Added auto correct with -a flag

README.md

@@ -25,6 +25,7 @@ Or install it yourself as:
     Usage: rubocop-git [options] [[commit] commit]
         -c, --config FILE                Specify configuration file
         -r, --require FILE               Require Ruby file
+        -a, --auto-correct               Auto-correct offenses
         -d, --debug                      Display debug info
         -D, --display-cop-names          Display cop names in offense messages
             --cached                     git diff --cached

lib/rubocop/git.rb

@@ -1,5 +1,7 @@
 require 'rubocop/git/version'
 require 'rubocop'
+require 'tempfile'
+require 'fileutils'
 
 module RuboCop
   module Git
@@ -15,5 +17,6 @@ module Git
     autoload :Runner,            'rubocop/git/runner'
     autoload :StyleChecker,      'rubocop/git/style_checker'
     autoload :StyleGuide,        'rubocop/git/style_guide'
+    autoload :RuboComment,       'rubocop/git/rubo_comment'
   end
 end

lib/rubocop/git/cli.rb

@@ -35,6 +35,10 @@ def option_parser
             require file
           end
 
+          opt.on('-a', '--auto-correct', 'Auto-correct offenses.') do
+            @options.rubocop[:auto_correct] = true
+          end
+
           opt.on('-d', '--debug', 'Display debug info') do
             @options.rubocop[:debug] = true
           end

lib/rubocop/git/patch.rb

@@ -4,15 +4,17 @@ class Patch
   RANGE_INFORMATION_LINE = /^@@ .+\+(?<line_number>\d+),/
   MODIFIED_LINE = /^\+(?!\+|\+)/
   NOT_REMOVED_LINE = /^[^-]/
+  PATCH_INFO_LINE = /\+([0-9,]+)/
 
   def initialize(body)
     @body = body || ''
+    @changes = []
   end
 
   def additions
     line_number = 0
 
-    lines.each_with_index.inject([]) do |additions, (content, patch_position)|
+    lines.each_with_index.inject(@changes) do |additions, (content, patch_position)|
       case content
       when RANGE_INFORMATION_LINE
         line_number = Regexp.last_match[:line_number].to_i
@@ -27,6 +29,31 @@ def additions
     end
   end
 
+  # maps out additions line numbers to indicate start and end of code changes
+  # [[5,7], [11,11]] indicates changes from line 5, 6, 7 and then
+  # another one at 11
+  def additions_map
+    if @changes.empty?
+      self.additions
+    end
+
+    map = []
+    starting_line = ending_line = 0
+
+    @changes.each do |addition|
+      if starting_line == 0
+        starting_line = ending_line = addition.line_number
+      elsif addition.line_number == ( ending_line + 1 )
+        ending_line = addition.line_number
+      else # this row is not part of the last rows "group"
+        map.push([starting_line, ending_line])
+        starting_line = ending_line = addition.line_number
+      end
+    end
+    map.push([starting_line, ending_line])
+    map
+  end
+
   private
 
   def lines

lib/rubocop/git/rubo_comment.rb

@@ -0,0 +1,92 @@
+module RuboCop::Git
+class RuboComment
+  RUBOCOP_DISABLE = "# rubocop:disable all\n"
+  RUBOCOP_ENABLE = "# rubocop:enable all\n"
+  WHITE_SPACE = /^\s*/
+
+  def initialize(files)
+    @edit_map = {}
+    @files = files
+  end
+
+  # adds rubocop enable and disabled comments to files
+  # making sure only edited lines are processed by rubocop
+  def add_comments
+    @files.each do |file|
+      patch_info = Patch.new(file.patch).additions_map
+      temp_file = Tempfile.new('temp')
+
+      line_count = edited_line_count = current_patch = 0
+      in_patch = false
+      edit_locations = []
+
+      begin
+        File.open(file.filename, "r").each_line do |line|
+          line_count += 1
+          edited_line_count += 1
+
+          if line_count == patch_info[current_patch].first
+            temp_file.puts generate_spaces(line) + RUBOCOP_ENABLE
+            in_patch = true
+            edit_locations.push edited_line_count
+            edited_line_count += 1
+
+          elsif in_patch && patch_info[current_patch].last + 1 == line_count
+            temp_file.puts generate_spaces(line) + RUBOCOP_DISABLE
+            in_patch = false
+            edit_locations.push edited_line_count
+            edited_line_count += 1
+            current_patch += 1 unless (current_patch + 1) >= patch_info.size
+
+          elsif line_count == 1 #adds disable at top of file
+            temp_file.puts generate_spaces(line) + RUBOCOP_DISABLE
+            edit_locations.push edited_line_count
+            edited_line_count += 1
+
+          end
+          temp_file.puts line
+        end
+
+        temp_file.close
+        FileUtils.mv(temp_file.path, file.filename)
+        @edit_map[file.filename] = edit_locations
+      ensure
+        temp_file.close
+        temp_file.unlink
+      end
+    end
+  end
+
+  # removes all added comments that where added from add_comments
+  def remove_comments
+    @files.each do |file|
+      temp_file = Tempfile.new('temp')
+      line_count = 0
+
+      begin
+        File.open(file.filename, "r").each_line do |line|
+          line_count += 1
+          temp_file.puts line unless @edit_map[file.filename].find_index line_count
+        end
+
+        temp_file.close
+        FileUtils.mv(temp_file.path, file.filename)
+      ensure
+        temp_file.close
+        temp_file.unlink
+      end
+    end
+  end
+
+  private
+
+  # generates whitespaces to make en/disable comments match line indent
+  # preventing rubocop errors
+  def generate_spaces(line)
+    whitespaces = ""
+    WHITE_SPACE.match(line).to_s.split('').size.times { whitespaces << " " }
+    whitespaces
+  end
+
+end
+end

lib/rubocop/git/runner.rb

@@ -9,8 +9,15 @@ def run(options)
 
         @options = options
         @files = DiffParser.parse(git_diff(options))
+        rubo_comment = RuboComment.new(@files)
+
+        #adds comments to files and reparses diff after changes are made
+        rubo_comment.add_comments
+        @files = DiffParser.parse(git_diff(options))
 
         display_violations($stdout)
+        #removes comments after rubocop processing
+        rubo_comment.remove_comments
 
         exit(1) if violations.any?
       end
@@ -45,7 +52,7 @@ def git_diff(options)
       def display_violations(io)
         formatter = RuboCop::Formatter::ClangStyleFormatter.new(io)
         formatter.started(nil)
-
+        
         violations.map do |violation|
           formatter.file_finished(
             violation.filename,