/*
 *  Copyright 2008-2013 NVIDIA Corporation
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */

/*! \file binary_search.h
 *  \brief Sequential implementation of binary search algorithms.
 */

#pragma once

#include <thrust/detail/config.h>

#include <thrust/advance.h>
#include <thrust/detail/function.h>
#include <thrust/distance.h>
#include <thrust/iterator/iterator_traits.h>

THRUST_NAMESPACE_BEGIN
namespace system
{
namespace detail
{
namespace sequential
{

THRUST_EXEC_CHECK_DISABLE
template <typename DerivedPolicy, typename ForwardIterator, typename T, typename StrictWeakOrdering>
THRUST_HOST_DEVICE ForwardIterator lower_bound(
  sequential::execution_policy<DerivedPolicy>&,
  ForwardIterator first,
  ForwardIterator last,
  const T& val,
  StrictWeakOrdering comp)
{
  // wrap comp
  thrust::detail::wrapped_function<StrictWeakOrdering, bool> wrapped_comp{comp};

  using difference_type = typename thrust::iterator_difference<ForwardIterator>::type;

  difference_type len = thrust::distance(first, last);

  while (len > 0)
  {
    difference_type half   = len >> 1;
    ForwardIterator middle = first;

    thrust::advance(middle, half);

    if (wrapped_comp(*middle, val))
    {
      first = middle;
      ++first;
      len = len - half - 1;
    }
    else
    {
      len = half;
    }
  }

  return first;
}

THRUST_EXEC_CHECK_DISABLE
template <typename DerivedPolicy, typename ForwardIterator, typename T, typename StrictWeakOrdering>
THRUST_HOST_DEVICE ForwardIterator upper_bound(
  sequential::execution_policy<DerivedPolicy>&,
  ForwardIterator first,
  ForwardIterator last,
  const T& val,
  StrictWeakOrdering comp)
{
  // wrap comp
  thrust::detail::wrapped_function<StrictWeakOrdering, bool> wrapped_comp{comp};

  using difference_type = typename thrust::iterator_difference<ForwardIterator>::type;

  difference_type len = thrust::distance(first, last);

  while (len > 0)
  {
    difference_type half   = len >> 1;
    ForwardIterator middle = first;

    thrust::advance(middle, half);

    if (wrapped_comp(val, *middle))
    {
      len = half;
    }
    else
    {
      first = middle;
      ++first;
      len = len - half - 1;
    }
  }

  return first;
}

THRUST_EXEC_CHECK_DISABLE
template <typename DerivedPolicy, typename ForwardIterator, typename T, typename StrictWeakOrdering>
THRUST_HOST_DEVICE bool binary_search(
  sequential::execution_policy<DerivedPolicy>& exec,
  ForwardIterator first,
  ForwardIterator last,
  const T& val,
  StrictWeakOrdering comp)
{
  ForwardIterator iter = sequential::lower_bound(exec, first, last, val, comp);

  // wrap comp
  thrust::detail::wrapped_function<StrictWeakOrdering, bool> wrapped_comp{comp};

  return iter != last && !wrapped_comp(val, *iter);
}

} // end namespace sequential
} // end namespace detail
} // end namespace system
THRUST_NAMESPACE_END
