#!/usr/bin/env python3
# Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved


# misc.py
# modules that are used in different places but are not a specific type (e.g., backbone)

import torch
import torch.nn as nn


class SplitAndConcat(nn.Module):
    """Split the data from split_dim and concatenate in concat_dim.

    @param split_dim from which axis the data will be chunk
    @param concat_dim to which axis the data will be concatenated
    @param chunk size of the data to be chunk/concatenated
    """

    def __init__(self, split_dim: int = 1, concat_dim: int = 0, chunk: int = 2):
        super(SplitAndConcat, self).__init__()
        self.split_dim = split_dim
        self.concat_dim = concat_dim
        self.chunk = chunk

    def forward(self, x):
        x = torch.chunk(x, self.chunk, dim=self.split_dim)
        x = torch.cat(x, dim=self.concat_dim)
        return x

    def extra_repr(self):
        return (
            f"split_dim={self.split_dim}, concat_dim={self.concat_dim}, "
            f"chunk={self.chunk}"
        )


class AddCoordChannels(nn.Module):
    """Appends coordinate location values to the channel dimension.

    @param with_r include radial distance from centroid as additional channel (default: False)
    """
    def __init__(self, with_r: bool = False) -> None:
        super().__init__()
        self.with_r = with_r

    def forward(self, input_tensor):
        batch_size_shape, channel_in_shape, dim_y, dim_x = input_tensor.shape
        device = input_tensor.device

        xx_ones = torch.ones([1, 1, 1, dim_x], dtype=torch.int32)
        yy_ones = torch.ones([1, 1, 1, dim_y], dtype=torch.int32)

        xx_range = torch.arange(dim_y, dtype=torch.int32)
        yy_range = torch.arange(dim_x, dtype=torch.int32)
        xx_range = xx_range[None, None, :, None]
        yy_range = yy_range[None, None, :, None]

        xx_channel = torch.matmul(xx_range, xx_ones)
        yy_channel = torch.matmul(yy_range, yy_ones)

        # transpose y
        yy_channel = yy_channel.permute(0, 1, 3, 2)

        xx_channel = xx_channel.float() / (dim_y - 1)
        yy_channel = yy_channel.float() / (dim_x - 1)

        xx_channel = xx_channel * 2 - 1
        yy_channel = yy_channel * 2 - 1

        xx_channel = xx_channel.repeat(batch_size_shape, 1, 1, 1)
        yy_channel = yy_channel.repeat(batch_size_shape, 1, 1, 1)

        out = torch.cat([input_tensor, xx_channel.to(device), yy_channel.to(device)], dim=1)

        if self.with_r:
            rr = torch.sqrt(torch.pow(xx_channel - 0.5, 2) + torch.pow(yy_channel - 0.5, 2))
            out = torch.cat([out, rr], dim=1)

        return out
