from enum import Enum
from typing import List, Union
from warnings import warn

import torch

from ..extension import _load_library
from ..utils import _log_api_usage_once


try:
    _load_library("image")
except (ImportError, OSError) as e:
    warn(
        f"Failed to load image Python extension: '{e}'"
        f"If you don't plan on using image functionality from `torchvision.io`, you can ignore this warning. "
        f"Otherwise, there might be something wrong with your environment. "
        f"Did you have `libjpeg` or `libpng` installed before building `torchvision` from source?"
    )


class ImageReadMode(Enum):
    """Allow automatic conversion to RGB, RGBA, etc while decoding.

    .. note::

        You don't need to use this struct, you can just pass strings to all
        ``mode`` parameters, e.g. ``mode="RGB"``.

    The different available modes are the following.

    - UNCHANGED: loads the image as-is
    - RGB: converts to RGB
    - RGBA: converts to RGB with transparency (also aliased as RGB_ALPHA)
    - GRAY: converts to grayscale
    - GRAY_ALPHA: converts to grayscale with transparency

    .. note::

        Some decoders won't support all possible values, e.g. GRAY and
        GRAY_ALPHA are only supported for PNG and JPEG images.
    """

    UNCHANGED = 0
    GRAY = 1
    GRAY_ALPHA = 2
    RGB = 3
    RGB_ALPHA = 4
    RGBA = RGB_ALPHA  # Alias for convenience


def read_file(path: str) -> torch.Tensor:
    """
    Return the bytes contents of a file as a uint8 1D Tensor.

    Args:
        path (str or ``pathlib.Path``): the path to the file to be read

    Returns:
        data (Tensor)
    """
    if not torch.jit.is_scripting() and not torch.jit.is_tracing():
        _log_api_usage_once(read_file)
    data = torch.ops.image.read_file(str(path))
    return data


def write_file(filename: str, data: torch.Tensor) -> None:
    """
    Write the content of an uint8 1D tensor to a file.

    Args:
        filename (str or ``pathlib.Path``): the path to the file to be written
        data (Tensor): the contents to be written to the output file
    """
    if not torch.jit.is_scripting() and not torch.jit.is_tracing():
        _log_api_usage_once(write_file)
    torch.ops.image.write_file(str(filename), data)


def decode_png(
    input: torch.Tensor,
    mode: ImageReadMode = ImageReadMode.UNCHANGED,
    apply_exif_orientation: bool = False,
) -> torch.Tensor:
    """
    Decodes a PNG image into a 3 dimensional RGB or grayscale Tensor.

    The values of the output tensor are in uint8 in [0, 255] for most cases. If
    the image is a 16-bit png, then the output tensor is uint16 in [0, 65535]
    (supported from torchvision ``0.21``). Since uint16 support is limited in
    pytorch, we recommend calling
    :func:`torchvision.transforms.v2.functional.to_dtype()` with ``scale=True``
    after this function to convert the decoded image into a uint8 or float
    tensor.

    Args:
        input (Tensor[1]): a one dimensional uint8 tensor containing
            the raw bytes of the PNG image.
        mode (str or ImageReadMode): The mode to convert the image to, e.g. "RGB".
            Default is "UNCHANGED".  See :class:`~torchvision.io.ImageReadMode`
            for available modes.
        apply_exif_orientation (bool): apply EXIF orientation transformation to the output tensor.
            Default: False.

    Returns:
        output (Tensor[image_channels, image_height, image_width])
    """
    if not torch.jit.is_scripting() and not torch.jit.is_tracing():
        _log_api_usage_once(decode_png)
    if isinstance(mode, str):
        mode = ImageReadMode[mode.upper()]
    output = torch.ops.image.decode_png(input, mode.value, apply_exif_orientation)
    return output


def encode_png(input: torch.Tensor, compression_level: int = 6) -> torch.Tensor:
    """
    Takes an input tensor in CHW layout and returns a buffer with the contents
    of its corresponding PNG file.

    Args:
        input (Tensor[channels, image_height, image_width]): int8 image tensor of
            ``c`` channels, where ``c`` must 3 or 1.
        compression_level (int): Compression factor for the resulting file, it must be a number
            between 0 and 9. Default: 6

    Returns:
        Tensor[1]: A one dimensional int8 tensor that contains the raw bytes of the
            PNG file.
    """
    if not torch.jit.is_scripting() and not torch.jit.is_tracing():
        _log_api_usage_once(encode_png)
    output = torch.ops.image.encode_png(input, compression_level)
    return output


def write_png(input: torch.Tensor, filename: str, compression_level: int = 6):
    """
    Takes an input tensor in CHW layout (or HW in the case of grayscale images)
    and saves it in a PNG file.

