//  Copyright (c) 2017 Ajai V George
//
//  SPDX-License-Identifier: BSL-1.0
//  Distributed under the Boost Software License, Version 1.0. (See accompanying
//  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)

#pragma once

#include <hpx/config.hpp>
#include <hpx/algorithms/traits/segmented_iterator_traits.hpp>

#include <hpx/executors/execution_policy.hpp>
#include <hpx/parallel/algorithms/detail/dispatch.hpp>
#include <hpx/parallel/algorithms/find.hpp>
#include <hpx/parallel/segmented_algorithms/detail/dispatch.hpp>
#include <hpx/parallel/util/detail/algorithm_result.hpp>
#include <hpx/parallel/util/detail/handle_remote_exceptions.hpp>

#include <algorithm>
#include <exception>
#include <iterator>
#include <list>
#include <numeric>
#include <type_traits>
#include <utility>
#include <vector>

namespace hpx { namespace parallel {
    ///////////////////////////////////////////////////////////////////////////
    // segmented_find
    namespace detail {
        template <typename Algo, typename ExPolicy, typename FwdIter,
            typename U>
        inline typename util::detail::algorithm_result<ExPolicy, FwdIter>::type
        segmented_find(Algo&& algo, ExPolicy&& policy, FwdIter first,
            FwdIter last, U&& f_or_val, std::true_type)
        {
            typedef hpx::traits::segmented_iterator_traits<FwdIter> traits;
            typedef typename traits::segment_iterator segment_iterator;
            typedef typename traits::local_iterator local_iterator_type;
            typedef util::detail::algorithm_result<ExPolicy, FwdIter> result;

            segment_iterator sit = traits::segment(first);
            segment_iterator send = traits::segment(last);
            FwdIter output = last;
            if (sit == send)
            {
                // all elements are on the same partition
                local_iterator_type beg = traits::local(first);
                local_iterator_type end = traits::local(last);
                if (beg != end)
                {
                    local_iterator_type out = dispatch(traits::get_id(sit),
                        algo, policy, std::true_type(), beg, end, f_or_val);
                    output = traits::compose(send, out);
                }
            }
            else
            {
                // handle the remaining part of the first partition
                local_iterator_type beg = traits::local(first);
                local_iterator_type end = traits::end(sit);
                local_iterator_type out = traits::local(last);
                bool found = false;
                if (beg != end)
                {
                    out = dispatch(traits::get_id(sit), algo, policy,
                        std::true_type(), beg, end, f_or_val);
                    if (out != end)
                        found = true;
                }
                if (!found)
                {
                    // handle all of the full partitions
                    for (++sit; sit != send; ++sit)
                    {
                        beg = traits::begin(sit);
                        end = traits::end(sit);
                        out = traits::begin(send);
                        if (beg != end)
                        {
                            out = dispatch(traits::get_id(sit), algo, policy,
                                std::true_type(), beg, end, f_or_val);
                            if (out != end)
                            {
                                found = true;
                                break;
                            }
                        }
                    }
                }
                if (!found)
                {
                    // handle the beginning of the last partition
                    beg = traits::begin(sit);
                    end = traits::local(last);
                    if (beg != end)
                    {
                        out = dispatch(traits::get_id(sit), algo, policy,
                            std::true_type(), beg, end, f_or_val);
                        if (out != end)
                            found = true;
                    }
                }
                if (found)
                    output = traits::compose(sit, out);
            }
            return result::get(HPX_MOVE(output));
        }

        template <typename Algo, typename ExPolicy, typename FwdIter,
            typename U>
        inline typename util::detail::algorithm_result<ExPolicy, FwdIter>::type
        segmented_find(Algo&& algo, ExPolicy&& policy, FwdIter first,
            FwdIter last, U&& f_or_val, std::false_type)
        {
            typedef hpx::traits::segmented_iterator_traits<FwdIter> traits;
            typedef typename traits::segment_iterator segment_iterator;
            typedef typename traits::local_iterator local_iterator_type;
            typedef util::detail::algorithm_result<ExPolicy, FwdIter> result;

            typedef std::integral_constant<bool,
                !hpx::traits::is_forward_iterator<FwdIter>::value>
                forced_seq;

            segment_iterator sit = traits::segment(first);
            segment_iterator send = traits::segment(last);

            std::vector<future<FwdIter>> segments;
            segments.reserve(std::distance(sit, send));

