Reactively passing functions into tsibble index_by

Crossposting from stackoverflow link
I am having problems with reactively passing date-time collapsing functions into index_by function from package tsibble .

index_by takes as an argument a time function (for example week() or month() from lubridate ) and collapses the data accordingly.

I want the collapsing to be reactive to user input (specifically selected data-range).

Example: if selected date-range > 60 , collapse using week() , if selected date-range > 120 , collapse using month() .

EDIT: I am specifically refering to using tsibble in the context of server side of shiny module for plotting. Example:

mod_plot = function(input, output, session, df, date_Range){
  output$plot = renderPlotly({
    df() %>%
      index_by(collapse_time = week(.)/month(.)) %>%
      summarise(trace1 = sum(trace1))%>%
      plot_ly(type = 'bar', x = ~collapse_time, y = ~trace1)
  })
}

In order to avoid code duplicity, it would be great to somehow pass date collapsing functions into index_by. Example using tibbletime:

  mod_plot = function(input, output, session, df, date_Range){
      output$plot = renderPlotly({
      #create reactive variable collapse_time based on selected time range
      collapse_time = renderText(if(as.numeric(date_Range$selectdateRange[2] - date_Range$selectdateRange[1]) <= 60){"daily"}
                               else if(as.numeric(date_Range$selectdateRange[2] - date_Range$selectdateRange[1]) < 120){"weekly"}
                               else{"monthly"})
        df() %>%
          collapse_by(collapse_time ) %>%
          group_by(date) %>%
          summarise(trace1 = sum(trace1))%>%
          plot_ly(type = 'bar', x = ~date, y = ~trace1)
      })
    }

This allows for concise and readable pipeline.