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# Copyright (c) Soumith Chintala 2016, 
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# code taken from 
# https://github.com/pytorch/vision/blob/main/torchvision/datasets/folder.py
# added support for classes_fraction and data_per_class_fraction

from torchvision.datasets import VisionDataset
from PIL import Image

import os
import os.path
from typing import Any, Callable, cast, Dict, List, Optional, Tuple
import numpy as np

def has_file_allowed_extension(filename: str, extensions: Tuple[str, ...]) -> bool:
    """Checks if a file is an allowed extension.
    Args:
        filename (string): path to a file
        extensions (tuple of strings): extensions to consider (lowercase)
    Returns:
        bool: True if the filename ends with one of given extensions
    """
    return filename.lower().endswith(extensions)


def is_image_file(filename: str) -> bool:
    """Checks if a file is an allowed image extension.
    Args:
        filename (string): path to a file
    Returns:
        bool: True if the filename ends with a known image extension
    """
    return has_file_allowed_extension(filename, IMG_EXTENSIONS)


def make_dataset(
    directory: str,
    class_to_idx: Dict[str, int],
    data_per_class_fraction: float,
    extensions: Optional[Tuple[str, ...]] = None,
    is_valid_file: Optional[Callable[[str], bool]] = None,
) -> List[Tuple[str, int]]:
    """Generates a list of samples of a form (path_to_sample, class).
    Args:
        directory (str): root dataset directory
        class_to_idx (Dict[str, int]): dictionary mapping class name to class index
        extensions (optional): A list of allowed extensions.
            Either extensions or is_valid_file should be passed. Defaults to None.
        is_valid_file (optional): A function that takes path of a file
            and checks if the file is a valid file
            (used to check of corrupt files) both extensions and
            is_valid_file should not be passed. Defaults to None.
    Raises:
        ValueError: In case ``extensions`` and ``is_valid_file`` are None or both are not None.
    Returns:
        List[Tuple[str, int]]: samples of a form (path_to_sample, class)
    """
    instances = []
    directory = os.path.expanduser(directory)
    both_none = extensions is None and is_valid_file is None
    both_something = extensions is not None and is_valid_file is not None
    if both_none or both_something:
        raise ValueError("Both extensions and is_valid_file cannot be None or not None at the same time")
    if extensions is not None:
        def is_valid_file(x: str) -> bool:
            return has_file_allowed_extension(x, cast(Tuple[str, ...], extensions))
    is_valid_file = cast(Callable[[str], bool], is_valid_file)
    for target_class in sorted(class_to_idx.keys()):
        class_index = class_to_idx[target_class]
        target_dir = os.path.join(directory, target_class)
        if not os.path.isdir(target_dir):
            continue
        local_instances = []
        for root, _, fnames in sorted(os.walk(target_dir, followlinks=True)):
            for fname in sorted(fnames):
                path = os.path.join(root, fname)
                if is_valid_file(path):
                    item = path, class_index
                    local_instances.append(item)

        instances.extend(local_instances[0:int(len(local_instances) * data_per_class_fraction)])

    return instances


class DatasetFolder(VisionDataset):
    """A generic data loader where the samples are arranged in this way: ::
        root/class_x/xxx.ext
        root/class_x/xxy.ext
        root/class_x/[...]/xxz.ext
        root/class_y/123.ext
        root/class_y/nsdf3.ext
        root/class_y/[...]/asd932_.ext
    Args:
        root (string): Root directory path.
        loader (callable): A function to load a sample given its path.
        extensions (tuple[string]): A list of allowed extensions.
            both extensions and is_valid_file should not be passed.
        transform (callable, optional): A function/transform that takes in
            a sample and returns a transformed version.
            E.g, ``transforms.RandomCrop`` for images.
        target_transform (callable, optional): A function/transform that takes
            in the target and transforms it.
        is_valid_file (callable, optional): A function that takes path of a file
            and check if the file is a valid file (used to check of corrupt files)
            both extensions and is_valid_file should not be passed.
     Attributes:
        classes (list): List of the class names sorted alphabetically.
        class_to_idx (dict): Dict with items (class_name, class_index).
        samples (list): List of (sample path, class_index) tuples
        targets (list): The class_index value for each image in the dataset
    """

    def __init__(
            self,
            root: str,
            loader: Callable[[str], Any],
            extensions: Optional[Tuple[str, ...]] = None,
            transform: Optional[Callable] = None,
            target_transform: Optional[Callable] = None,
            classes_fraction=1.0,
            data_per_class_fraction=1.0,
            is_valid_file: Optional[Callable[[str], bool]] = None,
    ) -> None:
        super(DatasetFolder, self).__init__(root, transform=transform,
                                            target_transform=target_transform)
        self.classes_fraction = classes_fraction
        self.data_per_class_fraction = data_per_class_fraction
        classes, class_to_idx = self._find_classes(self.root)
        samples = self.make_dataset(self.root,
                                    class_to_idx,
                                    self.data_per_class_fraction,
                                    extensions,
                                    is_valid_file)
        if len(samples) == 0:
            msg = "Found 0 files in subfolders of: {}\n".format(self.root)
            if extensions is not None:
                msg += "Supported extensions are: {}".format(",".join(extensions))
            raise RuntimeError(msg)

        self.loader = loader
        self.extensions = extensions
        self.total = len(samples)
        self.classes = classes
        self.class_to_idx = class_to_idx
        self.samples = samples
        self.targets = [s[1] for s in samples]

