//
// Copyright (C) 2012 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.
//

#ifndef SHILL_DHCP_DHCP_PROVIDER_H_
#define SHILL_DHCP_DHCP_PROVIDER_H_

#include <map>
#include <memory>
#include <set>
#include <string>

#include <base/files/file_path.h>
#include <base/lazy_instance.h>
#include <gtest/gtest_prod.h>  // for FRIEND_TEST

#include "shill/refptr_types.h"

namespace shill {

class ControlInterface;
class DHCPCDListenerInterface;
class EventDispatcher;
class Metrics;

// DHCPProvider is a singleton providing the main DHCP configuration
// entrypoint. Once the provider is initialized through its Init method, DHCP
// configurations for devices can be obtained through its CreateConfig
// method. For example, a single DHCP configuration request can be initiated as:
//
// DHCPProvider::GetInstance()->CreateIPv4Config(device_name,
//                                               host_name,
//                                               lease_file_suffix,
//                                               arp_gateway)->Request();
class DHCPProvider {
 public:
  static constexpr char kDHCPCDPathFormatLease[] =
      "var/lib/dhcpcd/dhcpcd-%s.lease";
#ifndef DISABLE_DHCPV6
  static constexpr char kDHCPCDPathFormatLease6[] =
      "var/lib/dhcpcd/dhcpcd-%s.lease6";
#endif  // DISABLE_DHCPV6

  virtual ~DHCPProvider();

  // This is a singleton -- use DHCPProvider::GetInstance()->Foo().
  static DHCPProvider* GetInstance();

  // Initializes the provider singleton. This method hooks up a D-Bus signal
  // listener that catches signals from spawned DHCP clients and dispatches them
  // to the appropriate DHCP configuration instance.
  virtual void Init(ControlInterface* control_interface,
                    EventDispatcher* dispatcher,
                    Metrics* metrics);

  // Called on shutdown to release |listener_|.
  void Stop();

  // Creates a new DHCPv4Config for |device_name|. The DHCP configuration for
  // the device can then be initiated through DHCPConfig::Request and
  // DHCPConfig::Renew.  If |host_name| is not-empty, it is placed in the DHCP
  // request to allow the server to map the request to a specific user-named
  // origin.  The DHCP lease file will contain the suffix supplied
  // in |lease_file_suffix| if non-empty, otherwise |device_name|.  If
  // |arp_gateway| is true, the DHCP client will ARP for the gateway IP
  // address as an additional safeguard against the issued IP address being
  // in-use by another station.
  virtual DHCPConfigRefPtr CreateIPv4Config(
      const std::string& device_name,
      const std::string& host_name,
      const std::string& lease_file_suffix,
      bool arp_gateway);

#ifndef DISABLE_DHCPV6
  // Create a new DHCPv6Config for |device_name|.
  virtual DHCPConfigRefPtr CreateIPv6Config(
      const std::string& device_name, const std::string& lease_file_suffix);
#endif

  // Returns the DHCP configuration associated with DHCP client |pid|. Return
  // nullptr if |pid| is not bound to a configuration.
  DHCPConfigRefPtr GetConfig(int pid);

  // Binds a |pid| to a DHCP |config|. When a DHCP config spawns a new DHCP
  // client, it binds itself to that client's |pid|.
  virtual void BindPID(int pid, const DHCPConfigRefPtr& config);

  // Unbinds a |pid|. This method is used by a DHCP config to signal the
  // provider that the DHCP client has been terminated. This may result in
  // destruction of the DHCP config instance if its reference count goes to 0.
  virtual void UnbindPID(int pid);

  // Destroy lease file associated with this |name|.
  virtual void DestroyLease(const std::string& name);

  // Returns true if |pid| was recently unbound from the provider.
  bool IsRecentlyUnbound(int pid);

 protected:
  DHCPProvider();

 private:
  friend struct base::DefaultLazyInstanceTraits<DHCPProvider>;
  friend class CellularTest;
  friend class DHCPProviderTest;
  friend class DeviceInfoTest;
  friend class DeviceTest;
  FRIEND_TEST(DHCPProviderTest, CreateIPv4Config);
  FRIEND_TEST(DHCPProviderTest, DestroyLease);

  typedef std::map<int, DHCPConfigRefPtr> PIDConfigMap;

  // Retire |pid| from the set of recently retired PIDs.
  void RetireUnboundPID(int pid);

  // A single listener is used to catch signals from all DHCP clients and
  // dispatch them to the appropriate DHCP configuration instance.
  std::unique_ptr<DHCPCDListenerInterface> listener_;

  // A map that binds PIDs to DHCP configuration instances.
  PIDConfigMap configs_;

  base::FilePath root_;
  ControlInterface* control_interface_;
  EventDispatcher* dispatcher_;
  Metrics* metrics_;

  // Track the set of PIDs recently unbound from the provider in case messages
  // arrive addressed from them.
  std::set<int> recently_unbound_pids_;

  DISALLOW_COPY_AND_ASSIGN(DHCPProvider);
};

}  // namespace shill

#endif  // SHILL_DHCP_DHCP_PROVIDER_H_