#!/usr/bin/env python
import functools
import operator
import torch
from torch.autograd import grad
import numpy as np
from tqdm import *

def gather_nd(params, indices):
    """
    Args:
        params: Tensor to index
        indices: k-dimension tensor of integers. 
    Returns:
        output: 1-dimensional tensor of elements of ``params``, where
            output[i] = params[i][indices[i]]
            
            params   indices   output

            1 2       1 1       4
            3 4       2 0 ----> 5
            5 6       0 0       1
    """
    max_value = functools.reduce(operator.mul, list(params.size())) - 1
    indices = indices.t().long()
    ndim = indices.size(0)
    idx = torch.zeros_like(indices[0]).long()
    m = 1

    for i in range(ndim)[::-1]:
        idx += indices[i]*m
        m *= params.size(i)

    idx[idx < 0] = 0
    idx[idx > max_value] = 0
    return torch.take(params, idx)

class PathExplainerTorch(object):
    def __init__(self, model):
        self.model = model
        return
    
    def _get_ref_tensor(self,baseline,batch_size,num_samples):
        number_to_draw = num_samples * batch_size
        replace = baseline.shape[0] < number_to_draw
        sample_indices = np.random.choice(baseline.shape[0],
                                          size=number_to_draw,
                                          replace=replace)
        ref_tensor = baseline[sample_indices,:]
        
        return ref_tensor

    def _get_samples_input(self, input_tensor, baseline, 
                           num_samples, use_expectation):
        '''
        calculate interpolation points
        Args:
            input_tensor: Tensor of shape (batch, ...), where ... indicates
                          the input dimensions. 
            reference_tensor: A tensor of shape (batch, k, ...) where ... 
                indicates dimensions, and k represents the number of background 
                reference samples to draw per input in the batch.
        Returns: 
            samples_input: A tensor of shape (batch, k, ...) with the 
                interpolated points between input and ref.
            samples_delta: A tensor of shape (batch, 1, ...) with the
                difference between input and reference for each sample
        '''
        input_dims = list(input_tensor.size())[1:]
        num_input_dims = len(input_dims)
        batch_size = input_tensor.size()[0]
        
        if use_expectation:
            reference_tensor = self._get_ref_tensor(baseline,batch_size,num_samples)
            shape = reference_tensor.shape
            reference_tensor = reference_tensor.view(
                    batch_size, 
                    num_samples, 
                    *(shape[1:]))
            
            # Grab a [batch_size, k]-sized interpolation sample
            t_tensor = torch.FloatTensor(batch_size, num_samples).uniform_(0,1).to(reference_tensor.device)
            shape = [batch_size, num_samples] + [1] * num_input_dims
            interp_coef = t_tensor.view(*shape)

            # Evaluate the end points
            end_point_ref = (1.0 - interp_coef) * reference_tensor

            input_expand_mult = input_tensor.unsqueeze(1)
            end_point_input = interp_coef * input_expand_mult

            # Affine Combine
            samples_input = end_point_input + end_point_ref
            
        else:
            batch_size = input_tensor.size()[0]
            input_expand = input_tensor.unsqueeze(1)
            reps = np.ones(len(baseline.shape)).astype(int)
            reps[0] = batch_size
            reference_tensor = baseline.repeat(list(reps)).unsqueeze(1)
#             reference_tensor = torch.as_tensor(sampled_baseline).unsqueeze(1).to(baseline.device)
            scaled_inputs = [reference_tensor + (float(i)/(num_samples-1))*(input_expand - reference_tensor) \
                             for i in range(0,num_samples)]
            samples_input = torch.cat(scaled_inputs,dim=1)
        
        samples_delta = self._get_samples_delta(input_tensor, reference_tensor)
        samples_delta = samples_delta.to(samples_input.device)
        
        return samples_input, samples_delta
    
    def _get_samples_delta(self, input_tensor, reference_tensor):
        input_expand_mult = input_tensor.unsqueeze(1)
        sd = input_expand_mult - reference_tensor
        return sd
    
    def _get_grads(self, samples_input, output_indices=None):

        grad_tensor = torch.zeros(samples_input.shape).float().to(samples_input.device)
        
        k_ = samples_input.shape[1]

        for i in range(k_):
            particular_slice = samples_input[:,i]
            batch_output = self.model(particular_slice)
            # should check that users pass in sparse labels
            # Only look at the user-specified label
            if batch_output.size(1) > 1:
                sample_indices = torch.arange(0,batch_output.size(0)).to(samples_input.device)
                indices_tensor = torch.cat([
                        sample_indices.unsqueeze(1), 
                        output_indices.unsqueeze(1)], dim=1)
                batch_output = gather_nd(batch_output, indices_tensor)

            model_grads = grad(
                    outputs=batch_output,
                    inputs=particular_slice,
                    grad_outputs=torch.ones_like(batch_output).to(samples_input.device),
                    create_graph=True)
            grad_tensor[:,i,:] = model_grads[0]
        return grad_tensor
           
    def attributions(self, input_tensor, baseline,
                     num_samples = 50, use_expectation=True, 
                     output_indices=None):
        """
        Calculate either Expected or Integrated Gradients approximation of 
        Aumann-Shapley values for the sample ``input_tensor``.

