Rails Presenter Generator (TDD)

Creates presenters that wrap models for view-specific formatting with specs first.

Quick Start

• Write failing spec in spec/presenters/

• Run spec to confirm RED

• Implement presenter extending BasePresenter

• Run spec to confirm GREEN

Project Conventions

Presenters in this project:

• Extend BasePresenter < SimpleDelegator

• Include ActionView helpers for formatting

• Delegate model methods via SimpleDelegator

• Return HTML-safe strings for badges/formatted output

• Use I18n for all user-facing text

BasePresenter (Already Exists)

app/presenters/base_presenter.rb

class BasePresenter < SimpleDelegator include ActionView::Helpers::NumberHelper include ActionView::Helpers::DateHelper include ActionView::Helpers::UrlHelper include ActionView::Helpers::TagHelper include ActionView::Helpers::TextHelper

def initialize(model, view_context = nil) super(model) @view_context = view_context end

def model getobj end

alias_method :object, :model end

TDD Workflow

Step 1: Create Presenter Spec (RED)

spec/presenters/[resource]_presenter_spec.rb

RSpec.describe [Resource]Presenter do let(:resource) { create(:resource, name: "Test", status: :active) } let(:presenter) { described_class.new(resource) }

describe "delegation" do it "delegates to the model" do expect(presenter.name).to eq("Test") end

it "responds to model methods" do
  expect(presenter).to respond_to(:name, :status, :created_at)
end

it "exposes the underlying model" do
  expect(presenter.model).to eq(resource)
end

end

describe "#display_name" do it "returns the formatted name" do expect(presenter.display_name).to eq("Test") end end

describe "#formatted_date" do context "when date is present" do before { resource.update(event_date: Date.new(2026, 7, 15)) }

  it "returns formatted date in French" do
    I18n.with_locale(:fr) do
      expect(presenter.formatted_date).to include("2026")
    end
  end
end

context "when date is nil" do
  before { resource.update(event_date: nil) }

  it "returns placeholder span" do
    result = presenter.formatted_date
    expect(result).to include("text-slate-400")
    expect(result).to include("italic")
  end
end

end

describe "#status_badge" do it "returns HTML-safe string" do expect(presenter.status_badge).to be_html_safe end

it "includes status text" do
  expect(presenter.status_badge).to include("Active")
end

it "uses correct color classes for active" do
  resource.update(status: :active)
  expect(presenter.status_badge).to include("bg-green-100")
end

it "uses correct color classes for inactive" do
  resource.update(status: :inactive)
  expect(presenter.status_badge).to include("bg-red-100")
end

end

describe "#formatted_currency" do it "formats cents as euros" do resource.update(amount_cents: 15000) expect(presenter.formatted_amount).to eq("150,00 EUR") end end end

Step 2: Run Spec (Confirm RED)

bundle exec rspec spec/presenters/[resource]_presenter_spec.rb

Step 3: Implement Presenter (GREEN)

app/presenters/[resource]_presenter.rb

class [Resource]Presenter < BasePresenter

Color mapping for Open/Closed Principle

STATUS_COLORS = { active: "bg-green-100 text-green-800", inactive: "bg-red-100 text-red-800", pending: "bg-yellow-100 text-yellow-800" }.freeze

DEFAULT_COLOR = "bg-slate-100 text-slate-800"

def display_name name end

def formatted_date return not_specified_span if event_date.nil? I18n.l(event_date, format: :long) end

def status_badge tag.span( status_text, class: "inline-flex items-center px-2.5 py-0.5 rounded-full text-xs font-medium #{status_color}" ) end

def formatted_amount return "0,00 EUR" if amount_cents.nil? || amount_cents.zero? number_to_currency( amount_cents / 100.0, unit: "EUR", separator: ",", delimiter: " ", format: "%n %u" ) end

private

def status_text I18n.t("activerecord.attributes.[resource].statuses.#{status}", default: status.to_s.humanize) end

def status_color STATUS_COLORS.fetch(status.to_sym, DEFAULT_COLOR) end

def not_specified_span tag.span( I18n.t("presenters.common.not_specified"), class: "text-slate-400 italic" ) end end

Step 4: Run Spec (Confirm GREEN)

bundle exec rspec spec/presenters/[resource]_presenter_spec.rb

Common Presenter Methods

Date Formatting

def formatted_event_date return not_specified_span if event_date.nil? I18n.l(event_date, format: :long) end

def short_date return "—" if event_date.nil? event_date.strftime("%d/%m/%Y") end

def days_until return nil if event_date.nil? days = (event_date - Date.today).to_i case days when 0 then I18n.t("presenters.event.today") when 1 then I18n.t("presenters.event.tomorrow") when 2..7 then I18n.t("presenters.event.days_from_now", count: days) else distance_of_time_in_words_to_now(event_date) end end

Currency Formatting

def formatted_budget return not_specified_span if budget_cents.nil? number_to_currency( budget_cents / 100.0, unit: "EUR", separator: ",", delimiter: " ", format: "%n %u", precision: 0 ) end

Badge/Tag Generation

def type_badge tag.span( display_type, class: "inline-flex items-center px-2 py-1 rounded text-xs font-medium #{type_color}" ) end

def display_tags return not_specified_span if tags.blank? safe_join( tags.split(",").map(&:strip).map do |tag_text| tag.span(tag_text, class: "inline-block bg-slate-100 px-2 py-1 rounded text-xs mr-1") end ) end

Contact Links

def display_email return not_specified_span if email.blank? mail_to(email, email, class: "text-blue-600 hover:underline") end

def display_phone return not_specified_span if phone.blank? link_to(phone, "tel:#{phone}", class: "text-blue-600 hover:underline") end

Usage in Controllers

Single resource

@event = EventPresenter.new(@event)

Collection

@events = events.map { |e| EventPresenter.new(e) }

With view context (for route helpers)

@event = EventPresenter.new(@event, view_context)

Checklist

• Spec written first (RED)

• Extends BasePresenter

• Delegation tested

• HTML output is html_safe

• Uses I18n for all text

• Currency stored in cents, displayed in euros

• Color mappings use constants (Open/Closed)

• not_specified_span for nil values

• All specs GREEN