= Templater

Templater is a system for generating files. Templater has the ability to both copy files from A to B and also to render templates using ERB. Templater consists of four parts:

- Actions (File copying routines, templates generation and directories creation routines).
- Generators (set of rules).
- Manifolds (generator suites).
- The command line interface.

Hierarchy is pretty simple: manifold has one or many public and private generators. Public ones are supposed to be called
by end user. Generators have one or more action that specify what they do, where they take files, how they name resulting
files and so forth.

== Idea behind Templater

Templater is designed to be flexible and designed to be reflective. Generators created with templater are definitions of what goes where, they provide no interface for the user. This allows you to use templater generators inside your own code, or with the bundled CLI interface, or with your own interface.

== Example

This is how to create a very simple system for generating things:

    module MyGenerators

      extend Templater::Manifold

      class BlogGenerator < Templater::Generator
        # directory this generator uses as source root when searching
				# for files, directories, templates
        def self.source_root
          File.join(File.dirname(__FILE__), 'templates')
        end

				# uses blog.rbt template (note conventional trailing t)
				# placing resulting file to blog.rb relatively to
				# destination root
        template :blog, 'blog.rb'

				# does simple copy of me.jpg placing resulting file to me.jpg relatively to
				# destination root
        file :me, 'me.jpg'

				# creates empty directory public/javascripts relatively to
				# destination root
				empty_directory :javascripts, File.join("public", "javascripts")
      end

      class WikiGenerator < Templater::Generator

        def self.source_root
          File.join(File.dirname(__FILE__), 'templates')
        end

        template :wiki, 'wiki.rb'
        file :img, 'wiki.jpg'

      end

			# The generators are added to the manifold, and assigned the names 'wiki' and 'blog'.
			# So you can call them <script name> blog merb-blog-in-10-minutes and
			# <script name> blog merb-wiki-in-10-minutes, respectively
      add :blog, BlogGenerator
      add :wiki, WikiGenerator

    end

		# registers manifold with command line interface
    MyGenerators.run_cli Dir.pwd, 'my_generators', '0.1', ARGV
  
The generator classes override the source_root method to specify where templates will be located. All subclasses of Templater::Generator that have any actions must do this. The +template+ and +file+ methods add actions to the generator. In the first case, a template that is rendered with ERB and then put in its destination location, in the other case a file that is copied. +empty_directory+ action creates empty directory under destination root.

Neither manifolds or generators actually do anything by themselves, they are just abstract represenations. The last line invokes the command-line-interface, which fetches the desired generator, tells it to render its templates and checks with the user if there are any problems. The generators can easily be used without the command-line-interface, so it is easy to construct an alternative interface.

== Invoking other generators

Generators can invoke other generators, a WikiBlog generator that creates both a Wiki and a Blog could look like this:

    module MyGenerators

      extend Templater::Manifold

      class WikiBlogGenerator < Templater::Generator

        invoke :wiki
        invoke :blog

      end
      
      add :wiki_blog, WikiBlogGenerator

    end
    
It needs no source_root, since it has no actions. The generators are invoked by their name in the manifold, not by their class name; this gives the system a great deal of flexibility.

== Automatically adding actions

It can get tedious to declare each action, instead you can search in a given directory and automatically add all files to your generator, this is done with the glob! function.

    class MyGenerator < Templater::Generator
     
      def self.source_root
        File.join(File.dirname(__FILE__), 'templates')
      end
      
      glob!
    
    end
    
This will search the source root and add all files as actions.

== Templates

Templates are processed using generator instance scope as binding, so every instance method available on your
generator is available in template body.

There are a lot of ways of adding templates:

    template :one_argument, 'source_and_destination.rb'
  
    template :two_arguments, 'source.rb', 'destination.rb'
  
    template :block do
      source('source.rb')
      destination(some_instance_method)
    end
  
    template :expression, 'source.rb' '%some_instance_method%.rb'

In the last example, the characters enclosed in percentage signs will be replaced with the results of the instance method +some_instance_method+

Inside the templates normal ERB can be used. The templates are rendered in the same context as the generator instance, so generator instance methods can be called from inside the template.

    <% if name %>
    puts "My name is <%= name %>"
    <% else %>
    puts "I have no name"
    <% end %>
    
If you need to render templates where the result should contain actual erb, simply use a double percentage sign, this will prevent the statement from being executed.

    <%= 2 + 2 %>
    <%%= 2 + 2 %>

will result in

    4
    <%= 2 + 2 %>
    
== Callbacks

Sometimes it might be desirable to add a callback to your actions, an example might be to chmod a binary file after it is created.

    class MyGenerator < Templater::Generator
      template :something, 'something.rb', :after => :chmod
    
      def chmod(action)
        File.chmod(action.destination, 0750)
      end
    end

== An advanced example

A generator for creating a model class, such as it used by Merb or Rails, could look like this:

    module Merb::Generators
  
      class ModelGenerator < ComponentGenerator

        def self.source_root
          File.join(super, 'model')
        end

				# description end users see next to generator name
        desc <<-DESC
          This is a model generator
        DESC

				# options generator takes, their metadata, like description or arguments type
        option :testing_framework, :desc => 'Specify which testing framework to use (spec, test_unit)'
        option :orm, :desc => 'Specify which Object-Relation Mapper to use (none, activerecord, datamapper, sequel)'

				# you may use shortcuts for first 4 option positions
        first_argument :name, :required => true
        second_argument :attributes, :as => :hash, :default => {}

        invoke :migration do |generator|
          generator.new(destination_root, options.merge(:model => true), name, attributes)
        end
    
        template :model, :orm => :none do
          source('model.rbt')
          destination('app/models/' + file_name + '.rb')
        end
    
        template :model_activerecord, :orm => :activerecord do
          source('model_activerecord.rbt')
          destination('app/models/' + file_name + '.rb')
        end
    
        template :model_datamapper, :orm => :datamapper do
          source('model_datamapper.rbt')
          destination('app/models/' + file_name + '.rb')
        end
    
        template :model_sequel, :orm => :sequel do
          source('model_sequel.rbt')
          destination('app/models/' + file_name + '.rb')
        end
    
        template :spec, :testing_framework => :rspec do
          source('spec.rbt')
          destination('spec/models/' + file_name + '_spec.rb')
        end
    
        template :test_unit, :testing_framework => :test_unit do
          source('test_unit.rbt')
          destination('test/models/' + file_name + '_test.rb')
        end
    
        def class_name
          self.name.camel_case
        end
    
        def test_class_name
          self.class_name + "Test"
        end
    
        def file_name
          self.name.snake_case
        end
    
      end
  
      add :model, ModelGenerator
  
    end