Add sampler header file

sdk/include/opentelemetry/sdk/trace/sampler.h

@@ -0,0 +1,96 @@
+#pragma once
+
+#include "opentelemetry/common/attribute_value.h"
+#include "opentelemetry/nostd/string_view.h"
+#include "opentelemetry/nostd/span.h"
+#include "opentelemetry/sdk/common/atomic_shared_ptr.h"
+#include "opentelemetry/trace/span.h"
+#include "opentelemetry/trace/trace_id.h"
+#include "opentelemetry/trace/tracer.h"
+#include "opentelemetry/version.h"
+
+#include <map>
+#include <memory>
+#include <string>
+
+OPENTELEMETRY_BEGIN_NAMESPACE
+namespace sdk
+{
+namespace trace
+{
+namespace trace_api = opentelemetry::trace;
+class Sampler
+{
+private:
+  // Placeholder
+  class SpanContext
+  {};
+
+public:
+  virtual ~Sampler() = default;
+  /**
+   * Called during Span creation to make a sampling decision.
+   *
+   * @param parent_context TODO: the parent span's SpanContext. null if this is a root
+   *     span.
+   * @param traceId the TraceId for the new Span. This will be identical to that in
+   *     the parentContext, unless this is a root span.
+   * @param name the name of the new Span.
+   * @param parentLinks TODO: the parentLinks associated with the new Span.
+   * @param spanKind the trace_api::SpanKind of the Span.
+   * @param attributes TODO: current map is a placeholder.
+   *     list of AttributeValue with their keys.
+   * @return sampling decision whether span should be sampled or not.
+   * @since 0.1.0
+   */
+
+  virtual SamplingResult ShouldSample(
+      std::shared_ptr<SpanContext> parent_context,
+      trace_api::TraceId trace_id,
+      nostd::string_view name,
+      trace_api::SpanKind span_kind,
+      nostd::span<std::pair<nostd::string_view, common::AttributeValue>> attributes) noexcept = 0;
+
+  /**
+   * Returns the description of this {@code Sampler}. This may be displayed on debug pages or in the
+   * logs.
+   *
+   * <p>Example: "ProbabilitySampler{0.000100}"
+   *
+   * @return the description of this {@code Sampler}.
+   */
+  virtual std::string GetDescription() const noexcept = 0;
+};
+
+class SamplingResult
+{
+private:
+  enum Decision
+  {
+    NOT_RECORD,
+    RECORD,
+    RECORD_AND_SAMPLE
+  };
+
+public:
+  // TODO: add Decision enum
+  virtual ~SamplingResult() = default;
+  /**
+   * Return sampling decision whether span should be sampled or not.
+   *
+   * @return TODO: Decision.
+   */
+  virtual Decision GetDecision() const noexcept = 0;
+
+  /**
+   * Return attributes which will be attached to the span.
+   *
+   * TODO: Change return value to nostd::span<std::pair<nostd::string_view, common::AttributeValue>>
+   * @return attributes added to span. These attributes should be added to the span only for root
+   *     span or when sampling decision isSampled() changes from false to true.
+   */
+  virtual nostd::span<std::pair<nostd::string_view, common::AttributeValue>> GetAttributes() const noexcept = 0;
+};
+}  // namespace trace
+}  // namespace sdk
+OPENTELEMETRY_END_NAMESPACE