Get iterator and number for the range of available timeszone relative to the current time.

calculate_timezone_select_iterator.lua

function tz_calculate(crt,start_time,end_time)
        --[[ The function receives the current time, the start time and the end time.
         Counts the total time of work "job_time" and the difference between the end of work and the current time "calc". 
         Compares calc and job_time
         If calc is less than or equal to job_time, then the iterator LE (<=) and the calc result are selected to select the taason band.
         If job_time is greater than calc, then the GE iterator (> =) is selected, and the timezone is calculated as the difference (calc - job_time)
        --]]
        job_time = (end_time - start_time)
        calc = (end_time - crt)
        if (calc <= job_time) then
                return {tonumber(calc),"LE"}
        elseif (calc > job_time) then
                return {tonumber(calc - job_time),"GE"}
        else
                return nil
        end
end

When accessing the function, we get an iterator for searching in the tarantool db and data for the search index.
EXAMPLE:
tz_calculate (7,9,21) (the current time is 7 am, and we need a range of time zones available from 9 to 21 local time)
result - {2, GE}
We are looking for time zones >= 2