#!/usr/bin/env ruby

# regular expression for matching 5-min timeseries
re = /^(\d{4}-\d{2}-\d{2})T(\d{2}:\d{2})\s+(\d+)\s+(\d+)/

v = Array.new()			# array for timeseries
ARGF.each_line do |line|
  if re.match(line)
    v.push $3.to_f
  end
end

n = v.length		# n: number of samples
h = n / 2 - 1		# (half of n) - 1

r = Array.new(n/2)	# array for auto correlation
for k in 0 .. h		# for different timelag
  s = 0
  for i in 0 .. h
    s += v[i] * v[i + k]
  end
  r[k] = Float(s)
end

# normalize by dividing by r0
if r[0] != 0.0
  r0 = r[0]
  for k in 0 .. h
    r[k] = r[k] / r0
    puts "#{k} #{r[k]}"
  end
end