#pragma once

#include <chrono>

#include <vector>

#include "envoy/api/api.h"

#include "envoy/config/overload/v3/overload.pb.h"

#include "envoy/event/dispatcher.h"

#include "envoy/event/scaled_range_timer_manager.h"

#include "envoy/protobuf/message_validator.h"

#include "envoy/server/options.h"

#include "envoy/server/overload/overload_manager.h"

#include "envoy/server/resource_monitor.h"

#include "envoy/stats/scope.h"

#include "envoy/stats/stats.h"

#include "envoy/thread_local/thread_local.h"

#include "source/common/common/logger.h"

#include "source/common/event/scaled_range_timer_manager_impl.h"

#include "absl/container/node_hash_map.h"

#include "absl/container/node_hash_set.h"

namespace Envoy {

namespace Server {

/**

 * Trigger encapsulates translating resource pressure into the corresponding

 * OverloadActionState.

 */

class Trigger {

public:

  // Updates the current value of the metric and returns whether the trigger has changed state.

  virtual bool updateValue(double value) PURE;

  // Returns the action state for the trigger.

  virtual OverloadActionState actionState() const PURE;

};

class OverloadAction {

public:

  static absl::StatusOr<std::unique_ptr<OverloadAction>>

  create(const envoy::config::overload::v3::OverloadAction& config, Stats::Scope& stats_scope);

  // Updates the current pressure for the given resource and returns whether the action

  // has changed state.

  bool updateResourcePressure(const std::string& name, double pressure);

  // Returns the current action state, which is the max state across all registered triggers.

  OverloadActionState getState() const;

private:

  OverloadAction(const envoy::config::overload::v3::OverloadAction& config,

                 Stats::Scope& stats_scope, absl::Status& creation_status);

  using TriggerPtr = std::unique_ptr<Trigger>;

  absl::node_hash_map<std::string, TriggerPtr> triggers_;

  OverloadActionState state_;

  Stats::Gauge& active_gauge_;

  Stats::Gauge& scale_percent_gauge_;

};

/**

 * Implement a LoadShedPoint which is a particular point in the connection /

 * request lifecycle where we can either abort or continue the given work.

 */

class LoadShedPointImpl : public LoadShedPoint {

public:

  static absl::StatusOr<std::unique_ptr<LoadShedPointImpl>>

  create(const envoy::config::overload::v3::LoadShedPoint& config, Stats::Scope& stats_scope,

         Random::RandomGenerator& random_generator);

  LoadShedPointImpl(const LoadShedPointImpl&) = delete;

  LoadShedPointImpl& operator=(const LoadShedPointImpl&) = delete;

  bool shouldShedLoad() override;

  /**

   * Provide resource updates for the LoadShedPoint. It will update the

   * probability of shedding load at this point atomically if needed.

   * @param resource_name - the name of the resource that has been updated.

   * @param resource_utilization - utilization of this resource. A ratio of the

   *  current usage / the resource limit.

   */

  void updateResource(absl::string_view resource_name, double resource_utilization);

private:

  LoadShedPointImpl(const envoy::config::overload::v3::LoadShedPoint& config,

                    Stats::Scope& stats_scope, Random::RandomGenerator& random_generator,

                    absl::Status& creation_status);

  using TriggerPtr = std::unique_ptr<Trigger>;

  // Helper to handle updating the probability to shed load given the triggers.

  void updateProbabilityShedLoad();

  absl::flat_hash_map<std::string, TriggerPtr> triggers_;

  std::atomic<float> probability_shed_load_{0};

  Stats::Gauge& scale_percent_;

  Stats::Counter& shed_load_counter_;

  Random::RandomGenerator& random_generator_;

};

// Simple table that converts strings into Symbol instances. Symbols are guaranteed to start at 0

// and be indexed sequentially.

class NamedOverloadActionSymbolTable {

public:

  class Symbol {

  public:

    // Allow copy construction everywhere.

    Symbol(const Symbol&) = default;

    // Returns the index of the symbol in the table.

    // Support use as a map key.

    // Support absl::Hash.

    template <typename H>

  private:

    friend class NamedOverloadActionSymbolTable;

    // Only the symbol table class can create Symbol instances from indices.

    size_t index_;

  };

  // Finds an existing or adds a new entry for the given name.

