#!/usr/bin/ruby
# range STOP | START STOP | START STOP INCREMENT - print a sequence of numbers
#
# START and INCREMENT default to 1.
# Prefix START with leading spaces or zeroes as wanted.
# Increment can be "/NUMBER" to use (STOP-START)/NUMBER as INCREMENT.
# Increment can be "NUM/DENOM" for a rational increment.

start = 1.to_r
start_pre = 0
start_post = 0
incr = 1.to_r
incr_pre = 0
incr_post = 0
pad = "0"

class Rational
  def to_decimal(pre, post, pad="0")
    digits = (((10**post) * numerator + denominator/2) / denominator).
               abs.to_i.to_s
    digits = digits.rjust(post + (abs < 1 ? 1 : 0), "0")
    digits = digits.rjust(pre + post, pad)
    digits.insert(-post-1, '.')  if post > 0
    if self < 0
      if pad == "0"
        digits.insert(0, '-')
      else
        digits.sub!(/(.*)#{pad}/, '\1-') or digits.insert(0, '-')
      end
    end
    digits
  end
end

def parse(s)
  case s
  when /\A(\s*)-?(\d+)\z/
    [Rational(s), $1.size + $2.size, 0]
  when /\A(\s*)-?(\d*)\.(\d+)\z/
    [Rational(s), $1.size + $2.size, $3.size]
  when /\A-?\d+\/\d+\z/
    [Rational(s), 0, 0]
  else
    raise ArgumentError, "can't parse #{s}"
  end
end        

case ARGV.size
when 1
  stop, stop_pre, stop_post = parse(ARGV[0])
when 2, 3
  start, start_pre, start_post = parse(ARGV[0])
  stop, stop_pre, stop_post = parse(ARGV[1])
  pad = " "  if ARGV[0].start_with?(" ")
  if ARGV.size == 3
    if ARGV[2].start_with?("/")
      n = parse(ARGV[2][1..-1]).first
      incr = Rational(stop - start, n)
    else
      incr, incr_pre, incr_post = parse(ARGV[2])
    end
  end
else
  abort "Usage: range STOP | START STOP | START STOP INCREMENT"
end

# pre = [start_pre, incr_pre, stop_pre].max
pre = start_pre
post = [start_post, incr_post, stop_post].max

start.step(stop, incr) { |val|
  puts val.to_decimal(pre, post, pad)
}