label_backend/src/main/java/com/label/service/TaskClaimService.java

package com.label.service;

import com.baomidou.mybatisplus.core.conditions.update.LambdaUpdateWrapper;
import com.label.common.exception.BusinessException;
import com.label.common.shiro.TokenPrincipal;
import com.label.common.statemachine.StateValidator;
import com.label.common.statemachine.TaskStatus;
import com.label.entity.AnnotationTask;
import com.label.entity.AnnotationTaskHistory;
import com.label.mapper.AnnotationTaskMapper;
import com.label.mapper.TaskHistoryMapper;
import com.label.util.RedisUtil;

import lombok.RequiredArgsConstructor;
import lombok.extern.slf4j.Slf4j;
import org.springframework.http.HttpStatus;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

/**
 * 任务领取/放弃/重领服务。
 *
 * 并发安全设计：
 * 1. Redis SET NX 作为分布式预锁（TTL 30s），快速拒绝并发请求
 * 2. DB UPDATE WHERE status='UNCLAIMED' 作为兜底原子操作
 * 两层防护确保同一任务只有一人可领取
 */
@Slf4j
@Service
@RequiredArgsConstructor
public class TaskClaimService {

    /** Redis 分布式锁 TTL（秒） */
    private static final long CLAIM_LOCK_TTL = 30L;

    private final AnnotationTaskMapper taskMapper;
    private final TaskHistoryMapper historyMapper;
    private final RedisService redisService;

    // ------------------------------------------------------------------ 领取 --

    /**
     * 领取任务（双重防护：Redis NX + DB 原子更新）。
     *
     * @param taskId    任务 ID
     * @param principal 当前用户
     * @throws BusinessException TASK_CLAIMED(409) 任务已被他人领取
     */
    @Transactional
    public void claim(Long taskId, TokenPrincipal principal) {
        String lockKey = RedisUtil.taskClaimKey(taskId);

        // 1. Redis SET NX 预锁（快速失败）
        boolean lockAcquired = redisService.setIfAbsent(
                lockKey, principal.getUserId().toString(), CLAIM_LOCK_TTL);
        if (!lockAcquired) {
            throw new BusinessException("TASK_CLAIMED", "任务已被他人领取，请选择其他任务", HttpStatus.CONFLICT);
        }

        try {
            // 2. DB 原子更新（WHERE status='UNCLAIMED' 兜底）
            int affected = taskMapper.claimTask(taskId, principal.getUserId(), principal.getCompanyId());
            if (affected == 0) {
                // DB 更新失败说明任务状态已变，清除刚设置的锁
                redisService.delete(lockKey);
                throw new BusinessException("TASK_CLAIMED", "任务已被他人领取，请选择其他任务", HttpStatus.CONFLICT);
            }

            // 3. 写入状态历史
            insertHistory(taskId, principal.getCompanyId(),
                    "UNCLAIMED", "IN_PROGRESS",
                    principal.getUserId(), principal.getRole(), null);

            log.info("任务领取成功: taskId={}, userId={}", taskId, principal.getUserId());
        } catch (BusinessException e) {
            throw e;  // 业务异常直接上抛，锁已在上方清除
        } catch (Exception e) {
            // DB 写入异常（含 insertHistory 失败）：清除 Redis 锁，事务回滚
            redisService.delete(lockKey);
            throw e;
        }
    }

    // ------------------------------------------------------------------ 放弃 --

    /**
     * 放弃任务（IN_PROGRESS → UNCLAIMED）。
     *
     * @param taskId    任务 ID
     * @param principal 当前用户
     */
    @Transactional
    public void unclaim(Long taskId, TokenPrincipal principal) {
        AnnotationTask task = taskMapper.selectById(taskId);
        validateTaskExists(task, taskId);

        StateValidator.assertTransition(TaskStatus.TRANSITIONS,
                TaskStatus.valueOf(task.getStatus()), TaskStatus.UNCLAIMED);

        taskMapper.update(null, new LambdaUpdateWrapper<AnnotationTask>()
                .eq(AnnotationTask::getId, taskId)
                .set(AnnotationTask::getStatus, "UNCLAIMED")
                .set(AnnotationTask::getClaimedBy, null)
                .set(AnnotationTask::getClaimedAt, null));

        // 清除 Redis 分布式锁
        redisService.delete(RedisUtil.taskClaimKey(taskId));

        insertHistory(taskId, principal.getCompanyId(),
                "IN_PROGRESS", "UNCLAIMED",
                principal.getUserId(), principal.getRole(), null);
    }

    // ------------------------------------------------------------------ 重领 --

    /**
     * 重领任务（REJECTED → IN_PROGRESS，仅原领取人可重领）。
     *
     * @param taskId    任务 ID
     * @param principal 当前用户
     */
    @Transactional
    public void reclaim(Long taskId, TokenPrincipal principal) {
        AnnotationTask task = taskMapper.selectById(taskId);
        validateTaskExists(task, taskId);

        if (!"REJECTED".equals(task.getStatus())) {
            throw new BusinessException("INVALID_STATE_TRANSITION",
                    "只有 REJECTED 状态的任务可以重领", HttpStatus.CONFLICT);
        }

        if (!principal.getUserId().equals(task.getClaimedBy())) {
            throw new BusinessException("FORBIDDEN",
                    "只有原领取人可以重领该任务", HttpStatus.FORBIDDEN);
        }

        StateValidator.assertTransition(TaskStatus.TRANSITIONS,
                TaskStatus.valueOf(task.getStatus()), TaskStatus.IN_PROGRESS);

        taskMapper.update(null, new LambdaUpdateWrapper<AnnotationTask>()
                .eq(AnnotationTask::getId, taskId)
                .eq(AnnotationTask::getStatus, "REJECTED")
                .set(AnnotationTask::getStatus, "IN_PROGRESS")
                .set(AnnotationTask::getClaimedAt, java.time.LocalDateTime.now()));

        // 重新设置 Redis 锁（防止并发再次争抢）
        redisService.setIfAbsent(
                RedisUtil.taskClaimKey(taskId),
                principal.getUserId().toString(), CLAIM_LOCK_TTL);

        insertHistory(taskId, principal.getCompanyId(),
                "REJECTED", "IN_PROGRESS",
                principal.getUserId(), principal.getRole(), null);
    }

    // ------------------------------------------------------------------ 私有工具 --

    private void validateTaskExists(AnnotationTask task, Long taskId) {
        if (task == null) {
            throw new BusinessException("NOT_FOUND", "任务不存在: " + taskId, HttpStatus.NOT_FOUND);
        }
    }

    /**
     * 向 annotation_task_history 追加一条历史记录（仅 INSERT，禁止 UPDATE/DELETE）。
     */
    public void insertHistory(Long taskId, Long companyId,
                               String fromStatus, String toStatus,
                               Long operatorId, String operatorRole, String comment) {
        historyMapper.insert(AnnotationTaskHistory.builder()
                .taskId(taskId)
                .companyId(companyId)
                .fromStatus(fromStatus)
                .toStatus(toStatus)
                .operatorId(operatorId)
                .operatorRole(operatorRole)
                .comment(comment)
                .build());
    }
}