            if (sit == send)
            {
                // all elements are on the same partition
                local_iterator_type beg = traits::local(first);
                local_iterator_type end = traits::local(last);
                if (beg != end)
                {
                    segments.push_back(hpx::make_future<FwdIter>(
                        dispatch_async(traits::get_id(sit), algo, policy,
                            forced_seq(), beg, end, f_or_val),
                        [send, end, last](
                            local_iterator_type const& out) -> FwdIter {
                            if (out != end)
                                return traits::compose(send, out);
                            else
                                return last;
                        }));
                }
            }
            else
            {
                // handle the remaining part of the first partition
                local_iterator_type beg = traits::local(first);
                local_iterator_type end = traits::end(sit);
                if (beg != end)
                {
                    segments.push_back(hpx::make_future<FwdIter>(
                        dispatch_async(traits::get_id(sit), algo, policy,
                            forced_seq(), beg, end, f_or_val),
                        [sit, end, last](
                            local_iterator_type const& out) -> FwdIter {
                            if (out != end)
                                return traits::compose(sit, out);
                            else
                                return last;
                        }));
                }

                // handle all of the full partitions
                for (++sit; sit != send; ++sit)
                {
                    beg = traits::begin(sit);
                    end = traits::end(sit);
                    if (beg != end)
                    {
                        segments.push_back(hpx::make_future<FwdIter>(
                            dispatch_async(traits::get_id(sit), algo, policy,
                                forced_seq(), beg, end, f_or_val),
                            [sit, end, last](
                                local_iterator_type const& out) -> FwdIter {
                                if (out != end)
                                    return traits::compose(sit, out);
                                else
                                    return last;
                            }));
                    }
                }

                // handle the beginning of the last partition
                beg = traits::begin(sit);
                end = traits::local(last);
                if (beg != end)
                {
                    segments.push_back(hpx::make_future<FwdIter>(
                        dispatch_async(traits::get_id(sit), algo, policy,
                            forced_seq(), beg, end, f_or_val),
                        [sit, end, last](
                            local_iterator_type const& out) -> FwdIter {
                            if (out != end)
                                return traits::compose(sit, out);
                            else
                                return last;
                        }));
                }
            }
            return result::get(dataflow(
                [=](std::vector<hpx::future<FwdIter>>&& r) -> FwdIter {
                    // handle any remote exceptions, will throw on error
                    std::list<std::exception_ptr> errors;
                    parallel::util::detail::handle_remote_exceptions<
                        ExPolicy>::call(r, errors);

                    std::vector<FwdIter> res = hpx::unwrap(HPX_MOVE(r));
                    auto it = res.begin();
                    while (it != res.end())
                    {
                        if (*it != last)
                            return *it;
                        it++;
                    }
                    return res.back();
                },
                HPX_MOVE(segments)));
        }
    }    // namespace detail
}}       // namespace hpx::parallel

// The segmented iterators we support all live in namespace hpx::segmented
namespace hpx { namespace segmented {

    // clang-format off
    template <typename SegIter, typename T,
        HPX_CONCEPT_REQUIRES_(
            hpx::traits::is_iterator<SegIter>::value &&
            hpx::traits::is_segmented_iterator<SegIter>::value
        )>
    // clang-format on
    SegIter tag_invoke(hpx::find_t, SegIter first, SegIter last, T const& val)
    {
        static_assert(hpx::traits::is_input_iterator<SegIter>::value,
            "Requires at least input iterator.");

        if (first == last)
        {
            return first;
        }

        using iterator_traits = hpx::traits::segmented_iterator_traits<SegIter>;

        return hpx::parallel::detail::segmented_find(
            hpx::parallel::detail::find<
                typename iterator_traits::local_iterator>(),
            hpx::execution::seq, first, last, val, std::true_type{});
    }

    // clang-format off
    template <typename ExPolicy, typename SegIter, typename T,
        HPX_CONCEPT_REQUIRES_(
            hpx::is_execution_policy<ExPolicy>::value &&
            hpx::traits::is_iterator<SegIter>::value &&
            hpx::traits::is_segmented_iterator<SegIter>::value
        )>
    // clang-format on
    typename parallel::util::detail::algorithm_result<ExPolicy, SegIter>::type
    tag_invoke(hpx::find_t, ExPolicy&& policy, SegIter first, SegIter last,
        T const& val)
    {
        static_assert(hpx::traits::is_forward_iterator<SegIter>::value,
            "Requires at least forward iterator.");

        using is_seq = hpx::is_sequenced_execution_policy<ExPolicy>;

        if (first == last)
        {
            return parallel::util::detail::algorithm_result<ExPolicy,
                SegIter>::get(HPX_FORWARD(SegIter, first));
        }

        typedef hpx::traits::segmented_iterator_traits<SegIter> iterator_traits;

        return hpx::parallel::detail::segmented_find(
            hpx::parallel::detail::find<
                typename iterator_traits::local_iterator>(),
            HPX_FORWARD(ExPolicy, policy), first, last, val, is_seq());
    }

