#!/usr/bin/env python3
from typing import Any, Callable, List, Tuple, Union

import torch
from torch.nn import Module

from ..._utils.attribution import NeuronAttribution, PerturbationAttribution
from ..._utils.common import _verify_select_column
from ..._utils.gradient import _forward_layer_eval
from ..._utils.typing import BaselineType, TensorOrTupleOfTensorsGeneric
from ..feature_ablation import FeatureAblation


class NeuronFeatureAblation(NeuronAttribution, PerturbationAttribution):
    r"""
    A perturbation based approach to computing neuron attribution,
    involving replacing each input feature with a given baseline /
    reference, and computing the difference in the neuron's input / output.
    By default, each scalar value within
    each input tensor is taken as a feature and replaced independently. Passing
    a feature mask, allows grouping features to be ablated together. This can
    be used in cases such as images, where an entire segment or region
    can be ablated, measuring the importance of the segment (feature group).
    Each input scalar in the group will be given the same attribution value
    equal to the change in target as a result of ablating the entire feature
    group.
    """

    def __init__(
        self,
        forward_func: Callable,
        layer: Module,
        device_ids: Union[None, List[int]] = None,
    ) -> None:
        r"""
        Args:

            forward_func (callable):  The forward function of the model or any
                          modification of it
            layer (torch.nn.Module): Layer for which attributions are computed.
                          Attributions for a particular neuron in the input or output
                          of this layer are computed using the argument neuron_index
                          in the attribute method.
                          Currently, it is assumed that the inputs or the outputs
                          of the layer, depending on which one is used for
                          attribution, can only be a single tensor.
            device_ids (list(int)): Device ID list, necessary only if forward_func
                          applies a DataParallel model. This allows reconstruction of
                          intermediate outputs from batched results across devices.
                          If forward_func is given as the DataParallel model itself,
                          then it is not necessary to provide this argument.
        """
        NeuronAttribution.__init__(self, forward_func, layer, device_ids)
        PerturbationAttribution.__init__(self, forward_func)

    def attribute(
        self,
        inputs: TensorOrTupleOfTensorsGeneric,
        neuron_index: Union[int, Tuple[int, ...]],
        baselines: BaselineType = None,
        additional_forward_args: Any = None,
        feature_mask: Union[None, TensorOrTupleOfTensorsGeneric] = None,
        attribute_to_neuron_input: bool = False,
        perturbations_per_eval: int = 1,
    ) -> TensorOrTupleOfTensorsGeneric:
        r"""
        Args:

            inputs (tensor or tuple of tensors):  Input for which neuron
                        attributions are computed. If forward_func takes a single
                        tensor as input, a single input tensor should be provided.
                        If forward_func takes multiple tensors as input, a tuple
                        of the input tensors should be provided. It is assumed
                        that for all given input tensors, dimension 0 corresponds
                        to the number of examples, and if multiple input tensors
                        are provided, the examples must be aligned appropriately.
            neuron_index (int or tuple): Index of neuron in output of given
                            layer for which attribution is desired. The length of
                            this tuple must be one less than the number of
                            dimensions in the output of the given layer (since
                            dimension 0 corresponds to number of examples).
                            An integer may be provided instead of a tuple of
                            length 1.
            baselines (scalar, tensor, tuple of scalars or tensors, optional):
                        Baselines define reference value which replaces each
                        feature when ablated.
                        Baselines can be provided as:

                        - a single tensor, if inputs is a single tensor, with
                          exactly the same dimensions as inputs or
                          broadcastable to match the dimensions of inputs

                        - a single scalar, if inputs is a single tensor, which will
                          be broadcasted for each input value in input tensor.

                        - a tuple of tensors or scalars, the baseline corresponding
                          to each tensor in the inputs' tuple can be:

                          - either a tensor with matching dimensions to
                            corresponding tensor in the inputs' tuple
                            or the first dimension is one and the remaining
                            dimensions match with the corresponding
                            input tensor.

