module Nanoc::Helpers::Capturing

Provides functionality for “capturing” content in one place and reusing this content elsewhere.

For example, suppose you want the sidebar of your site to contain a short summary of the item. You could put the summary in the meta file, but that’s not possible when the summary contains eRuby. You could also put the sidebar inside the actual item, but that’s not very pretty. Instead, you write the summary on the item itself, but capture it, and print it in the sidebar layout.

This helper has been tested with ERB and Haml. Other filters may not work correctly.

@example Capturing content for a summary

<% content_for :summary do %>
  <p>On this item, Nanoc is introduced, blah blah.</p>
<% end %>

@example Showing captured content in a sidebar

<div id="sidebar">
  <h3>Summary</h3>
  <%= content_for(@item, :summary) || '(no summary)' %>
</div>

Public Instance Methods

capture() { || ... } click to toggle source

Evaluates the given block and returns its contents. The contents of the block is not outputted.

@return [String] The captured result

# File lib/nanoc/helpers/capturing.rb, line 174
def capture(&block)
  # Get erbout so far
  erbout = eval('_erbout', block.binding)
  erbout_length = erbout.length

  # Execute block
  yield

  # Get new piece of erbout
  erbout_addition = erbout[erbout_length..-1]

  # Remove addition
  erbout[erbout_length..-1] = ''

  # Depending on how the filter outputs, the result might be a
  # single string or an array of strings (slim outputs the latter).
  erbout_addition = erbout_addition.join if erbout_addition.is_a? Array

  # Done.
  erbout_addition
end
content_for(*args, &block) click to toggle source

@overload #content_for(name, params = {}, &block)

Captures the content inside the block and stores it so that it can be
referenced later on. The same method, {#content_for}, is used for
getting the captured content as well as setting it. When capturing,
the content of the block itself will not be outputted.

By default, capturing content with the same name will raise an error if the newly captured
content differs from the previously captured content. This behavior can be changed by
providing a different `:existing` option to this method:

* `:error`: When content already exists and is not identical, raise an error.

* `:overwrite`: Overwrite the previously captured content with the newly captured content.

* `:append`: Append the newly captured content to the previously captured content.

@param [Symbol, String] name The base name of the attribute into which
  the content should be stored

@option params [Symbol] existing Can be either `:error`, `:overwrite`, or `:append`

@return [void]

@overload #content_for(item, name)

Fetches the capture with the given name from the given item and
returns it.

@param [Nanoc::Int::Item] item The item for which to get the capture

@param [Symbol, String] name The name of the capture to fetch

@return [String] The stored captured content
# File lib/nanoc/helpers/capturing.rb, line 96
def content_for(*args, &block)
  if block_given? # Set content
    # Get args
    case args.size
    when 1
      name = args[0]
      params = {}
    when 2
      name = args[0]
      params = args[1]
    else
      raise ArgumentError, 'expected 1 or 2 argument (the name '              "of the capture, and optionally params) but got #{args.size} instead"
    end
    name = args[0]
    existing_behavior = params.fetch(:existing, :error)

    # Capture
    content = capture(&block)

    # Prepare for store
    store = @site.unwrap.captures_store
    case existing_behavior
    when :overwrite
      store[@item, name.to_sym] = ''
    when :append
      store[@item, name.to_sym] ||= ''
    when :error
      if store[@item, name.to_sym] && store[@item, name.to_sym] != content
        raise "a capture named #{name.inspect} for #{@item.identifier} already exists"
      else
        store[@item, name.to_sym] = ''
      end
    else
      raise ArgumentError, 'expected :existing_behavior param to #content_for to be one of '              ":overwrite, :append, or :error, but #{existing_behavior.inspect} was given"
    end

    # Store
    @site.unwrap.captures_store_compiled_items << @item.unwrap
    store[@item, name.to_sym] << content
  else # Get content
    # Get args
    if args.size != 2
      raise ArgumentError, 'expected 2 arguments (the item '              "and the name of the capture) but got #{args.size} instead"
    end
    item = args[0].is_a?(Nanoc::ItemWithRepsView) ? args[0].unwrap : args[0]
    name = args[1]

    # Create dependency
    if @item.nil? || item != @item.unwrap
      Nanoc::Int::NotificationCenter.post(:visit_started, item)
      Nanoc::Int::NotificationCenter.post(:visit_ended,   item)

      # This is an extremely ugly hack to get the compiler to recompile the
      # item from which we use content. For this, we need to manually edit
      # the content attribute to reset it. :(
      # FIXME: clean this up
      unless @site.unwrap.captures_store_compiled_items.include?(item)
        @site.unwrap.captures_store.reset_for(item)
        item.forced_outdated = true
        @site.unwrap.compiler.reps[item].each do |r|
          r.snapshot_contents = { last: item.content }
          raise Nanoc::Int::Errors::UnmetDependency.new(r)
        end
      end
    end

    # Get content
    @site.unwrap.captures_store[item, name.to_sym]
  end
end