1 files changed, 97 insertions, 0 deletions
diff --git a/railties/lib/rails/mailers_controller.rb b/railties/lib/rails/mailers_controller.rb
new file mode 100644
index 0000000000..95dae3ec2d
--- /dev/null
+++ b/railties/lib/rails/mailers_controller.rb
@@ -0,0 +1,97 @@
+# frozen_string_literal: true
+
+require "rails/application_controller"
+
+class Rails::MailersController < Rails::ApplicationController # :nodoc:
+  prepend_view_path ActionDispatch::DebugView::RESCUES_TEMPLATE_PATH
+
+  before_action :require_local!, unless: :show_previews?
+  before_action :find_preview, :set_locale, only: :preview
+
+  helper_method :part_query, :locale_query
+
+  content_security_policy(false)
+
+  def index
+    @previews = ActionMailer::Preview.all
+    @page_title = "Mailer Previews"
+  end
+
+  def preview
+    if params[:path] == @preview.preview_name
+      @page_title = "Mailer Previews for #{@preview.preview_name}"
+      render action: "mailer"
+    else
+      @email_action = File.basename(params[:path])
+
+      if @preview.email_exists?(@email_action)
+        @email = @preview.call(@email_action, params)
+
+        if params[:part]
+          part_type = Mime::Type.lookup(params[:part])
+
+          if part = find_part(part_type)
+            response.content_type = part_type
+            render plain: part.respond_to?(:decoded) ? part.decoded : part
+          else
+            raise AbstractController::ActionNotFound, "Email part '#{part_type}' not found in #{@preview.name}##{@email_action}"
+          end
+        else
+          @part = find_preferred_part(request.format, Mime[:html], Mime[:text])
+          render action: "email", layout: false, formats: %w[html]
+        end
+      else
+        raise AbstractController::ActionNotFound, "Email '#{@email_action}' not found in #{@preview.name}"
+      end
+    end
+  end
+
+  private
+    def show_previews? # :doc:
+      ActionMailer::Base.show_previews
+    end
+
+    def find_preview # :doc:
+      candidates = []
+      params[:path].to_s.scan(%r{/|$}) { candidates << $` }
+      preview = candidates.detect { |candidate| ActionMailer::Preview.exists?(candidate) }
+
+      if preview
+        @preview = ActionMailer::Preview.find(preview)
+      else
+        raise AbstractController::ActionNotFound, "Mailer preview '#{params[:path]}' not found"
+      end
+    end
+
+    def find_preferred_part(*formats) # :doc:
+      formats.each do |format|
+        if part = @email.find_first_mime_type(format)
+          return part
+        end
+      end
+
+      if formats.any? { |f| @email.mime_type == f }
+        @email
+      end
+    end
+
+    def find_part(format) # :doc:
+      if part = @email.find_first_mime_type(format)
+        part
+      elsif @email.mime_type == format
+        @email
+      end
+    end
+
+    def part_query(mime_type)
+      request.query_parameters.merge(part: mime_type).to_query
+    end
+
+    def locale_query(locale)
+      request.query_parameters.merge(locale: locale).to_query
+    end
+
+    def set_locale
+      I18n.locale = params[:locale] || I18n.default_locale
+    end
+end