import os
import time

import torch
import torch.backends.cudnn as cudnn


def init_seeds(seed=0):
    torch.manual_seed(seed)

    # Remove randomness (may be slower on Tesla GPUs) # https://pytorch.org/docs/stable/notes/randomness.html
    if seed == 0:
        cudnn.deterministic = True
        cudnn.benchmark = False


def select_device(device='', apex=False, batch_size=None):
    # device = 'cpu' or '0' or '0,1,2,3'
    cpu_request = device.lower() == 'cpu'
    if device and not cpu_request:  # if device requested other than 'cpu'
        os.environ['CUDA_VISIBLE_DEVICES'] = device  # set environment variable
        assert torch.cuda.is_available(
        ), 'CUDA unavailable, invalid device %s requested' % device  # check availablity

    cuda = False if cpu_request else torch.cuda.is_available()
    if cuda:
        c = 1024 ** 2  # bytes to MB
        ng = torch.cuda.device_count()
        if ng > 1 and batch_size:  # check that batch_size is compatible with device_count
            assert batch_size % ng == 0, 'batch-size %g not multiple of GPU count %g' % (
                batch_size, ng)
        x = [torch.cuda.get_device_properties(i) for i in range(ng)]
        # apex for mixed precision https://github.com/NVIDIA/apex
        s = 'Using CUDA ' + ('Apex ' if apex else '')
        for i in range(0, ng):
            if i == 1:
                s = ' ' * len(s)
            print("%sdevice%g _CudaDeviceProperties(name='%s', total_memory=%dMB)" %
                  (s, i, x[i].name, x[i].total_memory / c))
    else:
        print('Using CPU')

    print('')  # skip a line
    return torch.device('cuda:0' if cuda else 'cpu')


def time_synchronized():
    torch.cuda.synchronize() if torch.cuda.is_available() else None
    return time.time()


def fuse_conv_and_bn(conv, bn):
    # https://tehnokv.com/posts/fusing-batchnorm-and-conv/
    with torch.no_grad():
        # init
        fusedconv = torch.nn.Conv2d(conv.in_channels,
                                    conv.out_channels,
                                    kernel_size=conv.kernel_size,
                                    stride=conv.stride,
                                    padding=conv.padding,
                                    bias=True)

        # prepare filters
        w_conv = conv.weight.clone().view(conv.out_channels, -1)
        w_bn = torch.diag(bn.weight.div(torch.sqrt(bn.eps + bn.running_var)))
        fusedconv.weight.copy_(
            torch.mm(w_bn, w_conv).view(fusedconv.weight.size()))

        # prepare spatial bias
        if conv.bias is not None:
            b_conv = conv.bias
        else:
            b_conv = torch.zeros(conv.weight.size(0))
        b_bn = bn.bias - \
            bn.weight.mul(bn.running_mean).div(
                torch.sqrt(bn.running_var + bn.eps))
        fusedconv.bias.copy_(
            torch.mm(w_bn, b_conv.reshape(-1, 1)).reshape(-1) + b_bn)

        return fusedconv


def model_info(model, report='summary'):
    # Plots a line-by-line description of a PyTorch model
    n_p = sum(x.numel() for x in model.parameters())  # number parameters
    n_g = sum(x.numel() for x in model.parameters()
              if x.requires_grad)  # number gradients
    if report is 'full':
        print('%5s %40s %9s %12s %20s %10s %10s' %
              ('layer', 'name', 'gradient', 'parameters', 'shape', 'mu', 'sigma'))
        for i, (name, p) in enumerate(model.named_parameters()):
            name = name.replace('module_list.', '')
            print('%5g %40s %9s %12g %20s %10.3g %10.3g' %
                  (i, name, p.requires_grad, p.numel(), list(p.shape), p.mean(), p.std()))
    print('Model Summary: %g layers, %g parameters, %g gradients' %
          (len(list(model.parameters())), n_p, n_g))


def load_classifier(name='resnet101', n=2):
    # Loads a pretrained model reshaped to n-class output
    # https://github.com/Cadene/pretrained-models.pytorch#torchvision
    import pretrainedmodels
    model = pretrainedmodels.__dict__[name](
        num_classes=1000, pretrained='imagenet')

    # Display model properties
    for x in ['model.input_size', 'model.input_space', 'model.input_range', 'model.mean', 'model.std']:
        print(x + ' =', eval(x))

    # Reshape output to n classes
    filters = model.last_linear.weight.shape[1]
    model.last_linear.bias = torch.nn.Parameter(torch.zeros(n))
    model.last_linear.weight = torch.nn.Parameter(torch.zeros(n, filters))
    model.last_linear.out_features = n
    return model
