print(json.dumps(stats))


class AverageMeter(object):
    """Computes and stores the average and current value"""
    def __init__(self, name, fmt=':f'):
        self.name = name
        self.fmt = fmt
        self.reset()

    def reset(self):
        self.val = 0
        self.avg = 0
        self.sum = 0
        self.count = 0

    def update(self, val, n=1):
        self.val = val
        self.sum += val * n
        self.count += n
        self.avg = self.sum / self.count

    def __str__(self):
        fmtstr = '{name} {val' + self.fmt + '} ({avg' + self.fmt + '})'
        return fmtstr.format(**self.__dict__)


def accuracy(output, target, topk=(1,)):
    """Computes the accuracy over the k top predictions for the specified values of k"""
    with torch.no_grad():
        maxk = max(topk)
        batch_size = target.size(0)

        _, pred = output.topk(maxk, 1, True, True)
        pred = pred.t()
        correct = pred.eq(target.view(1, -1).expand_as(pred))

        res = []
        for k in topk:
            correct_k = correct[:k].reshape(-1).float().sum(0, keepdim=True)
            res.append(correct_k.mul_(100.0 / batch_size))
        return res


if __name__ == '__main__':
    main()
