/*
 * Copyright (C) 2010 Google Inc. All rights reserved.
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 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1.  Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 * 2.  Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *
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 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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#ifndef THIRD_PARTY_BLINK_RENDERER_PLATFORM_WTF_POD_INTERVAL_TREE_H_
#define THIRD_PARTY_BLINK_RENDERER_PLATFORM_WTF_POD_INTERVAL_TREE_H_

#include <optional>

#include "third_party/blink/renderer/platform/wtf/pod_arena.h"
#include "third_party/blink/renderer/platform/wtf/pod_interval.h"
#include "third_party/blink/renderer/platform/wtf/pod_red_black_tree.h"
#include "third_party/blink/renderer/platform/wtf/vector.h"

namespace blink {

// An interval tree, which is a form of augmented red-black tree. It
// supports efficient (O(lg n)) insertion, removal and querying of
// intervals in the tree.
template <class T, class UserData = void*>
class PodIntervalTree final : public PodRedBlackTree<PodInterval<T, UserData>> {
 public:
  // Typedef to reduce typing when declaring intervals to be stored in
  // this tree.
  using IntervalType = PodInterval<T, UserData>;

  PodIntervalTree() : PodRedBlackTree<IntervalType>() {}

  PodIntervalTree(const PodIntervalTree&) = delete;
  PodIntervalTree& operator=(const PodIntervalTree&) = delete;

  // Returns all intervals in the tree which overlap the given query
  // interval. The returned intervals are sorted by increasing low
  // endpoint.
  Vector<IntervalType> AllOverlaps(const T& low, const T& high) const {
    Vector<IntervalType> result;
    SearchForOverlapsFrom(this->Root(), low, high, result);
    return result;
  }

  // Helper to create interval objects.
  static IntervalType CreateInterval(const T& low,
                                     const T& high,
                                     const UserData data = nullptr) {
    return IntervalType(low, high, data);
  }

  bool CheckInvariants() const override {
    if (!PodRedBlackTree<IntervalType>::CheckInvariants()) {
      return false;
    }
    if (!this->Root())
      return true;
    return CheckInvariantsFromNode(this->Root());
  }

  // Returns the next interval point (start or end) after the given starting
  // point (non-inclusive). If there is no such point, returns |std::nullopt|.
  std::optional<T> NextIntervalPoint(T start) const {
    return NextIntervalPoint(start, this->Root());
  }

 private:
  using IntervalNode = typename PodRedBlackTree<IntervalType>::Node;

  // Starting from the given node, adds all overlaps with the given
  // interval to the result vector. The intervals are sorted by
  // increasing low endpoint.
  DISABLE_CFI_PERF static void SearchForOverlapsFrom(
      IntervalNode const* node,
      const T& low,
      const T& high,
      Vector<IntervalType>& result) {
    // This is phrased this way to avoid the need for operator
    // <= on type T.
    if (!node || high < node->Data().MinLow() || node->Data().MaxHigh() < low) {
      return;
    }

    // Because the intervals are sorted by left endpoint, inorder
    // traversal produces results sorted as desired.

    // Attempt to traverse left subtree
    SearchForOverlapsFrom(node->Left(), low, high, result);

    // Check for overlap with current node.
    if (node->Data().Overlaps(low, high)) {
      result.push_back(node->Data());
    }

    // Attempt to traverse right subtree
    SearchForOverlapsFrom(node->Right(), low, high, result);
  }

  static std::optional<T> NextIntervalPoint(T start, IntervalNode const* node) {
    // If this node doesn't exist or is entirely out of scope, just return. This
    // prevents recursing deeper than necessary on the left.
    if (!node || node->Data().MaxHigh() < start) {
      return std::nullopt;
    }
    // Easy shortcut: If the lowest point in this subtree is in scope, just
    // return that. This prevents recursing deeper than necessary on the right.
    if (start < node->Data().MinLow()) {
      return node->Data().MinLow();
    }

    auto left_candidate = NextIntervalPoint(start, node->Left());

    // If the current node's low point isn't out of scope, we don't even need to
    // look at the right branch.
    if (start < node->Data().Low()) {
      if (left_candidate.has_value()) {
        return std::min(node->Data().Low(), left_candidate.value());
      } else {
        return node->Data().Low();
      }
    }

