install: Adds confirmation before overwriting existing source_dir

Rakefile

@@ -27,6 +27,9 @@ server_port     = "4000"      # port for preview server eg. localhost:4000
 
 desc "Initial setup for Octopress: copies the default theme into the path of Jekyll's generator. Rake install defaults to rake install[classic] to install a different theme run rake install[some_theme_name]"
 task :install, :theme do |t, args|
+  if File.directory?(source_dir) || File.directory?("sass")
+    abort("rake aborted!") if ask("A theme is already installed, proceeding will overwrite existing files. Are you sure?", ['y', 'n']) == 'n'
+  end
   # copy theme into working Jekyll directories
   theme = args.theme || 'classic'
   puts "## Copying "+theme+" theme into ./#{source_dir} and ./sass"
@@ -293,6 +296,20 @@ def ok_failed(condition)
   end
 end
 
+def get_stdin(message)
+  print message
+  STDIN.gets.chomp
+end
+
+def ask(message, valid_options)
+  if valid_options
+    answer = get_stdin("#{message} #{valid_options.to_s.gsub(/"/, '').gsub(/, /,'/')} ") while !valid_options.include?(answer)
+  else
+    answer = get_stdin(message)
+  end
+  answer
+end
+
 desc "list tasks"
 task :list do
   puts "Tasks: #{(Rake::Task.tasks - [Rake::Task[:list]]).join(', ')}"