#include "leveldb/db.h"

leveldb::DB* db;
leveldb::Options options;

// 关键选项
options.create_if_missing = true;    // 不存在则创建
options.error_if_exists = false;     // 已存在不报错

leveldb::Status status = leveldb::DB::Open(options, "/path/to/db", &db);
if (!status.ok()) {
    std::cerr << "Open failed: " << status.ToString() << std::endl;
    // 处理错误...
}

// 使用完毕后关闭
delete db;

// LevelDB 的 Status 对象封装了错误信息
leveldb::Status s = db->Put(...);
if (!s.ok()) {
    if (s.IsNotFound()) {
        // Get 操作：Key 不存在
    } else if (s.IsCorruption()) {
        // 数据损坏
    } else if (s.IsIOError()) {
        // I/O 错误（磁盘满、权限等）
    } else if (s.IsInvalidArgument()) {
        // 参数错误
    }
    std::cerr << "Error: " << s.ToString() << std::endl;
}

// 基本用法
leveldb::Status s = db->Put(
    leveldb::WriteOptions(),    // 写选项
    "mykey",                     // Key
    "myvalue"                    // Value
);
assert(s.ok());

// 同步写入（保证持久化到磁盘）
leveldb::WriteOptions sync_opts;
sync_opts.sync = true;
s = db->Put(sync_opts, "critical_key", "important_data");

// 方式 1：字符串字面量
db->Put(wopts, "key1", "value1");

// 方式 2：std::string
std::string key = "user:1001";
std::string value = "张三";
db->Put(wopts, key, value);

// 方式 3：二进制数据
char binary_key[8];
memcpy(binary_key, &timestamp, 8);
db->Put(wopts, leveldb::Slice(binary_key, 8), binary_value);

#include <sstream>
#include "leveldb/db.h"

// 存储用户信息
void SaveUser(leveldb::DB* db, int user_id,
              const std::string& name, int age) {
    // Key: 带前缀的用户 ID
    std::string key = "user:" + std::to_string(user_id);

    // Value: 简单 JSON
    std::ostringstream json;
    json << "{\"name\":\"" << name
         << "\",\"age\":" << age << "}";

    leveldb::Status s = db->Put(leveldb::WriteOptions(), key, json.str());
    if (!s.ok()) {
        throw std::runtime_error("Put failed: " + s.ToString());
    }
}

// 读取用户信息
std::string GetUser(leveldb::DB* db, int user_id) {
    std::string key = "user:" + std::to_string(user_id);
    std::string value;
    leveldb::Status s = db->Get(leveldb::ReadOptions(), key, &value);
    if (s.IsNotFound()) {
        return "";  // 用户不存在
    }
    if (!s.ok()) {
        throw std::runtime_error("Get failed: " + s.ToString());
    }
    return value;
}

// ⚠️ 危险：Slice 不拥有数据！
leveldb::Slice key;
{
    std::string temp = "temporary_key";
    key = temp;
}  // temp 被销毁，key 变成悬空指针！

// ✅ 正确做法：确保 Slice 的底层数据在使用期间有效
std::string key_str = "safe_key";
db->Put(wopts, key_str, value);  // 直接传 std::string，隐式转换为 Slice

std::string value;
leveldb::Status s = db->Get(
    leveldb::ReadOptions(),    // 读选项
    "mykey",                    // Key
    &value                      // 输出参数
);

if (s.ok()) {
    std::cout << "Value: " << value << std::endl;
} else if (s.IsNotFound()) {
    std::cout << "Key not found" << std::endl;
} else {
    std::cerr << "Error: " << s.ToString() << std::endl;
}

leveldb::ReadOptions ropts;
ropts.verify_checksums = true;  // 启用 CRC 校验

std::string value;
leveldb::Status s = db->Get(ropts, "important_key", &value);

