// Copyright (c) 2017-2024 Advanced Micro Devices, Inc. All rights reserved.
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// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
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// THE SOFTWARE.

#ifndef ROCPRIM_DEVICE_DETAIL_DEVICE_MERGE_HPP_
#define ROCPRIM_DEVICE_DETAIL_DEVICE_MERGE_HPP_

#include <type_traits>
#include <iterator>

#include "../../config.hpp"
#include "../../detail/various.hpp"

#include "../../intrinsics.hpp"
#include "../../functional.hpp"
#include "../../types.hpp"

#include "../../block/block_store.hpp"
#include "../../detail/merge_path.hpp"

BEGIN_ROCPRIM_NAMESPACE

namespace detail
{

ROCPRIM_DEVICE ROCPRIM_INLINE
range_t compute_range(const unsigned int id,
                      const unsigned int size1,
                      const unsigned int size2,
                      const unsigned int spacing,
                      const unsigned int p1,
                      const unsigned int p2)
{
    unsigned int diag1 = id * spacing;
    unsigned int diag2 = min(size1 + size2, diag1 + spacing);

    return range_t{p1, p2, diag1 - p1, diag2 - p2};
}

template<
    class IndexIterator,
    class KeysInputIterator1,
    class KeysInputIterator2,
    class BinaryFunction
>
ROCPRIM_DEVICE ROCPRIM_INLINE
void partition_kernel_impl(IndexIterator indices,
                           KeysInputIterator1 keys_input1,
                           KeysInputIterator2 keys_input2,
                           const size_t input1_size,
                           const size_t input2_size,
                           const unsigned int spacing,
                           BinaryFunction compare_function)
{
    const unsigned int flat_id         = ::rocprim::detail::block_thread_id<0>();
    const unsigned int flat_block_id   = ::rocprim::detail::block_id<0>();
    const unsigned int flat_block_size = ::rocprim::detail::block_size<0>();
    const unsigned int input_size      = input1_size + input2_size;
    const unsigned int id              = flat_block_id * flat_block_size + flat_id;
    const unsigned int partition_id    = id * spacing;
    const unsigned int partitions      = (input_size + spacing - 1) / spacing;

    if(id > partitions)
    {
        return;
    }

    size_t diag = min(static_cast<size_t>(partition_id), input1_size + input2_size);

    unsigned int begin
        = merge_path(keys_input1, keys_input2, input1_size, input2_size, diag, compare_function);

    indices[id] = begin;
}

template<
    unsigned int BlockSize,
    unsigned int ItemsPerThread,
    class KeysInputIterator1,
    class KeysInputIterator2,
    class KeyType
>
ROCPRIM_DEVICE ROCPRIM_INLINE
void load(unsigned int flat_id,
          KeysInputIterator1 keys_input1,
          KeysInputIterator2 keys_input2,
          KeyType * keys_shared,
          const size_t input1_size,
          const size_t input2_size)
{
    ROCPRIM_UNROLL
    for(unsigned int i = 0; i < ItemsPerThread; ++i)
    {
        unsigned int index = BlockSize * i + flat_id;
        if(index < input1_size)
        {
            keys_shared[index] = keys_input1[index];
        }
        else if(index < input1_size + input2_size)
        {
            keys_shared[index] = keys_input2[index - input1_size];
        }
    }

    ::rocprim::syncthreads();
}

template<
    unsigned int BlockSize,
    class KeysInputIterator1,
    class KeysInputIterator2,
    class KeyType,
    unsigned int ItemsPerThread,
    class BinaryFunction
>
ROCPRIM_DEVICE ROCPRIM_INLINE
void merge_keys(unsigned int flat_id,
                KeysInputIterator1 keys_input1,
                KeysInputIterator2 keys_input2,
                KeyType (&key_inputs)[ItemsPerThread],
                unsigned int (&index)[ItemsPerThread],
                KeyType * keys_shared,
                range_t range,
                BinaryFunction compare_function)
{
    load<BlockSize, ItemsPerThread>(
        flat_id, keys_input1 + range.begin1, keys_input2 + range.begin2,
        keys_shared, range.count1(), range.count2()
    );

    range_t range_local =
        range_t {
            0, range.count1(), range.count1(),
            (range.count1() + range.count2())
        };

    unsigned int diag = ItemsPerThread * flat_id;
    unsigned int partition =
        merge_path(
            keys_shared + range_local.begin1,
            keys_shared + range_local.begin2,
            range_local.count1(),
            range_local.count2(),
            diag,
            compare_function
        );

    range_t range_partition =
        range_t {
            range_local.begin1 + partition,
            range_local.end1,
            range_local.begin2 + diag - partition,
            range_local.end2
        };

    serial_merge(
        keys_shared, key_inputs, index, range_partition,
        compare_function
    );
}

template<
    bool WithValues,
    unsigned int BlockSize,
    class ValuesInputIterator1,
    class ValuesInputIterator2,
    class ValuesOutputIterator,
    unsigned int ItemsPerThread
>
ROCPRIM_DEVICE ROCPRIM_INLINE
typename std::enable_if<WithValues>::type
merge_values(unsigned int flat_id,
             ValuesInputIterator1 values_input1,
             ValuesInputIterator2 values_input2,
             ValuesOutputIterator values_output,
             unsigned int (&index)[ItemsPerThread],
             const size_t input1_size,
             const size_t input2_size)
{
    using value_type = typename std::iterator_traits<ValuesInputIterator1>::value_type;