    Args:
        input (Tensor[channels, image_height, image_width]): int8 image tensor of
            ``c`` channels, where ``c`` must be 1 or 3.
        filename (str or ``pathlib.Path``): Path to save the image.
        compression_level (int): Compression factor for the resulting file, it must be a number
            between 0 and 9. Default: 6
    """
    if not torch.jit.is_scripting() and not torch.jit.is_tracing():
        _log_api_usage_once(write_png)
    output = encode_png(input, compression_level)
    write_file(filename, output)


def decode_jpeg(
    input: Union[torch.Tensor, List[torch.Tensor]],
    mode: ImageReadMode = ImageReadMode.UNCHANGED,
    device: Union[str, torch.device] = "cpu",
    apply_exif_orientation: bool = False,
) -> Union[torch.Tensor, List[torch.Tensor]]:
    """Decode JPEG image(s) into 3D RGB or grayscale Tensor(s), on CPU or CUDA.

    The values of the output tensor are uint8 between 0 and 255.

    .. note::
        When using a CUDA device, passing a list of tensors is more efficient than repeated individual calls to ``decode_jpeg``.
        When using CPU the performance is equivalent.
        The CUDA version of this function has explicitly been designed with thread-safety in mind.
        This function does not return partial results in case of an error.

    Args:
        input (Tensor[1] or list[Tensor[1]]): a (list of) one dimensional uint8 tensor(s) containing
            the raw bytes of the JPEG image. The tensor(s) must be on CPU,
            regardless of the ``device`` parameter.
        mode (str or ImageReadMode): The mode to convert the image to, e.g. "RGB".
            Default is "UNCHANGED".  See :class:`~torchvision.io.ImageReadMode`
            for available modes.
        device (str or torch.device): The device on which the decoded image will
            be stored. If a cuda device is specified, the image will be decoded
            with `nvjpeg <https://developer.nvidia.com/nvjpeg>`_. This is only
            supported for CUDA version >= 10.1

            .. betastatus:: device parameter

            .. warning::
                There is a memory leak in the nvjpeg library for CUDA versions < 11.6.
                Make sure to rely on CUDA 11.6 or above before using ``device="cuda"``.
        apply_exif_orientation (bool): apply EXIF orientation transformation to the output tensor.
            Default: False. Only implemented for JPEG format on CPU.

    Returns:
        output (Tensor[image_channels, image_height, image_width] or list[Tensor[image_channels, image_height, image_width]]):
            The values of the output tensor(s) are uint8 between 0 and 255.
            ``output.device`` will be set to the specified ``device``


    """
    if not torch.jit.is_scripting() and not torch.jit.is_tracing():
        _log_api_usage_once(decode_jpeg)
    if isinstance(device, str):
        device = torch.device(device)
    if isinstance(mode, str):
        mode = ImageReadMode[mode.upper()]

    if isinstance(input, list):
        if len(input) == 0:
            raise ValueError("Input list must contain at least one element")
        if not all(isinstance(t, torch.Tensor) for t in input):
            raise ValueError("All elements of the input list must be tensors.")
        if not all(t.device.type == "cpu" for t in input):
            raise ValueError("Input list must contain tensors on CPU.")
        if device.type == "cuda":
            return torch.ops.image.decode_jpegs_cuda(input, mode.value, device)
        else:
            return [torch.ops.image.decode_jpeg(img, mode.value, apply_exif_orientation) for img in input]

    else:  # input is tensor
        if input.device.type != "cpu":
            raise ValueError("Input tensor must be a CPU tensor")
        if device.type == "cuda":
            return torch.ops.image.decode_jpegs_cuda([input], mode.value, device)[0]
        else:
            return torch.ops.image.decode_jpeg(input, mode.value, apply_exif_orientation)


def encode_jpeg(
    input: Union[torch.Tensor, List[torch.Tensor]], quality: int = 75
) -> Union[torch.Tensor, List[torch.Tensor]]:
    """Encode RGB tensor(s) into raw encoded jpeg bytes, on CPU or CUDA.

