// SPDX-FileCopyrightText: 2017 - 2025 The Ginkgo authors
//
// SPDX-License-Identifier: BSD-3-Clause

#ifndef GKO_DPCPP_COMPONENTS_REDUCTION_DP_HPP_
#define GKO_DPCPP_COMPONENTS_REDUCTION_DP_HPP_


#include <type_traits>

#include <sycl/sycl.hpp>

#include <ginkgo/core/base/array.hpp>
#include <ginkgo/core/base/executor.hpp>
#include <ginkgo/core/synthesizer/containers.hpp>

#include "core/base/array_access.hpp"
#include "core/base/types.hpp"
#include "core/synthesizer/implementation_selection.hpp"
#include "dpcpp/base/config.hpp"
#include "dpcpp/base/dim3.dp.hpp"
#include "dpcpp/base/dpct.hpp"
#include "dpcpp/base/helper.hpp"
#include "dpcpp/base/types.hpp"
#include "dpcpp/components/cooperative_groups.dp.hpp"
#include "dpcpp/components/thread_ids.dp.hpp"
#include "dpcpp/components/uninitialized_array.hpp"
#include "dpcpp/synthesizer/implementation_selection.hpp"


namespace gko {
namespace kernels {
namespace dpcpp {


static constexpr int default_block_size = 256;
static constexpr auto dcfg_1d_list = dcfg_1d_list_t();
static constexpr auto dcfg_1d_array = as_array(dcfg_1d_list);

/**
 * @internal
 *
 * Computes a reduction using the binary operation `reduce_op` on a group
 * `group`. Each thread contributes with one element `local_data`. The local
 * thread element is always passed as the first parameter to the `reduce_op`.
 * The function returns the result of the reduction on all threads.
 *
 * @note The function is guaranteed to return the correct value on all threads
 *       only if `reduce_op` is commutative (in addition to being associative).
 *       Otherwise, the correct value is returned only to the thread with
 *       subgroup index 0.
 */
template <
    typename Group, typename ValueType, typename Operator,
    typename = std::enable_if_t<group::is_communicator_group<Group>::value>>
__dpct_inline__ ValueType reduce(const Group& group, ValueType local_data,
                                 Operator reduce_op = Operator{})
{
#pragma unroll
    for (int32 bitmask = 1; bitmask < group.size(); bitmask <<= 1) {
        const auto remote_data = group.shfl_xor(local_data, bitmask);
        local_data = reduce_op(local_data, remote_data);
    }
    return local_data;
}


/**
 * @internal
 *
 * Returns the index of the thread that has the element with the largest
 * magnitude among all the threads in the group.
 * Only the values from threads which set `is_pivoted` to `false` will be
 * considered.
 */
template <
    typename Group, typename ValueType,
    typename = std::enable_if_t<group::is_communicator_group<Group>::value>>
__dpct_inline__ int choose_pivot(const Group& group, ValueType local_data,
                                 bool is_pivoted)
{
    using real = remove_complex<ValueType>;
    // intel SYCL has unary - operation but only accept non-const reference
    // before 2025.0.1. Thus, it can not accept the temporary value
    // one<value_type>(), which is rvalue, such that it converts to float first
    // then take minus.
    real lmag = is_pivoted ? static_cast<real>(-one<real>()) : abs(local_data);
    const auto pivot = ::gko::kernels::dpcpp::reduce(
        group, group.thread_rank(), [&](int lidx, int ridx) {
            const auto rmag = group.shfl(lmag, ridx);
            if (rmag > lmag) {
                lmag = rmag;
                lidx = ridx;
            }
            return lidx;
        });
    // pivot operator not commutative, make sure everyone has the same pivot
    return group.shfl(pivot, 0);
}


/**
 * @internal
 *
 * Computes a reduction using the binary operation `reduce_op` on entire block.
 * The data for the reduction is taken from the `data` array which has to be of
 * size `block_size` and accessible from all threads. The `data` array is also
 * used as work space (so its content will be destroyed in the process), as well
 * as to store the return value - which is stored in the 0-th position of the
 * array.
 */
template <
    unsigned int sg_size = config::warp_size, typename Group,
    typename ValueType, typename Operator,
    typename = std::enable_if_t<group::is_synchronizable_group<Group>::value>>
void reduce(const Group& __restrict__ group, ValueType* __restrict__ data,
            Operator reduce_op = Operator{})
{
    const auto local_id = group.thread_rank();

    for (int k = group.size() / 2; k >= sg_size; k /= 2) {
        group.sync();
        if (local_id < k) {
            data[local_id] = reduce_op(data[local_id], data[local_id + k]);
        }
    }

    const auto warp = group::tiled_partition<sg_size>(group);
    const auto warp_id = group.thread_rank() / warp.size();
    if (warp_id > 0) {
        return;
    }
    auto result = ::gko::kernels::dpcpp::reduce(warp, data[warp.thread_rank()],
                                                reduce_op);
    if (warp.thread_rank() == 0) {
        data[0] = result;
    }
}


