feat: ✨ break out the artefact wait functionality

lib/comfpile/artefact.rb

@@ -154,20 +154,44 @@ module Comfpile
         def reference_artefact(stage, target, required: false)
             artefact = craft_artefact(stage, target)
 
-            if(artefact.nil? and required)
+            wait_on(artefact) if required
-                fail! "Missing artefact dependency for #{stage} #{target}!"
-            elsif(required)
-                @waitlist << {
-                    artefact: artefact,
-                    required: true
-                }
-            end
 
             @referenced_artefacts << artefact
 
             artefact
         end
 
+        #
+        # Wait on a specific artefact to complete
+        #
+        # @param [Comfpile::Artefact, nil] artefact The artefact to wait on
+        # @param [Boolean] required Whether or not this artefact is required.
+        #  When set to true (default), a failed artefact will skip this artefact.
+        #  When set to false, this artefact will ignore the failure.
+        #
+        # @return [Boolean] true when we have to wait on this artefact or 
+        #  it failed, false if we're all good
+        def wait_on(artefact, required: true)
+            if(artefact.nil?)
+                fail! "Missing artefact dependency for #{stage} #{target}!" if required
+
+                true
+            elsif artefact.in_progress?
+                @waitlist << {
+                    artefact: artefact,
+                    required: true
+                }
+
+                true
+            elsif(required and not artefact.succeeded?)
+                skip! "Failed artefact dependency: #{artefact}"
+
+                true
+            end
+
+            false
+        end
+
         # Find or create a new artefact
         #
         # @param [Symbol] stage The type of item to create.