dry-operation + dry-monads + ActiveModelほかいくつかの処理を交えていい具合にViewに返す試み

confirm.erb

<% unless errors.empty? %>
エラーあります
<ul>
<% errors.each do |error| %>
  <% # ActiveModel::ErrorsとDry::Schema::Message的なエラーをいい具合に扱う %>
  <li><%= error.try(:attribute) || error.try(:path) %> : <%= error.try(:type) || error.try(:text) %></li>
<% end %>
</ul>
<% end %>
<% unless data.empty? %>
  <a href="<%= data[:url] %>">&gt;&gt; next</a>
<% end %>

dry-operation-monads-several-models.rb

require "sinatra"

get "/" do
  erb :new, locals: {anti_csrf_token: env["rack.session"][:csrf]}
end

post "/confirm" do
  result = GenerateMagiclink.new.call(params["entry"])
  
  erb: :confirm, locals: {
    data: result.success? ? {url: result.value!} : {},
    errors: result.failure? ? result.failure.errors: []
  }
end

generate_magiclink.rb

require "dry/operation"
require_relative "../models/email_form"
require_relative "../models/email_reachable"
require_relative "../models/magic_link"

class GenerateMagiclink < Dry::Operation
  #
  # 各stepに与えるメソッドはDry::Monads::Resultを返すこと
  # see https://dry-rb.org/gems/dry-monads/main/result/
  # Operationの中ではSucess(), Failure()はinclude済みだが、外部のModelを利用する場合は注意が必要
  # call全体がDry::Monads::Resultを返すので最終行はstepがないとResultがネストする可能性アリ
  #
  def call(user_input)
    email = step validate_input(user_input)
    step EmailReachable.new(email).reachable?
    step MagicLink.new(email).generate
  end

  def validate_input(params)
    form = EmailForm.new(params)

    form.valid? ? Success(form.email) : Failure(form)
  end
end