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+/*
+ *  Copyright (c) 2018 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef API_TEST_SIMULATED_NETWORK_H_
+#define API_TEST_SIMULATED_NETWORK_H_
+
+#include <stddef.h>
+#include <stdint.h>
+
+#include <deque>
+#include <queue>
+#include <vector>
+
+#include "absl/types/optional.h"
+#include "rtc_base/random.h"
+#include "rtc_base/thread_annotations.h"
+
+namespace webrtc {
+
+struct PacketInFlightInfo {
+  PacketInFlightInfo(size_t size, int64_t send_time_us, uint64_t packet_id)
+      : size(size), send_time_us(send_time_us), packet_id(packet_id) {}
+
+  size_t size;
+  int64_t send_time_us;
+  // Unique identifier for the packet in relation to other packets in flight.
+  uint64_t packet_id;
+};
+
+struct PacketDeliveryInfo {
+  static constexpr int kNotReceived = -1;
+  PacketDeliveryInfo(PacketInFlightInfo source, int64_t receive_time_us)
+      : receive_time_us(receive_time_us), packet_id(source.packet_id) {}
+
+  bool operator==(const PacketDeliveryInfo& other) const {
+    return receive_time_us == other.receive_time_us &&
+           packet_id == other.packet_id;
+  }
+
+  int64_t receive_time_us;
+  uint64_t packet_id;
+};
+
+// BuiltInNetworkBehaviorConfig is a built-in network behavior configuration
+// for built-in network behavior that will be used by WebRTC if no custom
+// NetworkBehaviorInterface is provided.
+struct BuiltInNetworkBehaviorConfig {
+  //  Queue length in number of packets.
+  size_t queue_length_packets = 0;
+  // Delay in addition to capacity induced delay.
+  int queue_delay_ms = 0;
+  // Standard deviation of the extra delay.
+  int delay_standard_deviation_ms = 0;
+  // Link capacity in kbps.
+  int link_capacity_kbps = 0;
+  // Random packet loss.
+  int loss_percent = 0;
+  // If packets are allowed to be reordered.
+  bool allow_reordering = false;
+  // The average length of a burst of lost packets.
+  int avg_burst_loss_length = -1;
+  // Additional bytes to add to packet size.
+  int packet_overhead = 0;
+};
+
+// Interface that represents a Network behaviour.
+//
+// It is clients of this interface responsibility to enqueue and dequeue
+// packets (based on the estimated delivery time expressed by
+// NextDeliveryTimeUs).
+//
+// To enqueue packets, call EnqueuePacket:
+// EXPECT_TRUE(network.EnqueuePacket(
+//     PacketInFlightInfo(/*size=*/1, /*send_time_us=*/0, /*packet_id=*/1)));
+//
+// To know when to call DequeueDeliverablePackets to pull packets out of the
+// network, call NextDeliveryTimeUs and schedule a task to invoke
+// DequeueDeliverablePackets (if not already scheduled).
+//
+// DequeueDeliverablePackets will return a vector of delivered packets, but this
+// vector can be empty in case of extra delay. In such case, make sure to invoke
+// NextDeliveryTimeUs and schedule a task to call DequeueDeliverablePackets for
+// the next estimated delivery of packets.
+//
+// std::vector<PacketDeliveryInfo> delivered_packets =
+//     network.DequeueDeliverablePackets(/*receive_time_us=*/1000000);
+class NetworkBehaviorInterface {
+ public:
+  // Enqueues a packet in the network and returns true if the action was
+  // successful, false otherwise (for example, because the network capacity has
+  // been saturated). If the return value is false, the packet should be
+  // considered as dropped and it will not be returned by future calls
+  // to DequeueDeliverablePackets.
+  // Packets enqueued will exit the network when DequeueDeliverablePackets is
+  // called and enough time has passed (see NextDeliveryTimeUs).
+  virtual bool EnqueuePacket(PacketInFlightInfo packet_info) = 0;
+  // Retrieves all packets that should be delivered by the given receive time.
+  // Not all the packets in the returned std::vector are actually delivered.
+  // In order to know the state of each packet it is necessary to check the
+  // `receive_time_us` field of each packet. If that is set to
+  // PacketDeliveryInfo::kNotReceived then the packet is considered lost in the
+  // network.
+  virtual std::vector<PacketDeliveryInfo> DequeueDeliverablePackets(
+      int64_t receive_time_us) = 0;
+  // Returns time in microseconds when caller should call
+  // DequeueDeliverablePackets to get the next set of delivered packets. It is
+  // possible that no packet will be delivered by that time (e.g. in case of
+  // random extra delay), in such case this method should be called again to get
+  // the updated estimated delivery time.
+  virtual absl::optional<int64_t> NextDeliveryTimeUs() const = 0;
+  virtual ~NetworkBehaviorInterface() = default;
+};
+
+// Class simulating a network link. This is a simple and naive solution just
+// faking capacity and adding an extra transport delay in addition to the
+// capacity introduced delay.
+class SimulatedNetworkInterface : public NetworkBehaviorInterface {
+ public:
+  // Sets a new configuration.
+  virtual void SetConfig(const BuiltInNetworkBehaviorConfig& config) = 0;
+  virtual void UpdateConfig(
+      std::function<void(BuiltInNetworkBehaviorConfig*)> config_modifier) = 0;
+  // Pauses the network until `until_us`. This affects both delivery (calling
+  // DequeueDeliverablePackets before `until_us` results in an empty std::vector
+  // of packets) and capacity (the network is paused, so packets are not
+  // flowing and they will restart flowing at `until_us`).
+  virtual void PauseTransmissionUntil(int64_t until_us) = 0;
+};
+
+}  // namespace webrtc
+
+#endif  // API_TEST_SIMULATED_NETWORK_H_