Convert Salesforce IDs from 15 character to 18 characters (and back)

salesforce_id.rb

# Salesforce originally used case-sensitive 15-character IDs.
# Later they added three error-correcting characters to make their 18-character ID.
# This class converts from one to the other and back
# 
# Usage:
#   SalesforceId.convert('a0D30000001n7Pi')  =>  'a0D30000001n7PiEAC'
# OR
#   SalesforceId.convert('a0D30000001n7PiEAC')  =>  'a0D30000001n7Pi'
#   SalesforceId.convert('A0d30000001N7pIeAc')  =>  'a0D30000001n7Pi'
#
class SalesforceId
  class << self
    def convert(str)
      raise 'can only convert strings' unless str.is_a?(String)
      return convert15to18(str) if str.length == 15
      return convert18to15(str) if str.length == 18
      raise 'must be either 15 or 18'
    end

    def base32todecimal(char)
      base32[char]
    end
    def decimaltobase32(dec)
      Array(base32.rassoc(dec)).first
    end

    private

    def base32
      @@b32 ||= begin
        hash = {}
        ('A'..'Z').each_with_index {|letter, idx| hash[letter] = idx }
        ('0'..'5').each_with_index {|digit, idx|  hash[digit]  = idx + 26 }
        hash
      end
    end

    def convert15to18(str)
      bits = str.split('').collect {|char| (char =~ /[A-Z]/) ? '1' : 0 }
      checkdigits = [
          bits[0..4].join.to_i(2),
          bits[5..9].join.to_i(2),
          bits[10..14].join.to_i(2),
      ]
      checkdigits = checkdigits.collect {|d| decimaltobase32(d) }.join
      str + checkdigits
    end

    def convert18to15(str)
      base = str[0..14].downcase.split('')
      dec = str[-3..-1].upcase.split('').collect {|char| base32todecimal(char) }
      bits = dec.map {|d| ("%05b" % d.to_i).split('') }.flatten
      base.zip(bits).map {|char,bit| bit == '1' ? char.upcase : char }.join
    end
  end
end