aggregate user stock

recon.js

db.getCollection('users').aggregate([
        {
            $match: {
                role: 'USER'
            }
        },
        {
            $lookup: {
                from: 'ledgers',
                localField: '_id',
                foreignField: 'userId',
                as: 'ledgers'
            }
        },
        {
            $lookup: {
                from: 'activities',
                localField: '_id',
                foreignField: 'userId',
                as: 'activities'
            }
        },
        {
            $project: {
                _id: 1,
                email: 1,
                stock: 1,
                fname: '$profile.firstName',
                lname: '$profile.lastName',
                credit: {
                    $sum:  {
            $map: {
                input: '$ledgers',
                as: 'item',
                in: {
                    "$cond": [
                        { "$eq": [ "$$item.type", 'credit' ] },
                        "$$item.qty",
                        0
                    ]
                }
            }
        }
                },
                debit: {
                    $sum:  {
            $map: {
                input: '$ledgers',
                as: 'item',
                in: {
                    "$cond": [
                        { "$eq": [ "$$item.type", 'debit' ] },
                        "$$item.qty",
                        0
                    ]
                }
            }
        }
                },
                totalDistribution: {
                    $sum: {
                        $map: {
                            input: '$activities',
                            as: 'item',
                            in: "$$item.samples"
                        }
                    }
                }
            }
        },
        {
            $project: {
                _id: 1,
                email: 1,
                fname: 1,
                lname: 1,
                stock: 1,
                creditTotal: '$credit',
                debitTotal: '$debit',
                totalDistribution: 1,
                ledgerBal: {
                    $subtract: ['$credit', '$debit']
                },
                activityBal: {
                      $subtract: ['$credit', '$totalDistribution']
                }
            }
        }
    ])