#pragma once
#include <memory>
#include <list>
#include <unordered_map>
#include <chrono>
#include <queue>



template <typename T, typename U>

class Memdb {


struct memdb_column {
    T key;
    U value;
    std::chrono::system_clock::time_point timestamp;
    bool be_del = false;
};

struct index_keys {
    T key;
    std::list <memdb_column>::iterator item;
};

struct index_timestamp {
    std::list <memdb_column>::iterator item;

    bool operator<(const index_timestamp& a) const;
};


private:
    std::list <memdb_column> db;
    std::unordered_map <T, index_keys> keys;
    std::priority_queue <index_timestamp> time_touch;
    size_t __size;
    void flush();


public:
    using key_t = T;
    using value_t = U;
    static constexpr int npos = -1;

    Memdb();
    Memdb& operator=(const Memdb& to_be_cp_memdb);
    ~Memdb();

    size_t size() const;
    const std::unordered_map <T, index_keys>& get_keys() const;
    const std::list <memdb_column>& get_db() const;
    const std::priority_queue <index_timestamp>& get_time_touch() const;

    void insert(key_t to_be_ins_k, value_t ins_v);                                  //TODO 要加返回值
    void remove(key_t to_be_del_k);                                                 //TODO 要加返回值
    void update(key_t to_be_udt_k, value_t udt_v, bool need_to_udt_timetouch=false);//TODO 要加返回值
    value_t search(key_t to_be_sch_k) const;
};