namespace.rb

# manages namespace abbreviations and expansions

class Namespace

  @@namespaces = Hash.new
  @@inverted_namespaces = Hash.new

  # registers a namespace prefix and its associated expansion (full URI)
  # e.g. :rdf and 'http://www.w3.org/1999/02/22-rdf-syntax-ns#'
  def self.register(prefix, fullURI)
		raise ActiveRdfError, 'prefix nor uri can be empty' if (prefix.to_s.empty? or fullURI.to_s.empty?)
    @@namespaces[prefix.to_sym] = fullURI.to_s
    @@inverted_namespaces[fullURI.to_s] = prefix.to_sym
  end

  # returns a resource whose URI is formed by concatenation of prefix and localname
  def self.lookup(prefix, localname)
    RDFS::Resource.new(expand(prefix, localname))
  end

  # returns URI (string) formed by concatenation of prefix and localname
  def self.expand(prefix, localname)
    @@namespaces[prefix.to_sym].to_s + localname.to_s
  end

  # returns prefix (if known) for the non-local part of the URI,
  # or nil if prefix not registered
  def self.prefix(resource)
    # get string representation of resource uri
    uri = case resource
    when RDFS::Resource: resource.uri
    else resource.to_s
    end

    # uri.to_s gives us the uri of the resource (if resource given)
    # then we find the last occurrence of # or / (heuristical namespace
    # delimitor)
    delimiter = uri.rindex(/#|\//)

    # if delimiter not found, URI cannot be split into (non)local-part
    return uri if delimiter.nil?

    # extract non-local part (including delimiter)
    nonlocal = uri[0..delimiter]

    @@inverted_namespaces[nonlocal]
  end

  # returns local-part of URI
  def self.localname(resource)
    # get string representation of resource uri
    uri = case resource
    when RDFS::Resource: resource.uri
    else resource.to_s
    end

    delimiter = uri.rindex(/#|\//)
    if delimiter.nil?
      uri
    else
      uri[delimiter+1..-1]
    end
  end
end

Namespace.register(:rdf, 'http://www.w3.org/1999/02/22-rdf-syntax-ns#')
Namespace.register(:rdfs, 'http://www.w3.org/2000/01/rdf-schema#')
Namespace.register(:owl, 'http://www.w3.org/2002/07/owl#')