DumpAssetHelper - Ruby On Rails helper module to look up precompiled assets

dump_asset_helper.rb

# Include this in ApplicationHelper, or another view helper module
module DumpAssetHelper

  # Helper for inlining compiled assets
  #   `dump_asset("lib/like_button.js")`
  #   `dump_asset("components/avatar.css", :once)`
  def dump_asset name, option=nil
    unless option == :once && dumped_assets.include?(name)
      dumped_assets << name
      asset = find_asset(name)
      if !Rails.env.production?
        raise "No content for asset at #{name}" if asset.blank?
        raise "Asset #{name} not added to precompile list" if !is_precompiled?(name)
      end
      asset
    end
  end

  private

  # Keeps track of what has been dumped for the current request (unique per instance)
  def dumped_assets
    @dumped ||= Set.new
  end

  # Cache of every precompiled asset that's looked up (unique per entire app process)
  @@asset_cache = {}
  
  ENVS_WITHOUT_PRECOMPILATION = ["development", "test"]

  def find_asset name
    if ENVS_WITHOUT_PRECOMPILATION.include?(Rails.env)
      Rails.application.assets.find_asset(name).to_s
    else
      @@asset_cache[name] ||= begin
        fingerprint = Rails.application.assets_manifest.assets[name]
        return nil unless fingerprint
        File.read(File.join(Rails.root, "public", "assets", fingerprint)).to_s.html_safe
      rescue Errno::ENOENT => e
        # Good place to surface an error about a missing precompiled asset
        nil
      end
    end
  end

  def is_precompiled? name
    Rails.application.config.assets.precompile.any? do |glob|
      case glob
      when String
        File.fnmatch(glob, name)
      when Regexp
        name =~ glob
      end
    end
  end

end