/**
 *  Copyright (c) 2016 by Contributors
 * @file dgl/runtime/device_api.h
 * @brief Abstract device memory management API
 */
#ifndef DGL_RUNTIME_DEVICE_API_H_
#define DGL_RUNTIME_DEVICE_API_H_

#include <string>

#include "c_runtime_api.h"
#include "packed_func.h"

namespace dgl {
namespace runtime {
/**
 * @brief the query type into GetAttr
 */
enum DeviceAttrKind : int {
  kExist = 0,
  kMaxThreadsPerBlock = 1,
  kWarpSize = 2,
  kMaxSharedMemoryPerBlock = 3,
  kComputeVersion = 4,
  kDeviceName = 5,
  kMaxClockRate = 6,
  kMultiProcessorCount = 7,
  kMaxThreadDimensions = 8
};

/** @brief Number of bytes each allocation must align to */
constexpr int kAllocAlignment = 64;

/** @brief Number of bytes each allocation must align to in temporary allocation
 */
constexpr int kTempAllocaAlignment = 64;

/** @brief Maximum size that can be allocated on stack */
constexpr int kMaxStackAlloca = 1024;

/**
 * @brief DGL Runtime Device API, abstracts the device
 *  specific interface for memory management.
 */
class DeviceAPI {
 public:
  /** @brief virtual destructor */
  virtual ~DeviceAPI() {}
  /**
   * @brief Check whether the device is available.
   */
  virtual bool IsAvailable() { return true; }
  /**
   * @brief Set the environment device id to ctx
   * @param ctx The context to be set.
   */
  virtual void SetDevice(DGLContext ctx) = 0;
  /**
   * @brief Get attribute of specified device.
   * @param ctx The device context
   * @param kind The result kind
   * @param rv The return value.
   * @sa DeviceAttrKind
   */
  virtual void GetAttr(
      DGLContext ctx, DeviceAttrKind kind, DGLRetValue* rv) = 0;
  /**
   * @brief Allocate a data space on device.
   * @param ctx The device context to perform operation.
   * @param nbytes The number of bytes in memory.
   * @param alignment The alignment of the memory.
   * @param type_hint The type of elements. Only needed by certain backends such
   * as OpenGL, as nbytes & alignment are sufficient for most backends.
   * @return The allocated device pointer.
   */
  virtual void* AllocDataSpace(
      DGLContext ctx, size_t nbytes, size_t alignment,
      DGLDataType type_hint) = 0;
  /**
   * @brief Free a data space on device.
   * @param ctx The device context to perform operation.
   * @param ptr The data space.
   */
  virtual void FreeDataSpace(DGLContext ctx, void* ptr) = 0;
  /**
   * @brief copy data from one place to another
   * @param from The source array.
   * @param from_offset The byte offeset in the from.
   * @param to The target array.
   * @param to_offset The byte offset in the to.
   * @param num_bytes The size of the memory in bytes
   * @param ctx_from The source context
   * @param ctx_to The target context
   * @param type_hint The type of elements, only neded by certain backends.
   *                  can be useful for cross device endian converison.
   */
  virtual void CopyDataFromTo(
      const void* from, size_t from_offset, void* to, size_t to_offset,
      size_t num_bytes, DGLContext ctx_from, DGLContext ctx_to,
      DGLDataType type_hint) = 0;
  /**
   * @brief Create a new stream of execution.
   *
   * @param ctx The context of allocation.
   */
  DGL_DLL virtual DGLStreamHandle CreateStream(DGLContext ctx);

  /**
   * @brief Free a stream of execution
   *
   * @param ctx The context of the stream
   * @param stream The pointer to be freed.
   */
  DGL_DLL virtual void FreeStream(DGLContext ctx, DGLStreamHandle stream);

  /**
   * @brief Synchronize the stream
   * @param ctx The context to perform operation.
   * @param stream The stream to be sync.
   */
  virtual void StreamSync(DGLContext ctx, DGLStreamHandle stream) = 0;
  /**
   * @brief Set the stream
   * @param ctx The context to set stream.
   * @param stream The stream to be set.
   */
  virtual void SetStream(DGLContext ctx, DGLStreamHandle stream) {}
  /**
   * @brief Get the stream
   */
  virtual DGLStreamHandle GetStream() const { return nullptr; }
  /**
   * @brief Synchronize 2 streams of execution.
   *
   * An event is created in event_src stream that the second then
   * stream waits on.  Neither event_src or event_dst need to be of
   * the same device ID as the context, but they must be of the same
   * device type.
   *
   * @param ctx The context of the streams.
   * @param event_src The source stream to synchronize.
   * @param event_dst The destination stream to synchronize.
   */
  DGL_DLL virtual void SyncStreamFromTo(
      DGLContext ctx, DGLStreamHandle event_src, DGLStreamHandle event_dst);

  /**
   * @brief Pin host memory using cudaHostRegister().
   *
   * @param ptr The host memory pointer to be pinned.
   * @param nbytes The size to be pinned.
   */
  DGL_DLL virtual void PinData(void* ptr, size_t nbytes);

  /**
   * @brief Unpin host memory using cudaHostUnregister().
   *
   * @param ptr The host memory pointer to be unpinned.
   */
  DGL_DLL virtual void UnpinData(void* ptr);

  /**
   * @brief Check whether the memory is in pinned memory.
   */
  DGL_DLL virtual bool IsPinned(const void* ptr) { return false; }

  /**
   * @brief Allocate temporal workspace for backend execution.
   *
   *  \note We have the following assumption about backend temporal
   *   workspace allocation, and backend will optimize for such assumption:
   *
   *  - Only a few allocation will happen, and space will be released after use.
   *  - The release order is usually in reverse order of allocate (stack style).
   *  - Repeative pattern of same allocations over different runs.
   *  - Workspace should not overlap between different threads(i.e. be
   * threadlocal)
   *
   * @param ctx The context of allocation.
   * @param nbytes The size to be allocated.
   * @param type_hint The type of elements. Only needed by certain backends such
   * as OpenGL, as nbytes is sufficient for most backends.
   */
  DGL_DLL virtual void* AllocWorkspace(
      DGLContext ctx, size_t nbytes, DGLDataType type_hint = {});
  /**
   * @brief Free temporal workspace in backend execution.
   *
   * @param ctx The context of allocation.
   * @param ptr The pointer to be freed.
   */
  DGL_DLL virtual void FreeWorkspace(DGLContext ctx, void* ptr);

  /**
   * @brief Get device API based on context.
   * @param ctx The context
   * @param allow_missing Whether allow missing
   * @return The corresponding device API.
   */
  DGL_DLL static DeviceAPI* Get(DGLContext ctx, bool allow_missing = false);

  /**
   * @brief Get device API based on context.
   * @param dev_type The device type
   * @param allow_missing Whether allow missing
   * @return The corresponding device API.
   */
  DGL_DLL static DeviceAPI* Get(
      DGLDeviceType dev_type, bool allow_missing = false);
};

/** @brief The device type bigger than this is RPC device */
constexpr int kRPCSessMask = 128;
}  // namespace runtime
}  // namespace dgl
#endif  // DGL_RUNTIME_DEVICE_API_H_
