// Copyright 2017 Google Inc. All Rights Reserved.
//
// This file contains the declarations for the Metric class and related
// types.
#ifndef WVCDM_METRICS_VALUE_METRIC_H_
#define WVCDM_METRICS_VALUE_METRIC_H_

#include <stdint.h>
#include <string>

#include "metric_serialization.h"

namespace wvcdm {
namespace metrics {

// Private namespace for some helper implementation functions.
namespace impl {

// These helper functions map the templated ValueMetric class
// Serialize call to the MetricSerializer explicit calls.
template<typename T>
void Serialize(MetricSerializer* serializer,
               const std::string& metric_name, const T& t);

inline void SerializeError(MetricSerializer* serializer,
                           const std::string& metric_name,
                           const int& error_code) {
  serializer->SetInt32(metric_name + "/error", error_code);
}

} // namespace impl

// The Metric class supports storing a single value which can be overwritten.
// the Metric class also supports the MetricSerializer interface through
// which the value can be serialized. If the value was never given a value
// or an error code, then the metric will not serialize anything.
//
// Example Usage:
//   Metric<string> cdm_version("drm/cdm/version")
//       .Record("a.b.c.d");
//
//   MyMetricSerializerImpl serialzer;
//   cdm_version.Serialize(&serializer);
//
// Example Error Usage:
//
//   Metric<string> cdm_version("drm/cdm/version")
//       .SetError(error_code);
//
// Note that serialization is the same. But the ValueMetric will serialize
// the error code to <metric_name>/error instead of just <metric_name>.
template<typename T>
class ValueMetric : public MetricSerializable {
 public:
  // Constructs a metric with the given metric name.
  explicit ValueMetric(const std::string& metric_name)
      : metric_name_(metric_name), error_code_(0),
        has_error_(false), has_value_(false) {}

  // Serialize the metric name and value using the given serializer.
  // Caller owns |serializer| which cannot be null.
  virtual void Serialize(MetricSerializer* serializer) {
    if (has_value_) {
      impl::Serialize(serializer, metric_name_, value_);
    } else if (has_error_) {
      impl::SerializeError(serializer, metric_name_, error_code_);
    } else {
      // Do nothing if there is no value and no error.
    }
  }

  // Record the value of the metric.
  void Record(const T& value) {
    value_ = value;
    has_value_ = true;
    has_error_ = false;
  }

  // Set the error code if an error was encountered.
  void SetError(int error_code) {
    error_code_ = error_code;
    has_value_ = false;
    has_error_ = true;
  }

  // Get the current value of the metric.
  const T& GetValue() { return value_; }

  // Clears the indicators that the metric or error was set.
  void Clear() {
    has_value_ = false;
    has_error_ = false;
  }

 private:
  std::string metric_name_;
  T value_;
  int error_code_;
  bool has_error_;
  bool has_value_;
};

}  // namespace metrics
}  // namespace wvcdm

#endif  // WVCDM_METRICS_VALUE_METRIC_H_