import numpy as np
import torch
from torchvision.transforms import Compose, Resize, ToTensor, CenterCrop, transforms

class ExpandChannels:
    """
    Transforms an image with one channel to an image with three channels by copying
    pixel intensities of the image along the 1st dimension.
    """

    def __call__(self, data: torch.Tensor) -> torch.Tensor:
        """
        :param data: Tensor of shape [1, H, W].
        :return: Tensor with channel copied three times, shape [3, H, W].
        """
        if data.shape[0] != 1:
            raise ValueError(f"Expected input of shape [1, H, W], found {data.shape}")
        return torch.repeat_interleave(data, 3, dim=0)

def create_chest_xray_transform_for_inference(resize: int, center_crop_size: int) -> Compose:
    """
    Defines the image transformation pipeline for Chest-Xray datasets.

    :param resize: The size to resize the image to. Linear resampling is used.
                   Resizing is applied on the axis with smaller shape.
    :param center_crop_size: The size to center crop the image to. Square crop is applied.
    """

    transforms = [Resize(resize), CenterCrop(center_crop_size), ToTensor(), ExpandChannels()]
    return Compose(transforms)

def remap_to_uint8(array: np.ndarray, percentiles=None) -> np.ndarray:
        """Remap values in input so the output range is :math:`[0, 255]`.

        Percentiles can be used to specify the range of values to remap.
        This is useful to discard outliers in the input data.

        :param array: Input array.
        :param percentiles: Percentiles of the input values that will be mapped to ``0`` and ``255``.
            Passing ``None`` is equivalent to using percentiles ``(0, 100)`` (but faster).
        :returns: Array with ``0`` and ``255`` as minimum and maximum values.
        """
        array = array.astype(float)
        if percentiles is not None:
            len_percentiles = len(percentiles)
            if len_percentiles != 2:
                message = (
                    'The value for percentiles should be a sequence of length 2,'
                    f' but has length {len_percentiles}'
                )
                raise ValueError(message)
            a, b = percentiles
            if a >= b:
                raise ValueError(f'Percentiles must be in ascending order, but a sequence "{percentiles}" was passed')
            if a < 0 or b > 100:
                raise ValueError(f'Percentiles must be in the range [0, 100], but a sequence "{percentiles}" was passed')
            cutoff: np.ndarray = np.percentile(array, percentiles)
            array = np.clip(array, *cutoff)
        array -= array.min()
        array /= array.max()
        array *= 255
        return array.astype(np.uint8)