import copy
import torch
from collections import OrderedDict


def get_ema_model(model):
    ema_model = copy.deepcopy(model)
    ema_model.eval()
    for param in ema_model.parameters():
        param.requires_grad = False
    return ema_model

@torch.no_grad()
def update_ema(ema_model, model, decay=0.9999):
    """
    Step the EMA model towards the current model.
    """
    ema_params = OrderedDict(ema_model.named_parameters())
    model_params = OrderedDict(model.named_parameters())

    for name, param in model_params.items():
        # TODO: Consider applying only to params that require_grad to avoid small numerical changes of pos_embed
        ema_params[name].mul_(decay).add_(param.data, alpha=1 - decay)