add Account class; build from Book

lib/gnucash/account.rb

@@ -0,0 +1,9 @@
+module Gnucash
+  class Account
+    def initialize(book, node)
+      @node = node
+      @name = node.xpath('act:name').text
+      @type = node.xpath('act:type').text
+    end
+  end
+end

lib/gnucash/book.rb

@@ -3,8 +3,24 @@ require "nokogiri"
 
 module Gnucash
   class Book
+    attr_accessor :accounts
+
     def initialize(fname)
       @ng = Nokogiri.XML(Zlib::GzipReader.open(fname).read)
+      book_nodes = @ng.xpath('/gnc-v2/gnc:book')
+      if book_nodes.count != 1
+        raise "Error: Expected to find one gnc:book entry"
+      end
+      @book_node = book_nodes.first
+      build_accounts
+    end
+
+    private
+
+    def build_accounts
+      @accounts = @book_node.xpath('gnc:account').map do |act_node|
+        Account.new(self, act_node)
+      end
     end
   end
 end