# ------------------------------------------------------------------------
# Modified from DETR (https://github.com/facebookresearch/detr)
# Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
# ------------------------------------------------------------------------

"""
positional encodings for the transformer.
"""
import math
import torch
import torch.nn as nn

from util.misc import NestedTensor


class PositionEmbeddingSine(nn.Module):
    """
    This is a more standard version of the position embedding, very similar to the one
    used by the Attention is all you need paper, generalized to work on images.
    """
    def __init__(self, num_pos_feats=64, temperature=10000, normalize=False, scale=None):
        super().__init__()
        self.num_pos_feats = num_pos_feats
        self.temperature = temperature
        self.normalize = normalize
        if scale is not None and normalize is False:
            raise ValueError("normalize should be True if scale is passed")
        if scale is None:
            scale = 2 * math.pi
        self.scale = scale

    def forward(self, tensor_list: NestedTensor):
        x = tensor_list.tensors
        mask = tensor_list.mask
        assert mask is not None
        not_mask = ~mask
        y_embed = not_mask.cumsum(1, dtype=torch.float32) - 0.5
        x_embed = not_mask.cumsum(2, dtype=torch.float32) - 0.5
        if self.normalize:
            eps = 1e-6
            y_embed = y_embed / (y_embed[:, -1:, :] + eps + 0.5) * self.scale
            x_embed = x_embed / (x_embed[:, :, -1:] + eps + 0.5) * self.scale

        dim_t = torch.arange(self.num_pos_feats, dtype=torch.float32, device=x.device)
        dim_t = self.temperature ** (2 * (dim_t // 2) / self.num_pos_feats)

        pos_x = x_embed[:, :, :, None] / dim_t
        pos_y = y_embed[:, :, :, None] / dim_t
        pos_x = torch.stack((pos_x[:, :, :, 0::2].sin(), pos_x[:, :, :, 1::2].cos()), dim=4).flatten(3)
        pos_y = torch.stack((pos_y[:, :, :, 0::2].sin(), pos_y[:, :, :, 1::2].cos()), dim=4).flatten(3)
        pos = torch.cat((pos_y, pos_x), dim=3).permute(0, 3, 1, 2)
        return pos


@torch.no_grad()
def gen_sineembed_for_position(pos_tensor):
    scale = 2 * math.pi
    dim_t = torch.arange(128, dtype=torch.float32, device=pos_tensor.device)
    dim_t = 10000 ** (2 * (dim_t // 2) / 128)
    x_embed = pos_tensor[:, :, 0] * scale
    y_embed = pos_tensor[:, :, 1] * scale
    pos_x = x_embed[:, :, None] / dim_t
    pos_y = y_embed[:, :, None] / dim_t
    pos_x = torch.stack((pos_x[:, :, 0::2].sin(), pos_x[:, :, 1::2].cos()), dim=3).flatten(2)
    pos_y = torch.stack((pos_y[:, :, 0::2].sin(), pos_y[:, :, 1::2].cos()), dim=3).flatten(2)
    pos = torch.cat((pos_y, pos_x), dim=2)
    return pos


def build_position_encoding(args):
    if args.position_embedding in ('sine'):
        position_embedding = PositionEmbeddingSine(args.hidden_dim // 2, normalize=True)
    else:
        raise ValueError(f"Unknown args.position_embedding: {args.position_embedding}.")
    return position_embedding
