refactor code structure (#1738)

pkg/simple/client/cache/simple_cache.go

@@ -0,0 +1,40 @@
+package cache
+
+import "time"
+
+type simpleObject struct {
+    value  string
+    expire time.Time
+}
+
+type SimpleCache struct {
+    store map[string]simpleObject
+}
+
+func NewSimpleCache() Interface {
+    return &SimpleCache{store: make(map[string]simpleObject)}
+}
+
+func (s *SimpleCache) Keys(pattern string) ([]string, error) {
+    panic("implement me")
+}
+
+func (s *SimpleCache) Set(key string, value string, duration time.Duration) error {
+    panic("implement me")
+}
+
+func (s *SimpleCache) Del(key string) error {
+    panic("implement me")
+}
+
+func (s *SimpleCache) Get(key string) (string, error) {
+    return "", nil
+}
+
+func (s *SimpleCache) Exists(key string) (bool, error) {
+    panic("implement me")
+}
+
+func (s *SimpleCache) Expire(key string, duration time.Duration) error {
+    panic("implement me")
+}