import functools
import gzip
import lzma
import pathlib
import pickle
import tempfile
from collections import defaultdict
from typing import Any, Dict, Tuple

import numpy as np
import pytest
import torch
from datasets_utils import create_image_folder, make_tar, make_zip
from torch.testing import make_tensor as _make_tensor
from torchdata.datapipes.iter import IterDataPipe
from torchvision.prototype import datasets
from torchvision.prototype.datasets._api import DEFAULT_DECODER_MAP, DEFAULT_DECODER
from torchvision.prototype.datasets._api import find
from torchvision.prototype.utils._internal import add_suggestion

make_tensor = functools.partial(_make_tensor, device="cpu")

__all__ = ["load"]

DEFAULT_TEST_DECODER = object()


class DatasetMocks:
    def __init__(self):
        self._mock_data_fns = {}
        self._tmp_home = pathlib.Path(tempfile.mkdtemp())
        self._cache = {}

    def register_mock_data_fn(self, mock_data_fn):
        name = mock_data_fn.__name__
        if name not in datasets.list():
            raise pytest.UsageError(
                add_suggestion(
                    f"The name of the mock data function '{name}' has no corresponding dataset.",
                    word=name,
                    possibilities=datasets.list(),
                    close_match_hint=lambda close_match: f"Did you mean to name it '{close_match}'?",
                    alternative_hint=lambda _: "",
                )
            )
        self._mock_data_fns[name] = mock_data_fn
        return mock_data_fn

    def _parse_mock_info(self, mock_info, *, name):
        if mock_info is None:
            raise pytest.UsageError(
                f"The mock data function for dataset '{name}' returned nothing. It needs to at least return an integer "
                f"indicating the number of samples for the current `config`."
            )
        elif isinstance(mock_info, int):
            mock_info = dict(num_samples=mock_info)
        elif not isinstance(mock_info, dict):
            raise pytest.UsageError(
                f"The mock data function for dataset '{name}' returned a {type(mock_info)}. The returned object should "
                f"be a dictionary containing at least the number of samples for the current `config` for the key "
                f"`'num_samples'`. If no additional information is required for specific tests, the number of samples "
                f"can also be returned as an integer."
            )
        elif "num_samples" not in mock_info:
            raise pytest.UsageError(
                f"The dictionary returned by the mock data function for dataset '{name}' must contain a `'num_samples'` "
                f"entry indicating the number of samples for the current `config`."
            )
        return mock_info

    def _get(self, dataset, config):
        name = dataset.info.name
        resources_and_mock_info = self._cache.get((name, config))
        if resources_and_mock_info:
            return resources_and_mock_info

        try:
            fakedata_fn = self._mock_data_fns[name]
        except KeyError:
            raise pytest.UsageError(
                f"No mock data available for dataset '{name}'. "
                f"Did you add a new dataset, but forget to provide mock data for it? "
                f"Did you register the mock data function with `@DatasetMocks.register_mock_data_fn`?"
            )

        root = self._tmp_home / name
        root.mkdir(exist_ok=True)
        mock_info = self._parse_mock_info(fakedata_fn(dataset.info, root, config), name=name)

        mock_resources = []
        for resource in dataset.resources(config):
            path = root / resource.file_name
            if not path.exists() and path.is_file():
                raise pytest.UsageError(
                    f"Dataset '{name}' requires the file {path.name} for {config}, but this file does not exist."
                )

            mock_resources.append(datasets.utils.LocalResource(path))

        self._cache[(name, config)] = mock_resources, mock_info
        return mock_resources, mock_info

    def load(
        self, name: str, decoder=DEFAULT_DECODER, split="train", **options: Any
    ) -> Tuple[IterDataPipe, Dict[str, Any]]:
        dataset = find(name)
        config = dataset.info.make_config(split=split, **options)
        resources, mock_info = self._get(dataset, config)
        datapipe = dataset._make_datapipe(
            [resource.to_datapipe() for resource in resources],
            config=config,
            decoder=DEFAULT_DECODER_MAP.get(dataset.info.type) if decoder is DEFAULT_DECODER else decoder,
        )
        return datapipe, mock_info


dataset_mocks = DatasetMocks()
load = dataset_mocks.load


class MNISTFakedata:
    _DTYPES_ID = {
        torch.uint8: 8,
        torch.int8: 9,
        torch.int16: 11,
        torch.int32: 12,
        torch.float32: 13,
        torch.float64: 14,
    }

