The start of mud - the micro data model (#1811)

* The start of mud - the micro data model

* add comments

model/mud/entity.go

@@ -0,0 +1,52 @@
+package mud
+
+import (
+	"github.com/google/uuid"
+	"github.com/micro/go-micro/v2/codec"
+	"github.com/micro/go-micro/v2/model"
+)
+
+type mudEntity struct {
+	id         string
+	name       string
+	value      interface{}
+	codec      codec.Marshaler
+	attributes map[string]interface{}
+}
+
+func (m *mudEntity) Attributes() map[string]interface{} {
+	return m.attributes
+}
+
+func (m *mudEntity) Id() string {
+	return m.id
+}
+
+func (m *mudEntity) Name() string {
+	return m.name
+}
+
+func (m *mudEntity) Value() interface{} {
+	return m.value
+}
+
+func (m *mudEntity) Read(v interface{}) error {
+	switch m.value.(type) {
+	case []byte:
+		b := m.value.([]byte)
+		return m.codec.Unmarshal(b, v)
+	default:
+		v = m.value
+	}
+	return nil
+}
+
+func newEntity(name string, value interface{}, codec codec.Marshaler) model.Entity {
+	return &mudEntity{
+		id:         uuid.New().String(),
+		name:       name,
+		value:      value,
+		codec:      codec,
+		attributes: make(map[string]interface{}),
+	}
+}