    // clang-format off
    template <typename FwdIter, typename F,
        HPX_CONCEPT_REQUIRES_(
            hpx::traits::is_iterator<FwdIter>::value &&
            hpx::traits::is_segmented_iterator<FwdIter>::value
        )>
    // clang-format on
    FwdIter tag_invoke(hpx::find_if_t, FwdIter first, FwdIter last, F&& f)
    {
        static_assert(hpx::traits::is_input_iterator<FwdIter>::value,
            "Requires at least input iterator.");

        if (first == last)
        {
            return first;
        }

        using iterator_traits = hpx::traits::segmented_iterator_traits<FwdIter>;

        return hpx::parallel::detail::segmented_find(
            hpx::parallel::detail::find_if<
                typename iterator_traits::local_iterator>(),
            hpx::execution::seq, first, last, HPX_FORWARD(F, f),
            std::true_type{});
    }

    // clang-format off
    template <typename ExPolicy, typename FwdIter, typename F,
        HPX_CONCEPT_REQUIRES_(
            hpx::is_execution_policy<ExPolicy>::value &&
            hpx::traits::is_iterator<FwdIter>::value &&
            hpx::traits::is_segmented_iterator<FwdIter>::value
        )>
    // clang-format on
    typename parallel::util::detail::algorithm_result<ExPolicy, FwdIter>::type
    tag_invoke(
        hpx::find_if_t, ExPolicy&& policy, FwdIter first, FwdIter last, F&& f)
    {
        static_assert(hpx::traits::is_forward_iterator<FwdIter>::value,
            "Requires at least forward iterator.");

        using is_seq = hpx::is_sequenced_execution_policy<ExPolicy>;

        if (first == last)
        {
            return parallel::util::detail::algorithm_result<ExPolicy,
                FwdIter>::get(HPX_FORWARD(FwdIter, first));
        }

        using iterator_traits = hpx::traits::segmented_iterator_traits<FwdIter>;

        return hpx::parallel::detail::segmented_find(
            hpx::parallel::detail::find_if<
                typename iterator_traits::local_iterator>(),
            HPX_FORWARD(ExPolicy, policy), first, last, HPX_FORWARD(F, f),
            is_seq());
    }

    // clang-format off
    template <typename FwdIter, typename F,
        HPX_CONCEPT_REQUIRES_(
            hpx::traits::is_iterator<FwdIter>::value &&
            hpx::traits::is_segmented_iterator<FwdIter>::value
        )>
    // clang-format on
    FwdIter tag_invoke(hpx::find_if_not_t, FwdIter first, FwdIter last, F&& f)
    {
        static_assert(hpx::traits::is_input_iterator<FwdIter>::value,
            "Requires at least input iterator.");

        if (first == last)
        {
            return first;
        }

        using iterator_traits = hpx::traits::segmented_iterator_traits<FwdIter>;

        return hpx::parallel::detail::segmented_find(
            hpx::parallel::detail::find_if_not<
                typename iterator_traits::local_iterator>(),
            hpx::execution::seq, first, last, HPX_FORWARD(F, f),
            std::true_type{});
    }

    // clang-format off
    template <typename ExPolicy, typename FwdIter, typename F,
        HPX_CONCEPT_REQUIRES_(
            hpx::is_execution_policy<ExPolicy>::value &&
            hpx::traits::is_iterator<FwdIter>::value &&
            hpx::traits::is_segmented_iterator<FwdIter>::value
        )>
    // clang-format on
    typename parallel::util::detail::algorithm_result<ExPolicy, FwdIter>::type
    tag_invoke(hpx::find_if_not_t, ExPolicy&& policy, FwdIter first,
        FwdIter last, F&& f)
    {
        static_assert(hpx::traits::is_forward_iterator<FwdIter>::value,
            "Requires at least forward iterator.");

        using is_seq = hpx::is_sequenced_execution_policy<ExPolicy>;

        if (first == last)
        {
            return parallel::util::detail::algorithm_result<ExPolicy,
                FwdIter>::get(HPX_FORWARD(FwdIter, first));
        }

        using iterator_traits = hpx::traits::segmented_iterator_traits<FwdIter>;

        return hpx::parallel::detail::segmented_find(
            hpx::parallel::detail::find_if_not<
                typename iterator_traits::local_iterator>(),
            HPX_FORWARD(ExPolicy, policy), first, last, HPX_FORWARD(F, f),
            is_seq());
    }
}}    // namespace hpx::segmented
