// Copyright 2020 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.

#include "src/local_aggregation/aggregation_procedures/string_histogram_aggregation_procedure.h"

#include <tuple>

#include "src/lib/util/datetime_util.h"
#include "src/lib/util/hash.h"
#include "src/local_aggregation/aggregation_procedures/aggregation_procedure.h"
#include "src/logger/encoder.h"
#include "src/pb/observation.pb.h"
#include "src/public/lib/statusor/status_macros.h"

namespace cobalt::local_aggregation {

void StringHistogramAggregationProcedure::UpdateAggregateData(
    const logger::EventRecord &event_record, AggregateData &aggregate_data,
    AggregationPeriodBucket &bucket) {
  StringHistogram *histogram = aggregate_data.mutable_string_histogram();

  // TODO(https://fxbug.dev/322409910): Delete usage of legacy hash after clients no longer store
  // them. Continue to use legacy hashes if they're already stored in the current aggregation period
  // bucket. Use Farmhash Fingerprint 64 hashes otherwise.
  bool use_legacy_hash = !bucket.string_hashes().empty();
  std::string bytes =
      use_legacy_hash
          ? util::FarmhashFingerprint(event_record.event()->string_event().string_value())
          : util::FarmhashFingerprint64(event_record.event()->string_event().string_value());
  const google::protobuf::RepeatedPtrField<std::string> &string_hashes =
      use_legacy_hash ? bucket.string_hashes() : bucket.string_hashes_ff64();

  for (int i = 0; i < string_hashes.size(); i++) {
    if (string_hashes.at(i) == bytes) {
      (*histogram->mutable_histogram())[i] += 1;
      return;
    }
  }

  if (string_hashes.size() < string_buffer_max_) {
    // Add new entry
    (*histogram->mutable_histogram())[string_hashes.size()] += 1;
    if (use_legacy_hash) {
      bucket.add_string_hashes(bytes);
    } else {
      bucket.add_string_hashes_ff64(bytes);
    }
  }
}

void StringHistogramAggregationProcedure::MergeAggregateData(AggregateData &merged_aggregate_data,
                                                             const AggregateData &aggregate_data) {
  // Merge in the aggregate data's mapping of indexes to their count.
  // This only works correctly if the AggregateData objects are both part of the same
  // AggregationPeriodBucket, such that their string_index values both refer to the same repeated
  // string_hashes field in the bucket.
  for (const auto &[string_index, count] : aggregate_data.string_histogram().histogram()) {
    (*merged_aggregate_data.mutable_string_histogram()->mutable_histogram())[string_index] += count;
  }
}

lib::statusor::StatusOr<std::unique_ptr<Observation>>
StringHistogramAggregationProcedure::GenerateHourlyObservation(
    const AggregateDataToGenerate &bucket) {
  std::vector<std::tuple<std::vector<uint32_t>, std::vector<std::tuple<uint32_t, int64_t>>>> data;
  data.reserve(bucket.aggregate_data.size());

  for (const EventCodesAggregateData &aggregate_data : bucket.aggregate_data) {
    const StringHistogram &histogram = aggregate_data.data().string_histogram();
    std::vector<uint32_t> event_codes(aggregate_data.event_codes().begin(),
                                      aggregate_data.event_codes().end());
    std::vector<std::tuple<uint32_t, int64_t>> event_code_histogram;
    for (const auto &[index, count] : histogram.histogram()) {
      event_code_histogram.emplace_back(index, count);
    }

    data.emplace_back(event_codes, event_code_histogram);
  }

  if (data.empty()) {
    return {nullptr};
  }

  std::vector<std::string> hashes;
  for (const std::string &hash : bucket.string_hashes) {
    hashes.push_back(hash);
  }

  return logger::encoder::EncodeStringHistogramObservation(hashes, data, bucket.use_legacy_hash);
}

std::string StringHistogramAggregationProcedure::DebugString() const { return "STRING_HISTOGRAM"; }

}  // namespace cobalt::local_aggregation