                          - or a scalar, corresponding to a tensor in the
                            inputs' tuple. This scalar value is broadcasted
                            for corresponding input tensor.
                        In the cases when `baselines` is not provided, we internally
                        use zero scalar corresponding to each input tensor.
                        Default: None
            additional_forward_args (any, optional): If the forward function
                        requires additional arguments other than the inputs for
                        which attributions should not be computed, this argument
                        can be provided. It must be either a single additional
                        argument of a Tensor or arbitrary (non-tuple) type or a
                        tuple containing multiple additional arguments including
                        tensors or any arbitrary python types. These arguments
                        are provided to forward_func in order following the
                        arguments in inputs.
                        Note that attributions are not computed with respect
                        to these arguments.
                        Default: None
            feature_mask (tensor or tuple of tensors, optional):
                        feature_mask defines a mask for the input, grouping
                        features which should be ablated together. feature_mask
                        should contain the same number of tensors as inputs.
                        Each tensor should
                        be the same size as the corresponding input or
                        broadcastable to match the input tensor. Each tensor
                        should contain integers in the range 0 to num_features
                        - 1, and indices corresponding to the same feature should
                        have the same value.
                        Note that features within each input tensor are ablated
                        independently (not across tensors).
                        If None, then a feature mask is constructed which assigns
                        each scalar within a tensor as a separate feature, which
                        is ablated independently.
                        Default: None
            attribute_to_neuron_input (bool, optional): Indicates whether to
                        compute the attributions with respect to the neuron input
                        or output. If `attribute_to_neuron_input` is set to True
                        then the attributions will be computed with respect to
                        neuron's inputs, otherwise it will be computed with respect
                        to neuron's outputs.
                        Note that currently it is assumed that either the input
                        or the output of internal neurons, depending on whether we
                        attribute to the input or output, is a single tensor.
                        Support for multiple tensors will be added later.
                        Default: False
            perturbations_per_eval (int, optional): Allows ablation of multiple
                        features to be processed simultaneously in one call to
                        forward_fn.
                        Each forward pass will contain a maximum of
                        perturbations_per_eval * #examples samples.
                        For DataParallel models, each batch is split among the
                        available devices, so evaluations on each available
                        device contain at most
                        (perturbations_per_eval * #examples) / num_devices
                        samples.
                        Default: 1

        Returns:
            *tensor* or tuple of *tensors* of **attributions**:
            - **attributions** (*tensor* or tuple of *tensors*):
                        Attributions of particular neuron with respect to each input
                        feature. Attributions will always be the same size as the
                        provided inputs, with each value providing the attribution
                        of the corresponding input index.
                        If a single tensor is provided as inputs, a single tensor is
                        returned. If a tuple is provided for inputs, a tuple of
                        corresponding sized tensors is returned.

        Examples::

            >>> # SimpleClassifier takes a single input tensor of size Nx4x4,
            >>> # and returns an Nx3 tensor of class probabilities.
            >>> # It contains an attribute conv1, which is an instance of nn.conv2d,
            >>> # and the output of this layer has dimensions Nx12x3x3.
            >>> net = SimpleClassifier()
            >>> # Generating random input with size 2 x 4 x 4
            >>> input = torch.randn(2, 4, 4)
            >>> # Defining NeuronFeatureAblation interpreter
            >>> ablator = NeuronFeatureAblation(net, net.conv1)
            >>> # To compute neuron attribution, we need to provide the neuron
            >>> # index for which attribution is desired. Since the layer output
            >>> # is Nx12x3x3, we need a tuple in the form (0..11,0..2,0..2)
            >>> # which indexes a particular neuron in the layer output.
            >>> # For this example, we choose the index (4,1,2).
            >>> # Computes neuron gradient for neuron with
            >>> # index (4,1,2).
            >>> # Computes ablation attribution, ablating each of the 16
            >>> # scalar inputs independently.
            >>> attr = ablator.attribute(input, neuron_index=(4,1,2))

            >>> # Alternatively, we may want to ablate features in groups, e.g.
            >>> # grouping each 2x2 square of the inputs and ablating them together.
            >>> # This can be done by creating a feature mask as follows, which
            >>> # defines the feature groups, e.g.:
            >>> # +---+---+---+---+
            >>> # | 0 | 0 | 1 | 1 |
            >>> # +---+---+---+---+
            >>> # | 0 | 0 | 1 | 1 |
            >>> # +---+---+---+---+
            >>> # | 2 | 2 | 3 | 3 |
            >>> # +---+---+---+---+
            >>> # | 2 | 2 | 3 | 3 |
            >>> # +---+---+---+---+
            >>> # With this mask, all inputs with the same value are ablated
            >>> # simultaneously, and the attribution for each input in the same
            >>> # group (0, 1, 2, and 3) per example are the same.
            >>> # The attributions can be calculated as follows:
            >>> # feature mask has dimensions 1 x 4 x 4
            >>> feature_mask = torch.tensor([[[0,0,1,1],[0,0,1,1],
            >>>                             [2,2,3,3],[2,2,3,3]]])
            >>> attr = ablator.attribute(input, neuron_index=(4,1,2),
            >>>                          feature_mask=feature_mask)
        """

        def neuron_forward_func(*args: Any):
            with torch.no_grad():
                layer_eval, _ = _forward_layer_eval(
                    self.forward_func,
                    args,
                    self.layer,
                    device_ids=self.device_ids,
                    attribute_to_layer_input=attribute_to_neuron_input,
                )
                assert len(layer_eval) == 1, (
                    "Layers with multiple inputs /"
                    " outputs are not supported for neuron ablation."
                )
                return _verify_select_column(layer_eval[0], neuron_index)

        ablator = FeatureAblation(neuron_forward_func)

        return ablator.attribute(
            inputs,
            baselines=baselines,
            additional_forward_args=additional_forward_args,
            feature_mask=feature_mask,
            perturbations_per_eval=perturbations_per_eval,
        )
