#pragma once

#include <memory>

#include <string>

#include "envoy/common/pure.h"

#include "envoy/config/typed_config.h"

#include "envoy/http/header_map.h"

#include "envoy/server/factory_context.h"

#include "envoy/upstream/upstream.h"

namespace Envoy {

namespace Http {

/**

 * Interface class for session state. Session state is used to get address of upstream host

 * assigned to the session.

 */

class SessionState {

public:

  /**

   * Get address of upstream host that the current session stuck on.

   *

   * @return absl::optional<absl::string_view> optional upstream address. If there is no available

   * session or no available address, absl::nullopt will be returned.

   */

  virtual absl::optional<absl::string_view> upstreamAddress() const PURE;

  /**

   * Called when a request is completed to update the session state.

   *

   * @param host_address the upstream host that was finally selected.

   * @param headers the response headers.

   * @return bool true if the selected host differs from the previously stored session host.

   */

  virtual bool onUpdate(absl::string_view host_address, ResponseHeaderMap& headers) PURE;

};

using SessionStatePtr = std::unique_ptr<SessionState>;

/**

 * Interface class for creating session state from request headers.

 */

class SessionStateFactory {

public:

  /**

   * Create session state from request headers.

   *

   * @param headers request headers.

   */

  virtual SessionStatePtr create(RequestHeaderMap& headers) const PURE;

};

using SessionStateFactorySharedPtr = std::shared_ptr<SessionStateFactory>;

/*

 * Extension configuration for session state factory.

 */

class SessionStateFactoryConfig : public Envoy::Config::TypedFactory {

public:

  /**

   * Creates a particular session state factory implementation.

   *

   * @param config supplies the configuration for the session state factory extension.

   * @param context supplies the factory context. Please don't store the reference to

   * the context as it is only valid during the call.

   * @return SessionStateFactorySharedPtr the session state factory.

   */

  virtual SessionStateFactorySharedPtr

  createSessionStateFactory(const Protobuf::Message& config,

                            Server::Configuration::GenericFactoryContext& context) PURE;

};

using SessionStateFactoryConfigPtr = std::unique_ptr<SessionStateFactoryConfig>;

} // namespace Http

} // namespace Envoy