  Symbol get(absl::string_view name);

  // Returns the symbol for the name if there is one, otherwise nullopt.

  absl::optional<Symbol> lookup(absl::string_view string) const;

  // Translates a symbol back into a name.

  const absl::string_view name(Symbol symbol) const;

  // Returns the number of symbols in the table. All symbols are guaranteed to have an index less

  // than size().

private:

  absl::flat_hash_map<std::string, size_t> table_;

  std::vector<std::string> names_;

};

class ThreadLocalOverloadStateImpl;

class OverloadManagerImpl : Logger::Loggable<Logger::Id::main>, public OverloadManager {

public:

  static absl::StatusOr<std::unique_ptr<OverloadManagerImpl>>

  create(Event::Dispatcher& dispatcher, Stats::Scope& stats_scope,

         ThreadLocal::SlotAllocator& slot_allocator,

         const envoy::config::overload::v3::OverloadManager& config,

         ProtobufMessage::ValidationVisitor& validation_visitor, Api::Api& api,

         const Server::Options& options);

  // Server::OverloadManager

  void start() override;

  bool registerForAction(const std::string& action, Event::Dispatcher& dispatcher,

                         OverloadActionCb callback) override;

  ThreadLocalOverloadState& getThreadLocalOverloadState() override;

  LoadShedPoint* getLoadShedPoint(absl::string_view point_name) override;

  Event::ScaledRangeTimerManagerFactory scaledTimerFactory() override;

  void stop() override;

protected:

  OverloadManagerImpl(Event::Dispatcher& dispatcher, Stats::Scope& stats_scope,

                      ThreadLocal::SlotAllocator& slot_allocator,

                      const envoy::config::overload::v3::OverloadManager& config,

                      ProtobufMessage::ValidationVisitor& validation_visitor, Api::Api& api,

                      const Server::Options& options, absl::Status& creation_status);

  // Factory for timer managers. This allows test-only subclasses to inject a mock implementation.

  virtual Event::ScaledRangeTimerManagerPtr createScaledRangeTimerManager(

      Event::Dispatcher& dispatcher,

      const Event::ScaledTimerTypeMapConstSharedPtr& timer_minimums) const;

private:

  using FlushEpochId = uint64_t;

  class Resource : public ResourceUpdateCallbacks {

  public:

    Resource(const std::string& name, ResourceMonitorPtr monitor, OverloadManagerImpl& manager,

             Stats::Scope& stats_scope);

    // ResourceMonitor::ResourceUpdateCallbacks

    void onSuccess(const ResourceUsage& usage) override;

    void onFailure(const EnvoyException& error) override;

    void update(FlushEpochId flush_epoch);

  private:

    const std::string name_;

    ResourceMonitorPtr monitor_;

    OverloadManagerImpl& manager_;

    bool pending_update_{false};

    FlushEpochId flush_epoch_;

    Stats::Gauge& pressure_gauge_;

    Stats::Counter& failed_updates_counter_;

    Stats::Counter& skipped_updates_counter_;

  };

  struct ActionCallback {

    ActionCallback(Event::Dispatcher& dispatcher, OverloadActionCb callback)

    Event::Dispatcher& dispatcher_;

    OverloadActionCb callback_;

  };

  void updateResourcePressure(const std::string& resource, double pressure,

                              FlushEpochId flush_epoch);

  // Flushes any enqueued action state updates to all worker threads.

  void flushResourceUpdates();

  bool started_{false};

  Event::Dispatcher& dispatcher_;

  TimeSource& time_source_;

  ThreadLocal::TypedSlot<ThreadLocalOverloadStateImpl> tls_;

  NamedOverloadActionSymbolTable action_symbol_table_;

  const std::chrono::milliseconds refresh_interval_;

  // Tracks the latency between resource refresh updates.

  Stats::Histogram& refresh_interval_delays_;

  // Tracks when we last ran the resource monitor refresh loop.

  // For the first measurement, we use the time when When the Overload Manager first starts.

  MonotonicTime time_resources_last_measured_;

  Event::TimerPtr timer_;

  absl::node_hash_map<std::string, Resource> resources_;

  std::shared_ptr<absl::node_hash_map<OverloadProactiveResourceName, ProactiveResource>>

      proactive_resources_;

  absl::node_hash_map<NamedOverloadActionSymbolTable::Symbol, std::unique_ptr<OverloadAction>>

      actions_;

  absl::flat_hash_map<std::string, std::unique_ptr<LoadShedPointImpl>> loadshed_points_;

  Event::ScaledTimerTypeMapConstSharedPtr timer_minimums_;

  absl::flat_hash_map<NamedOverloadActionSymbolTable::Symbol, OverloadActionState>

      state_updates_to_flush_;

  absl::flat_hash_map<ActionCallback*, OverloadActionState> callbacks_to_flush_;

  FlushEpochId flush_epoch_ = 0;

  uint64_t flush_awaiting_updates_ = 0;

  using ResourceToActionMap =

      std::unordered_multimap<std::string, NamedOverloadActionSymbolTable::Symbol>;

  ResourceToActionMap resource_to_actions_;

  using ActionToCallbackMap =

      std::unordered_multimap<NamedOverloadActionSymbolTable::Symbol, ActionCallback,

                              absl::Hash<NamedOverloadActionSymbolTable::Symbol>>;

  ActionToCallbackMap action_to_callbacks_;

};

} // namespace Server

} // namespace Envoy