class ActiveFedora::FilePathBuilder

def self.build(digital_object, name, prefix)

Builds a relative path for a file 
def self.build(digital_object, name, prefix)
  name = nil if name == ''
  prefix ||= 'DS'
  name || generate_dsid(digital_object, prefix)
end

def self.format_dsid(prefix, suffix)

## Provided so that an application can override how generated ids are formatted (e.g DS01 instead of DS1) 
def self.format_dsid(prefix, suffix)
  format "%s%i", prefix, suffix
end

def self.generate_dsid(digital_object, prefix)

Example: if there are already datastreams with IDs DS1 and DS2, this method will return DS3. If you specify FOO as the prefix, it will return FOO1.
return a valid dsid that is not currently in use. Uses a prefix (default "DS") and an auto-incrementing integer 
def self.generate_dsid(digital_object, prefix)
  return unless digital_object
  matches = digital_object.attached_files.keys.map do |d|
    data = /^#{prefix}(\d+)$/.match(d)
    data && data[1].to_i
  end.compact
  val = matches.empty? ? 1 : matches.max + 1
  format_dsid(prefix, val)
end