import { Injectable, NotFoundException, ForbiddenException } from '@nestjs/common';
import { PrismaService } from '../common/prisma/prisma.service';

@Injectable()
export class GroupsService {
  constructor(private prisma: PrismaService) {}

  async createGroup(courseId: string, userId: string, name: string, description?: string): Promise<any> {
    const course = await this.prisma.course.findFirst({ where: { id: courseId, authorId: userId } });
    if (!course) throw new ForbiddenException('Only course author can create groups');

    return this.prisma.courseGroup.create({
      data: { courseId, name, description },
    });
  }

  async addMember(groupId: string, userId: string, role = 'student'): Promise<any> {
    return this.prisma.groupMember.create({
      data: { groupId, userId, role },
    });
  }

  async getGroupMessages(groupId: string, userId: string): Promise<any> {
    const member = await this.prisma.groupMember.findUnique({
      where: { groupId_userId: { groupId, userId } },
    });
    if (!member) throw new ForbiddenException('Not a member of this group');

    return this.prisma.groupMessage.findMany({
      where: { groupId },
      include: { user: { select: { id: true, name: true, avatarUrl: true } } },
      orderBy: { createdAt: 'asc' },
      take: 100,
    });
  }

  async sendMessage(groupId: string, userId: string, content: string): Promise<any> {
    const member = await this.prisma.groupMember.findUnique({
      where: { groupId_userId: { groupId, userId } },
    });
    if (!member) throw new ForbiddenException('Not a member of this group');

    return this.prisma.groupMessage.create({
      data: { groupId, userId, content },
      include: { user: { select: { id: true, name: true, avatarUrl: true } } },
    });
  }
}