diff --git a/app.rb b/app.rb
index b9ef9e5..9bc3c61 100644
--- a/app.rb
+++ b/app.rb
@@ -1,9 +1,12 @@
+# frozen_string_literal: true
+
 require 'roda'
 require 'securerandom'
 require 'json'
 require 'sequel'
 require 'open-uri'
 
+# URL Shortener App class
 class App < Roda
   plugin :sessions, secret: ENV.delete('APP_SESSION_SECRET')
   plugin :render, escape: true
@@ -11,92 +14,92 @@ class App < Roda
   plugin :json_parser
   plugin :request_headers
 
-  DB = Sequel.sqlite("db/#{ENV['DB_NAME']}")
+  DB = Sequel.sqlite("db/#{ENV.fetch('DB_NAME', nil)}")
   links = DB[:links]
 
   route do |r|
     r.root do
-      @message = flash['message'] || "Enter a URL"
+      @message = flash['message'] || 'Enter a URL'
       view :home
     end
 
-    r.get String do | url_code |
-      link = links.filter(:code => url_code)
+    r.get String do |url_code|
+      link = links.filter(code: url_code)
       r.redirect link.first[:url] unless link.first.nil?
       @message = "Link #{url_code} doesn't exist"
       response.status = 404
       view :home
     end
 
-    r.post "create" do
+    r.post 'create' do
       url = r.params['url']
-      if url.nil? or url.empty? 
-        flash['message'] = "Please enter a valid URL";
+      if url.nil? || url.empty?
+        flash['message'] = 'Please enter a valid URL'
         r.redirect '/'
       end
 
       begin
         OpenURI.open_uri(url)
       rescue URI::BadURIError
-        flash['message'] = "Invalid URL"
+        flash['message'] = 'Invalid URL'
         r.redirect '/'
       rescue OpenURI::HTTPError
-        flash['message'] = "URL not found"
+        flash['message'] = 'URL not found'
         r.redirect '/'
-      rescue SocketError => e
-        flash['message'] = "URL does not resolve"
+      rescue SocketError
+        flash['message'] = 'URL does not resolve'
         r.redirect '/'
       end
 
-      if links.filter(:url => url).first.nil?
+      if links.filter(url:).first.nil?
         code = SecureRandom.urlsafe_base64 4
-        links.insert(url: url, code: code) 
-        @message = "Link created"
+        links.insert(url:, code:)
+        @message = 'Link created'
       end
-      code = links.filter(:url => url).first[:code]
-      @message ||= "Link exists"
-      @new_link = 'http://' + request.env['HTTP_HOST'] + '/' + code
-      view :create   
+      code = links.filter(url:).first[:code]
+      @message ||= 'Link exists'
+      @new_link = "http://#{request.env['HTTP_HOST']}/#{code}"
+      view :create
     end
-    r.on "links" do
+    r.on 'links' do
       r.post do
-        if 'application/json' != r.headers['CONTENT_TYPE']
+        if r.headers['CONTENT_TYPE'] != 'application/json'
           response.status = 400
-          return {message: "not a valid json request"}.to_json
+          return { message: 'not a valid json request' }.to_json
         end
 
         url = r.params['url']
         if url.nil?
           response.status = 400
-          return {message: "missing url parameter"}.to_json
+          return { message: 'missing url parameter' }.to_json
         end
 
-        if url.empty? 
+        if url.empty?
           response.status = 400
-          return {message: "invalid url parameter"}.to_json
+          return { message: 'invalid url parameter' }.to_json
         end
 
         begin
           OpenURI.open_uri(url)
         rescue URI::BadURIError
           response.status = 400
-          return {message: "invalid url parameter"}.to_json
+          return { message: 'invalid url parameter' }.to_json
         rescue OpenURI::HTTPError
           response.status = 400
-          return {message: "url not found"}.to_json
-        rescue SocketError => e
+          return { message: 'url not found' }.to_json
+        rescue SocketError
           response.status = 400
-          return {message: "url does not resolve"}.to_json
+          return { message: 'url does not resolve' }.to_json
         end
 
-        if links.filter(:url => url).first.nil?
+        if links.filter(url:).first.nil?
           code = SecureRandom.urlsafe_base64 4
-          links.insert(url: url, code: code) 
+          links.insert(url:, code:)
         end
 
-        code = links.filter(:url => url).first[:code]
-        @new_link = 'http://' + request.env['HTTP_HOST'] + '/' + code
-        return {url: url, code: code, link: @new_link}.to_json
+        code = links.filter(url:).first[:code]
+        @new_link = "http://#{request.env['HTTP_HOST']}/#{code}"
+        return { url:, code:, link: @new_link }.to_json
       end
     end
   end