add Pdfium acro fields detector

lib/templates/build_pdfium_annotations.rb

@@ -0,0 +1,47 @@
+# frozen_string_literal: true
+
+module Templates
+  module BuildPdfiumAnnotations
+    URI_PREFIXES = %w[https:// http://].freeze
+    LINKS_LIMIT = 250
+
+    module_function
+
+    def call(doc)
+      annotations = []
+
+      doc.page_count.times do |page_index|
+        break if annotations.size >= LINKS_LIMIT
+        next if doc.annot_count(page_index).zero?
+
+        page = doc.get_page(page_index)
+        geometry = { box: page.box, rotation: page.rotation }
+
+        page.annotations.each do |annotation|
+          next unless annotation.link? && annotation.rect?
+
+          url = annotation.link.url
+
+          next if url.blank? || URI_PREFIXES.none? { |prefix| url.start_with?(prefix) }
+
+          annotations << build_external_link_hash(url, annotation, geometry).merge('page' => page_index)
+        end
+      end
+
+      annotations
+    end
+
+    def build_external_link_hash(url, area, geometry)
+      x, y, w, h, page_width, page_height = Pdfium.transform_rect(area.bounds, **geometry)
+
+      {
+        'type' => 'external_link',
+        'value' => url,
+        'x' => x / page_width,
+        'y' => y / page_height,
+        'w' => w / page_width,
+        'h' => h / page_height
+      }
+    end
+  end
+end