Parse ERB template ruby output expressions (using the temple gem)

erb_parser.rb

# An example to extract the ruby output expressions from an ERB template using the temple gem:
#
# 1. Install 'temple' gem https://github.com/judofyr/temple
# 2. Require this erb_parser.rb file and run:
#
# ErbParser.call
#
# Dynamics will be:
# [[[:dynamic, " @page.title "],
#   [:dynamic, " an_image "],
#   [:dynamic, " a_heading "],
#   [:dynamic, " simple_format some_text "],
#   [:dynamic, " sanitize html_text "],
#   [:dynamic, " shared_content( 'the_email' ) "]],
#
# Abstract Syntax Tree will be:
# [:multi,
#  [:code, " @page_title = @page.title "],
#  [:static, "\n"],
#  [:newline],
#  [:static, "<h1>\n"],
#  [:newline],
#  [:static, "  "],
#  [:escape, true, [:dynamic, " @page.title "]],
#  [:static, "\n"],
#  [:newline],
#  [:static, "</h1>\n"],
#  [:newline],
#  [:static, "<p>\n"],
#  [:newline],
#  [:static, "  <img src=\"/images/shinycms/"],
#  [:escape, true, [:dynamic, " an_image "]],
#  [:static, "\" alt=\"\">\n"],
#  [:newline],
#  [:static, "</p>\n"],
#  [:newline],
#  [:static, "<h2>\n"],
#  [:newline],
#  [:static, "  "],
#  [:escape, true, [:dynamic, " a_heading "]],
#  [:static, "\n"],
#  [:newline],
#  [:static, "</h2>\n"],
#  [:newline],
#  [:static, "\n"],
#  [:newline],
#  [:escape, true, [:dynamic, " simple_format some_text "]],
#  [:static, "\n"],
#  [:newline],
#  [:static, "\n"],
#  [:newline],
#  [:escape, true, [:dynamic, " sanitize html_text "]],
#  [:static, "\n"],
#  [:newline],
#  [:static, "\n"],
#  [:newline],
#  [:static, "<p class=\"small\">\n"],
#  [:newline],
#  [:static, "  Contact: "],
#  [:escape, true, [:dynamic, " shared_content( 'the_email' ) "]],
#  [:static, "\n"],
#  [:newline],
#  [:static, "</p>\n"],
#  [:newline],
#  [:static, ""]]]
class ErbParser

  def self.call
    self.new.call
  end

  def call
    parser = Temple::ERB::Parser.new
    erb_source = <<~ERB
      <% @page_title = @page.title %>
      <h1>
        <%= @page.title %>
      </h1>
      <p>
        <img src="/images/shinycms/<%= an_image %>" alt="">
      </p>
      <h2>
        <%= a_heading %>
      </h2>

      <%= simple_format some_text %>

      <%= sanitize html_text %>

      <p class="small">
        Contact: <%= shared_content( 'the_email' ) %>
      </p>
    ERB

    # Abstract Syntax Tree
    ast = parser.call(erb_source)
    dynamics = extract_dynamics(ast)
    [dynamics, ast]
  end

  def extract_dynamics(ast)
    dynamics = []
    ast.each do |node|
      next unless node.is_a?(Array)
      if node[0] == :dynamic
        dynamics << node
      else
        dynamics += extract_dynamics(node)
      end
    end
    dynamics
  end
end