versioned-map/Facade.h

#pragma once

#include "VersionedMap.h"

#include <assert.h>
#include <map>
#include <string>
#include <vector>

using String = std::basic_string<uint8_t>;

struct Facade {

  explicit Facade(int64_t version)
      : oldestVersion(version), nextPurgeVersion(version),
        unversionedVersion(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);

      // Make sure versionedIter[1] param1 is >= `end`
      if (versionedIter[1] != facade->versioned.end(version)) {
        auto m = *versionedIter[1];
        if (String(m.param1, m.param1Len) < end) {
          ++versionedIter[1];
        }
      }

      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;

        do {
          --iter;
          auto m = *iter;
          const auto mBegin = String(m.param1, m.param1Len);
          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(mBegin, String(m.param2, m.param2Len));
            --limit;
            if (limit == 0) {
              return result;
            }
            readUntil = mBegin;
          } break;
          case weaselab::VersionedMap::Clear:
            readUntil = mBegin;
            break;
          }
        } while (iter != endIter);

        facade->unversionedRead(begin, readUntil, limit, true, result);
        return result;
      } else {
        auto unversionedIter = facade->unversioned.lower_bound(begin);
        for (auto iter = versionedIter[0]; iter != versionedIter[1]; ++iter) {
          auto m = *iter;
          const auto mBegin = String(m.param1, m.param1Len);
          const auto mEnd =
              m.type == weaselab::VersionedMap::Set || m.param2Len == 0
                  ? String(m.param1, m.param1Len) + zero
                  : String(m.param2, m.param2Len);
          auto c = unversionedIter->first <=> mBegin;
          for (; unversionedIter != facade->unversioned.end() && c < 0 &&
                 limit > 0;) {
            result.push_back(*unversionedIter);
            --limit;
            ++unversionedIter;
            c = unversionedIter->first <=> mBegin;
          }
          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;
            }
          } break;
          case weaselab::VersionedMap::Clear:
            break;
          }
          if (m.type == weaselab::VersionedMap::Set || m.param2Len == 0) {
            if (unversionedIter != facade->unversioned.end() && c == 0) {
              ++unversionedIter;
            }
            assert(unversionedIter == facade->unversioned.lower_bound(mEnd));
          } else {
            unversionedIter = facade->unversioned.lower_bound(mEnd);
          }
        }

        for (; unversionedIter != facade->unversioned.end() &&
               unversionedIter->first < end && limit > 0;
             ++unversionedIter) {
          result.push_back(*unversionedIter);
          --limit;
        }
        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) {
    // Don't scan and apply mutations every time setOldestVersion is called.

    oldestVersion = version;
    if (version >= nextPurgeVersion) {
      nextPurgeVersion = versioned.getVersion();
    } else {
      return;
    }

    for (auto iter = versioned.begin(version), end = versioned.end(version);
         iter != end; ++iter) {
      auto m = *iter;
      assert(m.version <= version);
      if (m.version <= unversionedVersion) {
        continue;
      }
      switch (m.type) {
      case weaselab::VersionedMap::Set:
        unversioned[String(m.param1, m.param1Len)] =
            String(m.param2, m.param2Len);
        break;
      case weaselab::VersionedMap::Clear:
        if (m.param2Len == 0) {
          unversioned.erase(String(m.param1, m.param1Len));
        } else {
          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;
      }
    }

    unversionedVersion = version;
    versioned.setOldestVersion(version);
  }

  View viewAt(int64_t version) const {
    assert(version >= oldestVersion);
    assert(version <= versioned.getVersion());
    return View{this, version};
  }

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

  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) {
      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;
      }
    }
  }

  int64_t oldestVersion;
  int64_t nextPurgeVersion;
  int64_t unversionedVersion;
  std::map<String, String> unversioned;
  weaselab::VersionedMap versioned;
};