package com.learn.service.mp;

import com.baomidou.mybatisplus.core.conditions.query.LambdaQueryWrapper;
import com.baomidou.mybatisplus.core.metadata.IPage;
import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
import com.learn.entity.Student;
import com.learn.repository.mp.StudentMapper;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

import java.util.List;
import java.util.Optional;

/**
 * MyBatis-Plus 版本的学生服务
 *
 * 重点对比与 JPA 版本的差异：
 *   1. 新增：MP 用 insert()，JPA 用 save()
 *   2. 查询：MP 用 LambdaQueryWrapper 构建条件，JPA 用方法命名或 JPQL
 *   3. 分页：MP 用 Page + IPage，JPA 用 PageRequest + Page
 *   4. 更新：MP 用 updateById()，JPA 用 save()
 *
 * 关键武器：LambdaQueryWrapper
 *   用它构建条件，不用担心列名写错（基于 Lambda 表达式，编译期安全）
 *   例如：wrapper.eq(Student::getName, "张三")  →  WHERE name = '张三'
 */
@Service
public class StudentMpService {

    private final StudentMapper mapper;

    public StudentMpService(StudentMapper mapper) {
        this.mapper = mapper;
    }

    // ==================== 增删改查 ====================

    @Transactional
    public Student add(Student student) {
        mapper.insert(student);  // MP: insert() 只用于新增
        return student;          // insert 后 student.id 已被自动回填
    }

    @Transactional(readOnly = true)
    public List<Student> list() {
        // MP 条件构造器：空的 wrapper → 查全部
        // orderByDesc 让结果按成绩降序
        LambdaQueryWrapper<Student> wrapper = new LambdaQueryWrapper<>();
        wrapper.orderByDesc(Student::getScore);
        return mapper.selectList(wrapper);
    }

    @Transactional(readOnly = true)
    public Optional<Student> getById(Long id) {
        return Optional.ofNullable(mapper.selectById(id));
    }

    @Transactional
    public Optional<Student> update(Long id, Student updated) {
        Student existing = mapper.selectById(id);
        if (existing == null) {
            return Optional.empty();
        }
        if (updated.getName() != null) existing.setName(updated.getName());
        if (updated.getAge() > 0) existing.setAge(updated.getAge());
        if (updated.getEmail() != null) existing.setEmail(updated.getEmail());
        if (updated.getScore() >= 0) existing.setScore(updated.getScore());

        mapper.updateById(existing);  // MP 用 updateById
        return Optional.of(existing);
    }

    @Transactional
    public boolean delete(Long id) {
        return mapper.deleteById(id) > 0;
    }

    // ==================== 搜索 ====================

    @Transactional(readOnly = true)
    public List<Student> searchByKeyword(String keyword) {
        return mapper.searchByKeyword(keyword);
    }

    @Transactional(readOnly = true)
    public List<Student> findByName(String name) {
        // MP 的 Lambda 方式构建条件
        LambdaQueryWrapper<Student> wrapper = new LambdaQueryWrapper<>();
        wrapper.like(Student::getName, name);   // WHERE name LIKE '%name%'
        return mapper.selectList(wrapper);
    }

    // ==================== 分页（第 5 天） ====================

    @Transactional(readOnly = true)
    public IPage<Student> page(int pageNum, int pageSize) {
        // MP 分页：Page<Student>(页码, 每页条数)
        Page<Student> page = new Page<>(pageNum, pageSize);

        // 按成绩降序
        LambdaQueryWrapper<Student> wrapper = new LambdaQueryWrapper<>();
        wrapper.orderByDesc(Student::getScore);

        return mapper.selectPage(page, wrapper);
    }

    // ==================== 统计 ====================

    @Transactional(readOnly = true)
    public long count() {
        return mapper.selectCount(null);  // null = 无筛选条件
    }

    @Transactional(readOnly = true)
    public long countByScoreRange(int min, int max) {
        // MP 的 Lambda 方式构建范围条件
        LambdaQueryWrapper<Student> wrapper = new LambdaQueryWrapper<>();
        wrapper.between(Student::getScore, min, max);  // WHERE score BETWEEN min AND max
        return mapper.selectCount(wrapper);
    }

    // ==================== 高级查询（演示 LambdaQueryWrapper 的威力） ====================

    @Transactional(readOnly = true)
    public List<Student> findExcellentStudents(int threshold) {
        LambdaQueryWrapper<Student> wrapper = new LambdaQueryWrapper<>();
        wrapper.ge(Student::getScore, threshold)     // WHERE score >= ?
               .orderByDesc(Student::getScore);
        return mapper.selectList(wrapper);
    }
}