#####
# tt_add_missing_rows()
# Many rolling functions require an integer input for the length of periods
# to roll over. Missing data may cause differencing or other to have strange
# behavior because it specifies integer 365 as a year, but with missing data
# there are only 200 days in one year and 360 in another year and 355 in another
# year.
# In order to make sure the integer length of each period is correct, this
# function adds missing rows.
# User should also make sure there are not extra rows using tt_period_apply().
#####

require('dplyr')
require('tibbletime')
require('rlang')

tt_add_missing_rows <- function(in.tbl_time, by = 'hour') {
  # Programatically find the index column
  index_column <- attributes(in.tbl_time)$index_quo[[2]]

  # Programatically find the first and last date/time in the index
  start.idx <- start(in.tbl_time[,paste0(index_column)][[1]])
  end.idx <- end(in.tbl_time[,paste0(index_column)][[1]])

  start <- in.tbl_time[start.idx,paste0(index_column)][[1]][[1]]
  end <- in.tbl_time[end.idx,paste0(index_column)][[1]][[1]]

  seq.vec <- seq(start,end,by=by)
  seq.df <- data.frame(seq.vec)
    # Make the date/time column the same as for the other vector
    # so that merge by will auto detect.
    names(seq.df)[1] <- paste(index_column)

  out.tbl_time <- merge(in.tbl_time,seq.df,all = TRUE)
}