// 场景：大量顺序读取不需要缓存
leveldb::ReadOptions ropts;
ropts.fill_cache = false;  // 不污染 Block Cache

std::string value;
db->Get(ropts, "cold_key", &value);

leveldb::Status s = db->Delete(leveldb::WriteOptions(), "mykey");
if (!s.ok()) {
    // 注意：Delete 一个不存在的 Key 也返回 OK
    // 因为 LSM-Tree 中删除只是写入一个 "删除标记"（Tombstone）
}

db->Put(wopts, "key1", "value1");     // 写入
db->Delete(wopts, "key1");             // 删除
db->Put(wopts, "key1", "value2");     // 重新写入

std::string value;
db->Get(ropts, "key1", &value);       // 返回 "value2"

leveldb::Iterator* it = db->NewIterator(leveldb::ReadOptions());

// 使用完毕必须删除
delete it;

leveldb::Iterator* it = db->NewIterator(leveldb::ReadOptions());

// 正向遍历所有数据
for (it->SeekToFirst(); it->Valid(); it->Next()) {
    std::cout << it->key().ToString() << " = "
              << it->value().ToString() << std::endl;
}

// 检查遍历是否出错
if (!it->status().ok()) {
    std::cerr << "Iterator error: " << it->status().ToString() << std::endl;
}

delete it;

leveldb::Iterator* it = db->NewIterator(leveldb::ReadOptions());

for (it->SeekToLast(); it->Valid(); it->Prev()) {
    std::cout << it->key().ToString() << " = "
              << it->value().ToString() << std::endl;
}

delete it;

leveldb::Iterator* it = db->NewIterator(leveldb::ReadOptions());

// Seek 到第一个 >= "user:100" 的 Key
it->Seek("user:100");
if (it->Valid()) {
    std::cout << "Found: " << it->key().ToString() << std::endl;
}

delete it;

// 查找所有以 "user:" 开头的键
leveldb::Iterator* it = db->NewIterator(leveldb::ReadOptions());

std::string prefix = "user:";
for (it->Seek(prefix);
     it->Valid() && it->key().starts_with(prefix);
     it->Next()) {
    std::cout << it->key().ToString() << " = "
              << it->value().ToString() << std::endl;
}

delete it;

// 查找 Key 在 [start, end) 范围内的数据
leveldb::Iterator* it = db->NewIterator(leveldb::ReadOptions());

std::string start = "user:1000";
std::string end = "user:2000";

for (it->Seek(start); it->Valid(); it->Next()) {
    if (it->key().compare(end) >= 0) {
        break;  // 超出范围
    }
    std::cout << it->key().ToString() << " = "
              << it->value().ToString() << std::endl;
}

delete it;

// 取最新的 10 条记录
leveldb::Iterator* it = db->NewIterator(leveldb::ReadOptions());

int count = 0;
it->SeekToLast();
while (it->Valid() && count < 10) {
    std::cout << it->key().ToString() << std::endl;
    it->Prev();
    count++;
}

delete it;

// RAII 封装，确保迭代器被正确释放
class ScopedIterator {
public:
    explicit ScopedIterator(leveldb::DB* db,
                            const leveldb::ReadOptions& opts = leveldb::ReadOptions())
        : iter_(db->NewIterator(opts)) {}

    ~ScopedIterator() { delete iter_; }

    leveldb::Iterator* operator->() { return iter_; }
    leveldb::Iterator* get() { return iter_; }

    // 禁止复制
    ScopedIterator(const ScopedIterator&) = delete;
    ScopedIterator& operator=(const ScopedIterator&) = delete;

private:
    leveldb::Iterator* iter_;
};

// 使用
void ScanUsers(leveldb::DB* db) {
    ScopedIterator it(db);
    for (it->Seek("user:"); it->Valid(); it->Next()) {
        // ...
    }  // 自动 delete iter_
}

