package nju.seec.helper.service.impl;

import nju.seec.helper.dao.ChooseDAO;
import nju.seec.helper.dao.CourseDAO;
import nju.seec.helper.dao.UserDAO;
import nju.seec.helper.dto.course.ChooseDTO;
import nju.seec.helper.dto.course.CourseDTO;
import nju.seec.helper.dto.user.LoginUser;
import nju.seec.helper.entity.Choose;
import nju.seec.helper.entity.Course;
import nju.seec.helper.service.CourseService;
import nju.seec.helper.service.util.AuthUtils;
import nju.seec.helper.service.util.StringUtils;
import nju.seec.helper.util.EncryptUtils;
import nju.seec.helper.util.enums.ExceptionType;
import nju.seec.helper.util.exception.HelperException;
import nju.seec.helper.vo.CourseVO;
import nju.seec.helper.vo.UserVO;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.Pageable;
import org.springframework.data.jpa.domain.Specification;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

import javax.persistence.criteria.JoinType;
import java.util.Set;

/**
 * @author cst
 */
@Service
public class CourseServiceImpl implements CourseService {
    private final UserDAO userDAO;
    private final CourseDAO courseDAO;
    private final ChooseDAO chooseDAO;

    public CourseServiceImpl(UserDAO userDAO, CourseDAO courseDAO, ChooseDAO chooseDAO) {
        this.userDAO = userDAO;
        this.courseDAO = courseDAO;
        this.chooseDAO = chooseDAO;
    }

    @Transactional(rollbackFor = Exception.class)
    @Override
    public CourseVO createCourse(LoginUser teacher, CourseDTO courseDTO) {
        // 检查
        checkSameCourseName(0L, teacher.getId(), courseDTO.getName());

        Course course = new Course()
                .setTeacher(userDAO.findUserById(teacher.getId()))
                .setName(courseDTO.getName())
                .setBio(courseDTO.getBio())
                .setCode(EncryptUtils.encode(courseDTO.getCode()));
        course = courseDAO.save(course);
        return new CourseVO(course);
    }

    @Transactional(rollbackFor = Exception.class)
    @Override
    public CourseVO modifyCourse(LoginUser user, Long courseId, CourseDTO courseDTO) {
        Course course = courseDAO.findCourseById(courseId);

        // 检查
        AuthUtils.checkDataAuth(user.getId(), course.getTeacher().getId(), "您无权修改该课程");
        checkSameCourseName(course.getId(), user.getId(), courseDTO.getName());

        course.setName(courseDTO.getName())
                .setBio(courseDTO.getBio())
                .setCode(EncryptUtils.encode(courseDTO.getCode()));
        course = courseDAO.save(course);
        return new CourseVO(course);
    }

    @Transactional(rollbackFor = Exception.class)
    @Override
    public void removeCourse(LoginUser user, Long courseId) {
        Course course = courseDAO.findCourseById(courseId);
        AuthUtils.checkDataAuth(user.getId(), course.getTeacher().getId(), "您无权删除该课程");

        course.setDeleteAt(System.currentTimeMillis());
        courseDAO.save(course);
    }

    @Transactional(rollbackFor = Exception.class)
    @Override
    public void chooseCourse(LoginUser student, Long courseId, ChooseDTO chooseDTO) {
        Long studentId = student.getId();
        if (chooseDAO.existsByStudentIdAndCourseId(studentId, courseId)) {
            throw HelperException.of(ExceptionType.CONFLICT, "您已选课");
        }

        if (!courseDAO.existsByIdAndCode(courseId, EncryptUtils.encode(chooseDTO.getCode()))) {
            throw HelperException.of(ExceptionType.NOT_FOUND, "选课码错误");
        }

        Choose choose = new Choose()
                .setCourseId(courseId)
                .setStudentId(studentId);
        chooseDAO.save(choose);
    }

    @Transactional(rollbackFor = Exception.class)
    @Override
    public void quitCourse(LoginUser user, Long courseId) {
        chooseDAO.deleteByStudentIdAndCourseId(user.getId(), courseId);
    }

    @Transactional(readOnly = true)
    @Override
    public Page<CourseVO> getCourses(String key, Pageable pageable) {
        return findByKey(key, pageable).map(CourseVO::new);
    }

