1 files changed, 52 insertions, 5 deletions
diff --git a/railties/lib/rails_generator/generators/components/migration/migration_generator.rb b/railties/lib/rails_generator/generators/components/migration/migration_generator.rb
index 3dff3bf396..65f5e6c74e 100644
--- a/railties/lib/rails_generator/generators/components/migration/migration_generator.rb
+++ b/railties/lib/rails_generator/generators/components/migration/migration_generator.rb
@@ -1,11 +1,58 @@
 class MigrationGenerator < Rails::Generator::NamedBase
   def manifest
     record do |m|
-      m.directory File.join('db/migrate')
-      existing_migrations = Dir.glob("db/migrate/[0-9]*_#{file_name}.rb")
-      raise "Another migration already exists with the same name" unless existing_migrations.empty?
-      next_migration_number = Dir.glob("db/migrate/[0-9]*.rb").size + 1
-      m.template 'migration.rb', File.join('db/migrate', "#{next_migration_number}_#{file_name}.rb")
+      m.directory 'db/migrate'
+      m.migration_template 'migration.rb', 'db/migrate'
+    end
+  end
+end
+
+module Rails::Generator::Commands
+  class Base
+    def existing_migrations(file_name)
+      Dir.glob("db/migrate/[0-9]*_#{file_name}.rb")
+    end
+
+    def migration_exists?(file_name)
+      not existing_migrations(file_name).empty?
+    end
+
+    def current_migration_number
+      Dir.glob('db/migrate/[0-9]*.rb').inject(0) do |max, file_path|
+        n = File.basename(file_path).split('_', 2).first.to_i
+        if n > max then n else max end
+      end
+    end
+
+    def next_migration_number
+      current_migration_number + 1
+    end
+
+    def next_migration_string(padding = 3)
+      "%.#{padding}d" % next_migration_number
+    end
+  end
+
+  # When creating, it knows to find the first available file in db/migrate and use the migration.rb template. When deleting, it knows to delete every file named "[0-9]*_#{file_name}".
+  class Create
+    def migration_template(relative_source, relative_destination, template_options = {})
+      raise "Another migration is already named #{file_name}: #{existing_migrations(file_name).first}" if migration_exists?(file_name)
+      template(relative_source, "#{relative_destination}/#{next_migration_string}_#{file_name}.rb", template_options)
+    end
+  end
+
+  class Destroy
+    def migration_template(relative_source, relative_destination, template_options = {})
+      raise "There is no migration named #{file_name}" unless migration_exists?(file_name)
+      existing_migrations(file_name).each do |file_path|
+        file(relative_source, file_path, template_options)
+      end
+    end
+  end
+
+  class List
+    def migration_template(relative_source, relative_destination, options = {})
+      logger.migration_template file_name
     end
   end
 end