    .. note::
        Passing a list of CUDA tensors is more efficient than repeated individual calls to ``encode_jpeg``.
        For CPU tensors the performance is equivalent.

    Args:
        input (Tensor[channels, image_height, image_width] or List[Tensor[channels, image_height, image_width]]):
            (list of) uint8 image tensor(s) of ``c`` channels, where ``c`` must be 1 or 3
        quality (int): Quality of the resulting JPEG file(s). Must be a number between
            1 and 100. Default: 75

    Returns:
        output (Tensor[1] or list[Tensor[1]]): A (list of) one dimensional uint8 tensor(s) that contain the raw bytes of the JPEG file.
    """
    if not torch.jit.is_scripting() and not torch.jit.is_tracing():
        _log_api_usage_once(encode_jpeg)
    if quality < 1 or quality > 100:
        raise ValueError("Image quality should be a positive number between 1 and 100")
    if isinstance(input, list):
        if not input:
            raise ValueError("encode_jpeg requires at least one input tensor when a list is passed")
        if input[0].device.type == "cuda":
            return torch.ops.image.encode_jpegs_cuda(input, quality)
        else:
            return [torch.ops.image.encode_jpeg(image, quality) for image in input]
    else:  # single input tensor
        if input.device.type == "cuda":
            return torch.ops.image.encode_jpegs_cuda([input], quality)[0]
        else:
            return torch.ops.image.encode_jpeg(input, quality)


def write_jpeg(input: torch.Tensor, filename: str, quality: int = 75):
    """
    Takes an input tensor in CHW layout and saves it in a JPEG file.

    Args:
        input (Tensor[channels, image_height, image_width]): int8 image tensor of ``c``
            channels, where ``c`` must be 1 or 3.
        filename (str or ``pathlib.Path``): Path to save the image.
        quality (int): Quality of the resulting JPEG file, it must be a number
            between 1 and 100. Default: 75
    """
    if not torch.jit.is_scripting() and not torch.jit.is_tracing():
        _log_api_usage_once(write_jpeg)
    output = encode_jpeg(input, quality)
    assert isinstance(output, torch.Tensor)  # Needed for torchscript
    write_file(filename, output)


def decode_image(
    input: Union[torch.Tensor, str],
    mode: ImageReadMode = ImageReadMode.UNCHANGED,
    apply_exif_orientation: bool = False,
) -> torch.Tensor:
    """Decode an image into a uint8 tensor, from a path or from raw encoded bytes.

    Currently supported image formats are jpeg, png, gif and webp.

    The values of the output tensor are in uint8 in [0, 255] for most cases.

    If the image is a 16-bit png, then the output tensor is uint16 in [0, 65535]
    (supported from torchvision ``0.21``). Since uint16 support is limited in
    pytorch, we recommend calling
    :func:`torchvision.transforms.v2.functional.to_dtype()` with ``scale=True``
    after this function to convert the decoded image into a uint8 or float
    tensor.

    Args:
        input (Tensor or str or ``pathlib.Path``): The image to decode. If a
            tensor is passed, it must be one dimensional uint8 tensor containing
            the raw bytes of the image. Otherwise, this must be a path to the image file.
        mode (str or ImageReadMode): The mode to convert the image to, e.g. "RGB".
            Default is "UNCHANGED".  See :class:`~torchvision.io.ImageReadMode`
            for available modes.
        apply_exif_orientation (bool): apply EXIF orientation transformation to the output tensor.
           Only applies to JPEG and PNG images. Default: False.

    Returns:
        output (Tensor[image_channels, image_height, image_width])
    """
    if not torch.jit.is_scripting() and not torch.jit.is_tracing():
        _log_api_usage_once(decode_image)
    if not isinstance(input, torch.Tensor):
        input = read_file(str(input))
    if isinstance(mode, str):
        mode = ImageReadMode[mode.upper()]
    output = torch.ops.image.decode_image(input, mode.value, apply_exif_orientation)
    return output


def read_image(
    path: str,
    mode: ImageReadMode = ImageReadMode.UNCHANGED,
    apply_exif_orientation: bool = False,
) -> torch.Tensor:
    """[OBSOLETE] Use :func:`~torchvision.io.decode_image` instead."""
    if not torch.jit.is_scripting() and not torch.jit.is_tracing():
        _log_api_usage_once(read_image)
    data = read_file(path)
    return decode_image(data, mode, apply_exif_orientation=apply_exif_orientation)


def decode_gif(input: torch.Tensor) -> torch.Tensor:
    """
    Decode a GIF image into a 3 or 4 dimensional RGB Tensor.

