#include <gtest/gtest.h>
#include <xgboost/base.h>
#include "../../../../src/tree/hist/evaluate_splits.h"
#include "../../../../src/tree/updater_quantile_hist.h"
#include "../../../../src/common/hist_util.h"
#include "../../helpers.h"

namespace xgboost {
namespace tree {

template <typename GradientSumT> void TestEvaluateSplits() {
  int static constexpr kRows = 8, kCols = 16;
  auto orig = omp_get_max_threads();
  int32_t n_threads = std::min(omp_get_max_threads(), 4);
  omp_set_num_threads(n_threads);
  auto sampler = std::make_shared<common::ColumnSampler>();

  TrainParam param;
  param.UpdateAllowUnknown(Args{{}});
  param.min_child_weight = 0;
  param.reg_lambda = 0;

  auto dmat = RandomDataGenerator(kRows, kCols, 0).Seed(3).GenerateDMatrix();

  auto evaluator =
      HistEvaluator<GradientSumT, CPUExpandEntry>{param, dmat->Info(), n_threads, sampler};
  common::HistCollection<GradientSumT> hist;
  std::vector<GradientPair> row_gpairs = {
      {1.23f, 0.24f}, {0.24f, 0.25f}, {0.26f, 0.27f},  {2.27f, 0.28f},
      {0.27f, 0.29f}, {0.37f, 0.39f}, {-0.47f, 0.49f}, {0.57f, 0.59f}};

  size_t constexpr kMaxBins = 4;
  // dense, no missing values

  GHistIndexMatrix gmat(dmat.get(), kMaxBins);
  common::RowSetCollection row_set_collection;
  std::vector<size_t> &row_indices = *row_set_collection.Data();
  row_indices.resize(kRows);
  std::iota(row_indices.begin(), row_indices.end(), 0);
  row_set_collection.Init();

  auto hist_builder = GHistBuilder<GradientSumT>(n_threads, gmat.cut.Ptrs().back());
  hist.Init(gmat.cut.Ptrs().back());
  hist.AddHistRow(0);
  hist.AllocateAllData();
  hist_builder.template BuildHist<false>(row_gpairs, row_set_collection[0],
                                         gmat, hist[0]);

  // Compute total gradient for all data points
  GradientPairPrecise total_gpair;
  for (const auto &e : row_gpairs) {
    total_gpair += GradientPairPrecise(e);
  }

  RegTree tree;
  std::vector<CPUExpandEntry> entries(1);
  entries.front().nid = 0;
  entries.front().depth = 0;

  evaluator.InitRoot(GradStats{total_gpair});
  evaluator.EvaluateSplits(hist, gmat.cut, tree, &entries);

  auto best_loss_chg =
      evaluator.Evaluator().CalcSplitGain(
          param, 0, entries.front().split.SplitIndex(),
          entries.front().split.left_sum, entries.front().split.right_sum) -
      evaluator.Stats().front().root_gain;
  ASSERT_EQ(entries.front().split.loss_chg, best_loss_chg);
  ASSERT_GT(entries.front().split.loss_chg, 16.2f);

  // Assert that's the best split
  for (size_t i = 1; i < gmat.cut.Ptrs().size(); ++i) {
    GradStats left, right;
    for (size_t j = gmat.cut.Ptrs()[i-1]; j < gmat.cut.Ptrs()[i]; ++j) {
      auto loss_chg =
          evaluator.Evaluator().CalcSplitGain(param, 0, i - 1, left, right) -
          evaluator.Stats().front().root_gain;
      ASSERT_GE(best_loss_chg, loss_chg);
      left.Add(hist[0][j].GetGrad(), hist[0][j].GetHess());
      right.SetSubstract(GradStats{total_gpair}, left);
    }
  }

  omp_set_num_threads(orig);
}

TEST(HistEvaluator, Evaluate) {
  TestEvaluateSplits<float>();
  TestEvaluateSplits<double>();
}

TEST(HistEvaluator, Apply) {
  RegTree tree;
  int static constexpr kNRows = 8, kNCols = 16;
  TrainParam param;
  param.UpdateAllowUnknown(Args{{}});
  auto dmat = RandomDataGenerator(kNRows, kNCols, 0).Seed(3).GenerateDMatrix();
  auto sampler = std::make_shared<common::ColumnSampler>();
  auto evaluator_ =
      HistEvaluator<float, CPUExpandEntry>{param, dmat->Info(), 4, sampler};

  CPUExpandEntry entry{0, 0, 10.0f};
  entry.split.left_sum = GradStats{0.4, 0.6f};
  entry.split.right_sum = GradStats{0.5, 0.7f};

  evaluator_.ApplyTreeSplit(entry, &tree);
  ASSERT_EQ(tree.NumExtraNodes(), 2);
  ASSERT_EQ(tree.Stat(tree[0].LeftChild()).sum_hess, 0.6f);
  ASSERT_EQ(tree.Stat(tree[0].RightChild()).sum_hess, 0.7f);
}
}  // namespace tree
}  // namespace xgboost