#include <iostream>
#include <string>
#include <sstream>
#include "leveldb/db.h"

class ContactBook {
public:
    ContactBook(const std::string& path) {
        leveldb::Options opts;
        opts.create_if_missing = true;
        opts.write_buffer_size = 2 * 1024 * 1024;  // 2MB
        leveldb::Status s = leveldb::DB::Open(opts, path, &db_);
        if (!s.ok()) throw std::runtime_error(s.ToString());
    }
    ~ContactBook() { delete db_; }

    // 添加联系人
    bool Add(const std::string& name, const std::string& phone,
             const std::string& email) {
        std::string key = "contact:" + name;
        std::ostringstream val;
        val << phone << "|" << email;
        return db_->Put(leveldb::WriteOptions(), key, val.str()).ok();
    }

    // 查找联系人
    bool Find(const std::string& name, std::string& phone,
              std::string& email) {
        std::string value;
        leveldb::Status s = db_->Get(leveldb::ReadOptions(),
                                     "contact:" + name, &value);
        if (!s.ok()) return false;
        auto pos = value.find('|');
        phone = value.substr(0, pos);
        email = value.substr(pos + 1);
        return true;
    }

    // 删除联系人
    bool Remove(const std::string& name) {
        return db_->Delete(leveldb::WriteOptions(),
                           "contact:" + name).ok();
    }

    // 列出所有联系人
    void List() {
        leveldb::Iterator* it = db_->NewIterator(leveldb::ReadOptions());
        for (it->Seek("contact:"); it->Valid(); it->Next()) {
            if (!it->key().starts_with("contact:")) break;
            std::string name = it->key().ToString().substr(8);
            std::string val = it->value().ToString();
            auto pos = val.find('|');
            std::cout << "  " << name
                      << " | " << val.substr(0, pos)
                      << " | " << val.substr(pos + 1) << "\n";
        }
        delete it;
    }

    // 搜索（按名字前缀）
    void Search(const std::string& prefix) {
        leveldb::Iterator* it = db_->NewIterator(leveldb::ReadOptions());
        std::string seek_key = "contact:" + prefix;
        for (it->Seek(seek_key); it->Valid(); it->Next()) {
            if (!it->key().starts_with("contact:")) break;
            std::string name = it->key().ToString().substr(8);
            if (name.substr(0, prefix.size()) != prefix) break;
            std::string val = it->value().ToString();
            auto pos = val.find('|');
            std::cout << "  " << name
                      << " | " << val.substr(0, pos)
                      << " | " << val.substr(pos + 1) << "\n";
        }
        delete it;
    }

private:
    leveldb::DB* db_;
};

int main() {
    ContactBook book("/tmp/contacts");

    book.Add("张三", "138-0000-0001", "zhangsan@example.com");
    book.Add("张伟", "139-0000-0002", "zhangwei@example.com");
    book.Add("李四", "137-0000-0003", "lisi@example.com");
    book.Add("王五", "136-0000-0004", "wangwu@example.com");

    std::cout << "=== 所有联系人 ===\n";
    book.List();

    std::cout << "\n=== 搜索 '张' ===\n";
    book.Search("张");

    std::cout << "\n=== 查找 '李四' ===\n";
    std::string phone, email;
    if (book.Find("李四", phone, email)) {
        std::cout << "  电话: " << phone << "\n";
        std::cout << "  邮箱: " << email << "\n";
    }

    return 0;
}

g++ -std=c++17 -O2 -o contacts contacts.cpp -lleveldb -lpthread
./contacts

# 输出:
# === 所有联系人 ===
#   张三 | 138-0000-0001 | zhangsan@example.com
#   张伟 | 139-0000-0002 | zhangwei@example.com
#   李四 | 137-0000-0003 | lisi@example.com
#   王五 | 136-0000-0004 | wangwu@example.com
#
# === 搜索 '张' ===
#   张三 | 138-0000-0001 | zhangsan@example.com
#   张伟 | 139-0000-0002 | zhangwei@example.com
#
# === 查找 '李四' ===
#   电话: 137-0000-0003
#   邮箱: lisi@example.com