add chain

pkg/chain/selector.go

@@ -0,0 +1,41 @@
+package chain
+
+var (
+	defaultSelector Selector = NewSelector(nil)
+)
+
+type Filter interface {
+	Filter(nodes ...*Node) []*Node
+	String() string
+}
+
+type Strategy interface {
+	Apply(nodes ...*Node) *Node
+	String() string
+}
+
+type Selector interface {
+	Select(nodes ...*Node) *Node
+}
+
+type selector struct {
+	strategy Strategy
+	filters  []Filter
+}
+
+func NewSelector(strategy Strategy, filters ...Filter) Selector {
+	return &selector{
+		filters:  filters,
+		strategy: strategy,
+	}
+}
+
+func (s *selector) Select(nodes ...*Node) *Node {
+	for _, filter := range s.filters {
+		nodes = filter.Filter(nodes...)
+	}
+	if len(nodes) == 0 {
+		return nil
+	}
+	return s.strategy.Apply(nodes...)
+}