class NHIValidator

The National Health Index (NHI) number is used by many national and local systems to provide a safe and secure reference key for patient data. Because of its importance, the NHI number has a built-in validation routine that has been designed to allow systems to minimise typographical errors as NHI numbers are keyed in. NHI number structure The NHI number is a unique 7-character identifier (3 alphabetical characters followed by 4 numeric characters) assigned to a healthcare user by the NHI. The first 3 characters of an NHI number must be alphabetic, but not 'I' or 'O', to avoid confusion with one and zero. The 4th to 6th characters must be numeric. The 7th character is also numeric, and is a check digit based on modulus 11.

Constants

ALPHABET_OMITTING_I_AND_O
PATTERN
VERSION

Public Class Methods

valid?(nhi) click to toggle source

# File lib/nhi_validator.rb, line 24
def valid?(nhi)
  return false unless nhi =~ PATTERN # steps 1-2

  cs = checksum(nhi[0..5]) # steps 3-10
  return false if cs.zero? # step 11

  cs = 11 - cs # step 12
  cs = 0 if cs == 10 # step 13

  nhi[6].to_i == cs
end

Private Class Methods

checksum(characters) click to toggle source

# File lib/nhi_validator.rb, line 38
def checksum(characters)
  total = 0
  characters.each_char.with_index do |character, index|
    total += multiply(character, index)
  end
  total % 11
end

multiply(character, position) click to toggle source

# File lib/nhi_validator.rb, line 50
def multiply(character, position)
  multiplier = (7 - position)
  return character.to_i * multiplier if character =~ /[0-9]/

  position_in_alphabet(character) * multiplier
end

position_in_alphabet(character) click to toggle source

# File lib/nhi_validator.rb, line 46
def position_in_alphabet(character)
  ALPHABET_OMITTING_I_AND_O.index(character.downcase) + 1
end