#include <migraphx/config.hpp>
#include <migraphx/context.hpp>
#include <migraphx/cpu/context.hpp>
#include <migraphx/op/gather.hpp>

namespace migraphx {
inline namespace MIGRAPHX_INLINE_NS {
namespace cpu {

struct cpu_gather : auto_register_op<cpu_gather>
{
    op::gather op;

    template <class Self, class F>
    static auto reflect(Self& self, F f)
    {
        return migraphx::reflect(self.op, f);
    }
    std::string name() const { return "cpu::" + op.name(); }
    shape compute_shape(std::vector<shape> inputs) const
    {
        // Compensate for allocation
        inputs.pop_back();
        check_shapes(inputs, *this).standard();
        return migraphx::compute_shape(op, inputs);
    }

    argument
    compute(context& ctx, const shape& output_shape, const std::vector<argument>& args) const
    {
        std::size_t nelements = output_shape.elements();
        auto lens             = args[0].get_shape().lens();
        auto axis_dim_size    = lens[op.axis];
        lens[op.axis]         = args[1].get_shape().elements();
        shape out_comp{output_shape.type(), lens};

        visit_all(args.back(), args[0])([&](auto output, auto input) {
            args[1].visit([&](auto indices) {
                const auto* indices_ptr = indices.data();
                auto* output_ptr        = output.data();
                ctx.bulk_execute(nelements, 1024, [=](auto start, auto end) {
                    for(auto i = start; i < end; i++)
                    {
                        auto idx      = out_comp.multi(i);
                        auto in_index = indices_ptr[idx[op.axis]];
                        in_index      = (in_index < 0) ? in_index + axis_dim_size : in_index;
                        idx[op.axis]  = in_index;
                        output_ptr[i] = input(idx.begin(), idx.end());
                    }
                });
            });
        });

        return args.back();
    }

    std::ptrdiff_t output_alias(const std::vector<shape>& shapes) const
    {
        return shapes.size() - 1;
    }
};

} // namespace cpu
} // namespace MIGRAPHX_INLINE_NS
} // namespace migraphx
