feat: conf inherit (#2568)

* feat: add ValuerWithParent

* feat: make etcd config inherit from parents

* chore: add more tests

* chore: add more tests

* chore: add more comments

* chore: refactor

* chore: add more comments

* fix: fix duplicated code and refactor

* fix: remove unnecessary code

* fix: fix test case for removing print

* feat: support partial inherit

core/mapping/valuer.go

@@ -7,12 +7,94 @@ type (
 		Value(key string) (interface{}, bool)
 	}
 
-	// A MapValuer is a map that can use Value method to get values with given keys.
-	MapValuer map[string]interface{}
+	// A valuerWithParent defines a node that has a parent node.
+	valuerWithParent interface {
+		Valuer
+		// Parent get the parent valuer for current node.
+		Parent() valuerWithParent
+	}
+
+	// A node is a map that can use Value method to get values with given keys.
+	node struct {
+		current Valuer
+		parent  valuerWithParent
+	}
+
+	// A valueWithParent is used to wrap the value with its parent.
+	valueWithParent struct {
+		value  interface{}
+		parent valuerWithParent
+	}
+
+	// mapValuer is a type for map to meet the Valuer interface.
+	mapValuer map[string]interface{}
+	// simpleValuer is a type to get value from current node.
+	simpleValuer node
+	// recursiveValuer is a type to get the value recursively from current and parent nodes.
+	recursiveValuer node
 )
 
-// Value gets the value associated with the given key from mv.
-func (mv MapValuer) Value(key string) (interface{}, bool) {
+// Value gets the value assciated with the given key from mv.
+func (mv mapValuer) Value(key string) (interface{}, bool) {
 	v, ok := mv[key]
 	return v, ok
 }
+
+// Value gets the value associated with the given key from sv.
+func (sv simpleValuer) Value(key string) (interface{}, bool) {
+	v, ok := sv.current.Value(key)
+	return v, ok
+}
+
+// Parent get the parent valuer from sv.
+func (sv simpleValuer) Parent() valuerWithParent {
+	if sv.parent == nil {
+		return nil
+	}
+
+	return recursiveValuer{
+		current: sv.parent,
+		parent:  sv.parent.Parent(),
+	}
+}
+
+// Value gets the value associated with the given key from rv,
+// and it will inherit the value from parent nodes.
+func (rv recursiveValuer) Value(key string) (interface{}, bool) {
+	val, ok := rv.current.Value(key)
+	if !ok {
+		if parent := rv.Parent(); parent != nil {
+			return parent.Value(key)
+		}
+
+		return nil, false
+	}
+
+	if vm, ok := val.(map[string]interface{}); ok {
+		if parent := rv.Parent(); parent != nil {
+			pv, pok := parent.Value(key)
+			if pok {
+				if pm, ok := pv.(map[string]interface{}); ok {
+					for k, v := range vm {
+						pm[k] = v
+					}
+					return pm, true
+				}
+			}
+		}
+	}
+
+	return val, true
+}
+
+// Parent get the parent valuer from rv.
+func (rv recursiveValuer) Parent() valuerWithParent {
+	if rv.parent == nil {
+		return nil
+	}
+
+	return recursiveValuer{
+		current: rv.parent,
+		parent:  rv.parent.Parent(),
+	}
+}