    @classmethod
    def _magic(cls, dtype, ndim):
        return cls._DTYPES_ID[dtype] * 256 + ndim + 1

    @staticmethod
    def _encode(t):
        return torch.tensor(t, dtype=torch.int32).numpy().tobytes()[::-1]

    @staticmethod
    def _big_endian_dtype(dtype):
        np_dtype = getattr(np, str(dtype).replace("torch.", ""))().dtype
        return np.dtype(f">{np_dtype.kind}{np_dtype.itemsize}")

    @classmethod
    def _create_binary_file(cls, root, filename, *, num_samples, shape, dtype, compressor, low=0, high):
        with compressor(root / filename, "wb") as fh:
            for meta in (cls._magic(dtype, len(shape)), num_samples, *shape):
                fh.write(cls._encode(meta))

            data = make_tensor((num_samples, *shape), dtype=dtype, low=low, high=high)

            fh.write(data.numpy().astype(cls._big_endian_dtype(dtype)).tobytes())

    @classmethod
    def generate(
        cls,
        root,
        *,
        num_categories,
        num_samples=None,
        images_file,
        labels_file,
        image_size=(28, 28),
        image_dtype=torch.uint8,
        label_size=(),
        label_dtype=torch.uint8,
        compressor=None,
    ):
        if num_samples is None:
            num_samples = num_categories
        if compressor is None:
            compressor = gzip.open

        cls._create_binary_file(
            root,
            images_file,
            num_samples=num_samples,
            shape=image_size,
            dtype=image_dtype,
            compressor=compressor,
            high=float("inf"),
        )
        cls._create_binary_file(
            root,
            labels_file,
            num_samples=num_samples,
            shape=label_size,
            dtype=label_dtype,
            compressor=compressor,
            high=num_categories,
        )

        return num_samples


@dataset_mocks.register_mock_data_fn
def mnist(info, root, config):
    train = config.split == "train"
    images_file = f"{'train' if train else 't10k'}-images-idx3-ubyte.gz"
    labels_file = f"{'train' if train else 't10k'}-labels-idx1-ubyte.gz"
    return MNISTFakedata.generate(
        root,
        num_categories=len(info.categories),
        images_file=images_file,
        labels_file=labels_file,
    )


@dataset_mocks.register_mock_data_fn
def fashionmnist(info, root, config):
    train = config.split == "train"
    images_file = f"{'train' if train else 't10k'}-images-idx3-ubyte.gz"
    labels_file = f"{'train' if train else 't10k'}-labels-idx1-ubyte.gz"
    return MNISTFakedata.generate(
        root,
        num_categories=len(info.categories),
        images_file=images_file,
        labels_file=labels_file,
    )


@dataset_mocks.register_mock_data_fn
def kmnist(info, root, config):
    train = config.split == "train"
    images_file = f"{'train' if train else 't10k'}-images-idx3-ubyte.gz"
    labels_file = f"{'train' if train else 't10k'}-labels-idx1-ubyte.gz"
    return MNISTFakedata.generate(
        root,
        num_categories=len(info.categories),
        images_file=images_file,
        labels_file=labels_file,
    )


