require 'active_support/core_ext/object/blank'

module ActionView
  # = Action View Partials
  #
  # There's also a convenience method for rendering sub templates within the current controller that depends on a
  # single object (we call this kind of sub templates for partials). It relies on the fact that partials should
  # follow the naming convention of being prefixed with an underscore -- as to separate them from regular
  # templates that could be rendered on their own.
  #
  # In a template for Advertiser#account:
  #
  #  <%= render :partial => "account" %>
  #
  # This would render "advertiser/_account.erb" and pass the instance variable @account in as a local variable
  # +account+ to the template for display.
  #
  # In another template for Advertiser#buy, we could have:
  #
  #   <%= render :partial => "account", :locals => { :account => @buyer } %>
  #
  #   <% for ad in @advertisements %>
  #     <%= render :partial => "ad", :locals => { :ad => ad } %>
  #   <% end %>
  #
  # This would first render "advertiser/_account.erb" with @buyer passed in as the local variable +account+, then
  # render "advertiser/_ad.erb" and pass the local variable +ad+ to the template for display.
  #
  # == The :as and :object options
  #
  # By default <tt>ActionView::Partials::PartialRenderer</tt> has its object in a local variable with the same
  # name as the template. So, given
  #
  #   <%= render :partial => "contract" %>
  #
  # within contract we'll get <tt>@contract</tt> in the local variable +contract+, as if we had written
  #
  #   <%= render :partial => "contract", :locals => { :contract  => @contract } %>
  #
  # With the <tt>:as</tt> option we can specify a different name for said local variable. For example, if we
  # wanted it to be +agreement+ instead of +contract+ we'd do:
  #
  #   <%= render :partial => "contract", :as => :agreement %>
  #
  # The <tt>:object</tt> option can be used to directly specify which object is rendered into the partial;
  # useful when the template's object is elsewhere, in a different ivar or in a local variable for instance.
  # 
  # Revisiting a previous example we could have written this code:
  # 
  #   <%= render :partial => "account", :object => @buyer %>
  #
  #   <% for ad in @advertisements %>
  #     <%= render :partial => "ad", :object => ad %>
  #   <% end %>
  #
  # The <tt>:object</tt> and <tt>:as</tt> options can be used together.
  #
  # == Rendering a collection of partials
  #
  # The example of partial use describes a familiar pattern where a template needs to iterate over an array and
  # render a sub template for each of the elements. This pattern has been implemented as a single method that
  # accepts an array and renders a partial by the same name as the elements contained within. So the three-lined
  # example in "Using partials" can be rewritten with a single line:
  #
  #   <%= render :partial => "ad", :collection => @advertisements %>
  #
  # This will render "advertiser/_ad.erb" and pass the local variable +ad+ to the template for display. An
  # iteration counter will automatically be made available to the template with a name of the form
  # +partial_name_counter+. In the case of the example above, the template would be fed +ad_counter+.
  #
  # The <tt>:as</tt> option may be used when rendering partials.
  # 
  # You can specify a partial to be rendered between elements via the <tt>:spacer_template</tt> option.
  # The following example will render <tt>advertiser/_ad_divider.html.erb</tt> between each ad partial:
  #
  #   <%= render :partial => "ad", :collection => @advertisements, :spacer_template => "ad_divider" %>
  #
  # NOTE: Due to backwards compatibility concerns, the collection can't be one of hashes. Normally you'd also
  # just keep domain objects, like Active Records, in there.
  #
  # == Rendering shared partials
  #
  # Two controllers can share a set of partials and render them like this:
  #
  #   <%= render :partial => "advertisement/ad", :locals => { :ad => @advertisement } %>
  #
  # This will render the partial "advertisement/_ad.erb" regardless of which controller this is being called from.
  #
  # == Rendering objects with the RecordIdentifier
  #
  # Instead of explicitly naming the location of a partial, you can also let the RecordIdentifier do the work if
  # you're following its conventions for RecordIdentifier#partial_path. Examples:
  #
  #  # @account is an Account instance, so it uses the RecordIdentifier to replace
  #  # <%= render :partial => "accounts/account", :locals => { :account => @account} %>
  #  <%= render :partial => @account %>
  #
  #  # @posts is an array of Post instances, so it uses the RecordIdentifier to replace
  #  # <%= render :partial => "posts/post", :collection => @posts %>
  #  <%= render :partial => @posts %>
  #
  # == Rendering the default case
  #
  # If you're not going to be using any of the options like collections or layouts, you can also use the short-hand
  # defaults of render to render partials. Examples:
  #
  #  # Instead of <%= render :partial => "account" %>
  #  <%= render "account" %>
  #
  #  # Instead of <%= render :partial => "account", :locals => { :account => @buyer } %>
  #  <%= render "account", :account => @buyer %>
  #
  #  # @account is an Account instance, so it uses the RecordIdentifier to replace
  #  # <%= render :partial => "accounts/account", :locals => { :account => @account } %>
  #  <%= render(@account) %>
  #
  #  # @posts is an array of Post instances, so it uses the RecordIdentifier to replace
  #  # <%= render :partial => "posts/post", :collection => @posts %>
  #  <%= render(@posts) %>
  #
  # == Rendering partials with layouts
  #
  # Partials can have their own layouts applied to them. These layouts are different than the ones that are
  # specified globally for the entire action, but they work in a similar fashion. Imagine a list with two types
  # of users:
  #
  #   <%# app/views/users/index.html.erb &>
  #   Here's the administrator:
  #   <%= render :partial => "user", :layout => "administrator", :locals => { :user => administrator } %>
  #
  #   Here's the editor:
  #   <%= render :partial => "user", :layout => "editor", :locals => { :user => editor } %>
  #
  #   <%# app/views/users/_user.html.erb &>
  #   Name: <%= user.name %>
  #
  #   <%# app/views/users/_administrator.html.erb &>
  #   <div id="administrator">
  #     Budget: $<%= user.budget %>
  #     <%= yield %>
  #   </div>
  #
  #   <%# app/views/users/_editor.html.erb &>
  #   <div id="editor">
  #     Deadline: <%= user.deadline %>
  #     <%= yield %>
  #   </div>
  #
  # ...this will return:
  #
  #   Here's the administrator:
  #   <div id="administrator">
  #     Budget: $<%= user.budget %>
  #     Name: <%= user.name %>
  #   </div>
  #
  #   Here's the editor:
  #   <div id="editor">
  #     Deadline: <%= user.deadline %>
  #     Name: <%= user.name %>
  #   </div>
  #
  # You can also apply a layout to a block within any template:
  #
  #   <%# app/views/users/_chief.html.erb &>
  #   <%= render(:layout => "administrator", :locals => { :user => chief }) do %>
  #     Title: <%= chief.title %>
  #   <% end %>
  #
  # ...this will return:
  #
  #   <div id="administrator">
  #     Budget: $<%= user.budget %>
  #     Title: <%= chief.name %>
  #   </div>
  #
  # As you can see, the <tt>:locals</tt> hash is shared between both the partial and its layout.
  #
  # If you pass arguments to "yield" then this will be passed to the block. One way to use this is to pass
  # an array to layout and treat it as an enumerable.
  #
  #   <%# app/views/users/_user.html.erb &>
  #   <div class="user">
  #     Budget: $<%= user.budget %>
  #     <%= yield user %>
  #   </div>
  #
  #   <%# app/views/users/index.html.erb &>
  #   <%= render :layout => @users do |user| %>
  #     Title: <%= user.title %>
  #   <% end %>
  #
  # This will render the layout for each user and yield to the block, passing the user, each time.
  #
  # You can also yield multiple times in one layout and use block arguments to differentiate the sections.
  #
  #   <%# app/views/users/_user.html.erb &>
  #   <div class="user">
  #     <%= yield user, :header %>
  #     Budget: $<%= user.budget %>
  #     <%= yield user, :footer %>
  #   </div>
  #
  #   <%# app/views/users/index.html.erb &>
  #   <%= render :layout => @users do |user, section| %>
  #     <%- case section when :header -%>
  #       Title: <%= user.title %>
  #     <%- when :footer -%>
  #       Deadline: <%= user.deadline %>
  #     <%- end -%>
  #   <% end %>
  module Partials
    extend ActiveSupport::Concern

    class PartialRenderer
      PARTIAL_NAMES = Hash.new {|h,k| h[k] = {} }

      def initialize(view_context, options, block)
        @view           = view_context
        @partial_names  = PARTIAL_NAMES[@view.controller.class.name]
        setup(options, block)
      end

      def setup(options, block)
        partial = options[:partial]