    // If the current node's high point is in scope, consider that against the
    // left branch
    std::optional<T> current_candidate;
    if (start < node->Data().High()) {
      if (left_candidate.has_value()) {
        current_candidate =
            std::min(node->Data().High(), left_candidate.value());
      } else {
        current_candidate = node->Data().High();
      }
    } else {
      current_candidate = left_candidate;
    }

    // If the current (and left) nodes fail, tail-recurse on the right node
    if (!current_candidate.has_value()) {
      return NextIntervalPoint(start, node->Right());
    }

    // Otherwise, pick the min between the |current_candidate| and the right
    // node
    auto right_candidate = NextIntervalPoint(start, node->Right());
    if (right_candidate.has_value()) {
      return std::min(current_candidate.value(), right_candidate.value());
    } else {
      return current_candidate;
    }
  }

  bool UpdateNode(IntervalNode* node) override {
    T cur_max(node->Data().High());
    T cur_min(node->Data().Low());

    IntervalNode* left = node->Left();
    if (left) {
      // Left node will always have a lower MinLow than the right node, so just
      // reassign immediately.
      cur_min = left->Data().MinLow();
      cur_max = std::max(cur_max, left->Data().MaxHigh());
    }

    IntervalNode* right = node->Right();
    if (right) {
      // Right node will always have greater min than current node or left
      // branch, so don't bother checking it.
      cur_max = std::max(cur_max, right->Data().MaxHigh());
    }

    bool updated = false;
    if (!(cur_min == node->Data().MinLow())) {
      node->Data().SetMinLow(cur_min);
      updated = true;
    }
    if (!(cur_max == node->Data().MaxHigh())) {
      node->Data().SetMaxHigh(cur_max);
      updated = true;
    }

    return updated;
  }

  static bool CheckInvariantsFromNode(IntervalNode const* node) {
    IntervalNode const* left = node->Left();
    IntervalNode const* right = node->Right();

    T observed_min_value(node->Data().Low());
    T observed_max_value(node->Data().High());

    if (left) {
      // Ensure left branch is entirely valid
      if (!CheckInvariantsFromNode(left)) {
        return false;
      }
      // Ensure that this node's MinLow is equal to MinLow of the left branch
      if (!(left->Data().MinLow() == node->Data().MinLow())) {
        LogVerificationFailedAtNode(node);
        return false;
      }
      // Ensure that this node's MaxHigh is at least MaxHigh of left branch
      if (node->Data().MaxHigh() < left->Data().MaxHigh()) {
        LogVerificationFailedAtNode(node);
        return false;
      }

      observed_min_value = left->Data().MinLow();
      observed_max_value = std::max(observed_max_value, left->Data().MaxHigh());
    }

    if (right) {
      // Ensure right branch is entirely valid
      if (!CheckInvariantsFromNode(right)) {
        return false;
      }
      // Ensure this node's MinLow is not greater than the right node's MinLow
      if (right->Data().MinLow() < node->Data().MinLow()) {
        LogVerificationFailedAtNode(node);
        return false;
      }
      // Ensure that this node's MaxHigh is at least MaxHigh of right branch
      if (node->Data().MaxHigh() < right->Data().MaxHigh()) {
        LogVerificationFailedAtNode(node);
        return false;
      }

      observed_max_value =
          std::max(observed_max_value, right->Data().MaxHigh());
    }

    // Ensure this node's MinLow is the min we actually observed
    if (!(observed_min_value == node->Data().MinLow())) {
      LogVerificationFailedAtNode(node);
      return false;
    }
    // Ensure that this node's MaxHigh is the max we actually observed
    if (!(observed_max_value == node->Data().MaxHigh())) {
      LogVerificationFailedAtNode(node);
      return false;
    }

    return true;
  }

#ifndef NDEBUG
  static void LogVerificationFailedAtNode(IntervalNode const* node) {
    DLOG(ERROR) << "PodIntervalTree verification failed at node " << node
                << ": data=" << node->Data().ToString();
  }
#else
  static void LogVerificationFailedAtNode(IntervalNode const*) {}
#endif
};

#ifndef NDEBUG
// Support for printing PodIntervals at the PodRedBlackTree level.
template <class T, class UserData>
struct ValueToString<PodInterval<T, UserData>> {
  static String ToString(const PodInterval<T, UserData>& interval) {
    return interval.ToString();
  }
};
#endif

}  // namespace blink

#endif  // THIRD_PARTY_BLINK_RENDERER_PLATFORM_WTF_POD_INTERVAL_TREE_H_