How to calculate the total value of two object arrays with the same key but different fields and combine them into one using aggregation in MongoDB?

I have data returned as an array like this:

[{
    "_id" : ObjectId("65aa4921c767f95a70b8867f"),
    "creator" : "Henry",
    "date" : "2023-12-22",
    "channels" : [
        {
            "key" : "HTV",
            "value" : 1
        }
    ]
},
{
    "_id" : ObjectId("65aa4921c767f95a70b8867f"),
    "creator" : "Max",
    "date" : "2023-12-23",
    "channels" : [
        {
            "key" : "VTC",
            "value" : 1
        }
    ]
},
{
    "_id" : ObjectId("65aa4921c767f95a70b88689"),
    "creator" : "John",
    "date" : "2023-12-23",
    "channels" : [
        {
            "key" : "VTC",
            "value" : 2
        },
        {
            "key" : "HTV",
            "value" : 1
        }
    ]
}]

I want to group by date and elements in the "channels" array with the same key will merge into one (Total value of channels with the same key and sum of all values of channels)

I used aggregate to group "date":

model.aggregate([
      {
        $group: {
          _id: {
            date: '$date'
          },
          Total: { $sum: { $sum: '$channels.value' } }
        }
      }
    ])

But don't know what to do next (merge duplicate keys into one, and calculate the sum of the value)

My expected results:

[{
    "date": "2023-12-22",
    "channels" : [
        {
            "key" : "HTV",
            "value" : 1
        }
    ],
    "Total" : 1
},
{
    "date": "2023-12-23",
    "channels" : [
        {
            "key" : "VTC",
            "value" : 3   // 1 + 2
        },
        {
            "key" : "HTV",
            "value" : 1
        }
    ],
    "Total" : 4
}]

Can anyone help me solve this problem? Very grateful for the responses

Solution

One option is:

$unwind to separate the channels into documents
$group by both date and key to sum the value
$group by date only
Format the response

db.collection.aggregate([
  {$unwind: "$channels"},
  {$group: {
      _id: {date: "$date", key: "$channels.key"},
      value: {$sum: "$channels.value"}}
  },
  {$group: {
      _id: "$_id.date",
      channels: {$push: {key: "$_id.key", value: "$value"}},
      Total: {$sum: "$value"}
  }},
  {$set: {date: "$_id", _id: "$$REMOVE"}}
])

See how it works on the playground example