Allow switching on instance or class for provider

Prior to this commit, instance methods of the Provider class were
passing the instance's class to the associated response classes. This
was a surprise; Why would an instance method send as a parameter
it's class instead of the instance method's instance?

This made it difficult to add context to the Provider on a request by
request basis; In our implementation, we wanted to pass the controller
to the instantiated provider instance.

Further, the following line of code was dangerous, in that it would
override the URL for the entire class and all future uses. (Perhaps
that's the OAI specification, but it's a dangerous class mutation)

```ruby
self.class.url = params['url'] ? params.delete('url') : self.class.url
```

All told, this commit seeks to:

* preserve backwards compatibility by adding instance methods that
  mirror the expected class methods used by the Response module's
  classes.
* provide extensibility for downstream implementers when they
  instantiate an OAI::Provider

Author: jeremyf

lib/oai/provider.rb

@@ -240,9 +240,10 @@ module OAI::Provider
   class Base
     include OAI::Provider
 
+    OAI_PMH_ATTRIBUTES = [:name, :url, :prefix, :email, :delete_support, :granularity, :model, :identifier, :description]
     class << self
       attr_reader :formats
-      attr_accessor :name, :url, :prefix, :email, :delete_support, :granularity, :model, :identifier, :description
+      attr_accessor(*OAI_PMH_ATTRIBUTES)
 
       def register_format(format)
         @formats ||= {}
@@ -292,39 +293,72 @@ def inherited(klass)
 
     Base.register_format(OAI::Provider::Metadata::DublinCore.instance)
 
+    PROVIDER_CONTEXTS = {
+      :class_based => :class_based,
+      :instance_based => :instance_based
+    }
+
+    def initialize(provider_context = :class_based)
+      @provider_context = PROVIDER_CONTEXTS.fetch(provider_context)
+      OAI_PMH_ATTRIBUTES.each do |attr|
+        instance_variable_set("@#{attr}", self.class.public_send(attr))
+      end
+    end
+    attr_accessor(*OAI_PMH_ATTRIBUTES)
+
+    def provider_context
+      if @provider_context == :class_based
+        self.class
+      else
+        self
+      end
+    end
+
+    def format_supported?(*args)
+      self.class.format_supported?(*args)
+    end
+
+    def format(*args)
+      self.class.format(*args)
+    end
+
+    def formats
+      self.class.formats
+    end
+
     # Equivalent to '&verb=Identify', returns information about the repository
     def identify(options = {})
-      Response::Identify.new(self.class, options).to_xml
+      Response::Identify.new(provider_context, options).to_xml
     end
 
     # Equivalent to '&verb=ListSets', returns a list of sets that are supported
     # by the repository or an error if sets are not supported.
     def list_sets(options = {})
-      Response::ListSets.new(self.class, options).to_xml
+      Response::ListSets.new(provider_context, options).to_xml
     end
 
     # Equivalent to '&verb=ListMetadataFormats', returns a list of metadata formats
     # supported by the repository.
     def list_metadata_formats(options = {})
-      Response::ListMetadataFormats.new(self.class, options).to_xml
+      Response::ListMetadataFormats.new(provider_context, options).to_xml
     end
 
     # Equivalent to '&verb=ListIdentifiers', returns a list of record headers that
     # meet the supplied criteria.
     def list_identifiers(options = {})
-      Response::ListIdentifiers.new(self.class, options).to_xml
+      Response::ListIdentifiers.new(provider_context, options).to_xml
     end
 
     # Equivalent to '&verb=ListRecords', returns a list of records that meet the
     # supplied criteria.
     def list_records(options = {})
-      Response::ListRecords.new(self.class, options).to_xml
+      Response::ListRecords.new(provider_context, options).to_xml
     end
 
     # Equivalent to '&verb=GetRecord', returns a record matching the required
     # :identifier option
     def get_record(options = {})
-      Response::GetRecord.new(self.class, options).to_xml
+      Response::GetRecord.new(provider_context, options).to_xml
     end
 
     #  xml_response = process_verb('ListRecords', :from => 'October 1, 2005',
@@ -336,7 +370,7 @@ def process_request(params = {})
       begin
 
         # Allow the request to pass in a url
-        self.class.url = params['url'] ? params.delete('url') : self.class.url
+        provider_context.url = params['url'] ? params.delete('url') : self.class.url
 
         verb = params.delete('verb') || params.delete(:verb)
 

test/provider/tc_instance_provider.rb

@@ -0,0 +1,32 @@
+require 'test_helper_provider'
+
+class TestInstanceProvider < Test::Unit::TestCase
+
+  # Prior to the commit introducing this code, the InstanceProvider#identify
+  # method would instantiate a Response::Identify object, passing the
+  # InstanceProvider class as the provider for the Response::Identify
+  # instance. With the commit introducing this test, the
+  # InstanceProvider#identify now passes the instance of InstanceProvider
+  # to the instantiation of Response::Identify.
+  #
+  # Thus we can override, on an instance by instance basis, the behavior of a
+  # response object.
+  def test_instance_used_in_responses
+    @url_path = "/stringy-mc-string-face"
+    @instance_provider = InstanceProvider.new(:instance_based, @url_path)
+
+    xml = @instance_provider.identify
+    doc =  REXML::Document.new(xml)
+    assert_equal "http://localhost#{@url_path}", doc.elements["OAI-PMH/Identify/baseURL"].text
+  end
+
+  def test_class_used_in_responses
+    @url_path = "/stringy-mc-string-face"
+    @instance_provider = InstanceProvider.new(:class_based, @url_path)
+
+    xml = @instance_provider.identify
+    doc =  REXML::Document.new(xml)
+    assert_equal "http://localhost", doc.elements["OAI-PMH/Identify/baseURL"].text
+  end
+
+end

test/provider/test_helper_provider.rb

@@ -43,3 +43,20 @@ class DescribedProvider < Provider::Base
   sample_id '13900'
   extra_description "<my_custom_xml />"
 end
+
+class InstanceProvider < Provider::Base
+  repository_name 'Instance Provider'
+  record_prefix 'oai:test'
+  repository_url 'http://localhost'
+  source_model SimpleModel.new
+
+  def initialize(context_provider, url_path)
+    super(context_provider)
+    @url_path = url_path
+  end
+  attr_reader :url_path
+
+  def url
+    File.join(super, url_path)
+  end
+end