用c++11写一个unqlite的单例，并提供unqlite_kv_store_fmt的封装存储接口和读取数据库的接口，以及删除数据的接口，和删除90天前的数据接口

在C++11中，我们可以创建一个UnQLite的单例模式，同时封装`sqlite3`库的功能，以便提供KV存储、读取、删除数据以及删除旧数据等功能。以下是一个基本的示例：

#include <iostream>
#include <sqlite3.h>
#include <chrono>

class UnQLiteSingleton {
private:
    static std::unique_ptr<sqlite3> instance;
    explicit UnQLiteSingleton() { openDatabase(); }
    ~UnQLiteSingleton() { closeConnection(); }

public:
    // 单例获取接口
    static UnQLiteSingleton& getInstance() {
        if (!instance) {
            instance = std::make_unique<sqlite3>();
            if (sqlite3_open("my_database.db", &instance->db_) != SQLITE_OK) {
                throw std::runtime_error{"Failed to open SQLite database"};
            }
        }
        return *instance;
    }

    // KV存储接口
    void store(const std::string& key, const std::string& value) {
        sqlite3_stmt* stmt;
        std::string sql = "INSERT INTO kv_store(key, value) VALUES (?, ?)";
        int rc = sqlite3_prepare_v2(instance->db_, sql.c_str(), -1, &stmt, nullptr);
        if (rc == SQLITE_OK) {
            sqlite3_bind_text(stmt, 1, key.c_str(), -1, SQLITE_STATIC);
            sqlite3_bind_text(stmt, 2, value.c_str(), -1, SQLITE_STATIC);
            if (sqlite3_step(stmt) != SQLITE_DONE) {
                std::cerr << "Error storing data: " << sqlite3_errmsg(instance->db_) << std::endl;
            }
            sqlite3_finalize(stmt);
        } else {
            std::cerr << "Error preparing SQL statement: " << sqlite3_errmsg(instance->db_) << std::endl;
        }
    }

    // 读取数据接口
    std::optional<std::string> read(const std::string& key) {
        std::optional<std::string> result;
        sqlite3_stmt* stmt;
        std::string sql = "SELECT value FROM kv_store WHERE key = ?";
        int rc = sqlite3_prepare_v2(instance->db_, sql.c_str(), -1, &stmt, nullptr);
        if (rc == SQLITE_OK) {
            sqlite3_bind_text(stmt, 1, key.c_str(), -1, SQLITE_STATIC);
            if (sqlite3_step(stmt) == SQLITE_ROW) {
                char* value = reinterpret_cast<char*>(sqlite3_column_text(stmt, 0));
                result = value ? std::string{value} : std::nullopt;
            }
            sqlite3_finalize(stmt);
        } else {
            std::cerr << "Error preparing SQL statement: " << sqlite3_errmsg(instance->db_) << std::endl;
        }
        return result;
    }

    // 删除数据接口
    bool remove(const std::string& key) {
        sqlite3_stmt* stmt;
        std::string sql = "DELETE FROM kv_store WHERE key = ?";
        int rc = sqlite3_prepare_v2(instance->db_, sql.c_str(), -1, &stmt, nullptr);
        if (rc == SQLITE_OK) {
            sqlite3_bind_text(stmt, 1, key.c_str(), -1, SQLITE_STATIC);
            int status = sqlite3_step(stmt);
            if (status == SQLITE_DONE) {
                return true;
            } else if (status == SQLITE_ERROR) {
                std::cerr << "Error deleting data: " << sqlite3_errmsg(instance->db_) << std::endl;
            }
        }
        sqlite3_finalize(stmt);
        return false;
    }

    // 删除90天前数据接口（这里假设有一个timestamp字段）
    bool pruneOldData(int days_to_prune = 90) {
        sqlite3_stmt* stmt;
        std::string sql = R"(DELETE FROM kv_store WHERE timestamp < datetime('now', '-days', ?))";
        int rc = sqlite3_prepare_v2(instance->db_, sql.c_str(), -1, &stmt, nullptr);
        if (rc == SQLITE_OK) {
            sqlite3_bind_int(stmt, 1, days_to_prune);
            int status = sqlite3_step(stmt);
            if (status == SQLITE_DONE) {
                return true;
            } else if (status == SQLITE_ERROR) {
                std::cerr << "Error pruning old data: " << sqlite3_errmsg(instance->db_) << std::endl;
            }
        }
        sqlite3_finalize(stmt);
        return false;
    }

private:
    void openDatabase() {
        // 初始化SQLite连接并处理错误
        // 这里省略具体的打开过程，实际操作需要处理可能出现的错误
    }

    void closeConnection() {
        // 关闭SQLite连接
        if (sqlite3_close(instance->db_)) {
            std::cerr << "Error closing SQLite connection" << std::endl;
        }
        instance.reset();
    }

    sqlite3* db_ = nullptr; // SQLite数据库句柄
};

std::unique_ptr<sqlite3> UnQLiteSingleton::instance;

// 使用示例
int main() {
    UnQLiteSingleton::getInstance().store("test_key", "test_value");
    auto value = UnQLiteSingleton::getInstance().read("test_key");
    if (value) {
        std::cout << "Read value: " << *value << std::endl;
    }
    UnQLiteSingleton::getInstance().remove("test_key");

    // 删除90天前的数据
    if (UnQLiteSingleton::getInstance().pruneOldData(90)) {
        std::cout << "Pruned old data." << std::endl;
    }

    return 0;
}