    unsigned int count = input1_size + input2_size;

    value_type values[ItemsPerThread];

    if(count >= ItemsPerThread * BlockSize)
    {
        ROCPRIM_UNROLL
        for(unsigned int i = 0; i < ItemsPerThread; ++i)
        {
            values[i] = (index[i] < input1_size) ? values_input1[index[i]] :
                                                   values_input2[index[i] - input1_size];
        }
    }
    else
    {
        ROCPRIM_UNROLL
        for(unsigned int i = 0; i < ItemsPerThread; ++i)
        {
            if(flat_id * ItemsPerThread + i < count)
            {
                values[i] = (index[i] < input1_size) ? values_input1[index[i]] :
                                                       values_input2[index[i] - input1_size];
            }
        }
    }

    ::rocprim::syncthreads();

    block_store_direct_blocked(
        flat_id,
        values_output,
        values,
        count
    );
}

template<
    bool WithValues,
    unsigned int BlockSize,
    class ValuesInputIterator1,
    class ValuesInputIterator2,
    class ValuesOutputIterator,
    unsigned int ItemsPerThread
>
ROCPRIM_DEVICE ROCPRIM_INLINE
typename std::enable_if<!WithValues>::type
merge_values(unsigned int flat_id,
             ValuesInputIterator1 values_input1,
             ValuesInputIterator2 values_input2,
             ValuesOutputIterator values_output,
             unsigned int (&index)[ItemsPerThread],
             const size_t input1_size,
             const size_t input2_size)
{
    (void) flat_id;
    (void) values_input1;
    (void) values_input2;
    (void) values_output;
    (void) index;
    (void) input1_size;
    (void) input2_size;
}

template<
    unsigned int BlockSize,
    unsigned int ItemsPerThread,
    class IndexIterator,
    class KeysInputIterator1,
    class KeysInputIterator2,
    class KeysOutputIterator,
    class ValuesInputIterator1,
    class ValuesInputIterator2,
    class ValuesOutputIterator,
    class BinaryFunction
>
ROCPRIM_DEVICE ROCPRIM_FORCE_INLINE
void merge_kernel_impl(IndexIterator indices,
                       KeysInputIterator1 keys_input1,
                       KeysInputIterator2 keys_input2,
                       KeysOutputIterator keys_output,
                       ValuesInputIterator1 values_input1,
                       ValuesInputIterator2 values_input2,
                       ValuesOutputIterator values_output,
                       const size_t input1_size,
                       const size_t input2_size,
                       BinaryFunction compare_function)
{
    using key_type = typename std::iterator_traits<KeysInputIterator1>::value_type;
    using value_type = typename std::iterator_traits<ValuesInputIterator1>::value_type;
    using keys_store_type = ::rocprim::block_store<
        key_type, BlockSize, ItemsPerThread,
        ::rocprim::block_store_method::block_store_transpose
    >;
    constexpr bool with_values = !std::is_same<value_type, ::rocprim::empty_type>::value;

    constexpr unsigned int items_per_block = BlockSize * ItemsPerThread;
    constexpr unsigned int input_block_size = BlockSize * ItemsPerThread + 1;

    ROCPRIM_SHARED_MEMORY union
    {
        typename detail::raw_storage<key_type[input_block_size]> keys_shared;
        typename keys_store_type::storage_type keys_store;
    } storage;

    key_type input[ItemsPerThread];
    unsigned int index[ItemsPerThread];

    const unsigned int flat_id = ::rocprim::detail::block_thread_id<0>();
    const unsigned int flat_block_id = ::rocprim::detail::block_id<0>();
    const unsigned int block_offset = flat_block_id * items_per_block;
    const unsigned int count = input1_size + input2_size;
    const unsigned int valid_in_last_block = count - block_offset;
    const bool         is_incomplete_block = valid_in_last_block < items_per_block;

    const unsigned int partitions = (count + items_per_block - 1) / items_per_block;

    const unsigned int p1 = indices[rocprim::min(flat_block_id, partitions)];
    const unsigned int p2 = indices[rocprim::min(flat_block_id + 1, partitions)];

    range_t range =
        compute_range(
            flat_block_id, input1_size, input2_size, items_per_block,
            p1, p2
        );

    merge_keys<BlockSize>(
        flat_id, keys_input1, keys_input2, input, index,
        storage.keys_shared.get(),
        range, compare_function
    );

    ::rocprim::syncthreads();

    if(is_incomplete_block) // # elements in last block may not equal items_per_block for the last block
    {
        keys_store_type().store(
            keys_output + block_offset,
            input,
            valid_in_last_block,
            storage.keys_store
        );
    }
    else
    {
        keys_store_type().store(
            keys_output + block_offset,
            input,
            storage.keys_store
        );
    }

    merge_values<with_values, BlockSize>(
        flat_id, values_input1 + range.begin1, values_input2 + range.begin2,
        values_output + block_offset, index,
        range.count1(), range.count2()
    );
}

} // end of detail namespace

END_ROCPRIM_NAMESPACE

#endif // ROCPRIM_DEVICE_DETAIL_DEVICE_MERGE_HPP_
