//
// Copyright (C) 2020 The Android Open Source Project
//
// 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.

#pragma once

#include <cstdint>
#include <memory>
#include <set>

#include <tss2/tss2_esys.h>

/**
 * Object slot manager for TPM memory. The TPM can only hold a fixed number of
 * objects at once. Some TPM operations are defined to consume slots either
 * temporarily or until the resource is explicitly unloaded.
 *
 * This implementation is intended for future extension, to track what objects
 * are resident if we run out of space, or implement optimizations like LRU
 * caching to avoid re-loading often-used resources.
 */
class TpmResourceManager {
public:
  class ObjectSlot {
  public:
    friend class TpmResourceManager;

    ~ObjectSlot();

    ESYS_TR get();
    void set(ESYS_TR resource);
  private:
    ObjectSlot(TpmResourceManager* resource_manager);
    ObjectSlot(TpmResourceManager* resource_manager, ESYS_TR resource);

    TpmResourceManager* resource_manager_;
    ESYS_TR resource_;
  };

  TpmResourceManager(ESYS_CONTEXT* esys);
  ~TpmResourceManager();

  ESYS_CONTEXT* Esys();
  std::shared_ptr<ObjectSlot> ReserveSlot();
private:
  ESYS_CONTEXT* esys_;
  const std::uint32_t maximum_object_slots_;
  std::atomic<std::uint32_t> used_slots_;
};

using TpmObjectSlot = std::shared_ptr<TpmResourceManager::ObjectSlot>;