Containers.h

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#ifndef INCLUDE_MOLASSEMBLER_TEMPLE_CONSTEXPR_CONTAINERS_H
#define INCLUDE_MOLASSEMBLER_TEMPLE_CONSTEXPR_CONTAINERS_H

#include "Molassembler/Temple/Preprocessor.h"

#include <array>
#include <limits>
#include <functional>

namespace Scine {
namespace Molassembler {
namespace Temple {
namespace Traits {

template<class Function, typename ...Args>
using functionReturnType = std::result_of_t<Function(Args...)>;

} // namespace Traits

namespace Detail {

template<
  template<typename, std::size_t> class ArrayType,
  typename T,
  std::size_t size,
  class UnaryFunction,
  std::size_t ... Inds
> constexpr auto mapImpl(
  const ArrayType<T, size>& array,
  UnaryFunction&& function,
  std::index_sequence<Inds...> /* inds */
) {
  return ArrayType<
    Traits::functionReturnType<UnaryFunction, T>,
    size
  > {
    function(array.at(Inds))...
  };
}

} // namespace Detail

template<
  template<typename, std::size_t> class ArrayType,
  typename T,
  std::size_t size,
  class UnaryFunction
> constexpr auto map(
  const ArrayType<T, size>& array,
  UnaryFunction&& function
) {
  return Detail::mapImpl(
    array,
    std::forward<UnaryFunction>(function),
    std::make_index_sequence<size>{}
  );
}

template<
  template<typename, std::size_t> class ArrayType,
  typename T,
  std::size_t size,
  class BinaryFunction
> constexpr T reduce(
  const ArrayType<T, size>& array,
  T init,
  BinaryFunction&& reduction
) {
  for(const auto& element : array) {
    init = reduction(init, element);
  }

  return init;
}

template<
  template<typename, std::size_t> class ArrayType,
  typename T,
  std::size_t size
> constexpr T sum(const ArrayType<T, size>& array) {
  T sum {0};

  for(unsigned i = 0; i < size; ++i) {
    sum += array.at(i);
  }

  return sum;
}

namespace Detail {


template<
  template<typename, std::size_t> class ArrayType,
  typename T,
  std::size_t size,
  std::size_t ... Inds
> constexpr ArrayType<T, size> iotaHelper(
  std::index_sequence<Inds...> /* inds */
) {
  return ArrayType<T, size> { static_cast<T>(Inds)...  };
}

} // namespace Detail

template<
  template<typename, std::size_t> class ArrayType,
  typename T,
  std::size_t size
> PURITY_STRONG constexpr std::enable_if_t<
  std::is_arithmetic<T>::value,
  ArrayType<T, size>
> iota() {
  return Detail::iotaHelper<ArrayType, T, size>(
    std::make_index_sequence<size>()
  );
}

namespace Detail {

template<
  template<typename, std::size_t> class ArrayType,
  typename T,
  std::size_t begin,
  std::size_t end,
  std::size_t ... Inds
> constexpr ArrayType<T, (end - begin)> rangeHelper(
  std::index_sequence<Inds...> /* inds */
) {
  return ArrayType<T, (end - begin)> {
    (begin + Inds)...
  };
}

} // namespace Detail

template<
  template<typename, std::size_t> class ArrayType,
  typename T,
  std::size_t begin, // inclusive
  std::size_t end // exclusive
> constexpr ArrayType<T, (end - begin)> range() {
  return Detail::rangeHelper<ArrayType, T, begin, end>(
    std::make_index_sequence<(end - begin)>()
  );
}

namespace Detail {

template<
  template<typename, std::size_t> class ArrayType,
  typename T,
  std::size_t N1,
  std::size_t... AIndices,
  std::size_t N2,
  std::size_t... BIndices
>
constexpr ArrayType<T, N1+N2> arrayConcatenateImpl(
  const ArrayType<T, N1>& a,
  const ArrayType<T, N2>& b,
  std::index_sequence<AIndices...> /* aInds */,
  std::index_sequence<BIndices...> /* bInds */
) {
  return {
    a.at(AIndices)...,
    b.at(BIndices)...
  };
}

} // namespace Detail

template<
  template<typename, std::size_t> class ArrayType,
  typename T,
  std::size_t N1,
  std::size_t N2
>
constexpr ArrayType<T, N1+N2> arrayConcatenate(
  const ArrayType<T, N1>& a,
  const ArrayType<T, N2>& b
) {
  return Detail::arrayConcatenateImpl(
    a,
    b,
    std::make_index_sequence<N1>{},
    std::make_index_sequence<N2>{}
  );
}

namespace Detail {

template<
  template<typename, std::size_t> class ArrayType,
  typename T,
  std::size_t concatenatedSize
> constexpr ArrayType<T, concatenatedSize> concatenateHelper(
  const ArrayType<T, concatenatedSize>& concatenated
) {
  return concatenated;
}

template<
  template<typename, std::size_t> class ArrayType,
  typename T,
  std::size_t concatenatedSize,
  std::size_t curSize,
  std::size_t ... Ns
> constexpr auto concatenateHelper(
  const ArrayType<T, concatenatedSize>& concatenated,
  const ArrayType<T, curSize>& array,
  const ArrayType<T, Ns>& ... arrays
) {
  return concatenateHelper(
    arrayConcatenate(
      concatenated,
      array
    ),
    arrays...
  );
}

