Find any pairs of numbers in a sequence that add up to sum N (Using builtin combination method)

Output

##### OUTPUT
1
  Enter comma seperated integers
  1,2,3,4,6,7,8
  Enter pair sum
  10
  [[2, 8], [3, 7], [4, 6]]
 
 
2
  Enter comma seperated integers
  1,2,3,4,6,7,8
  Enter pair sum
  5
  [[1, 4], [2, 3]]
  
3
  Enter comma seperated integers
  1,2,3,4,6,7,8
  Enter pair sum
  20
  []
  
4
  Enter comma seperated integers
  1,2,3,4,6,7,a
  Invalid Input (Only Integers allowed)

pairs.rb

# Find any pairs of numbers in a sequence that add up to sum N.
# Given input 1, 8, 2, 3, 5, 7
# Expected Output (8,2), (3, 7)

# Using built-in function combination to check and compare sum pair value

class CheckPairs 
    #  Base class to instantiate utility class
    def find_pairs
        nums,sum = user_input
        num_pairs = NumPairs.new(nums, sum)
        pairs = num_pairs.pairs
        p pairs
    end

    def user_input # Takes user input and returns to calling function as arrays
        p 'Enter comma seperated integers'
        nums = gets.chomp
        if nums.split(',').join('').scan(/\D/).empty?
            p 'Enter pair sum'
            sum = gets.chomp.to_i
            return [nums, sum]
        else
            p 'Invalid Input (Only Integers allowed)' 
            exit
        end
    end
end

class NumPairs
    # Utility class to perform required functions
    def initialize(numbers, sum) # Initialize numbers and sum
        @numbers = numbers.split(',').map(&:to_i).uniq
        @sum = sum.to_i
    end

    def pairs
        @numbers.combination(2).select { |x, y| x + y == @sum}
    end
end

pairs = CheckPairs.new
pairs.find_pairs