#include "source/common/stats/recent_lookups.h"

#include "source/common/common/assert.h"

namespace Envoy {

namespace Stats {

void RecentLookups::lookup(absl::string_view str) {

  ++total_;

  if (capacity_ == 0) {

    return;

  }

  auto map_iter = map_.find(str);

  if (map_iter != map_.end()) {

    // The item is already in the list. Bump its reference-count and move it to

    // the front of the list.

    auto list_iter = map_iter->second;

    ++list_iter->count_;

    if (list_iter != list_.begin()) {

      list_.splice(list_.begin(), list_, list_iter);

    }

  } else {

    ASSERT(list_.size() <= capacity_);

    // Evict oldest item if needed.

    if (list_.size() >= capacity_) {

      evictOne();

    }

    // The string storage is in the list entry.

    list_.push_front(ItemCount{std::string(str), 1});

    auto list_iter = list_.begin();

    map_[list_iter->item_] = list_iter;

  }

  ASSERT(list_.size() == map_.size());

}

void RecentLookups::forEach(const IterFn& fn) const {

  for (const ItemCount& item_count : list_) {

    fn(item_count.item_, item_count.count_);

  }

}

void RecentLookups::setCapacity(uint64_t capacity) {

  capacity_ = capacity;

  while (capacity_ < list_.size()) {

    evictOne();

  }

}

void RecentLookups::evictOne() {

  ASSERT(!list_.empty());

  ASSERT(!map_.empty());

  const ItemCount& item_count = list_.back();

  int erased = map_.erase(item_count.item_);

  ASSERT(erased == 1);

  list_.pop_back();

}

} // namespace Stats

} // namespace Envoy