1 files changed, 58 insertions, 0 deletions
diff --git a/lib/declarative_policy.rb b/lib/declarative_policy.rb
new file mode 100644
index 00000000000..d9959bc1aff
--- /dev/null
+++ b/lib/declarative_policy.rb
@@ -0,0 +1,58 @@
+require_dependency 'declarative_policy/cache'
+require_dependency 'declarative_policy/condition'
+require_dependency 'declarative_policy/dsl'
+require_dependency 'declarative_policy/preferred_scope'
+require_dependency 'declarative_policy/rule'
+require_dependency 'declarative_policy/runner'
+require_dependency 'declarative_policy/step'
+
+require_dependency 'declarative_policy/base'
+
+module DeclarativePolicy
+  class << self
+    def policy_for(user, subject, opts = {})
+      cache = opts[:cache] || {}
+      key = Cache.policy_key(user, subject)
+
+      cache[key] ||= class_for(subject).new(user, subject, opts)
+    end
+
+    def class_for(subject)
+      return GlobalPolicy if subject == :global
+      return NilPolicy if subject.nil?
+
+      subject = find_delegate(subject)
+
+      subject.class.ancestors.each do |klass|
+        next unless klass.name
+
+        begin
+          policy_class = "#{klass.name}Policy".constantize
+
+          # NOTE: the < operator here tests whether policy_class
+          # inherits from Base. We can't use #is_a? because that
+          # tests for *instances*, not *subclasses*.
+          return policy_class if policy_class < Base
+        rescue NameError
+          nil
+        end
+      end
+
+      raise "no policy for #{subject.class.name}"
+    end
+
+    private
+
+    def find_delegate(subject)
+      seen = Set.new
+
+      while subject.respond_to?(:declarative_policy_delegate)
+        raise ArgumentError, "circular delegations" if seen.include?(subject.object_id)
+        seen << subject.object_id
+        subject = subject.declarative_policy_delegate
+      end
+
+      subject
+    end
+  end
+end