Range reference to easily use some feature (#504)

This patch introduce following methods to easily use auto_filter,
table, etc.

- Worksheet#top_left_reference
- Worksheet#bottom_right_reference
- Worksheet#range_reference

Author: sato-s

examples/auto_filter.rb

@@ -5,12 +5,11 @@
 require 'axlsx'
 Axlsx::Package.new do |p|
   p.workbook.add_worksheet(:name => "Table") do |sheet|
-    sheet.add_row ["Build Matrix"]
     sheet.add_row ["Build", "Duration", "Finished", "Rvm"]
     sheet.add_row ["19.1", "1 min 32 sec", "about 10 hours ago", "1.8.7"]
     sheet.add_row ["19.2", "1 min 28 sec", "about 10 hours ago", "1.9.2"]
     sheet.add_row ["19.3", "1 min 35 sec", "about 10 hours ago", "1.9.3"]
-    sheet.auto_filter = 'A2:D5'
+    sheet.auto_filter = sheet.range_reference # => "A1:D4"
     sheet.auto_filter.add_column 3, :filters, :filter_items => ['1.9.2']
   end
   p.workbook.add_worksheet(:name => "Table 2") do |sheet|
@@ -19,7 +18,7 @@
     sheet.add_row ["19.1", "1 min 32 sec", "about 10 hours ago", "1.8.7"]
     sheet.add_row ["19.2", "1 min 28 sec", "about 10 hours ago", "1.9.2"]
     sheet.add_row ["19.3", "1 min 35 sec", "about 10 hours ago", "1.9.3"]
-    sheet.auto_filter = 'A2:D5'
+    sheet.auto_filter = "A2:#{sheet.bottom_right_reference}" # => 'A2:D5'
     sheet.auto_filter.add_column 3, :filters, :filter_items => ['1.9.2']
   end
 end.serialize('auto_filter.xlsx')

lib/axlsx/workbook/worksheet/worksheet.rb

@@ -682,6 +682,53 @@ def outline_level_columns(start_index, end_index, level = 1, collapsed = true)
       outline column_info, (start_index..end_index), level, collapsed
     end
 
+    # The excel-style reference of the top-left cell of this worksheet, e.g., A1
+    # @return String
+    def top_left_reference
+      raise "worksheet has no data" if rows.empty? or rows.first.empty?
+      rows.first.first.r
+    end
+
+    # The excel-style reference of the bottom-right cell of this worksheet, e.g., D5
+    # This method is useful when you want to apply auto_filter or table to dynamic length data.
+    #
+    # @example
+    #     Axlsx::Package.new do |p|
+    #       p.workbook.add_worksheet(:name => "Table 2") do |sheet|
+    #         sheet.add_row ["Build Matrix"]
+    #         sheet.add_row ["Build", "Duration", "Finished", "Rvm"]
+    #         sheet.add_row ["19.1", "1 min 32 sec", "about 10 hours ago", "1.8.7"]
+    #         sheet.add_row ["19.2", "1 min 28 sec", "about 10 hours ago", "1.9.2"]
+    #         sheet.add_row ["19.3", "1 min 35 sec", "about 10 hours ago", "1.9.3"]
+    #         sheet.auto_filter = "A2:#{sheet.bottom_right_reference}" # => 'A2:D5'
+    #         sheet.auto_filter.add_column 3, :filters, :filter_items => ['1.9.2']
+    #       end
+    #    end
+    # @return String
+    def bottom_right_reference
+      raise "worksheet has no data" if rows.empty? or rows.last.empty?
+      rows.last.last.r
+    end
+
+    # The excel-style reference of the range of this worksheet, e.g., A1:D5
+    # This method is useful when you just want to apply auto_filter or table to whole worksheet.
+    #
+    # @example
+    #     Axlsx::Package.new do |p|
+    #       p.workbook.add_worksheet(:name => "Table") do |sheet|
+    #         sheet.add_row ["Build", "Duration", "Finished", "Rvm"]
+    #         sheet.add_row ["19.1", "1 min 32 sec", "about 10 hours ago", "1.8.7"]
+    #         sheet.add_row ["19.2", "1 min 28 sec", "about 10 hours ago", "1.9.2"]
+    #         sheet.add_row ["19.3", "1 min 35 sec", "about 10 hours ago", "1.9.3"]
+    #         sheet.auto_filter = sheet.range_reference # => "A1:D4"
+    #         sheet.auto_filter.add_column 3, :filters, :filter_items => ['1.9.2']
+    #       end
+    #    end
+    # @return String
+    def range_reference
+      "#{top_left_reference}:#{bottom_right_reference}"
+    end
+
     private
 
     def xml_space

test/workbook/worksheet/tc_worksheet.rb

@@ -163,6 +163,28 @@ def test_referencing
     assert_equal(range.last, @ws.rows.last.cells.last)
   end
 
+  def test_corner_reference
+    @ws.add_row [1, 2, 3]
+    @ws.add_row [4, 5, 6]
+    assert_equal(@ws.top_left_reference, "A1")
+    assert_equal(@ws.bottom_right_reference, "C2")
+  end
+
+  def test_corner_reference_raise_exception_if_no_row
+    assert_raise(RuntimeError, "worksheet has no data"){ @ws.top_left_reference }
+    assert_raise(RuntimeError, "worksheet has no data"){ @ws.bottom_right_reference }
+  end
+
+  def test_range_reference
+    @ws.add_row [1, 2, 3]
+    @ws.add_row [4, 5, 6]
+    assert_equal(@ws.range_reference, 'A1:C2')
+  end
+
+  def test_range_reference_raise_exception_if_no_row
+    assert_raise(RuntimeError, "worksheet has no data"){ @ws.range_reference }
+  end
+
   def test_add_row
     assert(@ws.rows.empty?, "sheet has no rows by default")
     r = @ws.add_row([1,2,3])