"""
Copyright (c) Facebook, Inc. and its affiliates.

This source code is licensed under the MIT license found in the
LICENSE file in the root directory of this source tree.
"""

import torch


class Normalizer:
    """Normalize a Tensor and restore it later."""

    def __init__(self, tensor=None, mean=None, std=None, device=None) -> None:
        """tensor is taken as a sample to calculate the mean and std"""
        if tensor is None and mean is None:
            return

        if device is None:
            device = "cpu"

        if tensor is not None:
            self.mean = torch.mean(tensor, dim=0).to(device)
            self.std = torch.std(tensor, dim=0).to(device)
            return

        if mean is not None and std is not None:
            self.mean = torch.tensor(mean).to(device)
            self.std = torch.tensor(std).to(device)

    def to(self, device) -> None:
        self.mean = self.mean.to(device)
        self.std = self.std.to(device)

    def norm(self, tensor):
        return (tensor - self.mean) / self.std

    def denorm(self, normed_tensor):
        return normed_tensor * self.std + self.mean

    def state_dict(self):
        return {"mean": self.mean, "std": self.std}

    def load_state_dict(self, state_dict) -> None:
        self.mean = state_dict["mean"].to(self.mean.device)
        self.std = state_dict["std"].to(self.mean.device)
