import torch
import torch.nn as nn
from torch.nn import init
import functools
from torch.optim import lr_scheduler
from util.util import to_device, load_network

###############################################################################
# Helper Functions
###############################################################################


def init_weights(net, init_type='normal', init_gain=0.02):
    """Initialize network weights.

    Parameters:
        net (network)   -- network to be initialized
        init_type (str) -- the name of an initialization method: normal | xavier | kaiming | orthogonal
        init_gain (float)    -- scaling factor for normal, xavier and orthogonal.

    We use 'normal' in the original pix2pix and CycleGAN paper. But xavier and kaiming might
    work better for some applications. Feel free to try yourself.
    """
    def init_func(m):  # define the initialization function
        classname = m.__class__.__name__
        if (isinstance(m, nn.Conv2d)
                or isinstance(m, nn.Linear)
                or isinstance(m, nn.Embedding)):
        # if hasattr(m, 'weight') and (classname.find('Conv') != -1 or classname.find('Linear') != -1):
            if init_type == 'N02':
                init.normal_(m.weight.data, 0.0, init_gain)
            elif init_type in ['glorot', 'xavier']:
                init.xavier_normal_(m.weight.data, gain=init_gain)
            elif init_type == 'kaiming':
                init.kaiming_normal_(m.weight.data, a=0, mode='fan_in')
            elif init_type == 'ortho':
                init.orthogonal_(m.weight.data, gain=init_gain)
            else:
                raise NotImplementedError('initialization method [%s] is not implemented' % init_type)
            # if hasattr(m, 'bias') and m.bias is not None:
            #     init.constant_(m.bias.data, 0.0)
        # elif classname.find('BatchNorm2d') != -1:  # BatchNorm Layer's weight is not a matrix; only normal distribution applies.
        #     init.normal_(m.weight.data, 1.0, init_gain)
        #     init.constant_(m.bias.data, 0.0)
    if init_type in ['N02', 'glorot', 'xavier', 'kaiming', 'ortho']:
        print('initialize network with %s' % init_type)
        net.apply(init_func)  # apply the initialization function <init_func>
    else:
        print('loading the model from %s' % init_type)
        net = load_network(net, init_type, 'latest')
    return net

def init_net(net, init_type='normal', init_gain=0.02, gpu_ids=[]):
    """Initialize a network: 1. register CPU/GPU device (with multi-GPU support); 2. initialize the network weights
    Parameters:
        net (network)      -- the network to be initialized
        init_type (str)    -- the name of an initialization method: normal | xavier | kaiming | orthogonal
        gain (float)       -- scaling factor for normal, xavier and orthogonal.
        gpu_ids (int list) -- which GPUs the network runs on: e.g., 0,1,2

    Return an initialized network.
    """
    if len(gpu_ids) > 0:
        assert(torch.cuda.is_available())
        net.to(gpu_ids[0])
        net = torch.nn.DataParallel(net, gpu_ids)  # multi-GPUs
    init_weights(net, init_type, init_gain=init_gain)
    return net


def get_scheduler(optimizer, opt):
    """Return a learning rate scheduler

    Parameters:
        optimizer          -- the optimizer of the network
        opt (option class) -- stores all the experiment flags; needs to be a subclass of BaseOptions．　
                              opt.lr_policy is the name of learning rate policy: linear | step | plateau | cosine

    For 'linear', we keep the same learning rate for the first <opt.niter> epochs
    and linearly decay the rate to zero over the next <opt.niter_decay> epochs.
    For other schedulers (step, plateau, and cosine), we use the default PyTorch schedulers.
    See https://pytorch.org/docs/stable/optim.html for more details.
    """
    if opt.lr_policy == 'linear':
        def lambda_rule(epoch):
            lr_l = 1.0 - max(0, epoch + opt.epoch_count - opt.niter) / float(opt.niter_decay + 1)
            return lr_l
        scheduler = lr_scheduler.LambdaLR(optimizer, lr_lambda=lambda_rule)
    elif opt.lr_policy == 'step':
        scheduler = lr_scheduler.StepLR(optimizer, step_size=opt.lr_decay_iters, gamma=0.1)
    elif opt.lr_policy == 'plateau':
        scheduler = lr_scheduler.ReduceLROnPlateau(optimizer, mode='min', factor=0.2, threshold=0.01, patience=5)
    elif opt.lr_policy == 'cosine':
        scheduler = lr_scheduler.CosineAnnealingLR(optimizer, T_max=opt.niter, eta_min=0)
    else:
        return NotImplementedError('learning rate policy [%s] is not implemented', opt.lr_policy)
    return scheduler

