Adding time offsets to create future dates

Question

How can I shorten this (working) code to create future dates in ruby for use as params in URLs?

I'm doing:

require 'cgi'
require 'time'

now=Time.new()
now_year=now.strftime('%Y').to_i
now_month=now.strftime('%m').to_i
now_day=now.strftime('%d').to_i
now_hour=now.strftime('%H').to_i

start_hour=(now_hour + 1)
end_hour=(now_hour + 2)

start_datetime=Time.new(now_year, now_month, now_day, start_hour)
end_datetime=Time.new(now_year, now_month, now_day, end_hour)

starts=CGI.escape(start_datetime.utc.strftime("%Y-%m-%dT%H:%M:%S.%3NZ"))
ends=CGI.escape(end_datetime.utc.strftime("%Y-%m-%dT%H:%M:%S.%3NZ"))

and it works, but it seems long and clumsy. Is there an easier way?

Answer 1

You can add seconds directly to a Time object, so you could do:

now = Time.now.utc
starts = now + 3600 # Add 1 hour's worth of seconds (60 * 60)
ends   = now + 7200 # Add 2 hours

and then do the strftime-formatting.

Of course, since you need to do this twice, I'd suggest adding a method to avoid the repetition, i.e.:

def offset_utc_timestamp(offset, format = "%Y-%m-%dT%H:%M:%S.%3NZ")
  time = Time.now.utc + offset
  time.strftime(format)
end

You may want to split it up differently (i.e. have the method just return a Time object, which you make into a string elsewhere; or have the method also do the URL escaping).

I'd also recommend using the URI.escape method instead, if this is intended for URLs

With all that your code becomes:

starts = URI.escape(offset_utc_timestamp(3600))
ends   = URI.escape(offset_utc_timestamp(7200))

Alternatively, the ActiveSupport gem has a ton of helpful time stuff, letting you do things like 2.hours.from_now.utc

Answer 2

Once you start storing some strings in percent-encoded form, you have the added burden of keeping track of which strings are encoded, and which strings aren't.¹ Therefore, you should avoid ad hoc escaping.

Instead, I recommend keeping all strings in unescaped form, and performing the escaping at the last minute when constructing the URL. That also forces you to use a URL-construction procedure that handles all escaping for you — the way it should be done. For example,

import urllib

start = (Time.now.utc + 3600).strftime(…)
end   = (Time.now.utc + 7200).strftime(…)

query_string = urllib.urlencode({ 'start': start, 'end', end })

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¹ One way to keep track of which variables contain encoded strings is to use some form of Hungarian Notation (see the section called The Real Solution).