// Copyright 2017 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
//
// This class maintains an inverted index for fuchsia::modular::ContextMetadata
// structs. It helps answer the question "what objects have metadata that
// matches these key/value pairs" very efficiently.

#ifndef PERIDOT_BIN_CONTEXT_ENGINE_INDEX_H_
#define PERIDOT_BIN_CONTEXT_ENGINE_INDEX_H_

#include <map>
#include <set>
#include <string>

#include <fuchsia/modular/cpp/fidl.h>

namespace modular {

namespace internal {

// Returns a set of strings which encode both the keys and values in |metadata|
// and |type| for use in an inverted index.
std::set<std::string> EncodeMetadataAndType(
    fuchsia::modular::ContextValueType node_type,
    const fuchsia::modular::ContextMetadataPtr& metadata);
std::set<std::string> EncodeMetadataAndType(
    fuchsia::modular::ContextValueType node_type,
    const fuchsia::modular::ContextMetadata& metadata);
}  // namespace internal

class ContextIndex {
 public:
  // TODO(thatguy): Move this enum into context_repository.cc.
  using Id = std::string;

  ContextIndex();
  ~ContextIndex();

  void Add(Id id, fuchsia::modular::ContextValueType type,
           const fuchsia::modular::ContextMetadata& metadata);
  void Remove(Id id, fuchsia::modular::ContextValueType type,
              const fuchsia::modular::ContextMetadata& metadata);

  // Intersects the ids in |out| with those of type |type| and match every
  // field in |metadata|.
  void Query(fuchsia::modular::ContextValueType type,
             const fuchsia::modular::ContextMetadataPtr& metadata,
             std::set<Id>* out);

 private:
  // A posting list from encoded value list to ids.
  std::map<std::string, std::set<Id>> index_;
};

}  // namespace modular

#endif  // PERIDOT_BIN_CONTEXT_ENGINE_INDEX_H_