Refactor for fods (ODF flat XML) file support

lib/roo/open_office.rb

@@ -24,7 +24,7 @@ def initialize(filename, options = {})
       file_warning = options[:file_warning] || :error
 
       @only_visible_sheets = options[:only_visible_sheets]
-      file_type_check(filename, '.ods', 'an Roo::OpenOffice', file_warning, packed)
+      file_type_check(filename, supported_extension, 'an Roo::OpenOffice', file_warning, packed)
       # NOTE: Create temp directory and allow Ruby to cleanup the temp directory
       #       when the object is garbage collected. Initially, the finalizer was
       #       created in the Roo::Tempdir module, but that led to a segfault
@@ -53,6 +53,10 @@ def initialize(filename, options = {})
       raise
     end
 
+    def supported_extension
+      '.ods'
+    end
+
     def open_oo_file(options)
       Zip::File.open(@filename) do |zip_file|
         content_entry = zip_file.glob('content.xml').first
@@ -446,6 +450,10 @@ def set_cell_values(sheet, x, y, i, v, value_type, formula, table_cell, str_v, s
       end
     end
 
+    def cell_elements(table_element)
+      table_element.children
+    end
+
     # read all cells in the selected sheet
     #--
     # the following construct means '4 blanks'
@@ -471,7 +479,7 @@ def read_cells(sheet = default_sheet)
               skip_row = attribute(table_element, 'number-rows-repeated').to_s.to_i
               row      = row + skip_row - 1
             end
-            table_element.children.each do |cell|
+            cell_elements(table_element).each do |cell|
               skip_col   = attribute(cell, 'number-columns-repeated')
               formula    = attribute(cell, 'formula')
               value_type = attribute(cell, 'value-type')