import torch
from torch import Tensor


def _box_cxcywh_to_xyxy(boxes: Tensor) -> Tensor:
    """
    Converts bounding boxes from (cx, cy, w, h) format to (x1, y1, x2, y2) format.
    (cx, cy) refers to center of bounding box
    (w, h) are width and height of bounding box
    Arguments:
        boxes (Tensor[N, 4]): boxes in (cx, cy, w, h) format which will be converted.

    Returns:
        boxes (Tensor(N, 4)): boxes in (x1, y1, x2, y2) format.
    """
    # We need to change all 4 of them so some temporary variable is needed.
    cx, cy, w, h = boxes.unbind(-1)
    x1 = cx - 0.5 * w
    y1 = cy - 0.5 * h
    x2 = cx + 0.5 * w
    y2 = cy + 0.5 * h

    boxes = torch.stack((x1, y1, x2, y2), dim=-1)

    return boxes


def _box_xyxy_to_cxcywh(boxes: Tensor) -> Tensor:
    """
    Converts bounding boxes from (x1, y1, x2, y2) format to (cx, cy, w, h) format.
    (x1, y1) refer to top left of bounding box
    (x2, y2) refer to bottom right of bounding box
    Arguments:
        boxes (Tensor[N, 4]): boxes in (x1, y1, x2, y2) format which will be converted.

    Returns:
        boxes (Tensor(N, 4)): boxes in (cx, cy, w, h) format.
    """
    x1, y1, x2, y2 = boxes.unbind(-1)
    cx = (x1 + x2) / 2
    cy = (y1 + y2) / 2
    w = x2 - x1
    h = y2 - y1

    boxes = torch.stack((cx, cy, w, h), dim=-1)

    return boxes


def _box_xywh_to_xyxy(boxes: Tensor) -> Tensor:
    """
    Converts bounding boxes from (x, y, w, h) format to (x1, y1, x2, y2) format.
    (x, y) refers to top left of bouding box.
    (w, h) refers to width and height of box.
    Arguments:
        boxes (Tensor[N, 4]): boxes in (x, y, w, h) which will be converted.

    Returns:
        boxes (Tensor[N, 4]): boxes in (x1, y1, x2, y2) format.
    """
    x, y, w, h = boxes.unbind(-1)
    boxes = torch.stack([x, y, x + w, y + h], dim=-1)
    return boxes


def _box_xyxy_to_xywh(boxes: Tensor) -> Tensor:
    """
    Converts bounding boxes from (x1, y1, x2, y2) format to (x, y, w, h) format.
    (x1, y1) refer to top left of bounding box
    (x2, y2) refer to bottom right of bounding box
    Arguments:
        boxes (Tensor[N, 4]): boxes in (x1, y1, x2, y2) which will be converted.

    Returns:
        boxes (Tensor[N, 4]): boxes in (x, y, w, h) format.
    """
    x1, y1, x2, y2 = boxes.unbind(-1)
    w = x2 - x1  # x2 - x1
    h = y2 - y1  # y2 - y1
    boxes = torch.stack((x1, y1, w, h), dim=-1)
    return boxes
