FEATURE: Add onebox for loom (discourse#26016)

Loom share links will now onebox and use the embedded loom player.

app/assets/stylesheets/common/base/onebox.scss

@@ -980,14 +980,16 @@ aside.onebox.mixcloud-preview {
   }
 }
 
-iframe.vimeo-onebox {
+iframe.vimeo-onebox,
+iframe.loom-onebox {
   width: 100%;
   height: auto;
   aspect-ratio: 16/9;
 }
 
 @supports not (aspect-ratio: auto) {
-  iframe.vimeo-onebox {
+  iframe.vimeo-onebox,
+  iframe.loom-onebox {
     width: 690px;
     height: 388px;
   }

lib/onebox/engine.rb

@@ -211,3 +211,4 @@ def always_https?
 require_relative "engine/hackernews_onebox"
 require_relative "engine/motoko_onebox"
 require_relative "engine/tiktok_onebox"
+require_relative "engine/loom_onebox"

lib/onebox/engine/loom_onebox.rb

@@ -0,0 +1,34 @@
+# frozen_string_literal: true
+
+module Onebox
+  module Engine
+    class LoomOnebox
+      include Engine
+      include StandardEmbed
+
+      matches_regexp(%r{^https?://(www\.)?loom\.com/share/\w+(/\w+)?/?})
+      requires_iframe_origins "https://www.loom.com"
+      always_https
+
+      def placeholder_html
+        ::Onebox::Helpers.video_placeholder_html
+      end
+
+      def to_html
+        video_id = url.split("/").last
+        video_src = "https://www.loom.com/embed/#{video_id}"
+
+        <<~HTML
+          <iframe
+            class="loom-onebox"
+            src="#{video_src}"
+            frameborder="0"
+            webkitallowfullscreen
+            mozallowfullscreen
+            allowfullscreen
+          </iframe>
+        HTML
+      end
+    end
+  end
+end

spec/lib/onebox/engine/loom_onebox_spec.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+RSpec.describe Onebox::Engine::LoomOnebox do
+  it "returns the right HTML markup for the onebox" do
+    expect(
+      Onebox
+        .preview(
+          "https://www.loom.com/share/c9695e5dc084496c80b7d7516d2a569a?sid=e1279914-ecaa-4faf-afa8-89cbab488240",
+        )
+        .to_s
+        .chomp,
+    ).to eq(
+      '<iframe class="loom-onebox" src="https://www.loom.com/embed/c9695e5dc084496c80b7d7516d2a569a?sid=e1279914-ecaa-4faf-afa8-89cbab488240" frameborder="0" allowfullscreen="" seamless="seamless" sandbox="allow-same-origin allow-scripts allow-forms allow-popups allow-popups-to-escape-sandbox allow-presentation"></iframe>',
+    )
+  end
+end