Add proper version handling to Pairtree.at()

lib/pairtree.rb

@@ -8,13 +8,19 @@
 module Pairtree
   class IdentifierError < Exception; end
   class PathError < Exception; end
+  class VersionMismatch < Exception; end
+
+  SPEC_VERSION = 0.1
 
   def self.at path, args = {}
     args = { :prefix => nil, :version => nil, :create => false }.merge(args)
+    args[:version] ||= SPEC_VERSION
+    args[:version] = args[:version].to_f
 
     root_path = File.join(path, 'pairtree_root')
     prefix_file = File.join(path, 'pairtree_prefix')
-
+    version_file = File.join(path, pairtree_version_filename(args[:version]))
+    existing_version_file = Dir[File.join(path, "pairtree_version*")].sort.last
 
     if args.delete(:create)
       if File.exists?(path) and not File.directory?(path)
@@ -25,6 +31,18 @@ def self.at path, args = {}
       unless File.exists? prefix_file
         File.open(prefix_file, 'w') { |f| f.write(args[:prefix].to_s) }
       end
+
+      if existing_version_file
+        if existing_version_file != version_file
+          stored_version = existing_version_file.scan(/([0-9]+)_([0-9]+)/).flatten.join('.').to_f
+          raise VersionMismatch, "Version #{args[:version]} specified, but #{stored_version} found."
+        end
+      else
+        args[:version] ||= SPEC_VERSION
+        version_file = File.join(path, pairtree_version_filename(args[:version]))
+        File.open(version_file, 'w') { |f| f.write %{This directory conforms to Pairtree Version #{args[:version]}. Updated spec: http://www.cdlib.org/inside/diglib/pairtree/pairtreespec.html} }
+        existing_version_file = version_file
+      end
     else
       unless File.directory? root_path
         raise PathError, "#{path} does not point to an existing pairtree"
@@ -36,8 +54,18 @@ def self.at path, args = {}
       raise IdentifierError, "Specified prefix #{args[:prefix].inspect} does not match stored prefix #{stored_prefix.inspect}"
     end
     args[:prefix] = stored_prefix
+
+    stored_version = existing_version_file.scan(/([0-9]+)_([0-9]+)/).flatten.join('.').to_f
+    args[:version] ||= stored_version
+    unless args[:version] == stored_version
+      raise VersionMismatch, "Version #{args[:version]} specified, but #{stored_version} found."
+    end
 
     Pairtree::Root.new(File.join(path, 'pairtree_root'), args)
   end
-
+
+  private
+  def self.pairtree_version_filename(version)
+    "pairtree_version#{version.to_s.gsub(/\./,'_')}"
+  end
 end

spec/pairtree/pairtree_spec.rb

@@ -22,7 +22,7 @@
       pt.prefix.should == prefix
       File.read(File.join(@base_path, 'pairtree_prefix')).should == prefix
       pt.root.should == File.join(@base_path, 'pairtree_root')
-      pt.pairtree_root.class.should == Dir
+      pt.pairtree_version.should == Pairtree::SPEC_VERSION
     end
 
   end
@@ -54,6 +54,16 @@
       lambda { Pairtree.at(@base_path, :prefix => 'wrong-prefix:') }.should raise_error(Pairtree::IdentifierError)
     end
 
+    it "should not complain if the given version matches the saved version" do
+      Pairtree.at(@base_path, :version => Pairtree::SPEC_VERSION).pairtree_version.should == Pairtree::SPEC_VERSION
+      Pairtree.at(@base_path, :version => Pairtree::SPEC_VERSION, :create => true).pairtree_version.should == Pairtree::SPEC_VERSION
+    end
+
+    it "should raise an error if the given version does not match the saved version" do
+      lambda { Pairtree.at(@base_path, :version => 0.2) }.should raise_error(Pairtree::VersionMismatch)
+      lambda { Pairtree.at(@base_path, :version => 0.2, :create => true) }.should raise_error(Pairtree::VersionMismatch)
+    end
+
   end
 
 end

spec/test_data/fixtures/pairtree_root_spec/pairtree_version0_1

@@ -0,0 +1 @@
+This directory conforms to Pairtree Version 0.1. Updated spec: http://www.cdlib.org/inside/diglib/pairtree/pairtreespec.html