1 files changed, 98 insertions, 0 deletions
diff --git a/lib/declarative_policy.rb b/lib/declarative_policy.rb
new file mode 100644
index 00000000000..1dd2855063d
--- /dev/null
+++ b/lib/declarative_policy.rb
@@ -0,0 +1,98 @@
+require_dependency 'declarative_policy/cache'
+require_dependency 'declarative_policy/condition'
+require_dependency 'declarative_policy/delegate_dsl'
+require_dependency 'declarative_policy/policy_dsl'
+require_dependency 'declarative_policy/rule_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'
+
+require 'thread'
+
+module DeclarativePolicy
+  CLASS_CACHE_MUTEX = Mutex.new
+  CLASS_CACHE_IVAR = :@__DeclarativePolicy_CLASS_CACHE
+
+  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)
+
+      policy_class = class_for_class(subject.class)
+      raise "no policy for #{subject.class.name}" if policy_class.nil?
+
+      policy_class
+    end
+
+    def has_policy?(subject)
+      !class_for_class(subject.class).nil?
+    end
+
+    private
+
+    # This method is heavily cached because there are a lot of anonymous
+    # modules in play in a typical rails app, and #name performs quite
+    # slowly for anonymous classes and modules.
+    #
+    # See https://bugs.ruby-lang.org/issues/11119
+    #
+    # if the above bug is resolved, this caching could likely be removed.
+    def class_for_class(subject_class)
+      unless subject_class.instance_variable_defined?(CLASS_CACHE_IVAR)
+        CLASS_CACHE_MUTEX.synchronize do
+          # re-check in case of a race
+          break if subject_class.instance_variable_defined?(CLASS_CACHE_IVAR)
+
+          policy_class = compute_class_for_class(subject_class)
+          subject_class.instance_variable_set(CLASS_CACHE_IVAR, policy_class)
+        end
+      end
+
+      subject_class.instance_variable_get(CLASS_CACHE_IVAR)
+    end
+
+    def compute_class_for_class(subject_class)
+      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
+
+      nil
+    end
+
+    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