Adding Faker::IDNumber.brazilian_citizen_number (faker-ruby#1382)

doc/id_number.md

@@ -20,4 +20,7 @@ Faker::IDNumber.valid_south_african_id_number #=> "8105128870184"
 
 # Generate an invalid South African ID Number
 Faker::IDNumber.invalid_south_african_id_number #=> "1642972065088"
+
+# Generate a Brazilian citizen number (CPF)
+Faker::IDNumber.brazilian_citizen_number #=> "53540542221"
 ```

lib/faker/id_number.rb

@@ -75,6 +75,13 @@ def invalid_south_african_id_number
         [id_number, south_african_id_checksum_digit(id_number)].join
       end
 
+      def brazilian_citizen_number
+        digits = Faker::Number.leading_zero_number(9) until digits&.match(/(\d)((?!\1)\d)+/)
+        first_digit = brazilian_citizen_number_checksum_digit(digits)
+        second_digit = brazilian_citizen_number_checksum_digit(digits + first_digit)
+        [digits, first_digit, second_digit].join
+      end
+
       private
 
       def south_african_id_checksum_digit(id_number)
@@ -95,6 +102,14 @@ def south_african_id_checksum_digit(id_number)
         ((10 - (total_sum % 10)) % 10).to_s
       end
 
+      def brazilian_citizen_number_checksum_digit(digits)
+        digit_sum = digits.chars.each_with_index.inject(0) do |acc, (digit, i)|
+          acc + digit.to_i * (digits.size + 1 - i)
+        end * 10
+        remainder = digit_sum % 11
+        remainder == 10 ? '0' : remainder.to_s
+      end
+
       def _translate(key)
         parse("id_number.#{key}")
       end

test/test_faker_id_number.rb

@@ -63,6 +63,24 @@ def test_invalid_south_african_id_number
     end
   end
 
+  def test_brazilian_citizen_number
+    sample = @tester.brazilian_citizen_number
+    assert_match(/^\d{11}$/, sample)
+    assert_match(/(\d)((?!\1)\d)+/, sample)
+    digit_sum = sample[0..8].chars.each_with_index.inject(0) do |acc, (digit, i)|
+      acc + digit.to_i * (10 - i)
+    end * 10
+    remainder = digit_sum % 11
+    first_digit = remainder == 10 ? '0' : remainder.to_s
+    assert_equal sample[9], first_digit
+    digit_sum = sample[0..9].chars.each_with_index.inject(0) do |acc, (digit, i)|
+      acc + digit.to_i * (11 - i)
+    end * 10
+    remainder = digit_sum % 11
+    second_digit = remainder == 10 ? '0' : remainder.to_s
+    assert_equal sample[10], second_digit
+  end
+
   private
 
   def south_african_id_number_to_date_of_birth_string(sample)