        @options = options
        @locals  = options[:locals] || {}
        @block   = block

        if String === partial
          @object     = options[:object]
          @path       = partial
          @collection = collection
        else
          @object = partial

          if @collection = collection_from_object || collection
            paths = @collection_data = @collection.map { |o| partial_path(o) }
            @path = paths.uniq.size == 1 ? paths.first : nil
          else
            @path = partial_path
          end
        end

        if @path
          @variable, @variable_counter = retrieve_variable(@path)
        else
          paths.map! { |path| retrieve_variable(path).unshift(path) }
        end
      end

      def retrieve_variable(path)
        variable = @options[:as] || path[%r'_?(\w+)(\.\w+)*$', 1].to_sym
        variable_counter = :"#{variable}_counter" if @collection
        [variable, variable_counter]
      end

      def render
        identifier = ((@template = find_partial) ? @template.identifier : @path)

        if @collection
          ActiveSupport::Notifications.instrument("render_collection.action_view",
            :identifier => identifier || "collection", :count => @collection.size) do
            render_collection
          end
        else
          if !@block && (layout = @options[:layout])
            layout = find_template(layout)
          end

          content = ActiveSupport::Notifications.instrument("render_partial.action_view",
            :identifier => identifier) do
            render_partial
          end

          content = @view._render_layout(layout, @locals){ content } if layout
          content
        end
      end

      def render_collection
        return nil if @collection.blank?

        if @options.key?(:spacer_template)
          spacer = find_template(@options[:spacer_template]).render(@view, @locals)
        end

        result = @template ? collection_with_template : collection_without_template
        result.join(spacer).html_safe
      end

      def collection_with_template
        segments, locals, template = [], @locals, @template
        as, counter = @variable, @variable_counter

        locals[counter] = -1

        @collection.each do |object|
          locals[counter] += 1
          locals[as] = object
          segments << template.render(@view, locals)
        end

        segments
      end

      def collection_without_template
        segments, locals, collection_data = [], @locals, @collection_data
        index, template, cache = -1, nil, {}
        keys = @locals.keys

        @collection.each_with_index do |object, i|
          path, *data = collection_data[i]
          template = (cache[path] ||= find_template(path, keys + data))
          locals[data[0]] = object
          locals[data[1]] = (index += 1)
          segments << template.render(@view, locals)
        end

        @template = template
        segments
      end

      def render_partial
        locals, view = @locals, @view
        object, as = @object, @variable

        object ||= locals[as]
        locals[as] = object

        @template.render(view, locals) do |*name|
          view._layout_for(*name, &@block)
        end
      end

    private

      def collection
        if @options.key?(:collection)
          @options[:collection] || []
        end
      end

      def collection_from_object
        if @object.respond_to?(:to_ary)
          @object
        end
      end

      def find_partial
        if path = @path
          locals = @locals.keys
          locals << @variable
          locals << @variable_counter if @collection
          find_template(path, locals)
        end
      end 

      def find_template(path=@path, locals=@locals.keys)
        prefix = @view.controller_path unless path.include?(?/)
        @view.find_template(path, prefix, true, locals)
      end

      def partial_path(object = @object)
        @partial_names[object.class.name] ||= begin
          object = object.to_model if object.respond_to?(:to_model)

          object.class.model_name.partial_path.dup.tap do |partial|
            path = @view.controller_path
            partial.insert(0, "#{File.dirname(path)}/") if partial.include?(?/) && path.include?(?/)
          end
        end
      end
    end

    def _render_partial(options, &block) #:nodoc:
      _wrap_formats(options[:partial]) do
        if defined?(@renderer)
          @renderer.setup(options, block)
        else
          @renderer = PartialRenderer.new(self, options, block)
        end

        @renderer.render
      end
    end

  end
end