Sum By User ID Between Two Dynamic Dates

Hi jackj ,
for performance reasons, I would to this on grouped data (user level). So the code gets a lit complicated, unfortunately:

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMjQyVtIBkvrGhvpGBkZGQI6KoYGegYGCUqwOkrShAVzaFEnWBCJrZILQjEUaSbMRstmmGLqhmmMB", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [UserID = _t, Date = _t, Sales = _t]),
#"Changed Type" = Table.TransformColumnTypes(Source, {{"UserID", Int64.Type}, {"Date", type date}, {"Sales", Currency.Type}}), 
    Custom1 = Table.Group(
        #"Changed Type", 
        {"UserID"}, 
        {
            {
                "UserID_Partition", 
                (P) =>
                    Table.AddColumn(
                        Table.Buffer(P), 
                        "SalesM", 
                        each [Sales14 = List.Sum(Table.SelectRows(
                            P, 
                            (Partition) => Partition[Date] >= Date.AddDays(_[Date], - 14) and Partition[Date] <= _[Date]
                        )[Sales]),
                        Sales7 = List.Sum(Table.SelectRows(
                            P, 
                            (Partition) => Partition[Date] >= Date.AddDays(_[Date], - 7) and Partition[Date] <= _[Date]
                        )[Sales])
                        ]
                    )
            }
        }
    ),
    #"Expanded UserID_Partition" = Table.ExpandTableColumn(Custom1, "UserID_Partition", {"Date", "Sales", "SalesM"}, {"Date", "Sales", "SalesM"}),
    #"Expanded SalesM" = Table.ExpandRecordColumn(#"Expanded UserID_Partition", "SalesM", {"Sales14", "Sales7"}, {"Sales14", "Sales7"})
in
    #"Expanded SalesM"

Pls also check the file enclosed.