////////////////////////////////////////////////////////////////////////////////
/// DISCLAIMER
///
/// Copyright 2016 ArangoDB GmbH, Cologne, Germany
///
/// Licensed under the Apache License, Version 2.0 (the "License");
/// you may not use this file except in compliance with the License.
/// You may obtain a copy of the License at
///
///     http://www.apache.org/licenses/LICENSE-2.0
///
/// Unless required by applicable law or agreed to in writing, software
/// distributed under the License is distributed on an "AS IS" BASIS,
/// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
/// See the License for the specific language governing permissions and
/// limitations under the License.
///
/// Copyright holder is ArangoDB GmbH, Cologne, Germany
///
/// @author Simon Grätzer
////////////////////////////////////////////////////////////////////////////////

#include "SSSP.h"
#include "Pregel/Algorithm.h"
#include "Pregel/GraphStore.h"
#include "Pregel/IncomingCache.h"
#include "Pregel/VertexComputation.h"

using namespace arangodb;
using namespace arangodb::pregel;
using namespace arangodb::pregel::algos;

struct SSSPComputation : public VertexComputation<int64_t, int64_t, int64_t> {
  SSSPComputation() {}
  void compute(MessageIterator<int64_t> const& messages) override {
    int64_t tmp = vertexData();
    for (const int64_t* msg : messages) {
      if (*msg < tmp) {
        tmp = *msg;
      };
    }
    int64_t* state = mutableVertexData();
    if (tmp < *state || (tmp == 0 && localSuperstep() == 0)) {
      *state = tmp;  // update state

      RangeIterator<Edge<int64_t>> edges = getEdges();
      for (; edges.hasMore(); ++edges) {
        Edge<int64_t>* edge = *edges;
        int64_t val = edge->data() + tmp;
        sendMessage(edge, val);
      }
    }
    voteHalt();
  }
};

uint32_t SSSPAlgorithm::messageBatchSize(WorkerConfig const& config,
                                         MessageStats const& stats) const {
  if (config.localSuperstep() <= 1) {
    return 5;
  } else {
    double msgsPerSec = stats.sendCount / stats.superstepRuntimeSecs;
    msgsPerSec /= config.parallelism();  // per thread
    return msgsPerSec > 100.0 ? (uint32_t)msgsPerSec : 100;
  }
}

VertexComputation<int64_t, int64_t, int64_t>* SSSPAlgorithm::createComputation(
    WorkerConfig const* config) const {
  return new SSSPComputation();
}

struct SSSPGraphFormat : public InitGraphFormat<int64_t, int64_t> {
  std::string _sourceDocId, resultField;

 public:
  SSSPGraphFormat(application_features::ApplicationServer& server,
                  std::string const& source, std::string const& result)
      : InitGraphFormat<int64_t, int64_t>(server, result, 0, 1),
        _sourceDocId(source) {}

  void copyVertexData(std::string const& documentId, arangodb::velocypack::Slice document,
                        int64_t& targetPtr) override {
    targetPtr = (documentId == _sourceDocId) ? 0 : INT64_MAX;
  }

  bool buildEdgeDocument(arangodb::velocypack::Builder& b,
                         const int64_t* targetPtr, size_t size) const override {
    return false;
  }
};

GraphFormat<int64_t, int64_t>* SSSPAlgorithm::inputFormat() const {
  return new SSSPGraphFormat(_server, _sourceDocumentId, _resultField);
}

struct SSSPCompensation : public VertexCompensation<int64_t, int64_t, int64_t> {
  SSSPCompensation() {}
  void compensate(bool inLostPartition) override {
    if (inLostPartition) {
      int64_t* data = mutableVertexData();
      *data = INT64_MAX;
    }
    voteActive();
  }
};

VertexCompensation<int64_t, int64_t, int64_t>* SSSPAlgorithm::createCompensation(
    WorkerConfig const* config) const {
  return new SSSPCompensation();
}