1 files changed, 67 insertions, 0 deletions
diff --git a/lib/gitlab/cross_project_access.rb b/lib/gitlab/cross_project_access.rb
new file mode 100644
index 00000000000..6eaed51b64c
--- /dev/null
+++ b/lib/gitlab/cross_project_access.rb
@@ -0,0 +1,67 @@
+module Gitlab
+  class CrossProjectAccess
+    class << self
+      delegate :add_check, :find_check, :checks,
+               to: :instance
+    end
+
+    def self.instance
+      @instance ||= new
+    end
+
+    attr_reader :checks
+
+    def initialize
+      @checks = {}
+    end
+
+    def add_check(
+          klass,
+          actions: {},
+          positive_condition: nil,
+          negative_condition: nil,
+          skip: false)
+
+      new_check = CheckInfo.new(actions,
+                                positive_condition,
+                                negative_condition,
+                                skip
+                               )
+
+      @checks[klass] ||= Gitlab::CrossProjectAccess::CheckCollection.new
+      @checks[klass].add_check(new_check)
+      recalculate_checks_for_class(klass)
+
+      @checks[klass]
+    end
+
+    def find_check(object)
+      @cached_checks ||= Hash.new do |cache, new_class|
+        parent_classes = @checks.keys.select { |existing_class| new_class <= existing_class }
+        closest_class = closest_parent(parent_classes, new_class)
+        cache[new_class] = @checks[closest_class]
+      end
+
+      @cached_checks[object.class]
+    end
+
+    private
+
+    def recalculate_checks_for_class(klass)
+      new_collection = @checks[klass]
+
+      @checks.each do |existing_class, existing_check_collection|
+        if existing_class < klass
+          existing_check_collection.add_collection(new_collection)
+        elsif klass < existing_class
+          new_collection.add_collection(existing_check_collection)
+        end
+      end
+    end
+
+    def closest_parent(classes, subject)
+      relevant_ancestors = subject.ancestors & classes
+      relevant_ancestors.first
+    end
+  end
+end