@dataset_mocks.register_mock_data_fn
def emnist(info, root, config):
    # The image sets that merge some lower case letters in their respective upper case variant, still use dense
    # labels in the data files. Thus, num_categories != len(categories) there.
    num_categories = defaultdict(
        lambda: len(info.categories), **{image_set: 47 for image_set in ("Balanced", "By_Merge")}
    )

    num_samples = {}
    file_names = set()
    for _config in info._configs:
        prefix = f"emnist-{_config.image_set.replace('_', '').lower()}-{_config.split}"
        images_file = f"{prefix}-images-idx3-ubyte.gz"
        labels_file = f"{prefix}-labels-idx1-ubyte.gz"
        file_names.update({images_file, labels_file})
        num_samples[_config.image_set] = MNISTFakedata.generate(
            root,
            num_categories=num_categories[_config.image_set],
            images_file=images_file,
            labels_file=labels_file,
        )

    make_zip(root, "emnist-gzip.zip", *file_names)

    return num_samples[config.image_set]


@dataset_mocks.register_mock_data_fn
def qmnist(info, root, config):
    num_categories = len(info.categories)
    if config.split == "train":
        num_samples = num_samples_gen = num_categories + 2
        prefix = "qmnist-train"
        suffix = ".gz"
        compressor = gzip.open
    elif config.split.startswith("test"):
        # The split 'test50k' is defined as the last 50k images beginning at index 10000. Thus, we need to create more
        # than 10000 images for the dataset to not be empty.
        num_samples = num_samples_gen = 10001
        if config.split == "test10k":
            num_samples = min(num_samples, 10000)
        if config.split == "test50k":
            num_samples -= 10000
        prefix = "qmnist-test"
        suffix = ".gz"
        compressor = gzip.open
    else:  # config.split == "nist"
        num_samples = num_samples_gen = num_categories + 3
        prefix = "xnist"
        suffix = ".xz"
        compressor = lzma.open

    MNISTFakedata.generate(
        root,
        num_categories=num_categories,
        num_samples=num_samples_gen,
        images_file=f"{prefix}-images-idx3-ubyte{suffix}",
        labels_file=f"{prefix}-labels-idx2-int{suffix}",
        label_size=(8,),
        label_dtype=torch.int32,
        compressor=compressor,
    )

    return num_samples


class CIFARFakedata:
    NUM_PIXELS = 32 * 32 * 3

    @classmethod
    def _create_batch_file(cls, root, name, *, num_categories, labels_key, num_samples=1):
        content = {
            "data": make_tensor((num_samples, cls.NUM_PIXELS), dtype=torch.uint8).numpy(),
            labels_key: torch.randint(0, num_categories, size=(num_samples,)).tolist(),
        }
        with open(pathlib.Path(root) / name, "wb") as fh:
            pickle.dump(content, fh)

    @classmethod
    def generate(
        cls,
        root,
        name,
        *,
        folder,
        train_files,
        test_files,
        num_categories,
        labels_key,
    ):
        folder = root / folder
        folder.mkdir()
        files = (*train_files, *test_files)
        for file in files:
            cls._create_batch_file(
                folder,
                file,
                num_categories=num_categories,
                labels_key=labels_key,
            )

        make_tar(root, name, folder, compression="gz")


@dataset_mocks.register_mock_data_fn
def cifar10(info, root, config):
    train_files = [f"data_batch_{idx}" for idx in range(1, 6)]
    test_files = ["test_batch"]

    CIFARFakedata.generate(
        root=root,
        name="cifar-10-python.tar.gz",
        folder=pathlib.Path("cifar-10-batches-py"),
        train_files=train_files,
        test_files=test_files,
        num_categories=10,
        labels_key="labels",
    )

    return len(train_files if config.split == "train" else test_files)


@dataset_mocks.register_mock_data_fn
def cifar100(info, root, config):
    train_files = ["train"]
    test_files = ["test"]

    CIFARFakedata.generate(
        root=root,
        name="cifar-100-python.tar.gz",
        folder=pathlib.Path("cifar-100-python"),
        train_files=train_files,
        test_files=test_files,
        num_categories=100,
        labels_key="fine_labels",
    )

    return len(train_files if config.split == "train" else test_files)


