write_ahead_log.h

#ifndef STORAGE_WRITE_AHEAD_LOG_H
#define STORAGE_WRITE_AHEAD_LOG_H
 
#include <vkdb/lsm_tree.h>
#include <vkdb/wal_lsm.h>
 
namespace vkdb {
const FilePath WAL_FILENAME{"wal.log"};
 
template <ArithmeticNoCVRefQuals TValue>
class WriteAheadLog {
public:
  WriteAheadLog() = delete;
 
  explicit WriteAheadLog(FilePath lsm_tree_path) noexcept
    : path_{lsm_tree_path / WAL_FILENAME} {}
 
  WriteAheadLog(WriteAheadLog&&) noexcept = default;
  
  WriteAheadLog& operator=(WriteAheadLog&&) noexcept = default;
 
  WriteAheadLog(const WriteAheadLog&) = delete;
  
  WriteAheadLog& operator=(const WriteAheadLog&) = delete;
 
  ~WriteAheadLog() noexcept = default;
 
  void append(const WALRecord<TValue>& record) {
    std::ofstream file{path_, std::ios::app};
    if (!file.is_open()) {
      throw std::runtime_error{
        "WriteAheadLog::append(): Unable to open file "
        + std::string(path_) + "."
      };
    }
    file << std::to_string(static_cast<int>(record.type));
    file << " " << entryToString(record.entry) << "\n";
    file.close();
  }
 
  void replay(LSMTree<TValue>& lsm_tree) {
    if (!std::filesystem::exists(path_)) {
      return;
    }
    std::ifstream file{path_};
    if (!file.is_open()) {
      throw std::runtime_error{
        "WriteAheadLog::replay(): Unable to open file "
        + std::string(path_) + "."
      };
    }
 
    std::string line;
    while (std::getline(file, line)) {
      WALRecordType type{std::stoi(line.substr(0))};
      TimeSeriesEntry<TValue> entry{
        entryFromString<TValue>(line.substr(line.find(' ') + 2))
      };
      switch (type) {
      case WALRecordType::PUT:
        lsm_tree.put(entry.first, entry.second.value(), false);
        break;
      case WALRecordType::REMOVE:
        lsm_tree.remove(entry.first, false);
        break;
      }
    }
    
    file.close();
    clear();
  }
 
  void clear() {
    std::ofstream file{path_};
    if (!file.is_open()) {
      throw std::runtime_error{
        "WriteAheadLog::clear(): Unable to open file "
        + std::string(path_) + "."
      };
    }
    file.close();
  }
 
  [[nodiscard]] FilePath path() const noexcept {
    return path_;
  }
 
private:
  FilePath path_;
};
}  // namespace vkdb
 
#endif // STORAGE_WRITE_AHEAD_LOG_H