[PLAY-1426] Redirect If Guide Doesn't Exist (#3653)

**What does this PR do?**

- ✅ Redirect to parent guide if child guide doesn't exist
(`guides/#{@parent}/#{@page}`)
- ✅ Redirect to home if parent guide doesn't exist (`guides/#{@parent}`)
- ✅ Add spec tests for guides controller
- ✅ Fix TypeError by adding conditional

**How to test?** Steps to confirm the desired behavior:
1. Go to /guides/getting_started/nonsense
2. You should be redirected to /guides/getting_started/
3. Go to /guides/design_guidelines/nonsense
4. You should be redirected to /guides/design_guidelines/
5. Go to /guides/nonsense
6. You should be redirected to the home page
7. Go to /guides/design_guidelines/typography
8. You should see a document on Typography
9. Go to /guides/getting_started/rails_&_react_setup
10. You should see a document on Ruby & React Setup

#### Checklist:
- [x] **LABELS** Add a label: `enhancement`, `bug`, `improvement`, `new
kit`, `deprecated`, or `breaking`. See [Changelog &
Labels](https://github.com/powerhome/playbook/wiki/Changelog-&-Labels)
for details.
- [x] **DEPLOY** I have added the `milano` label to show I'm ready for a
review.
- [x] **TESTS** I have added test coverage to my code.

---------

Co-authored-by: Sam Duncan <[email protected]>

playbook-website/app/controllers/guides_controller.rb

@@ -7,14 +7,16 @@ class GuidesController < ApplicationController
 
   def md_doc
     @show_sidebar = true
-    if @parent
+    if @guide_exists
       if @page
         render template: "guides/#{@parent}/#{@page}"
       else
         render template: "guides/#{@parent}"
       end
-    else
+    elsif @parent_not_found
       redirect_to root_path, flash: { error: "That doc does not exist" }
+    else
+      redirect_to "/guides/#{@parent}", flash: { error: "That doc does not exist" }
     end
   end
 
@@ -30,8 +32,16 @@ def set_page_vars
            else
              Dir.glob("#{Dir[search_path].first}*.md").first
            end
-    @link_extension = File.basename(file)
-    @front_matter = render_frontmatter(file)
-    @page_title = @front_matter["title"] || File.basename(file, ".*").split(".")[0].tr("_", " ")
+    if file == "README.md"
+      @parent_not_found = true
+      @guide_exists = false
+    elsif file
+      @link_extension = File.basename(file)
+      @front_matter = render_frontmatter(file)
+      @page_title = @front_matter["title"] || File.basename(file, ".*").split(".")[0].tr("_", " ")
+      @guide_exists = true
+    else
+      @guide_exists = false
+    end
   end
 end

playbook-website/spec/controllers/guides_controller_spec.rb

@@ -0,0 +1,30 @@
+# frozen_string_literal: true
+
+# spec/controllers/guides_controller_spec.rb
+require "rails_helper"
+
+RSpec.describe GuidesController, type: :controller do
+  describe "GET #md_doc" do
+    it "renders 'child' guide" do
+      get :md_doc, params: { parent: "getting_started", page: "rails_&_react_setup" }
+      expect(response).to be_successful
+      expect(response).to render_template("guides/getting_started/rails_&_react_setup")
+    end
+
+    it "renders 'parent' guide" do
+      get :md_doc, params: { parent: "design_guidelines" }
+      expect(response).to be_successful
+      expect(response).to render_template("guides/design_guidelines")
+    end
+
+    it "redirects to 'parent' guide if 'child' guide does not exist" do
+      get :md_doc, params: { parent: "getting_started", page: "johncena" }
+      expect(response).to redirect_to("/guides/getting_started")
+    end
+
+    it "redirects to home if 'parent' guide does not exist" do
+      get :md_doc, params: { parent: "johncena" }
+      expect(response).to redirect_to(root_path)
+    end
+  end
+end