import json
import warnings
import numpy as np

from ..utils.data_utils import get_file
from .. import backend as K

CLASS_INDEX = None
CLASS_INDEX_PATH = 'https://s3.amazonaws.com/deep-learning-models/image-models/imagenet_class_index.json'

# Global Numpy arrays of imagenet mean for preprocessing symbolic inputs
_IMAGENET_MEAN = None


def _preprocess_numpy_input(x, data_format, mode):
    if mode == 'tf':
        x /= 127.5
        x -= 1.
        return x

    if data_format == 'channels_first':
        if x.ndim == 3:
            # 'RGB'->'BGR'
            x = x[::-1, ...]
            # Zero-center by mean pixel
            x[0, :, :] -= 103.939
            x[1, :, :] -= 116.779
            x[2, :, :] -= 123.68
        else:
            x = x[:, ::-1, ...]
            x[:, 0, :, :] -= 103.939
            x[:, 1, :, :] -= 116.779
            x[:, 2, :, :] -= 123.68
    else:
        # 'RGB'->'BGR'
        x = x[..., ::-1]
        # Zero-center by mean pixel
        x[..., 0] -= 103.939
        x[..., 1] -= 116.779
        x[..., 2] -= 123.68
    return x


def _preprocess_symbolic_input(x, data_format, mode):
    global _IMAGENET_MEAN

    if mode == 'tf':
        x /= 127.5
        x -= 1.
        return x

    if data_format == 'channels_first':
        # 'RGB'->'BGR'
        if K.ndim(x) == 3:
            x = x[::-1, ...]
        else:
            x = x[:, ::-1, ...]
    else:
        # 'RGB'->'BGR'
        x = x[..., ::-1]

    if _IMAGENET_MEAN is None:
        _IMAGENET_MEAN = K.constant(-np.array([103.939, 116.779, 123.68]))
    # Zero-center by mean pixel
    if K.dtype(x) != K.dtype(_IMAGENET_MEAN):
        x = K.bias_add(x, K.cast(_IMAGENET_MEAN, K.dtype(x)), data_format)
    else:
        x = K.bias_add(x, _IMAGENET_MEAN, data_format)
    return x


def preprocess_input(x, data_format=None, mode='caffe'):
    """Preprocesses a tensor encoding a batch of images.

    # Arguments
        x: input Numpy or symoblic tensor, 3D or 4D.
        data_format: data format of the image tensor.
        mode: One of "caffe", "tf".
            - caffe: will convert the images from RGB to BGR,
                then will zero-center each color channel with
                respect to the ImageNet dataset,
                without scaling.
            - tf: will scale pixels between -1 and 1,
                sample-wise.

    # Returns
        Preprocessed tensor.
    """
    if data_format is None:
        data_format = K.image_data_format()
    if data_format not in {'channels_first', 'channels_last'}:
        raise ValueError('Unknown data_format ' + str(data_format))

    if isinstance(x, np.ndarray):
        return _preprocess_numpy_input(x, data_format=data_format, mode=mode)
    else:
        return _preprocess_symbolic_input(x, data_format=data_format,
                                          mode=mode)


def decode_predictions(preds, top=5):
    """Decodes the prediction of an ImageNet model.

    # Arguments
        preds: Numpy tensor encoding a batch of predictions.
        top: integer, how many top-guesses to return.

    # Returns
        A list of lists of top class prediction tuples
        `(class_name, class_description, score)`.
        One list of tuples per sample in batch input.

    # Raises
        ValueError: in case of invalid shape of the `pred` array
            (must be 2D).
    """
    global CLASS_INDEX
    if len(preds.shape) != 2 or preds.shape[1] != 1000:
        raise ValueError('`decode_predictions` expects '
                         'a batch of predictions '
                         '(i.e. a 2D array of shape (samples, 1000)). '
                         'Found array with shape: ' + str(preds.shape))
    if CLASS_INDEX is None:
        fpath = get_file('imagenet_class_index.json',
                         CLASS_INDEX_PATH,
                         cache_subdir='models',
                         file_hash='c2c37ea517e94d9795004a39431a14cb')
        CLASS_INDEX = json.load(open(fpath))
    results = []
    for pred in preds:
        top_indices = pred.argsort()[-top:][::-1]
        result = [tuple(CLASS_INDEX[str(i)]) + (pred[i],) for i in top_indices]
        result.sort(key=lambda x: x[2], reverse=True)
        results.append(result)
    return results


def _obtain_input_shape(input_shape,
                        default_size,
                        min_size,
                        data_format,
                        require_flatten,
                        weights=None):
    """Internal utility to compute/validate an ImageNet model's input shape.

