encoach_frontend/src/pages/api/users/controller.ts

import { sessionOptions } from '@/lib/session';
import { withIronSessionApiRoute } from 'iron-session/next';
import type { NextApiRequest, NextApiResponse } from 'next'
import client from "@/lib/mongodb";

const db = client.db(process.env.MONGODB_DB);

export default withIronSessionApiRoute(handler, sessionOptions);

async function handler(req: NextApiRequest, res: NextApiResponse) {
  const { op } = req.query

  if (req.method === 'GET') {
    switch (op) {
      default:
        res.status(400).json({ error: 'Invalid operation!' })
    }
  }
  else if (req.method === 'POST') {
    switch (op) {
      case 'crossRefEmails':
        res.status(200).json(await crossRefEmails(req.body.emails));
        break;
      case 'dontExist':
        res.status(200).json(await dontExist(req.body.emails))
        break;
      case 'entityCheck':
        res.status(200).json(await entityCheck(req.body));
        break;
      case 'crossRefClassrooms':
        res.status(200).json(await crossRefClassrooms(req.body.sets));
        break;
      default:
        res.status(400).json({ error: 'Invalid operation!' })
    }
  } else {
    res.status(400).end(`Method ${req.method} Not Allowed`)
  }
}

async function crossRefEmails(emails: string[]) {
  return await db.collection("users").aggregate([
    {
      $match: {
        email: { $in: emails }
      }
    },
    {
      $project: {
        _id: 0,
        email: 1
      }
    }
  ]).toArray();
}

async function dontExist(emails: string[]): Promise<string[]> {
  const existingUsers = await db.collection('users')
    .find(
      { email: { $in: emails } },
      { projection: { _id: 0, email: 1 } }
    )
    .toArray();

  const existingEmails = new Set(existingUsers.map(u => u.email));
  return emails.filter(email => !existingEmails.has(email));
}


async function entityCheck(body: Record<string, any>): Promise<string[]> {
  const { entities, emails } = body;
  
  const pipeline = [
    // Match users with the provided emails
    {
      $match: {
        email: { $in: emails }
      }
    },
    // Match users who don't have any of the entities
    {
      $match: {
        $or: [
          // Either they have no entities array
          { entities: { $exists: false } },
          // Or their entities array is empty
          { entities: { $size: 0 } },
          // Or none of their entities match the provided IDs
          {
            entities: {
              $not: {
                $elemMatch: {
                  id: { $in: entities.map((e: any) => e.id) }
                }
              }
            }
          }
        ]
      }
    },
    // Project only the email field
    {
      $project: {
        _id: 0,
        email: 1
      }
    }
  ];

  const results = await db.collection('users').aggregate(pipeline).toArray();
  return results.map((result: any) => result.email);
}

async function crossRefClassrooms(sets: { email: string, classroom: string }[]) {
  const pipeline = [
    // Match users with the provided emails
    {
      $match: {
        email: { $in: sets.map(set => set.email) }
      }
    },
    // Lookup groups that contain the user's ID in participants
    {
      $lookup: {
        from: 'groups',
        let: { userId: '$id', userEmail: '$email' },
        pipeline: [
          {
            $match: {
              $expr: {
                $and: [
                  { $in: ['$$userId', '$participants'] },
                  {
                    // Match the classroom that corresponds to this user's email
                    $let: {
                      vars: {
                        matchingSet: {
                          $arrayElemAt: [
                            {
                              $filter: {
                                input: sets,
                                cond: { $eq: ['$$this.email', '$$userEmail'] }
                              }
                            },
                            0
                          ]
                        }
                      },
                      in: { $eq: ['$name', '$$matchingSet.classroom'] }
                    }
                  }
                ]
              }
            }
          }
        ],
        as: 'matchingGroups'
      }
    },
    // Only keep users who have matching groups
    {
      $match: {
        matchingGroups: { $ne: [] }
      }
    },
    // Project only the email
    {
      $project: {
        _id: 0,
        email: 1
      }
    }
  ];
  
  const results = await db.collection('users').aggregate(pipeline).toArray();
  return results.map((result: any) => result.email);
}