Subtract value in array based on other collection mongoose

Question

I have the following collections

    const TransactionSchema = mongoose.Schema({
        schedule: {
            type: mongoose.Schema.ObjectId,
            required: true,
            ref: "Schedule"
        },
        uniqueCode: {
            type: String,
            required: true
        },
item: {
            type: mongoose.Schema.ObjectId,
            required: false,
            ref: "Item"
        },
        created: {
            type: Date,
            default: Date.now
        },
    
        status: {
            type: String,
            required: false
        },
    })

schedule

const ScheduleSchema = mongoose.Schema({
start: {
    type: Date,
    required: true,
},
end: {
    type: Date,
    required: false,
},
questions: {
    type: Array,
    default: [],
},
items: [{
    item: {
        type: mongoose.Schema.ObjectId,
        require: true,
        ref: "Item"
    },
    stock: {
        type: Number,
        required: true
    }
}],

status: {
    type: String,
    required: false
},
})

I want to return how many times the item appear in transaction and reduce it with the number of total item I have in array of objects items in schedule collection.

For example I have the following data:

transaction

 [
   {
      "_id":ObjectId('626134d547c28b6ecc6d0c6c'),
      "schedule":624edc44ac2edc1cf07821de,
      "uniqueCode":"312312312312",
      "created":2022-04-21T10:41:25.901+00:00,
      "item": 61efd8a812432135c08a748d,
      "status": "Active"
   },
   {
      "_id":ObjectId('62615ea3db7d00061b7cc437'),
      "schedule":624edc44ac2edc1cf07821de,
      "uniqueCode":"1213123123",
      "created":2022-04-21T13:39:47.351+00:00,
      "item": 624c6b26a41c439987b1eb42,
      "status": "Active"


   }
]

schedule

[
   {
      "_id":ObjectId('624edc44ac2edc1cf07821de'),
      "start":2000-01-01T00:00:00.000+00:00,
      "end":2000-01-01T00:00:00.000+00:00,
      "questions":[
         12,
         32,
         122
      ],
      "items":[
         {
            "item":61efd8a812432135c08a748d,
            "stock":120
         },
         {
            "item":624c6b26a41c439987b1eb42,
            "stock":1000
         }
      ],
      "status":"Active"
   },
]

Item

[
   {
      "_id": ObjectId('61efd8a812432135c08a748d'),
      "name": "Samsung S21"
      
   },
   {
     "_id": ObjectId('624c6b26a41c439987b1eb42'),
     "name": "Iphone 10"
     
   }
]

I want to get the following result:

[
   {
      "item":"Samsung S21",
      "total":119
   },
   {
      "item":"Iphone 10",
      "total":999
   }
]

Note: I want the query to query one schedule data only so the result only shows the items in that schedule. The first row shows 119 from total stock of item 120 - 1 which is how many times the item appeared in transaction (where the status is active). The second row shows 999 because the item has appeared in one transaction.

Thank you. Sorry for my bad English.