    @Transactional(readOnly = true)
    @Override
    public Page<CourseVO> getCourses(LoginUser user, String key, Pageable pageable) {
        switch (user.getType()) {
            case TEACHER:
                return teacherGetCourses(user.getId(), key, pageable);
            case STUDENT:
                return studentGetCourses(user.getId(), key, pageable);
            default:
                return Page.empty();
        }
    }

    private Page<CourseVO> teacherGetCourses(Long teacherId, String key, Pageable pageable) {
        return findByTeacherIdAndKey(teacherId, key, pageable).map(CourseVO::new);
    }

    private Page<CourseVO> studentGetCourses(Long studentId, String key, Pageable pageable) {
        return findByIdsAndKey(chooseDAO.findCourseIdsByStudentId(studentId), key, pageable).map(CourseVO::new);
    }

    @Transactional(readOnly = true)
    @Override
    public String getCourseCode(LoginUser user, Long courseId) {
        Course course = courseDAO.findCourseById(courseId);
        AuthUtils.checkDataAuth(user.getId(), course.getTeacher().getId(), "您无权获取该课程选课码");

        return EncryptUtils.decode(course.getCode());
    }

    @Transactional(readOnly = true)
    @Override
    public CourseVO getOneCourse(Long courseId) {
        return new CourseVO(courseDAO.findCourseById(courseId));
    }

    @Transactional(readOnly = true)
    @Override
    public Page<UserVO> getChooseStudents(LoginUser user, Long courseId, String key, Pageable pageable) {
        Course course = courseDAO.findCourseById(courseId);
        AuthUtils.checkDataAuth(user.getId(), course.getTeacher().getId(), "您无权获取该课程的选课名单");

        return userDAO.findByIdIn(chooseDAO.findStudentIdsByCourseId(courseId), pageable).map(UserVO::new);
    }

    @Override
    public boolean existsCourseResourcesGetAuth(LoginUser user, Long courseId) {
        switch (user.getType()) {
            case TEACHER:
                return courseDAO.findCourseById(courseId).getTeacher().getId().equals(user.getId());
            case STUDENT:
                return chooseDAO.existsByStudentIdAndCourseId(user.getId(), courseId);
            default:
                return false;
        }
    }

    private void checkSameCourseName(Long courseId, Long teacherId, String name) {
        long exists = courseDAO.count((Specification<Course>) (root, query, cb) ->
                cb.and(cb.notEqual(root.get("id"), courseId)
                        , cb.equal(root.get("teacher").get("id"), teacherId)
                        , cb.equal(root.get("deleteAt"), 0L)
                        , cb.equal(root.get("name"), name)
                ));
        if (exists > 0) {
            throw HelperException.of(ExceptionType.CONFLICT, "该课程名已使用");
        }
    }

    private Page<Course> findByTeacherIdAndKey(Long teacherId, String key, Pageable pageable) {
        return courseDAO.findAll(
                (Specification<Course>) (root, query, cb) -> cb.and(
                        cb.equal(root.get("teacher").get("id"), teacherId)
                        , cb.equal(root.get("deleteAt"), 0L)
//                        , cb.like(root.get("name"), StringUtils.keyPattern(key))
                        ),
                pageable);
    }

    private Page<Course> findByKey(String key, Pageable pageable) {
        final String keyPattern = StringUtils.keyPattern(key);

        return courseDAO.findAll(
                (Specification<Course>) (root, query, cb) -> cb.and(
                        cb.equal(root.get("deleteAt"), 0L)
                        , cb.or(cb.like(root.get("name"), keyPattern), cb.like(root.join("teacher", JoinType.LEFT).get("name"), keyPattern))
                ),
                pageable);
    }

    private Page<Course> findByIdsAndKey(Set<Long> courseIds, String key, Pageable pageable) {
        final String keyPattern = StringUtils.keyPattern(key);

        return courseDAO.findAll(
                (Specification<Course>) (root, query, cb) -> cb.and(
                        root.get("id").in(courseIds)
                        , cb.equal(root.get("deleteAt"), 0L)
                        , cb.or(cb.like(root.get("name"), keyPattern), cb.like(root.join("teacher", JoinType.LEFT).get("name"), keyPattern))
                ),
                pageable);
    }
}