} // namespace Detail

template<
  template<typename, std::size_t> class ArrayType,
  typename T,
  std::size_t N,
  std::size_t ... Ns
> constexpr auto arrayConcatenate(
  const ArrayType<T, N>& startingArray,
  const ArrayType<T, Ns>& ... remainingArrays
) {
  return Detail::concatenateHelper(startingArray, remainingArrays...);
}

template<
  template<typename, std::size_t> class ArrayType,
  typename T,
  std::size_t size
> constexpr bool arraysEqual(
  const ArrayType<T, size>& a,
  const ArrayType<T, size>& b
) {
  for(unsigned i = 0; i < size; ++i) {
    if(a.at(i) != b.at(i)) {
      return false;
    }
  }

  return true;
}

template<
  template<typename, std::size_t> class ArrayType,
  typename T,
  std::size_t sizeA,
  std::size_t sizeB
> constexpr std::enable_if_t<
  sizeA == sizeB,
  bool
> arraysLess(
  const ArrayType<T, sizeA>& a,
  const ArrayType<T, sizeB>& b
) {
  for(unsigned i = 0; i < sizeA; ++i) {
    if(!(a.at(i) < b.at(i))) {
      return false;
    }
  }

  return true;
}

template<
  template<typename, std::size_t> class ArrayType,
  typename T,
  std::size_t sizeA,
  std::size_t sizeB
> constexpr std::enable_if_t<
  sizeA < sizeB,
  bool
> arraysLess(
  const ArrayType<T, sizeA>& /* a */,
  const ArrayType<T, sizeB>& /* b */
) {
  return true;
}

template<
  template<typename, std::size_t> class ArrayType,
  typename T,
  std::size_t sizeA,
  std::size_t sizeB
> constexpr std::enable_if_t<
  (sizeA > sizeB),
  bool
> arraysLess(
  const ArrayType<T, sizeA>& /* a */,
  const ArrayType<T, sizeB>& /* b */
) {
  return false;
}

// C++17: Replace all arraysLess functions with this single function below:
/*template<
  template<typename, std::size_t> class ArrayType,
  typename T,
  std::size_t sizeA,
  std::size_t sizeB
> constexpr std::enable_if_t<
  (sizeA > sizeB),
  bool
> arraysLess(
  const ArrayType<T, sizeA>& a,
  const ArrayType<T, sizeB>& b
) {
  if constexpr(sizeA < sizeB) {
    return true;
  } else if constexpr(sizeA > sizeB) {
    return false;
  } else { // sizes equal
    for(unsigned i = 0; i < sizeA; ++i) {
      if(!(a.at(i) < b.at(i))) {
        return false;
      }
    }

    return true;
  }
}*/

template<
  typename T,
  class LessThanPredicate,
  class Iter
> constexpr Iter lowerBound(
  Iter bound,
  Iter last,
  const T& item,
  LessThanPredicate predicate
) {
  using DiffType = decltype(last - bound);
  static_assert(
    std::is_signed<DiffType>::value,
    "Difference between iterators must be a signed type!"
  );

  Iter it = bound;
  DiffType count = last - bound;
  DiffType step = 0;

  while(count > 0) {
    it = bound;
    step = count / 2;
    it += step; // C++17 std::advance (differentiates between RandomAccess / linear)

    if(predicate(*it, item)) {
      ++it;
      bound = it;
      count -= step + 1;
    } else {
      count = step;
    }
  }

  return bound;
}

template<
  class Container,
  typename T,
  class LessThanPredicate = std::less<>
> constexpr typename Container::const_iterator binarySearch(
  const Container& container,
  const T& item,
  LessThanPredicate predicate = LessThanPredicate()
) {
  auto bound = lowerBound<T, LessThanPredicate>(
    container.begin(),
    container.end(),
    item,
    predicate
  );

  /* Lower bound merely finds the first item not smaller than the sought one,
   * this does NOT mean that they're equal.
   *
   * a == b  <-->  !(a < b) && !(b < a)
   *
   * Lower bound guarantees the first condition of the right side, but we need
   * to check the second one to ensure that we have found what we seek, not just
   * merely something bigger than a.
   */
  if(predicate(item, *bound)) {
    return container.end();
  }

  return bound;
}

namespace Detail {
  template<class ContainerType>
  struct getValueTypeImpl {
    using type = typename std::remove_const<
      typename std::remove_reference<
        decltype(
          *(std::declval<ContainerType>()).begin()
        )
      >::type
    >::type;
  };
} // namespace Detail

template<class ContainerType>
using getValueType = typename Detail::getValueTypeImpl<ContainerType>::type;

template<
  class ContainerType,
  class LessThanComparator = std::less<
    getValueType<ContainerType>
  >
> constexpr bool isPartiallyOrdered(
  const ContainerType& container,
  LessThanComparator comparator = LessThanComparator {}
) {
  auto leftIter = container.begin();
  if(leftIter == container.end()) {
    return true;
  }

  auto rightIter = leftIter + 1;

  while(rightIter != container.end()) {
    // equivalent to *rightIter < *leftIter
    if(comparator(*rightIter, *leftIter)) {
      return false;
    }

    ++leftIter;
    ++rightIter;
  }

  return true;
}

template<
  class ContainerType,
  class LessThanComparator = std::less<
    getValueType<ContainerType>
  >
> constexpr bool isTotallyOrdered(
  const ContainerType& container,
  LessThanComparator comparator = LessThanComparator {}
) {
  auto leftIter = container.begin();
  if(leftIter == container.end()) {
    return true;
  }

  auto rightIter = leftIter + 1;


  while(rightIter != container.end()) {
    // Equivalent to !(*leftIter < *rightIter
    if(!comparator(*leftIter, *rightIter)) {
      return false;
    }

    ++leftIter;
    ++rightIter;
  }

  return true;
}

} // namespace Temple
} // namespace Molassembler
} // namespace Scine

#endif