distinct strings value and concatenating the results - node.js

Question

i'm trying to distinct different string values of "comment" and "dates" and concatenate them in two different strings one for comments and one for reclamation dates I used $addToSet to distinct values but every time the concatenating is giving empty result
and this is m code :
db.collection.aggregate([
{
$group: {
_id: {
b: "$type"
},
total: {
$sum: 1
},
root: {
$push: "$$ROOT"
}
}
},
{
"$unwind": "$root"
},
{
$group: {
_id: {
r: "$root.situation",
b: "$root.type"
},
cnt: {
$sum: 1
},
total: {
"$first": "$total"
},
}
},
{
$project: {
a: [
{
k: "$_id.r",
v: "$cnt"
}
],
type: "$_id.b",
total: "$total",
_id: 0,
}
},
{
$project: {
d: {
$arrayToObject: "$a"
},
type: 1,
total: 1
}
},
{
$group: {
_id: "$type",
situation: {
$push: "$d"
},
sum: {
"$first": "$total"
},
//add to set of commets and dates
comment: {
$addToSet: "$comment"
},
daterec: {
$addToSet: "$daterec"
},
}
},
{
$project: {
_id: 0,
type: "$_id",
sum: 1,
"options": {
$mergeObjects: "$situation"
},
//concatenating results
comment: {
$reduce: {
input: "$comment",
initialValue: "",
in: {
$cond: [
{
"$eq": [
"$$value",
""
]
},
"$$this",
{
$concat: [
"$$value",
" ",
"$$this"
]
}
]
}
}
},
daterec: {
$reduce: {
input: "$daterec",
initialValue: "",
in: {
$cond: [
{
"$eq": [
"$$value",
""
]
},
"$$this",
{
$concat: [
"$$value",
" ",
"$$this"
]
}
]
}
}
}
}
},
{
$replaceRoot: {
newRoot: {
$mergeObjects: [
"$$ROOT",
"$options"
]
}
}
},
{
$project: {
options: 0,
}
},
])
and this is the output :
{
"after sales management": 4,
"comment": "",
"daterec": "",
"instock": 1,
"sum": 5,
"type": "pc"
}
its always giving "comment" and"daterec": empty while i want it to show the concatenating of distinct strings it should looks something like this :
{
"after sales management": 4,
"comment": "waiting for pieces waiting for approval nothing",
"daterec": "1",//this is just an example beacause all dates are set to "1"
"instock": 1,
"sum": 5,
"type": "pc"
}
this is an example of my work with a collection example:
https://mongoplayground.net/p/dB3xBFsIfun
PS : i think the problem is in the of using the $addToSet insite $group