parsing-an-encoded-string.rb

# Provides a lookup map for a given unit and how many seconds one of
# those units represents.

TIME_UNIT_TO_SECONDS_MAP = {
  "h" => 60 * 60, # seconds in an hour
  "m" => 60,      # seconds in a minute
  "s" => 1        # seconds in a second
}

def convert_to_seconds_via_string_splitting(input)
  # Split on one or more numerals
  #
  # Because of the structure, the first element should always be an
  # empty string.  We may want to guard better.  On the other hand,
  # if the user's giving us junk, whatever.
  units = input.split(/\d+/)[1..-1]

  return input.to_i unless units

  # Split on a single alpha character
  times = input.split(/[a-z]/)

  seconds = 0

  units.each_with_index do |unit, i|
    seconds += TIME_UNIT_TO_SECONDS_MAP.fetch(unit, 0) * times[i].to_i
  end

  return seconds
end


# This regular expression is a unduly complicated, but highlights an
# alternative approach.
#
# Note there are nine capture regions:
#p
# 1,4,7: The scalar and it's unit (e.g., "10s", "1h")
# 2,5,8: The scalar (e.g., "10", "1")
# 3,6,9: The unit (e.g., "s", "h")
THREE_TIMES_AND_UNITS_REGEXP =
  /\A((\d+)([a-z]))?((\d+)([a-z]))?((\d+)([a-z]))?\Z/

def convert_to_seconds_via_verbose_regexp(input)
  match = THREE_TIMES_AND_UNITS_REGEXP.match(input)
  seconds = 0
  return input.to_i unless match

  seconds += match[2].to_i *
    TIME_UNIT_TO_SECONDS_MAP.fetch(match[3], 0) if match[1]
  seconds += match[5].to_i *
    TIME_UNIT_TO_SECONDS_MAP.fetch(match[6], 0) if match[4]
  seconds += match[8].to_i *
    TIME_UNIT_TO_SECONDS_MAP.fetch(match[9], 0) if match[7]
  seconds
end

# This regular expression is a simplified version of
# THREE_TIMES_AND_UNITS_REGEXP.
#
# Note there are three capture regions:
#
# 1: The scalar (e.g., "10", "1")
# 2: The unit (e.g., "s", "h")
TIME_AND_UNIT_REGEXP = /(\d+)([a-z])/

def convert_to_seconds_via_regexp_scanner(input)
  seconds = 0
  matched = false

  input.scan(TIME_AND_UNIT_REGEXP) do |time, unit|
    next if time.nil? || unit.nil?
    matched = true
    seconds += time.to_i *
      TIME_UNIT_TO_SECONDS_MAP.fetch(unit, 0)
  end
  return seconds if matched
  input.to_i
end


[
  ["1h4m2s", 3842],
  ["1m", 60],
  ["1s2m", 121],
  ["1d", 0],
  ["10", 10],
].each do |given, expected|
  puts "Given: #{given}\tExpected: #{expected}"
  [
    :convert_to_seconds_via_string_splitting,
    :convert_to_seconds_via_verbose_regexp,
    :convert_to_seconds_via_regexp_scanner,
  ].each do |method|
    returned_value = __send__(method, given)
    if returned_value == expected
      puts "\tSuccess for #{method}."
    else
      puts "\tFailure for #{method}.  Got: #{returned_value}"

    end
  end
end