package com.sztzjy.linkCommerce.service.impl;

import com.sztzjy.linkCommerce.config.exception.handler.ServiceException;
import com.sztzjy.linkCommerce.config.security.JwtUser;
import com.sztzjy.linkCommerce.config.security.TokenProvider;
import com.sztzjy.linkCommerce.entity.SchoolClass;
import com.sztzjy.linkCommerce.entity.StudentDemoSession;
import com.sztzjy.linkCommerce.entity.dto.StudentDemoSessionLogin;
import com.sztzjy.linkCommerce.entity.dto.StudentDemoSessionTicket;
import com.sztzjy.linkCommerce.mapper.SchoolClassMapper;
import com.sztzjy.linkCommerce.mapper.StudentDemoSessionMapper;
import com.sztzjy.linkCommerce.service.StudentDemoSessionService;
import org.apache.commons.lang3.StringUtils;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpStatus;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

import java.nio.charset.StandardCharsets;
import java.security.MessageDigest;
import java.security.SecureRandom;
import java.util.Base64;
import java.util.Date;
import java.util.UUID;

@Service
public class StudentDemoSessionServiceImpl implements StudentDemoSessionService {
    private static final long TICKET_EXPIRATION_MILLIS = 5 * 60 * 1000L;
    private static final SecureRandom RANDOM = new SecureRandom();

    @Autowired
    public SchoolClassMapper schoolClassMapper;
    @Autowired
    public StudentDemoSessionMapper studentDemoSessionMapper;

    @Override
    @Transactional(rollbackFor = Exception.class)
    public StudentDemoSessionTicket create(JwtUser teacher, String teachingClassId) {
        requireTeacher(teacher);
        SchoolClass schoolClass = schoolClassMapper.selectByPrimaryKey(StringUtils.trimToEmpty(teachingClassId));
        if (schoolClass == null || !"TEACHING".equals(schoolClass.getClassType())
                || !StringUtils.equals(teacher.getUserId(), schoolClass.getCreatedBy())
                || !StringUtils.equals(teacher.getSchoolId(), schoolClass.getSchoolId())) {
            throw new ServiceException(HttpStatus.FORBIDDEN, "Only the creator can demonstrate this teaching class");
        }

        Date now = new Date();
        Date expiresAt = new Date(now.getTime() + TICKET_EXPIRATION_MILLIS);
        String ticket = nextTicket();
        StudentDemoSession session = new StudentDemoSession();
        session.setId(UUID.randomUUID().toString());
        session.setTicketHash(hash(ticket));
        session.setTeacherUserId(teacher.getUserId());
        session.setTeacherName(teacher.getName());
        session.setSchoolId(teacher.getSchoolId());
        session.setTeachingClassId(schoolClass.getSchoolClassId());
        session.setTeachingClassName(schoolClass.getClassName());
        session.setExpiresAt(expiresAt);
        session.setCreateTime(now);
        studentDemoSessionMapper.insertSelective(session);

        StudentDemoSessionTicket result = new StudentDemoSessionTicket();
        result.setTicket(ticket);
        result.setExpiresAt(expiresAt);
        result.setTeachingClassId(session.getTeachingClassId());
        result.setClassName(session.getTeachingClassName());
        return result;
    }

    @Override
    @Transactional(rollbackFor = Exception.class)
    public StudentDemoSessionLogin exchange(String ticket) {
        String normalizedTicket = StringUtils.trimToEmpty(ticket);
        if (StringUtils.isBlank(normalizedTicket)) {
            throw new ServiceException(HttpStatus.BAD_REQUEST, "Demo ticket is required");
        }
        StudentDemoSession session = studentDemoSessionMapper.selectByTicketHash(hash(normalizedTicket));
        Date now = new Date();
        if (session == null || session.getUsedAt() != null || session.getExpiresAt() == null || !session.getExpiresAt().after(now)
                || studentDemoSessionMapper.markUsedIfActive(session.getId(), now) != 1) {
            throw new ServiceException(HttpStatus.FORBIDDEN, "Demo ticket is invalid or expired");
        }
        JwtUser demoUser = new JwtUser();
        demoUser.setUserId("demo:" + session.getId());
        demoUser.setName(StringUtils.defaultIfBlank(session.getTeacherName(), "Teacher") + "（演示）");
        demoUser.setUsername("demo:" + session.getTeacherUserId());
        demoUser.setRoleId(4);
        demoUser.setSchoolId(session.getSchoolId());
        demoUser.setDemoMode(true);
        demoUser.setDemoTeachingClassId(session.getTeachingClassId());
        demoUser.setSourceTeacherId(session.getTeacherUserId());

        StudentDemoSessionLogin result = new StudentDemoSessionLogin();
        result.setToken(TokenProvider.createDemoToken(demoUser));
        result.setUserId(demoUser.getUserId());
        result.setName(demoUser.getName());
        result.setUsername(demoUser.getUsername());
        result.setRoleId("4");
        result.setSchoolId(session.getSchoolId());
        result.setClassId(session.getTeachingClassId());
        result.setClassName(session.getTeachingClassName());
        result.setDemoMode(true);
        result.setDemoTeachingClassId(session.getTeachingClassId());
        return result;
    }

    private void requireTeacher(JwtUser teacher) {
        if (teacher == null || teacher.getRoleId() != 3 || StringUtils.isBlank(teacher.getUserId()) || StringUtils.isBlank(teacher.getSchoolId())) {
            throw new ServiceException(HttpStatus.FORBIDDEN, "Teacher only");
        }
    }

    private String nextTicket() {
        byte[] bytes = new byte[32];
        RANDOM.nextBytes(bytes);
        return Base64.getUrlEncoder().withoutPadding().encodeToString(bytes);
    }

    private String hash(String value) {
        try {
            byte[] bytes = MessageDigest.getInstance("SHA-256").digest(value.getBytes(StandardCharsets.UTF_8));
            StringBuilder builder = new StringBuilder(bytes.length * 2);
            for (byte valueByte : bytes) {
                builder.append(String.format("%02x", valueByte));
            }
            return builder.toString();
        } catch (Exception e) {
            throw new IllegalStateException("Unable to hash demo ticket", e);
        }
    }
}