/**
 * @internal
 *
 * Computes a reduction using the binary operation `reduce_op` on an array
 * `source` of any size. Has to be called a second time on `result` to reduce
 * an array larger than `block_size`.
 */
template <unsigned int sg_size = config::warp_size, typename Operator,
          typename ValueType>
void reduce_array(size_type size, const ValueType* __restrict__ source,
                  ValueType* __restrict__ result, sycl::nd_item<3> item_ct1,
                  Operator reduce_op = Operator{})
{
    const auto tidx = thread::get_thread_id_flat(item_ct1);
    auto thread_result = zero<ValueType>();
    for (auto i = tidx; i < size;
         i += item_ct1.get_local_range().get(2) * item_ct1.get_group_range(2)) {
        thread_result = reduce_op(thread_result, source[i]);
    }
    result[item_ct1.get_local_id(2)] = thread_result;

    group::this_thread_block(item_ct1).sync();

    // Stores the result of the reduction inside `result[0]`
    reduce<sg_size>(group::this_thread_block(item_ct1), result, reduce_op);
}


/**
 * @internal
 *
 * Computes a reduction using the add operation (+) on an array
 * `source` of any size. Has to be called a second time on `result` to reduce
 * an array larger than `block_size`.
 */
template <typename DeviceConfig, typename ValueType>
void reduce_add_array(
    size_type size, const ValueType* __restrict__ source,
    ValueType* __restrict__ result, sycl::nd_item<3> item_ct1,
    uninitialized_array<ValueType, DeviceConfig::block_size>& block_sum)
{
    reduce_array<DeviceConfig::subgroup_size>(
        size, source, static_cast<ValueType*>(block_sum), item_ct1,
        [](const ValueType& x, const ValueType& y) { return x + y; });

    if (item_ct1.get_local_id(2) == 0) {
        result[item_ct1.get_group(2)] = block_sum[0];
    }
}

template <typename DeviceConfig = device_config<256, 16>, typename ValueType>
void reduce_add_array(dim3 grid, dim3 block, size_type dynamic_shared_memory,
                      sycl::queue* queue, size_type size,
                      const ValueType* source, ValueType* result)
{
    queue->submit([&](sycl::handler& cgh) {
        sycl::local_accessor<uninitialized_array<device_type<ValueType>,
                                                 DeviceConfig::block_size>,
                             0>
            block_sum_acc_ct1(cgh);

        cgh.parallel_for(
            sycl_nd_range(grid, block),
            [=](sycl::nd_item<3> item_ct1)
                [[sycl::reqd_sub_group_size(DeviceConfig::subgroup_size)]] {
                    reduce_add_array<DeviceConfig>(
                        size, as_device_type(source), as_device_type(result),
                        item_ct1, *block_sum_acc_ct1.get_pointer());
                });
    });
}

GKO_ENABLE_IMPLEMENTATION_CONFIG_SELECTION_TOTYPE(reduce_add_array_config,
                                                  reduce_add_array, DCFG_1D);

GKO_ENABLE_DEFAULT_CONFIG_CALL(reduce_add_array_call, reduce_add_array_config,
                               dcfg_1d_list);


/**
 * Compute a reduction using add operation (+).
 *
 * @param exec  Executor associated to the array
 * @param size  size of the array
 * @param source  the pointer of the array
 *
 * @return the reduction result
 */
template <typename ValueType>
ValueType reduce_add_array(std::shared_ptr<const DpcppExecutor> exec,
                           size_type size, const ValueType* source)
{
    auto block_results_val = source;
    size_type grid_dim = size;
    auto block_results = array<ValueType>(exec);
    ValueType answer = zero<ValueType>();
    auto queue = exec->get_queue();
    constexpr auto dcfg_1d_array = as_array(dcfg_1d_list);
    const std::uint32_t cfg =
        get_first_cfg(dcfg_1d_array, [&queue](std::uint32_t cfg) {
            return validate(queue, DCFG_1D::decode<0>(cfg),
                            DCFG_1D::decode<1>(cfg));
        });
    const auto wg_size = DCFG_1D::decode<0>(cfg);
    const auto sg_size = DCFG_1D::decode<1>(cfg);

    if (size > wg_size) {
        const auto n = ceildiv(size, wg_size);
        grid_dim = (n <= wg_size) ? n : wg_size;

        block_results.resize_and_reset(grid_dim);

        reduce_add_array_call(cfg, grid_dim, wg_size, 0, exec->get_queue(),
                              size, source, block_results.get_data());

        block_results_val = block_results.get_const_data();
    }

    auto d_result = array<ValueType>(exec, 1);

    reduce_add_array_call(cfg, 1, wg_size, 0, exec->get_queue(), grid_dim,
                          block_results_val, d_result.get_data());
    answer = get_element(d_result, 0);
    return answer;
}


}  // namespace dpcpp
}  // namespace kernels
}  // namespace gko


#endif  // GKO_DPCPP_COMPONENTS_REDUCTION_DP_HPP_