    # Arguments
        input_shape: either None (will return the default network input shape),
            or a user-provided shape to be validated.
        default_size: default input width/height for the model.
        min_size: minimum input width/height accepted by the model.
        data_format: image data format to use.
        require_flatten: whether the model is expected to
            be linked to a classifier via a Flatten layer.
        weights: one of `None` (random initialization)
            or 'imagenet' (pre-training on ImageNet).
            If weights='imagenet' input channels must be equal to 3.

    # Returns
        An integer shape tuple (may include None entries).

    # Raises
        ValueError: in case of invalid argument values.
    """
    if weights != 'imagenet' and input_shape and len(input_shape) == 3:
        if data_format == 'channels_first':
            if input_shape[0] not in {1, 3}:
                warnings.warn(
                    'This model usually expects 1 or 3 input channels. '
                    'However, it was passed an input_shape with ' +
                    str(input_shape[0]) + ' input channels.')
            default_shape = (input_shape[0], default_size, default_size)
        else:
            if input_shape[-1] not in {1, 3}:
                warnings.warn(
                    'This model usually expects 1 or 3 input channels. '
                    'However, it was passed an input_shape with ' +
                    str(input_shape[-1]) + ' input channels.')
            default_shape = (default_size, default_size, input_shape[-1])
    else:
        if data_format == 'channels_first':
            default_shape = (3, default_size, default_size)
        else:
            default_shape = (default_size, default_size, 3)
    if weights == 'imagenet' and require_flatten:
        if input_shape is not None:
            if input_shape != default_shape:
                raise ValueError('When setting`include_top=True` '
                                 'and loading `imagenet` weights, '
                                 '`input_shape` should be ' +
                                 str(default_shape) + '.')
        return default_shape
    if input_shape:
        if data_format == 'channels_first':
            if input_shape is not None:
                if len(input_shape) != 3:
                    raise ValueError(
                        '`input_shape` must be a tuple of three integers.')
                if input_shape[0] != 3 and weights == 'imagenet':
                    raise ValueError('The input must have 3 channels; got '
                                     '`input_shape=' + str(input_shape) + '`')
                if ((input_shape[1] is not None and input_shape[1] < min_size) or
                   (input_shape[2] is not None and input_shape[2] < min_size)):
                    raise ValueError('Input size must be at least ' +
                                     str(min_size) + 'x' + str(min_size) + '; got '
                                     '`input_shape=' + str(input_shape) + '`')
        else:
            if input_shape is not None:
                if len(input_shape) != 3:
                    raise ValueError(
                        '`input_shape` must be a tuple of three integers.')
                if input_shape[-1] != 3 and weights == 'imagenet':
                    raise ValueError('The input must have 3 channels; got '
                                     '`input_shape=' + str(input_shape) + '`')
                if ((input_shape[0] is not None and input_shape[0] < min_size) or
                   (input_shape[1] is not None and input_shape[1] < min_size)):
                    raise ValueError('Input size must be at least ' +
                                     str(min_size) + 'x' + str(min_size) + '; got '
                                     '`input_shape=' + str(input_shape) + '`')
    else:
        if require_flatten:
            input_shape = default_shape
        else:
            if data_format == 'channels_first':
                input_shape = (3, None, None)
            else:
                input_shape = (None, None, 3)
    if require_flatten:
        if None in input_shape:
            raise ValueError('If `include_top` is True, '
                             'you should specify a static `input_shape`. '
                             'Got `input_shape=' + str(input_shape) + '`')
    return input_shape
