mongodb aggregate pipeline if else to execute one of the query

My objects looks like the following

{
    id: 1,
    a: "val7f",
    b: "online",
    c: "reg",
    d: "retd"
},
{
    id: 2,
    a: "val6f",
    b: "online",
    c: "reg",
    d: "new"
},
{
    id: 3,
    a: "val6f",
    b: "offline",
    c: "non-reg",
    d: "new"
}

I want to build a query in the following manner.

if (a=="val7f" && b=="offline" && c="reg") has objs > 1 return result Objs
else if(a=="val7f" && b=="offline" && c="reg") has objs > 1 return result objs
etc.

I built the following query but values displayed are from else query even if there are results for the if case:

db.Collection.aggregate([
    { $redact: {
        $cond: {
            if: { 
                $and: [ 
                    { $eq: [ "a", "val7f" ] }, 
                    { $eq: [ "b", "offline" ] }, 
                    { $eq: [ "c", "reg" ] } 
                ] 
            },
            then: "$$DESCEND",
            else: {
                $cond: {
                    if: { 
                        $and: [ 
                            { $eq: [ "$a", "val6f"] }, 
                            { $eq: [ "b", "offline"] }, 
                            { $eq: [ "c", "reg"] } 
                        ] 
                    },
                    else: "$$PRUNE"
                }
            }
        }
    } }
]);

Summarised as follows

I've put condition as follows

if: { 
    $and: [ 
            { $eq: [ "a", "val7f" ] }, 
            { $eq: [ "b", "offline" ] }, 
            { $eq: [ "c", "reg" ] } 
        ] 
    }  

if this has result say

{
    id: 6,
    a: "val7f",
    b: "online",
    c: "reg",
    d: "retd"
} 

it should return the above document. in case there are no document matching criteria

else case should execute

if: {
    $and: [ 
      { $eq: [ "$a", "val6f"] }, 
      { $eq: [ "b", "offline"] }, 
      { $eq: [ "c", "reg"] }
     ] 
    }  

and if there is match for this say

{
    id: 11,
    a: "val6f",
    b: "offline",
    c: "reg",
    d: "new"
} 

In my case, for the query built above I'm getting both the documents in the output shell.