#pragma once

#include <string>

#include "envoy/buffer/buffer.h"

#include "envoy/stats/custom_stat_namespaces.h"

#include "envoy/stats/histogram.h"

#include "envoy/stats/stats.h"

#include "source/server/admin/stats_params.h"

namespace Envoy {

namespace Server {

/**

 * Formatter for metric/labels exported to Prometheus.

 *

 * See: https://prometheus.io/docs/concepts/data_model

 */

class PrometheusStatsFormatter {

public:

  // Responsible for converting groups of metrics into the raw output format (such as prometheus

  // text exposition format or prometheus protobuf exposition format).

  class OutputFormat {

  public:

    enum class HistogramType {

      Summary,

      ClassicHistogram,

      NativeHistogram,

    };

    // Return the prometheus output for a group of Counters.

    virtual void generateOutput(Buffer::Instance& output,

                                const std::vector<const Stats::Counter*>& counters,

                                const std::string& prefixed_tag_extracted_name) const PURE;

    // Return the prometheus output for a group of PrimitiveCounters.

    virtual void generateOutput(Buffer::Instance& output,

                                const std::vector<const Stats::PrimitiveCounterSnapshot*>& counters,

                                const std::string& prefixed_tag_extracted_name) const PURE;

    // Return the prometheus output for a group of Gauges.

    virtual void generateOutput(Buffer::Instance& output,

                                const std::vector<const Stats::Gauge*>& gauges,

                                const std::string& prefixed_tag_extracted_name) const PURE;

    // Returns the prometheus output for a group of TextReadouts.

    virtual void generateOutput(Buffer::Instance& output,

                                const std::vector<const Stats::TextReadout*>& text_readouts,

                                const std::string& prefixed_tag_extracted_name) const PURE;

    // Return the prometheus output for a group of PrimitiveGauges.

    virtual void generateOutput(Buffer::Instance& output,

                                const std::vector<const Stats::PrimitiveGaugeSnapshot*>& gauges,

                                const std::string& prefixed_tag_extracted_name) const PURE;

    // Return the prometheus output for a group of Histograms.

    virtual void generateOutput(Buffer::Instance& output,

                                const std::vector<const Stats::ParentHistogram*>& histograms,

                                const std::string& prefixed_tag_extracted_name) const PURE;

  private:

    HistogramType histogram_type_;

  };

  /**

   * Extracts counters and gauges and relevant tags, appending them to

   * the response buffer after sanitizing the metric / label names.

   * Detects based on request headers whether to emit text or protobuf format.

   * @return uint64_t total number of metric types inserted in response.

   */

  static uint64_t statsAsPrometheus(const std::vector<Stats::CounterSharedPtr>& counters,

                                    const std::vector<Stats::GaugeSharedPtr>& gauges,

                                    const std::vector<Stats::ParentHistogramSharedPtr>& histograms,

                                    const std::vector<Stats::TextReadoutSharedPtr>& text_readouts,

                                    const Upstream::ClusterManager& cluster_manager,

                                    const Http::RequestHeaderMap& request_headers,

                                    Http::ResponseHeaderMap& response_headers,

                                    Buffer::Instance& response, const StatsParams& params,

                                    const Stats::CustomStatNamespaces& custom_namespaces);

  static uint64_t

  statsAsPrometheusText(const std::vector<Stats::CounterSharedPtr>& counters,

                        const std::vector<Stats::GaugeSharedPtr>& gauges,

                        const std::vector<Stats::ParentHistogramSharedPtr>& histograms,

                        const std::vector<Stats::TextReadoutSharedPtr>& text_readouts,

                        const Upstream::ClusterManager& cluster_manager, Buffer::Instance& response,

                        const StatsParams& params,

                        const Stats::CustomStatNamespaces& custom_namespaces);

  static uint64_t

  statsAsPrometheusProtobuf(const std::vector<Stats::CounterSharedPtr>& counters,

                            const std::vector<Stats::GaugeSharedPtr>& gauges,

                            const std::vector<Stats::ParentHistogramSharedPtr>& histograms,

                            const std::vector<Stats::TextReadoutSharedPtr>& text_readouts,

                            const Upstream::ClusterManager& cluster_manager,

                            Http::ResponseHeaderMap& response_headers, Buffer::Instance& response,

                            const StatsParams& params,

                            const Stats::CustomStatNamespaces& custom_namespaces);

  static uint64_t

  generateWithOutputFormat(const std::vector<Stats::CounterSharedPtr>& counters,

                           const std::vector<Stats::GaugeSharedPtr>& gauges,

                           const std::vector<Stats::ParentHistogramSharedPtr>& histograms,

                           const std::vector<Stats::TextReadoutSharedPtr>& text_readouts,

                           const Upstream::ClusterManager& cluster_manager,

                           Buffer::Instance& response, const StatsParams& params,

                           const Stats::CustomStatNamespaces& custom_namespaces,

                           OutputFormat& output_format);

  /**

   * Format the given tags, returning a string as a comma-separated list

   * of <tag_name>="<tag_value>" pairs.

   */

  static std::string formattedTags(const std::vector<Stats::Tag>& tags);

  /**

   * Validate the given params, returning an error on invalid arguments

   */

  static absl::Status validateParams(const StatsParams& params,

                                     const Http::RequestHeaderMap& headers);

  /**

   * Format the given metric name, and prefixed with "envoy_" if it does not have a custom

   * stat namespace. If it has a custom stat namespace AND the name without the custom namespace

   * has a valid prometheus namespace, the trimmed name is returned.

   * Otherwise, return nullopt.

   */

  static absl::optional<std::string>

  metricName(const std::string& extracted_name,

             const Stats::CustomStatNamespaces& custom_namespace_factory);

};

} // namespace Server

} // namespace Envoy