#398

backend/app/services/preview/thumbnail_fetcher.rb

@@ -0,0 +1,37 @@
+module Preview
+  class ThumbnailFetcher
+    class GenerationFailed < StandardError; end
+
+    def self.fetch(raw_url)
+      uri, = UrlSafety.validate(raw_url)
+      page = nil
+
+      known_url = KnownSiteExtractor.thumbnail_url(uri)
+      image = fetch_image(known_url) if known_url
+
+      unless image
+        page = HttpFetcher.fetch(uri.to_s)
+        metadata = HtmlMetadataExtractor.extract(page)
+        image = fetch_image(metadata[:image_url]) if metadata[:image_url]
+      end
+
+      image || Screenshot.capture(uri.to_s)
+    end
+
+    def self.title(raw_url)
+      uri, = UrlSafety.validate(raw_url)
+      HtmlMetadataExtractor.extract(HttpFetcher.fetch(uri.to_s))[:title]
+    end
+
+    def self.fetch_image(url)
+      response = HttpFetcher.fetch(url)
+      return unless response.content_type.downcase.start_with?('image/')
+
+      response.body
+    rescue HttpFetcher::FetchFailed
+      nil
+    end
+
+    private_class_method :fetch_image
+  end
+end