#pragma once

#include "envoy/http/header_map.h"

#include "envoy/tracing/trace_context.h"

namespace Envoy {

namespace Tracing {

using InlineHandle = Http::CustomInlineHeaderRegistry::Handle<

    Http::CustomInlineHeaderRegistry::Type::RequestHeaders>;

/**

 * A handler class for trace context. This class could be used to set, get and erase the key/value

 * pair in the trace context. This handler is optimized for HTTP to support reference semantics and

 * inline header. If HTTP header is used as the trace context and the key is registered in the

 * custom inline header registry, then inline handle will be used to improve the performance.

 */

class TraceContextHandler {

public:

  /**

   * Construct a handler with the given key. Note that the key will be lowercase and copied.

   * @param key the key of the handler.

   */

  TraceContextHandler(absl::string_view key);

  /**

   * Get the key of the handler.

   * @return absl::string_view the key of the handler. Note that the key is lowercase.

   */

  /**

   * Erase the key/value pair from the trace context.

   * @param trace_context the trace context to erase the key/value pair.

   */

  void remove(TraceContext& trace_context) const;

  /**

   * Get the value from the trace context by the key.

   * @param trace_context the trace context to get the value.

   * @return absl::optional<absl::string_view> the value of the key. If the key is not found, then

   * absl::nullopt will be returned.

   */

  absl::optional<absl::string_view> get(const TraceContext& trace_context) const;

  using GetAllResult = absl::InlinedVector<absl::string_view, 1>;

  /**

   * Get all values from the trace context by the key. If the underlying trace context is HTTP

   * header map, then there may be multiple values for the same key and the get() method will

   * return the first value only. This method will return all values for the key.

   * @param trace_context the trace context to get the values.

   */

  GetAllResult getAll(const TraceContext& trace_context) const;

  /*

   * Set the key/value pair in the trace context.

   * @param trace_context the trace context to set the key/value pair.

   * @param value the value to set.

   */

  void set(TraceContext& trace_context, absl::string_view value) const;

  /**

   * Set the key/value pair in the trace context. This method should only be used when the handler

   * has longer lifetime than current stream.

   * @param trace_context the trace context to set the key/value pair.

   * @param value the value to set.

   */

  void setRefKey(TraceContext& trace_context, absl::string_view value) const;

  /**

   * Set the key/value pair in the trace context. This method should only be used when both the

   * handler and the value have longer lifetime than current stream.

   * @param trace_context the trace context to set the key/value pair.

   * @param value the value to set.

   */

  void setRef(TraceContext& trace_context, absl::string_view value) const;

private:

  const Http::LowerCaseString key_;

  absl::optional<InlineHandle> handle_;

};

} // namespace Tracing

} // namespace Envoy