versioned-map/Facade.h

#pragma once

#include "VersionedMap.h"

#include <map>
#include <string>
#include <vector>

using String = std::basic_string<uint8_t>;

struct Facade {

  explicit Facade(int64_t version) : versioned{version} {}

  struct View {

    std::vector<std::pair<String, String>> rangeRead(const String &begin,
                                                     const String &end,
                                                     int limit,
                                                     bool reverse) const {
      std::vector<std::pair<String, String>> result;
      if (begin >= end) {
        return result;
      }

      weaselab::VersionedMap::Iterator versionedIter[2];
      const weaselab::VersionedMap::Key key[] = {
          {begin.data(), int(begin.size())}, {end.data(), int(end.size())}};
      const int64_t v[] = {version, version};
      facade->versioned.firstGeq(key, v, versionedIter, 2);

      if (versionedIter[0] == versionedIter[1]) {
        // No mutations intersect [begin, end)
        facade->unversionedRead(begin, end, limit, reverse, result);
        return result;
      }

      static const uint8_t zero_[] = {0};
      static const String zero{zero_, 1};

      if (reverse) {
        weaselab::VersionedMap::Iterator iter = versionedIter[1];
        weaselab::VersionedMap::Iterator endIter = versionedIter[0];
        String readUntil = end;

        // Make *iter intersect [begin, end)
        --iter;

        for (;; --iter) {
          auto m = *iter;
          const auto mEnd =
              m.type == weaselab::VersionedMap::Set || m.param2Len == 0
                  ? String(m.param1, m.param1Len) + zero
                  : String(m.param2, m.param2Len);
          facade->unversionedRead(mEnd, readUntil, limit, true, result);
          if (limit == 0) {
            return result;
          }
          switch (m.type) {
          case weaselab::VersionedMap::Set: {
            result.emplace_back(String(m.param1, m.param1Len),
                                String(m.param2, m.param2Len));
            --limit;
            if (limit == 0) {
              return result;
            }
            readUntil = String(m.param1, m.param1Len);
          } break;
          case weaselab::VersionedMap::Clear:
            readUntil = String(m.param1, m.param1Len);
            break;
          }
          if (iter == endIter) {
            break;
          }
        }
        facade->unversionedRead(begin, readUntil, limit, true, result);
        return result;
      } else {
        weaselab::VersionedMap::Iterator iter = versionedIter[0];
        weaselab::VersionedMap::Iterator endIter = versionedIter[1];
        String readFrom = begin;
        for (; iter != endIter; ++iter) {
          auto m = *iter;
          const auto mBegin = String(m.param1, m.param1Len);
          facade->unversionedRead(readFrom, mBegin, limit, false, result);
          if (limit == 0) {
            return result;
          }
          switch (m.type) {
          case weaselab::VersionedMap::Set: {
            result.emplace_back(mBegin, String(m.param2, m.param2Len));
            --limit;
            if (limit == 0) {
              return result;
            }
            readFrom = mBegin + zero;
          } break;
          case weaselab::VersionedMap::Clear:
            readFrom = String(m.param2, m.param2Len);
            break;
          }
        }
        facade->unversionedRead(readFrom, end, limit, false, result);
        return result;
      }
    }

    /** @private */
    View(const Facade *facade, int64_t version)
        : facade{facade}, version{version} {}

  private:
    const Facade *facade;
    int64_t version;
  };

  void addMutations(const weaselab::VersionedMap::Mutation *mutations,
                    int numMutations, int64_t version) {
    versioned.addMutations(mutations, numMutations, version);
  }

  void setOldestVersion(int64_t version) {
    for (auto iter = versioned.begin(version), end = versioned.end(version);
         iter != end; ++iter) {
      auto m = *iter;
      switch (m.type) {
      case weaselab::VersionedMap::Set:
        unversioned[String(m.param1, m.param1Len)] =
            String(m.param2, m.param2Len);
        break;
      case weaselab::VersionedMap::Clear:
        for (auto unversionedIter =
                 unversioned.lower_bound(String(m.param1, m.param1Len));
             unversionedIter != unversioned.end() &&
             unversionedIter->first < String(m.param2, m.param2Len);) {
          unversionedIter = unversioned.erase(unversionedIter);
        }
        break;
      }
    }

    versioned.setOldestVersion(version);
  }

  View viewAt(int64_t version) const { return View{this, version}; }

  int64_t getVersion() const { return versioned.getVersion(); }
  int64_t getOldestVersion() const { return versioned.getOldestVersion(); }

  void unversionedRead(const String &begin, const String &end, int &limit,
                       bool reverse,
                       std::vector<std::pair<String, String>> &result) const {
    if (begin >= end) {
      return;
    }
    if (reverse) {
      if (unversioned.empty()) {
        return;
      }
      auto iter = unversioned.lower_bound(end);
      const auto beginIter = unversioned.begin();
      if (iter == beginIter) {
        return;
      }
      --iter;
      for (; iter->first >= begin && limit > 0; --iter) {
        result.push_back(*iter);
        --limit;
        if (iter == beginIter) {
          return;
        }
      }
    } else {
      for (auto iter = unversioned.lower_bound(begin),
                iterEnd = unversioned.lower_bound(end);
           iter != iterEnd && limit > 0; ++iter) {
        result.push_back(*iter);
        --limit;
      }
    }
  }

  std::map<String, String> unversioned;
  weaselab::VersionedMap versioned;
};