#pragma once

#include "envoy/common/optref.h"

#include "envoy/server/admin.h"

#include "envoy/stats/stats.h"

#include "source/common/buffer/buffer_impl.h"

#include "source/common/json/json_streamer.h"

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

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

namespace Envoy {

namespace Server {

// Abstract class for rendering stats. Every method is called "generate"

// differing only by the data type, to facilitate templatized call-sites.

//

// There are currently Json and Text implementations of this interface, and in

// #19546 an HTML version will be added to provide a hierarchical view.

class StatsRender {

public:

  virtual ~StatsRender() = default;

  // Writes a fragment for a numeric value, for counters and gauges.

  virtual void generate(Buffer::Instance& response, const std::string& name, uint64_t value) PURE;

  // Writes a json fragment for a textual value, for text readouts.

  virtual void generate(Buffer::Instance& response, const std::string& name,

                        const std::string& value) PURE;

  // Writes a histogram value.

  virtual void generate(Buffer::Instance& response, const std::string& name,

                        const Stats::ParentHistogram& histogram) PURE;

  // Completes rendering any buffered data.

  virtual void finalize(Buffer::Instance& response) PURE;

  // Indicates that no stats for a particular type have been found.

  virtual void noStats(Buffer::Instance&, absl::string_view) {}

};

// Implements the Render interface for simple textual representation of stats.

class StatsTextRender : public StatsRender {

public:

  explicit StatsTextRender(const StatsParams& params);

  // StatsRender

  void generate(Buffer::Instance& response, const std::string& name, uint64_t value) override;

  void generate(Buffer::Instance& response, const std::string& name,

                const std::string& value) override;

  void generate(Buffer::Instance& response, const std::string& name,

                const Stats::ParentHistogram& histogram) override;

  void finalize(Buffer::Instance&) override;

private:

  // Computes disjoint buckets as text and adds them to the response buffer.

  void addDisjointBuckets(const std::string& name, const Stats::ParentHistogram& histogram,

                          Buffer::Instance& response);

  void addDetail(const std::vector<Stats::ParentHistogram::Bucket>& buckets,

                 Buffer::Instance& response);

  const Utility::HistogramBucketsMode histogram_buckets_mode_;

};

// Implements the Render interface for json output.

class StatsJsonRender : public StatsRender {

public:

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

                  const StatsParams& params);

  // StatsRender

  void generate(Buffer::Instance& response, const std::string& name, uint64_t value) override;

  void generate(Buffer::Instance& response, const std::string& name,

                const std::string& value) override;

  void generate(Buffer::Instance&, const std::string& name,

                const Stats::ParentHistogram& histogram) override;

  void finalize(Buffer::Instance& response) override;

  /**

   * Streams the supported percentiles into a JSON array. Note that no histogram

   * context is provided for this; this is a static property of the binary.

   *

   * @param array the json streaming array array to stream into.

   */

  static void populateSupportedPercentiles(Json::Streamer::Array& array);

  /**

   * Streams detail about the provided histogram into the provided JSON map.

   *

   * @param name the name of the histogram (usually the same as histogram.name(),

   *             but is passed in explicitly because it may already have been

   *             computed when filtering stats, and it is somewhat expensive

   *             to compute the name.

   * @param histogram the histogram to stream

   * @param map the json map to stream into.

   *

   */

  static void generateHistogramDetail(const std::string& name,

                                      const Stats::ParentHistogram& histogram,

                                      Json::Streamer::Map& map);

private:

  // Collects the buckets from the specified histogram.

  void collectBuckets(const std::string& name, const Stats::ParentHistogram& histogram,

                      const std::vector<uint64_t>& interval_buckets,

                      const std::vector<uint64_t>& cumulative_buckets);

  static void populateBucketsVerbose(const std::vector<Stats::ParentHistogram::Bucket>& buckets,

                                     Json::Streamer::Map& map);

  void renderHistogramStart();

  static void populatePercentiles(const Stats::ParentHistogram& histogram,

                                  Json::Streamer::Map& map);

  // This function irons out an API mistake made when defining the StatsRender

  // interface. The issue is that callers can provide a response buffer when

  // constructing a StatsRender instance, but can switch to a different response

  // buffer when rendering specific values.

  //

  // The problem comes with JSON histograms where each histogram is nested in a

  // structure with other histograms, so if you switch buffers you need to

  // ensure the pending bytes in the previous buffer is fully

  // drained. Unfortunately this buffer-switching is used in practice.

  void drainIfNeeded(Buffer::Instance& response);

  const Utility::HistogramBucketsMode histogram_buckets_mode_;

  std::string name_buffer_;  // Used for Json::sanitize for names.

  std::string value_buffer_; // Used for Json::sanitize for text-readout values.

  bool histograms_initialized_{false};

  // Captures the hierarchy of maps and arrays used to render scalar stats and

  // histograms in various formats. This is separated in its own structure to

  // facilitate clearing these structures in the reverse order of how they were

  // created during finalize().

  //

  // Another option to consider: flattening the member variables of JsonContext

  // into StatsJsonRender, and ensure that Render objects are always destructed

  // before the output stream is considered complete.

  struct JsonContext {

    explicit JsonContext(Buffer::Instance& response);

    Json::Streamer streamer_;

    Json::Streamer::MapPtr stats_map_;

    Json::Streamer::ArrayPtr stats_array_;

    Json::Streamer::MapPtr histogram_map1_;

    Json::Streamer::MapPtr histogram_map2_;

    Json::Streamer::ArrayPtr histogram_array_;

  };

  std::unique_ptr<JsonContext> json_;

  Buffer::Instance& response_;

};

} // namespace Server

} // namespace Envoy