@dataset_mocks.register_mock_data_fn
def caltech101(info, root, config):
    def create_ann_file(root, name):
        import scipy.io

        box_coord = make_tensor((1, 4), dtype=torch.int32, low=0).numpy().astype(np.uint16)
        obj_contour = make_tensor((2, int(torch.randint(3, 6, size=()))), dtype=torch.float64, low=0).numpy()

        scipy.io.savemat(str(pathlib.Path(root) / name), dict(box_coord=box_coord, obj_contour=obj_contour))

    def create_ann_folder(root, name, file_name_fn, num_examples):
        root = pathlib.Path(root) / name
        root.mkdir(parents=True)

        for idx in range(num_examples):
            create_ann_file(root, file_name_fn(idx))

    images_root = root / "101_ObjectCategories"
    anns_root = root / "Annotations"

    ann_category_map = {
        "Faces_2": "Faces",
        "Faces_3": "Faces_easy",
        "Motorbikes_16": "Motorbikes",
        "Airplanes_Side_2": "airplanes",
    }

    num_images_per_category = 2
    for category in info.categories:
        create_image_folder(
            root=images_root,
            name=category,
            file_name_fn=lambda idx: f"image_{idx + 1:04d}.jpg",
            num_examples=num_images_per_category,
        )
        create_ann_folder(
            root=anns_root,
            name=ann_category_map.get(category, category),
            file_name_fn=lambda idx: f"annotation_{idx + 1:04d}.mat",
            num_examples=num_images_per_category,
        )

    (images_root / "BACKGROUND_Goodle").mkdir()
    make_tar(root, f"{images_root.name}.tar.gz", images_root, compression="gz")

    make_tar(root, f"{anns_root.name}.tar", anns_root)

    return num_images_per_category * len(info.categories)


@dataset_mocks.register_mock_data_fn
def caltech256(info, root, config):
    dir = root / "256_ObjectCategories"
    num_images_per_category = 2

    for idx, category in enumerate(info.categories, 1):
        files = create_image_folder(
            dir,
            name=f"{idx:03d}.{category}",
            file_name_fn=lambda image_idx: f"{idx:03d}_{image_idx + 1:04d}.jpg",
            num_examples=num_images_per_category,
        )
        if category == "spider":
            open(files[0].parent / "RENAME2", "w").close()

    make_tar(root, f"{dir.name}.tar", dir)

    return num_images_per_category * len(info.categories)


@dataset_mocks.register_mock_data_fn
def imagenet(info, root, config):
    wnids = tuple(info.extra.wnid_to_category.keys())
    if config.split == "train":
        images_root = root / "ILSVRC2012_img_train"

        num_samples = len(wnids)

        for wnid in wnids:
            files = create_image_folder(
                root=images_root,
                name=wnid,
                file_name_fn=lambda image_idx: f"{wnid}_{image_idx:04d}.JPEG",
                num_examples=1,
            )
            make_tar(images_root, f"{wnid}.tar", files[0].parent)
    elif config.split == "val":
        num_samples = 3
        files = create_image_folder(
            root=root,
            name="ILSVRC2012_img_val",
            file_name_fn=lambda image_idx: f"ILSVRC2012_val_{image_idx + 1:08d}.JPEG",
            num_examples=num_samples,
        )
        images_root = files[0].parent
    else:  # config.split == "test"
        images_root = root / "ILSVRC2012_img_test_v10102019"

        num_samples = 3

        create_image_folder(
            root=images_root,
            name="test",
            file_name_fn=lambda image_idx: f"ILSVRC2012_test_{image_idx + 1:08d}.JPEG",
            num_examples=num_samples,
        )
    make_tar(root, f"{images_root.name}.tar", images_root)

    devkit_root = root / "ILSVRC2012_devkit_t12"
    devkit_root.mkdir()
    data_root = devkit_root / "data"
    data_root.mkdir()
    with open(data_root / "ILSVRC2012_validation_ground_truth.txt", "w") as file:
        for label in torch.randint(0, len(wnids), (num_samples,)).tolist():
            file.write(f"{label}\n")
    make_tar(root, f"{devkit_root}.tar.gz", devkit_root, compression="gz")

    return num_samples
