#!/usr/bin/env ruby

require 'set'

# Initialize variables
operation = :union
complement = false
files = []

# Process options
while arg = ARGV.shift
  if arg.start_with?('-')
    case arg
    when '-c'
      complement = true
    when '-d'
      operation = :difference
    when '-i'
      operation = :intersection
    when '-u'
      operation = :union
    else
      puts "Invalid option: #{arg}"
      puts "usage: [options] file ..."
      puts "options"
      puts "  -c  complement"
      puts "  -d  difference"
      puts "  -i  intersection"
      puts "  -u  union"
      exit 1
    end
  else
    files << arg
  end
end

# Ensure at least one file is provided
if files.empty?
  puts "No files provided."
  exit 1
end

# Read files into sets
sets = []

files.each do |filename|
  begin
    lines = File.readlines(filename).map(&:chomp)
    sets << Set.new(lines)
  rescue Errno::ENOENT
    puts "File not found: #{filename}"
    exit 1
  end
end

# Compute the universe (union of all sets)
universe = sets.reduce(Set.new, :|)

# Compute result_set based on the operation
case operation
when :union
  result_set = sets.reduce(Set.new, :|)
when :intersection
  result_set = sets.reduce { |a, b| a & b }
when :difference
  # Subtract all subsequent sets from the first set
  result_set = sets[0].dup
  sets[1..-1].each do |s|
    result_set -= s
  end
end

# Apply complement if specified
if complement
  result_set = universe - result_set
end

# Output the result
result_set.each do |line|
  puts line
end