breadcrumb.rb

breadcrumb.rb

class String
  def underscore
    self.scan(/[A-Z][a-z]+/).map { |name| name.tr('A-Z', 'a-z') }.join("_")
  end
end
class Crumb
  def initialize(mgr, &block)
    @mgr = mgr
    @block = block
  end
  def link(url, name)
    @link ||= "<a href='#{url}'>#{name}</a>"
  end
  def parent(obj)
    @parent ||= obj
  end
  def render(obj)
    instance_exec obj, &@block
    return [] if @parent.nil?
    [@link] + @mgr.render(@parent)
  end
end
class CrumbManager
  def initialize(&block)
    @crumbs = {}
    instance_eval(&block)
  end
  def crumb(key, &block)
    @crumbs[key] = Crumb.new(self, &block)
  end
  def lookup_key(obj)
    obj.is_a?(Symbol) ? obj : obj.class.to_s.underscore.to_sym
  end
  def lookup(obj)
    @crumbs[lookup_key(obj)]
  end
  def render(obj)
    (lookup(obj) || fail).render(obj)
  end
  def breadcrumb(obj)
    render(obj).reverse.join(" > ")
  end
end
Product  = Struct.new(:name, :id, :category, keyword_init: true)
Category = Struct.new(:name, :id, keyword_init: true)

def crumbs(&block)
  @mgr = CrumbManager.new(&block)
end
def breadcrumb(obj)
  @mgr&.breadcrumb(obj)
end

crumbs do
  crumb :home do
    link "Home", "https://google.co.jp/"
  end
  crumb :category do |category|
    link category.name, "https://example.com/categories/#{category.id}"
    parent :home
  end
  crumb :product do |product|
    link product.name, "https://example.com/products/#{product.id}"
    parent product.category
  end
end

product = Product.new(name: 'トヨタカローラ', id: 1, category: Category.new(name: '車', id: 2))
puts breadcrumb(product)