Initial implementation of --page-requisites

see StrawberryMaster/wayback-machine-downloader#39

lib/wayback_machine_downloader/page_requisites.rb

@@ -0,0 +1,33 @@
+module PageRequisites
+  # regex to find links in href, src, url(), and srcset
+  # this ignores data: URIs, mailto:, and anchors
+  ASSET_REGEX = /(?:href|src|data-src|data-url)\s*=\s*["']([^"']+)["']|url\(\s*["']?([^"'\)]+)["']?\s*\)|srcset\s*=\s*["']([^"']+)["']/i
+
+  def self.extract(html_content)
+    assets = []
+    
+    html_content.scan(ASSET_REGEX) do |match|
+      # match is an array of capture groups; find the one that matched
+      url = match.compact.first
+      next unless url
+      
+      # handle srcset (e.g. comma separated values like "image.jpg 1x, image2.jpg 2x")
+      if url.include?(',') && (url.include?(' 1x') || url.include?(' 2w'))
+        url.split(',').each do |src_def|
+          src_url = src_def.strip.split(' ').first
+          assets << src_url if valid_asset?(src_url)
+        end
+      else
+        assets << url if valid_asset?(url)
+      end
+    end
+
+    assets.uniq
+  end
+
+  def self.valid_asset?(url)
+    return false if url.strip.empty?
+    return false if url.start_with?('data:', 'mailto:', '#', 'javascript:')
+    true
+  end
+end