Support for runnable kotlin snippets #3776 (#3801)

app/liquid_tags/kotlin_tag.rb

@@ -0,0 +1,55 @@
+class KotlinTag < LiquidTagBase
+  PARTIAL = "liquids/kotlin".freeze
+
+  def initialize(tag_name, link, tokens)
+    super
+    stripped_link = ActionController::Base.helpers.strip_tags(link)
+    the_link = stripped_link.split(" ").first
+    @embedded_url = KotlinTag.embedded_url(the_link)
+  end
+
+  def render(_context)
+    ActionController::Base.new.render_to_string(
+      partial: PARTIAL,
+      locals: {
+        url: @embedded_url
+      }
+    )
+  end
+
+  def self.embedded_url(link)
+    "https://play.kotlinlang.org/embed?" + URI.encode_www_form(parse_link(link))
+  end
+
+  def self.parse_link(link)
+    begin
+      url = URI(link)
+    rescue
+      raise_error
+    end
+    hostname_ok = url.hostname == "pl.kotl.in"
+    short = url.path.delete("/")
+    raise_error unless hostname_ok && valid_param?(short)
+    parse_params(url, short)
+  end
+
+  def self.parse_params(url, short)
+    query = url.query.nil? ? [] : URI.decode_www_form(url.query)
+    result = { short: short }
+    %i[from to theme readOnly].each do |param|
+      value = query.assoc(param.id2name)&.last
+      result[param] = valid_param?(value) ? value : ""
+    end
+    result
+  end
+
+  def self.valid_param?(value)
+    !value&.match(/^[a-zA-Z0-9]+$/)&.nil?
+  end
+
+  def raise_error
+    raise StandardError, "Invalid Kotlin Playground URL"
+  end
+end
+
+Liquid::Template.register_tag("kotlin", KotlinTag)

app/views/liquids/_kotlin.html.erb

@@ -0,0 +1,6 @@
+<iframe
+  src="<%= url %>"
+  allowtransparency="true"
+  scrolling="no"
+  frameborder="0"
+></iframe>

app/views/pages/_editor_guide_text.html.erb

@@ -178,6 +178,10 @@
           <code>{% codepen https://codepen.io/twhite96/pen/XKqrJX default-tab=js,result %}</code>
         </dd>
       </dl>
+      <h3><strong>Kotlin Playground</strong></h3>
+      <p>To create a runnable kotlin snippet, create a Kotlin Snippet at <a href="https://play.kotlinlang.org">https://play.kotlinlang.org</a></p>
+      <p>Go to <code>Share</code> dialog and copy the full <code>link</code> from the <code>Medium</code> tab. Use it as follows:</p>
+      <code>{% kotlin https://pl.kotl.in/owreUFFUG?theme=darcula&from=3&to=6&readOnly=true %}</code>
       <h3><strong>RunKit Embed</strong></h3>
       <p>Put executable code within a runkit liquid block, as follows:</p>
       <pre>{% runkit<br>// hidden setup JavaScript code goes in this preamble area<br>const hiddenVar = 42<br>%}<br>// visible, reader-editable JavaScript code goes here<br>console.log(hiddenVar)<br>{% endrunkit %} <br></pre>

docs/frontend/liquid-tags.md

@@ -40,4 +40,5 @@ Here is a bunch of liquid tags supported on DEV:
 {% soundcloud https://soundcloud.com/user-261265215/dev-to-review-episode-1 %}
 {% spotify spotify:episode:5V4XZWqZQJvbddd31n56mf %}
 {% blogcast 1234 %}
+{% kotlin https://pl.kotl.in/owreUFFUG %}
 ```

spec/liquid_tags/kotlin_tag_spec.rb

@@ -0,0 +1,46 @@
+require "rails_helper"
+
+RSpec.describe KotlinTag, type: :liquid_template do
+  describe "#link" do
+    input = "https://pl.kotl.in/owreUFFUG?theme=darcula&from=3&to=6&readOnly=true"
+    expected = "https://play.kotlinlang.org/embed?short=owreUFFUG&from=3&to=6&theme=darcula&readOnly=true"
+
+    def generate_new_liquid(link)
+      Liquid::Template.register_tag("kotlin", KotlinTag)
+      Liquid::Template.parse("{% kotlin #{link} %}")
+    end
+
+    it "accepts only Kotlin Playground links" do
+      badurl = "https://example.com"
+      expect do
+        generate_new_liquid(badurl)
+      end.to raise_error(StandardError)
+
+      badurl = "not even an URL"
+      expect do
+        generate_new_liquid(badurl)
+      end.to raise_error(StandardError)
+    end
+
+    def check(url, expected)
+      expect(KotlinTag.parse_link(url)).to eq(expected)
+    end
+
+    it "parses URL correctly" do
+      check("https://pl.kotl.in/owreUFFUG", from: nil, readOnly: nil, short: "owreUFFUG", theme: nil, to: nil)
+      check("https://pl.kotl.in/owreUFFUG?theme=dracula&from=3&to=6&readOnly=true", from: "3", readOnly: "true", short: "owreUFFUG", theme: "dracula", to: "6")
+      check("https://pl.kotl.in/owreUFFUG?theme=dracula&readOnly=true", from: nil, readOnly: "true", short: "owreUFFUG", theme: "dracula", to: nil)
+      check("https://pl.kotl.in/owreUFFUG?from=3&to=6", from: "3", readOnly: nil, short: "owreUFFUG", theme: nil, to: "6")
+    end
+
+    it "produces a correct final URL" do
+      expect(KotlinTag.embedded_url(input)).to eq(expected)
+    end
+
+    it "renders correctly a Kotlin Playground link" do
+      liquid = generate_new_liquid(input)
+      rendered_kotlin_iframe = liquid.render
+      Approvals.verify(rendered_kotlin_iframe, name: "kotlin_liquid_tag", format: :html)
+    end
+  end
+end

spec/support/fixtures/approvals/kotlin_liquid_tag.approved.html

@@ -0,0 +1,6 @@
+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" "http://www.w3.org/TR/REC-html40/loose.dtd">
+<html xmlns="http://www.w3.org/1999/xhtml">
+  <body>
+    <iframe src="https://play.kotlinlang.org/embed?short=owreUFFUG&amp;from&amp;to&amp;theme=darcula&amp;readOnly" allowtransparency="true" scrolling="no" frameborder="0"></iframe>
+  </body>
+</html>