#pragma once

#include <cstdint>

#include <memory>

#include "envoy/common/pure.h"

#include "envoy/common/time.h"

#include "envoy/stats/histogram.h"

#include "envoy/stats/primitive_stats.h"

#include "envoy/stats/stats.h"

namespace Envoy {

namespace Stats {

class Histogram;

class MetricSnapshot {

public:

  struct CounterSnapshot {

    uint64_t delta_;

    std::reference_wrapper<const Counter> counter_;

  };

  /**

   * @return a snapshot of all counters with pre-latched deltas.

   */

  virtual const std::vector<CounterSnapshot>& counters() PURE;

  /**

   * @return a snapshot of all gauges.

   */

  virtual const std::vector<std::reference_wrapper<const Gauge>>& gauges() PURE;

  /**

   * @return a snapshot of all histograms.

   */

  virtual const std::vector<std::reference_wrapper<const ParentHistogram>>& histograms() PURE;

  /**

   * @return a snapshot of all text readouts.

   */

  virtual const std::vector<std::reference_wrapper<const TextReadout>>& textReadouts() PURE;

  /**

   * @return a snapshot of all host/endpoint-specific primitive counters.

   */

  virtual const std::vector<Stats::PrimitiveCounterSnapshot>& hostCounters() PURE;

  /**

   * @return a snapshot of all host/endpoint-specific primitive gauges.

   */

  virtual const std::vector<Stats::PrimitiveGaugeSnapshot>& hostGauges() PURE;

  /**

   * @return the time in UTC since epoch when the snapshot was created.

   */

  virtual SystemTime snapshotTime() const PURE;

};

/**

 * A class to define predicates to filter counters, gauges and text readouts for flushing to sinks.

 */

class SinkPredicates {

public:

  /**

   * @return true if @param counter needs to be flushed to sinks.

   */

  virtual bool includeCounter(const Counter& counter) PURE;

  /**

   * @return true if @param gauge needs to be flushed to sinks.

   */

  virtual bool includeGauge(const Gauge& gauge) PURE;

  /**

   * @return true if @param text_readout needs to be flushed to sinks.

   */

  virtual bool includeTextReadout(const TextReadout& text_readout) PURE;

  /*

   * @return true if @param histogram needs to be flushed to sinks.

   */

  virtual bool includeHistogram(const Histogram& histogram) PURE;

};

/**

 * A sink for stats. Each sink is responsible for writing stats to a backing store.

 */

class Sink {

public:

  /**

   * Periodic metric flush to the sink.

   * @param snapshot interface through which the sink can access all metrics being flushed.

   */

  virtual void flush(MetricSnapshot& snapshot) PURE;

  /**

   * Flush a single histogram sample. Note: this call is called synchronously as a part of recording

   * the metric, so implementations must be thread-safe.

   * @param histogram the histogram that this sample applies to.

   * @param value the value of the sample.

   */

  virtual void onHistogramComplete(const Histogram& histogram, uint64_t value) PURE;

};

using SinkPtr = std::unique_ptr<Sink>;

} // namespace Stats

} // namespace Envoy