# Copyright (c) Meta Platforms, Inc. and affiliates.
# All rights reserved.

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

from copy import deepcopy
from typing import Tuple

import numpy as np
import torch
from torch.nn import functional as F
from torchvision.transforms.functional import resize  # type: ignore
from torchvision.transforms.functional import to_pil_image

from mmseg.registry import TRANSFORMS


@TRANSFORMS.register_module()
class ResizeLongestSide:
    """Resizes images to longest side 'target_length', as well as provides
    methods for resizing coordinates and boxes.

    Provides methods for transforming both numpy array and batched torch
    tensors.
    """

    def __init__(self, target_length: int) -> None:
        self.target_length = target_length

    def apply_image(self, image: np.ndarray) -> np.ndarray:
        """Expects a numpy array with shape HxWxC in uint8 format."""
        target_size = self.get_preprocess_shape(image.shape[0], image.shape[1],
                                                self.target_length)
        return np.array(resize(to_pil_image(image), target_size))

    def apply_coords(self, coords: np.ndarray,
                     original_size: Tuple[int, ...]) -> np.ndarray:
        """Expects a numpy array of length 2 in the final dimension.

        Requires the original image size in (H, W) format.
        """
        old_h, old_w = original_size
        new_h, new_w = self.get_preprocess_shape(original_size[0],
                                                 original_size[1],
                                                 self.target_length)
        coords = deepcopy(coords).astype(float)
        coords[..., 0] = coords[..., 0] * (new_w / old_w)
        coords[..., 1] = coords[..., 1] * (new_h / old_h)
        return coords

    def apply_boxes(self, boxes: np.ndarray,
                    original_size: Tuple[int, ...]) -> np.ndarray:
        """Expects a numpy array shape Bx4.

        Requires the original image size in (H, W) format.
        """
        boxes = self.apply_coords(boxes.reshape(-1, 2, 2), original_size)
        return boxes.reshape(-1, 4)

    def apply_image_torch(self, image: torch.Tensor) -> torch.Tensor:
        """Expects batched images with shape BxCxHxW and float format.

        This transformation may not exactly match apply_image. apply_image is
        the transformation expected by the model.
        """
        # Expects an image in BCHW format. May not exactly match apply_image.
        target_size = self.get_preprocess_shape(image.shape[0], image.shape[1],
                                                self.target_length)
        return F.interpolate(
            image,
            target_size,
            mode='bilinear',
            align_corners=False,
            antialias=True)

    def apply_coords_torch(self, coords: torch.Tensor,
                           original_size: Tuple[int, ...]) -> torch.Tensor:
        """Expects a torch tensor with length 2 in the last dimension.

        Requires the original image size in (H, W) format.
        """
        old_h, old_w = original_size
        new_h, new_w = self.get_preprocess_shape(original_size[0],
                                                 original_size[1],
                                                 self.target_length)
        coords = deepcopy(coords).to(torch.float)
        coords[..., 0] = coords[..., 0] * (new_w / old_w)
        coords[..., 1] = coords[..., 1] * (new_h / old_h)
        return coords

    def apply_boxes_torch(self, boxes: torch.Tensor,
                          original_size: Tuple[int, ...]) -> torch.Tensor:
        """Expects a torch tensor with shape Bx4.

        Requires the original image size in (H, W) format.
        """
        boxes = self.apply_coords_torch(boxes.reshape(-1, 2, 2), original_size)
        return boxes.reshape(-1, 4)

    @staticmethod
    def get_preprocess_shape(oldh: int, oldw: int,
                             long_side_length: int) -> Tuple[int, int]:
        """Compute the output size given input size and target long side
        length."""
        scale = long_side_length * 1.0 / max(oldh, oldw)
        newh, neww = oldh * scale, oldw * scale
        neww = int(neww + 0.5)
        newh = int(newh + 0.5)
        return (newh, neww)
