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/* \file
  \brief Provides several functions for filling tensors with data.
*/

#pragma once

// Standard Library includes
#include <utility>
#include <cstdlib>
#include <cmath>

// Hute includes
#include "hute/tensor.hpp"

// Hytlass includes
#include "hytlass/hytlass.h"
#include "hytlass/complex.h"
#include "hytlass/functional.h"
#include "hytlass/numeric_conversion.h"
#include "hytlass/array.h"
#include "hytlass/numeric_types.h"

///////////////////////////////////////////////////////////////////////////////////////////////////

namespace hytlass {
namespace reference {
namespace host {

///////////////////////////////////////////////////////////////////////////////////////////////////
//
// Tensor reductions
//
///////////////////////////////////////////////////////////////////////////////////////////////////

/// Transform-reduce operation over the elements of a tensor. This helper allocates the device-side
/// workspace
template <
  typename Tensor,
  typename ComputeType,
  typename ReduceOp,
  typename TransformOp
>
ComputeType TensorTransformReduce(
  Tensor view,
  ComputeType identity,
  ReduceOp reduce,
  TransformOp transform
) {

  for (int64_t idx = 0; idx < hute::size(view); ++idx) {
    identity = reduce(identity, transform(view(idx)));
  }

  return identity;
}

/// Transform-reduce operation over the elements of a tensor. This helper allocates the device-side
/// workspace
template <
  typename TensorA,
  typename TensorB,
  typename ComputeType,
  typename ReduceOp,
  typename TransformOp
>
ComputeType TensorTransformReduce(
  TensorA view_A,
  TensorB view_B,
  ComputeType identity,
  ReduceOp reduce,
  TransformOp transform) {
  
  if (hute::size(view_A) != hute::size(view_B)) {
    throw std::runtime_error("Tensor sizes must match.");
  }

  for (int64_t idx = 0; idx < hute::size(view_A); ++idx) {
    identity = reduce(identity, transform(view_A(idx), view_B(idx)));
  }

  return identity;
}

/// Helper to compute the sum of the elements of a tensor
template <
  typename Tensor,
  typename ComputeType = typename Tensor::value_type
>
ComputeType TensorSum(
  Tensor view,
  ComputeType identity = ComputeType()
) {

  plus<ComputeType> reduce;
  NumericConverter<ComputeType, typename Tensor::value_type> transform;

  return TensorTransformReduce(
    view, identity, reduce, transform);
}

/// Helper to compute the sum of the squares of the elements of a tensor
template <
  typename Tensor,
  typename ComputeType = typename Tensor::value_type
>
ComputeType TensorSumSq(
  Tensor view,
  ComputeType identity = ComputeType()
) {

  plus<ComputeType> reduce;
  magnitude_squared<typename Tensor::value_type, ComputeType> transform;

  return TensorTransformReduce(
    view, identity, reduce, transform);
}

/// Helper to compute the norm of the elements of a tensor.
template <
  typename Tensor,
  typename ComputeType = double
>
ComputeType TensorNorm(
  Tensor view,
  ComputeType identity = ComputeType()
) {

  return std::sqrt(TensorSumSq(view, identity));
}

/// Helper to compute the sum of the squares of the differences of two tensors
template <
  typename TensorA,
  typename TensorB,
  typename ComputeType = double
>
ComputeType TensorSumSqDiff(
  TensorA view_A,
  TensorB view_B,
  ComputeType identity = ComputeType()
) {

  plus<ComputeType> reduce;
  magnitude_squared_difference<typename TensorA::value_type, ComputeType> transform;

  return TensorTransformReduce(
    view_A, view_B, identity, reduce, transform);
}


/// Helper to compute the norm of the tensor computed as the difference of two tensors in memory
template <
  typename TensorA,
  typename TensorB,
  typename ComputeType = double
>
ComputeType TensorNormDiff(
  TensorA view_A,
  TensorB view_B,
  ComputeType identity = ComputeType()
) {

  return std::sqrt(TensorSumSqDiff(view_A, view_B, identity));
}

///////////////////////////////////////////////////////////////////////////////////////////////////

} // namespace host
} // namespace reference
} // namespace hytlass

///////////////////////////////////////////////////////////////////////////////////////////////////
