/* Copyright 2026 The OpenXLA Authors.

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.
==============================================================================*/

#ifndef XLA_BACKENDS_GPU_RUNTIME_DYNAMIC_MEMCPY_THUNK_H_
#define XLA_BACKENDS_GPU_RUNTIME_DYNAMIC_MEMCPY_THUNK_H_

#include <cstdint>
#include <memory>
#include <tuple>
#include <vector>

#include "absl/container/flat_hash_map.h"
#include "absl/container/inlined_vector.h"
#include "absl/status/status.h"
#include "absl/status/statusor.h"
#include "absl/types/span.h"
#include "xla/backends/gpu/runtime/copy_thunk.pb.h"
#include "xla/backends/gpu/runtime/thunk.h"
#include "xla/backends/gpu/runtime/thunk.pb.h"
#include "xla/hlo/ir/hlo_instruction.h"
#include "xla/runtime/buffer_use.h"
#include "xla/service/buffer_assignment.h"
#include "xla/service/shaped_slice.h"

namespace xla {
namespace gpu {

class DynamicMemcpyThunk : public Thunk {
 public:
  // TODO(jreiffers): Move this to a more appropriate place.
  struct MemcpyDescriptor {
    struct DynamicOffset {
      // The while loop whose induction variable defines the offset.
      const HloInstruction* while_loop;
      const HloInstruction* induction_variable;

      // See documentation for ResolveFunctionalDependencyOnInductionVariable.
      absl::flat_hash_map<const HloComputation*, absl::InlinedVector<bool, 1>>
          required_parameters;

      // All dependencies of `offset` must end in `induction_variable` or
      // constants only.
      const HloInstruction* offset;

      // The size of the dimension that this offset corresponds to. As per HLO
      // semantics, values of `offset` will be clamped to one less than this.
      int64_t dimension_size;

      // The stride with which to multiply the induction variable's value.
      int64_t byte_stride;
    };

    std::vector<DynamicOffset> src_dynamic_offsets;
    int64_t src_byte_static_offset = 0;

    std::vector<DynamicOffset> dst_dynamic_offsets;
    int64_t dst_byte_static_offset = 0;
  };

  struct Offsets {
    bool depends_on_loop;
    std::vector<int64_t> src_offsets;
    std::vector<int64_t> dst_offsets;

    DynamicMemcpyThunkProto::Offsets ToProto() const;
    static absl::StatusOr<Offsets> FromProto(
        const DynamicMemcpyThunkProto::Offsets& proto);

    friend bool operator==(const Offsets& lhs, const Offsets& rhs) {
      return std::tie(lhs.depends_on_loop, lhs.src_offsets, lhs.dst_offsets) ==
             std::tie(rhs.depends_on_loop, rhs.src_offsets, rhs.dst_offsets);
    }
    friend bool operator!=(const Offsets& lhs, const Offsets& rhs) {
      return !(lhs == rhs);
    }
  };

  DynamicMemcpyThunk(ThunkInfo thunk_info, const ShapedSlice& source_buffer,
                     const ShapedSlice& destination_buffer, uint64_t mem_size,
                     Offsets offsets);

  DynamicMemcpyThunk(const DynamicMemcpyThunk&) = delete;
  DynamicMemcpyThunk& operator=(const DynamicMemcpyThunk&) = delete;

  Offsets offsets() const { return offsets_; }
  uint64_t mem_size() const { return mem_size_; }

  const ShapedSlice& source() const { return source_buffer_; }
  const ShapedSlice& destination() const { return destination_buffer_; }

  absl::Status ExecuteOnStream(const ExecuteParams& params) override;

  BufferUses buffer_uses() const override {
    return {
        BufferUse::Read(source_buffer_.slice, source_buffer_.shape),
        BufferUse::Write(destination_buffer_.slice, destination_buffer_.shape),
    };
  }

  absl::StatusOr<ThunkProto> ToProto() const override;

  static absl::StatusOr<std::unique_ptr<DynamicMemcpyThunk>> FromProto(
      ThunkInfo thunk_info, const DynamicMemcpyThunkProto& thunk_proto,
      absl::Span<const BufferAllocation> buffer_allocations);

 private:
  ShapedSlice source_buffer_;
  ShapedSlice destination_buffer_;
  uint64_t mem_size_;
  Offsets offsets_;
};

}  // namespace gpu
}  // namespace xla

#endif  // XLA_BACKENDS_GPU_RUNTIME_DYNAMIC_MEMCPY_THUNK_H_