    The values of the output tensor are uint8 between 0 and 255.
    The output tensor has shape ``(C, H, W)`` if there is only one image in the
    GIF, and ``(N, C, H, W)`` if there are ``N`` images.

    Args:
        input (Tensor[1]): a one dimensional contiguous uint8 tensor containing
            the raw bytes of the GIF image.

    Returns:
        output (Tensor[image_channels, image_height, image_width] or Tensor[num_images, image_channels, image_height, image_width])
    """
    if not torch.jit.is_scripting() and not torch.jit.is_tracing():
        _log_api_usage_once(decode_gif)
    return torch.ops.image.decode_gif(input)


def decode_webp(
    input: torch.Tensor,
    mode: ImageReadMode = ImageReadMode.UNCHANGED,
) -> torch.Tensor:
    """
    Decode a WEBP image into a 3 dimensional RGB[A] Tensor.

    The values of the output tensor are uint8 between 0 and 255.

    Args:
        input (Tensor[1]): a one dimensional contiguous uint8 tensor containing
            the raw bytes of the WEBP image.
        mode (str or ImageReadMode): The mode to convert the image to, e.g. "RGB".
            Default is "UNCHANGED".  See :class:`~torchvision.io.ImageReadMode`
            for available modes.

    Returns:
        Decoded image (Tensor[image_channels, image_height, image_width])
    """
    if not torch.jit.is_scripting() and not torch.jit.is_tracing():
        _log_api_usage_once(decode_webp)
    if isinstance(mode, str):
        mode = ImageReadMode[mode.upper()]
    return torch.ops.image.decode_webp(input, mode.value)


def _decode_avif(
    input: torch.Tensor,
    mode: ImageReadMode = ImageReadMode.UNCHANGED,
) -> torch.Tensor:
    """
    Decode an AVIF image into a 3 dimensional RGB[A] Tensor.

    The values of the output tensor are in uint8 in [0, 255] for most images. If
    the image has a bit-depth of more than 8, then the output tensor is uint16
    in [0, 65535]. Since uint16 support is limited in pytorch, we recommend
    calling :func:`torchvision.transforms.v2.functional.to_dtype()` with
    ``scale=True`` after this function to convert the decoded image into a uint8
    or float tensor.

    Args:
        input (Tensor[1]): a one dimensional contiguous uint8 tensor containing
            the raw bytes of the AVIF image.
        mode (str or ImageReadMode): The mode to convert the image to, e.g. "RGB".
            Default is "UNCHANGED".  See :class:`~torchvision.io.ImageReadMode`
            for available modes.

    Returns:
        Decoded image (Tensor[image_channels, image_height, image_width])
    """
    if not torch.jit.is_scripting() and not torch.jit.is_tracing():
        _log_api_usage_once(_decode_avif)
    if isinstance(mode, str):
        mode = ImageReadMode[mode.upper()]
    return torch.ops.image.decode_avif(input, mode.value)


def _decode_heic(input: torch.Tensor, mode: ImageReadMode = ImageReadMode.UNCHANGED) -> torch.Tensor:
    """
    Decode an HEIC image into a 3 dimensional RGB[A] Tensor.

    The values of the output tensor are in uint8 in [0, 255] for most images. If
    the image has a bit-depth of more than 8, then the output tensor is uint16
    in [0, 65535]. Since uint16 support is limited in pytorch, we recommend
    calling :func:`torchvision.transforms.v2.functional.to_dtype()` with
    ``scale=True`` after this function to convert the decoded image into a uint8
    or float tensor.

    Args:
        input (Tensor[1]): a one dimensional contiguous uint8 tensor containing
            the raw bytes of the HEIC image.
        mode (str or ImageReadMode): The mode to convert the image to, e.g. "RGB".
            Default is "UNCHANGED".  See :class:`~torchvision.io.ImageReadMode`
            for available modes.

    Returns:
        Decoded image (Tensor[image_channels, image_height, image_width])
    """
    if not torch.jit.is_scripting() and not torch.jit.is_tracing():
        _log_api_usage_once(_decode_heic)
    if isinstance(mode, str):
        mode = ImageReadMode[mode.upper()]
    return torch.ops.image.decode_heic(input, mode.value)