package nju.seec.helper.service.impl;

import com.google.common.collect.ImmutableSet;
import lombok.SneakyThrows;
import nju.seec.helper.dao.ChooseDAO;
import nju.seec.helper.dao.CourseDAO;
import nju.seec.helper.dao.SlideDAO;
import nju.seec.helper.dto.LoginUser;
import nju.seec.helper.dto.SlideDTO;
import nju.seec.helper.entity.Course;
import nju.seec.helper.entity.Page;
import nju.seec.helper.entity.Slide;
import nju.seec.helper.service.SlideService;
import nju.seec.helper.util.CacheUtils;
import nju.seec.helper.util.Consts;
import nju.seec.helper.util.FileUtils;
import nju.seec.helper.util.enums.SlideState;
import nju.seec.helper.util.exception.HelperException;
import nju.seec.helper.vo.SlideVO;
import org.apache.pdfbox.pdmodel.PDDocument;
import org.springframework.data.domain.Pageable;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;
import org.springframework.web.multipart.MultipartFile;

import java.time.LocalDateTime;
import java.util.List;
import java.util.Objects;
import java.util.concurrent.TimeUnit;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

/**
 * @author cst
 */
@Service
public class SlideServiceImpl implements SlideService {
    private static final long SLIDE_URL_LIVING_SECONDS = 20 * 60;

    private final CourseDAO courseDAO;
    private final SlideDAO slideDAO;
    private final ChooseDAO chooseDAO;

    private final FileUtils fileUtils;
    private final CacheUtils cacheUtils;

    public SlideServiceImpl(CourseDAO courseDAO, SlideDAO slideDAO, ChooseDAO chooseDAO, FileUtils fileUtils, CacheUtils cacheUtils) {
        this.courseDAO = courseDAO;
        this.slideDAO = slideDAO;
        this.chooseDAO = chooseDAO;
        this.fileUtils = fileUtils;
        this.cacheUtils = cacheUtils;
    }

    @Transactional(rollbackFor = Exception.class)
    @SneakyThrows
    @Override
    public SlideVO createSlide(LoginUser teacher, SlideDTO slideDTO) {
        Course course = courseDAO.findCourseById(slideDTO.getCourseId());
        if (!course.getTeacherId().equals(teacher.getId())) {
            throw HelperException.of(HelperException.ExceptionType.FORBIDDEN, "您无权创建该课程的幻灯片");
        }

        Slide slide = new Slide();
        slide.setCourseId(slideDTO.getCourseId())
                .setTeacherId(teacher.getId())
                .setName(slideDTO.getName())
                .setState(SlideState.DRAFT);

        // 解析文件页数
        MultipartFile file = slideDTO.getFile();
        int pageNum;
        switch (Objects.requireNonNull(file.getContentType())) {
            // pdf
            case "application/pdf":
                PDDocument doc = PDDocument.load(file.getInputStream());
                pageNum = doc.getNumberOfPages();
                break;
            default:
                throw HelperException.of(HelperException.ExceptionType.FORBIDDEN, "不支持的文件类型");
        }

        slide.setPages(IntStream.rangeClosed(1, pageNum)
                .mapToObj(number -> {
                    Page page = new Page();
                    page.setTeacherId(teacher.getId());
                    page.setNumber(number);
                    return page;
                })
                .collect(Collectors.toList())
        );

        // 上传文件
        String objectName = fileUtils.upload(LocalDateTime.now().toString() + "-" + file.getOriginalFilename(), file.getInputStream());
        slide.setObjectName(objectName);

        return new SlideVO(slideDAO.save(slide));
    }

    @Transactional(readOnly = true)
    @Override
    public List<SlideVO> teacherGetSlides(LoginUser teacher, String key, Pageable pageable) {
        return slideDAO
                .findByTeacherIdAndNameContains(teacher.getId(), key, pageable)
                .stream()
                .map(SlideVO::new)
                .collect(Collectors.toList());
    }

    @Transactional(readOnly = true)
    @Override
    public List<SlideVO> studentGetSlides(LoginUser student, Integer courseId, String key, Pageable pageable) {
        if (!chooseDAO.existsByStudentIdAndCourseId(student.getId(), courseId)) {
            throw HelperException.of(HelperException.ExceptionType.FORBIDDEN, "你无权查看该课程下的幻灯片");
        }

        return slideDAO
                .findByCourseIdAndStateNotInAndNameContains(courseId, ImmutableSet.of(SlideState.DRAFT), key, pageable)
                .stream()
                .map(SlideVO::new)
                .collect(Collectors.toList());
    }

    @Transactional(readOnly = true)
    @Override
    public String getSlideUrl(LoginUser user, Integer slideId) {
        checkDataAccessAuth(user, slideId);

        Slide slide = slideDAO.findSlideById(slideId);
        String url = cacheUtils.get(Consts.SLIDE_URL_CACHE_NAME, slide.getObjectName());

        if (url != null) {
            return url;
        }

        url = fileUtils.getUrl(slide.getObjectName(), SLIDE_URL_LIVING_SECONDS);
        cacheUtils.set(Consts.SLIDE_URL_CACHE_NAME, slide.getObjectName(), url, SLIDE_URL_LIVING_SECONDS, TimeUnit.SECONDS);
        return url;
    }

    private void checkDataAccessAuth(LoginUser user, Integer slideId) {
        HelperException forbiddenEx = HelperException.of(HelperException.ExceptionType.FORBIDDEN, "您无权访问该幻灯片");

        Slide slide = slideDAO.findSlideById(slideId);
        switch (user.getType()) {
            case TEACHER:
                if (!slide.getTeacherId().equals(user.getId())) {
                    throw forbiddenEx;
                }
                break;
            case STUDENT:
                if (!chooseDAO.existsByStudentIdAndCourseId(user.getId(), slide.getCourseId())) {
                    throw forbiddenEx;
                }
                break;
            default:
                throw forbiddenEx;
        }
    }
}