        Args:
            model (torch.nn.Module): Pytorch neural network model for which the
                output should be explained.
            input_tensor (torch.Tensor): Pytorch tensor representing the input
                to be explained.
            baseline (torch.Tensor): Pytorch tensor representing the baseline.
                If use_expectation is true, then baseline should be shape
                (num_refs, ...) where ... indicates the dimensionality
                of the input. Otherwise, baseline should be shape (1, ...).
            output_indices (optional, default=None): For multi-class prediction
        """
        equal_dims = baseline.shape[1:] == input_tensor.shape[1:]
        almost_equal_dims = baseline.shape == input_tensor.shape[1:]
        
        dev = input_tensor.device
        baseline = baseline.to(dev)
        
        input_tensor.requires_grad_ = True
        
        if use_expectation and not equal_dims:
            raise ValueError('baseline should be shape (num_refs, ...) \
                              where ... indicates the dimensionality   \
                              of the input')
            
        if not use_expectation and baseline.shape[0] != 1:
            if almost_equal_dims:
                baseline = baseline.unsqueeze(0)
            else:
                raise ValueError('baseline should be shape (...)           \
                                  where ... indicates the dimensionality   \
                                  of the input')
        
        samples_input, samples_delta = self._get_samples_input(input_tensor, baseline,
                                                               num_samples, use_expectation)
        grad_tensor = self._get_grads(samples_input, output_indices)
        mult_grads = samples_delta * grad_tensor
        attributions = mult_grads.mean(1)
        
        return attributions
    
    def interactions(self, input_tensor, baseline,
                     num_samples=50, use_expectation=True,
                     output_indices=None, interaction_index=None,
                     verbose=True):
        """
        samples_input: A tensor of shape (batch, k, features)
        ig_tensor: also size (batch, k, features), but contains IG values
        
        """
        
        if len(input_tensor.shape) != 2:
            raise ValueError('PyTorch Explainer only supports ' + \
                             'interaction for 2D input tensors!')
        
        equal_dims = baseline.shape[1:] == input_tensor.shape[1:]
        almost_equal_dims = baseline.shape == input_tensor.shape[1:]
        
        if use_expectation and not equal_dims:
            raise ValueError('baseline should be shape (num_refs, ...) \
                              where ... indicates the dimensionality   \
                              of the input')
            
        if not use_expectation and baseline.shape[0] != 1:
            if almost_equal_dims:
                baseline = baseline.unsqueeze(0)
            else:
                raise ValueError('baseline should be shape (...)           \
                                  where ... indicates the dimensionality   \
                                  of the input')
        
        inner_loop_nsamples = int(round(np.sqrt(num_samples)))
        
        samples_input, samples_delta = self._get_samples_input(input_tensor, baseline,
                                                               inner_loop_nsamples, use_expectation)
        
        if interaction_index is not None:
            interaction_mult_tensor = torch.zeros([input_tensor.size(0), samples_input.size(1), input_tensor.size(1)])
        else:
            interaction_mult_tensor = torch.zeros([input_tensor.size(0), samples_input.size(1), 
                                                   input_tensor.size(1), input_tensor.size(1)])
            
        ig_tensor = torch.zeros(samples_input.shape).float()
        
        if use_expectation:
            loop_num = inner_loop_nsamples
        else:
            loop_num = inner_loop_nsamples + 1
        
        if verbose:
            iterable = tqdm(range(loop_num))
        else:
            iterable = range(loop_num)
        
        for i in iterable:
            
            particular_slice = samples_input[:,i]
            ig_tensor[:,i,:] = self.attributions(particular_slice, baseline,
                                                 num_samples=inner_loop_nsamples, use_expectation=use_expectation,
                                                 output_indices=output_indices)
            
            if interaction_index is not None:
                second_grads = grad(
                        outputs=ig_tensor[:,i,interaction_index],
                        inputs=particular_slice,
                        grad_outputs=torch.ones_like(ig_tensor[:,i,interaction_index]),
                        create_graph=True)[0].detach()
                interaction_mult_tensor[:,i,:] = second_grads

            else:
                for feature in range(input_tensor.size(1)):
                    second_grads = grad(
                        outputs=ig_tensor[:,i,feature],
                        inputs=particular_slice,
                        grad_outputs=torch.ones_like(ig_tensor[:,i,feature]),
                        create_graph=True)[0].detach()
                    interaction_mult_tensor[:,i,feature,:] = second_grads

        interaction_mult_tensor = interaction_mult_tensor.to(samples_delta.device)
        if interaction_index is not None:
            interaction_tensor = interaction_mult_tensor * samples_delta
        else:
            interaction_tensor = interaction_mult_tensor * samples_delta.unsqueeze(2)
        interactions = interaction_tensor.mean(1)
        
        return interactions