    @staticmethod
    def make_dataset(
        directory: str,
        class_to_idx: Dict[str, int],
        data_per_class_fraction: float,
        extensions: Optional[Tuple[str, ...]] = None,
        is_valid_file: Optional[Callable[[str], bool]] = None,
    ) -> List[Tuple[str, int]]:
        return make_dataset(directory,
                            class_to_idx,
                            data_per_class_fraction,
                            extensions=extensions,
                            is_valid_file=is_valid_file)

    def _find_classes(self, dir: str) -> Tuple[List[str], Dict[str, int]]:
        """
        Finds the class folders in a dataset.
        Args:
            dir (string): Root directory path.
        Returns:
            tuple: (classes, class_to_idx) where classes are relative to (dir), and class_to_idx is a dictionary.
        Ensures:
            No class is a subdirectory of another.
        """
        all_classes = [d.name for d in os.scandir(dir) if d.is_dir()]
        classes = all_classes[0:int(len(all_classes) * self.classes_fraction)]
        classes.sort()
        class_to_idx = {cls_name: i for i, cls_name in enumerate(classes)}
        return classes, class_to_idx

    def __getitem__(self, index: int) -> Tuple[Any, Any]:
        """
        Args:
            index (int): Index
        Returns:
            tuple: (sample, target) where target is class_index of the target class.
        """
        curr_index = index
        for x in range(self.total):
            try:
                path, target = self.samples[curr_index]
                sample = self.loader(path)
                break
            except Exception as e:
                curr_index = np.random.randint(0, self.total)

        if self.transform is not None:
            sample = self.transform(sample)
        if self.target_transform is not None:
            target = self.target_transform(target)

        return sample, target

    def __len__(self) -> int:
        return len(self.samples)


IMG_EXTENSIONS = ('.jpg', '.jpeg', '.png', '.ppm', '.bmp', '.pgm', '.tif', '.tiff', '.webp')


def pil_loader(path: str) -> Image.Image:
    # open path as file to avoid ResourceWarning (https://github.com/python-pillow/Pillow/issues/835)
    with open(path, 'rb') as f:
        img = Image.open(f)
        return img.convert('RGB')


# TODO: specify the return type
def accimage_loader(path: str) -> Any:
    import accimage
    try:
        return accimage.Image(path)
    except IOError:
        # Potentially a decoding problem, fall back to PIL.Image
        return pil_loader(path)


def default_loader(path: str) -> Any:
    from torchvision import get_image_backend
    if get_image_backend() == 'accimage':
        return accimage_loader(path)
    else:
        return pil_loader(path)


class ImageFolder(DatasetFolder):
    """A generic data loader where the images are arranged in this way: ::
        root/dog/xxx.png
        root/dog/xxy.png
        root/dog/[...]/xxz.png
        root/cat/123.png
        root/cat/nsdf3.png
        root/cat/[...]/asd932_.png
    Args:
        root (string): Root directory path.
        transform (callable, optional): A function/transform that  takes in an PIL image
            and returns a transformed version. E.g, ``transforms.RandomCrop``
        target_transform (callable, optional): A function/transform that takes in the
            target and transforms it.
        loader (callable, optional): A function to load an image given its path.
        is_valid_file (callable, optional): A function that takes path of an Image file
            and check if the file is a valid file (used to check of corrupt files)
     Attributes:
        classes (list): List of the class names sorted alphabetically.
        class_to_idx (dict): Dict with items (class_name, class_index).
        imgs (list): List of (image path, class_index) tuples
    """

    def __init__(
            self,
            root: str,
            transform: Optional[Callable] = None,
            target_transform: Optional[Callable] = None,
            classes_fraction=1.0,
            data_per_class_fraction=1.0,
            loader: Callable[[str], Any] = default_loader,
            is_valid_file: Optional[Callable[[str], bool]] = None,
    ):
        super(ImageFolder, self).__init__(root, loader, IMG_EXTENSIONS if is_valid_file is None else None,
                                          transform=transform,
                                          target_transform=target_transform,
                                          classes_fraction=classes_fraction,
                                          data_per_class_fraction=data_per_class_fraction,
                                          is_valid_file=is_valid_file)
        self.imgs = self.samples