Forecasting on weekly basis

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let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMlTSUXIEYgMgNlWK1YlWMoKKgGSMwSLGUBEjsDqQCEjOCUXECCpiABaF6YKJGMN1OQOxCVyNEVTEFG6OMVTEECISCwA=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type text) meta [Serialized.Text = true]) in type table [Week = _t, Material = _t, Out = _t, In = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Week", Int64.Type}, {"Out", Int64.Type}, {"In", Int64.Type}, {"Material", type text}}),
    #"Grouped Rows" = Table.Group(#"Changed Type", {"Material"}, {{"AD", each _, type table}}),
    #"Added Custom" = Table.AddColumn(#"Grouped Rows", "Custom", each let
   Source=[AD],   
   In_Out= Table.AddColumn(Source,"In-Out", each [In]-[Out]),
   X=List.Skip(List.Accumulate(In_Out[#"In-Out"],{0},(state,current)=>state&{List.Last(state)+current})),
   Y= Table.FromColumns(Table.ToColumns(In_Out)&{X}),
   Z= Table.AddColumn(Y,"OB", each [Column6]-[Column4]+[Column3]),
   #"Renamed Columns" = Table.RenameColumns(Z,{{"Column1", "Week"}, {"Column2", "Material"}, {"Column3", "Out"}, {"Column4", "In"}, {"Column6", "CB"}}),
    #"Removed Columns" = Table.RemoveColumns(#"Renamed Columns",{"Column5"}),
  #"Reordered Columns" = Table.ReorderColumns(#"Removed Columns",{"Week", "Material", "Out", "In", "OB", "CB"})
in
    #"Reordered Columns"),
    #"Removed Other Columns" = Table.SelectColumns(#"Added Custom",{"Custom"}),
    #"Expanded Custom" = Table.ExpandTableColumn(#"Removed Other Columns", "Custom", {"Week", "Material", "Out", "In", "OB", "CB"}, {"Week", "Material", "Out", "In", "OB", "CB"})
in
    #"Expanded Custom"