/**
 *  Copyright (c) 2017 by Contributors
 * @file dgl/runtime/module.h
 * @brief Runtime container of the functions generated by DGL,
 *  This is used to support dynamically link, load and save
 *  functions from different convention under unified API.
 */
#ifndef DGL_RUNTIME_MODULE_H_
#define DGL_RUNTIME_MODULE_H_

#include <dmlc/io.h>

#include <memory>
#include <string>
#include <unordered_map>
#include <vector>

#include "c_runtime_api.h"

namespace dgl {
namespace runtime {

// The internal container of module.
class ModuleNode;
class PackedFunc;

/**
 * @brief Module container of DGL.
 */
class Module {
 public:
  Module() {}
  // constructor from container.
  explicit Module(std::shared_ptr<ModuleNode> n) : node_(n) {}
  /**
   * @brief Get packed function from current module by name.
   *
   * @param name The name of the function.
   * @param query_imports Whether also query dependency modules.
   * @return The result function.
   *  This function will return PackedFunc(nullptr) if function do not exist.
   * @note Implemented in packed_func.cc
   */
  inline PackedFunc GetFunction(
      const std::string& name, bool query_imports = false);
  /** @return internal container */
  inline ModuleNode* operator->();
  /** @return internal container */
  inline const ModuleNode* operator->() const;
  // The following functions requires link with runtime.
  /**
   * @brief Import another module into this module.
   * @param other The module to be imported.
   *
   * @note Cyclic dependency is not allowed among modules,
   *  An error will be thrown when cyclic dependency is detected.
   */
  DGL_DLL void Import(Module other);
  /**
   * @brief Load a module from file.
   * @param file_name The name of the host function module.
   * @param format The format of the file.
   * @note This function won't load the import relationship.
   *  Re-create import relationship by calling Import.
   */
  DGL_DLL static Module LoadFromFile(
      const std::string& file_name, const std::string& format = "");

 private:
  std::shared_ptr<ModuleNode> node_;
};

/**
 * @brief Base node container of module.
 *  Do not create this directly, instead use Module.
 */
class ModuleNode {
 public:
  /** @brief virtual destructor */
  virtual ~ModuleNode() {}
  /** @return The module type key */
  virtual const char* type_key() const = 0;
  /**
   * @brief Get a PackedFunc from module.
   *
   *  The PackedFunc may not be fully initialized,
   *  there might still be first time running overhead when
   *  executing the function on certain devices.
   *  For benchmarking, use prepare to eliminate
   *
   * @param name the name of the function.
   * @param sptr_to_self The shared_ptr that points to this module node.
   *
   * @return PackedFunc(nullptr) when it is not available.
   *
   * @note The function will always remain valid.
   *   If the function need resource from the module(e.g. late linking),
   *   it should capture sptr_to_self.
   */
  virtual PackedFunc GetFunction(
      const std::string& name,
      const std::shared_ptr<ModuleNode>& sptr_to_self) = 0;
  /**
   * @brief Save the module to file.
   * @param file_name The file to be saved to.
   * @param format The format of the file.
   */
  virtual void SaveToFile(
      const std::string& file_name, const std::string& format);
  /**
   * @brief Save the module to binary stream.
   * @param stream The binary stream to save to.
   * @note It is recommended to implement this for device modules,
   *   but not necessarily host modules.
   *   We can use this to do AOT loading of bundled device functions.
   */
  DGL_DLL virtual void SaveToBinary(dmlc::Stream* stream);
  /**
   * @brief Get the source code of module, when available.
   * @param format Format of the source code, can be empty by default.
   * @return Possible source code when available.
   */
  DGL_DLL virtual std::string GetSource(const std::string& format = "");
  /**
   * @brief Get a function from current environment
   *  The environment includes all the imports as well as Global functions.
   *
   * @param name name of the function.
   * @return The corresponding function.
   */
  DGL_DLL const PackedFunc* GetFuncFromEnv(const std::string& name);
  /** @return The module it imports from */
  const std::vector<Module>& imports() const { return imports_; }

 protected:
  friend class Module;
  /** @brief The modules this module depend on */
  std::vector<Module> imports_;

 private:
  /** @brief Cache used by GetImport */
  std::unordered_map<std::string, std::unique_ptr<PackedFunc> > import_cache_;
};

/** @brief namespace for constant symbols */
namespace symbol {
/** @brief Global variable to store module context. */
constexpr const char* dgl_module_ctx = "__dgl_module_ctx";
/** @brief Global variable to store device module blob */
constexpr const char* dgl_dev_mblob = "__dgl_dev_mblob";
/** @brief Number of bytes of device module blob. */
constexpr const char* dgl_dev_mblob_nbytes = "__dgl_dev_mblob_nbytes";
/** @brief global function to set device */
constexpr const char* dgl_set_device = "__dgl_set_device";
/** @brief Auxiliary counter to global barrier. */
constexpr const char* dgl_global_barrier_state = "__dgl_global_barrier_state";
/**
 * @brief Prepare the global barrier before kernels that uses global barrier.
 */
constexpr const char* dgl_prepare_global_barrier =
    "__dgl_prepare_global_barrier";
/** @brief Placeholder for the module's entry function. */
constexpr const char* dgl_module_main = "__dgl_main__";
}  // namespace symbol

// implementations of inline functions.
inline ModuleNode* Module::operator->() { return node_.get(); }

inline const ModuleNode* Module::operator->() const { return node_.get(); }

}  // namespace runtime
}  // namespace dgl

#include "packed_func.h"
#endif  // DGL_RUNTIME_MODULE_H_