From 4f80dfb07b253a01a6354bd651759e1e5e73fc24 Mon Sep 17 00:00:00 2001
From: Edward <chenlulei@gmail.com>
Date: Mon, 11 May 2020 21:23:42 +0800
Subject: [PATCH] Create registry.go

---
 behavioral/registry/registry.go | 99 +++++++++++++++++++++++++++++++++
 1 file changed, 99 insertions(+)
 create mode 100644 behavioral/registry/registry.go

diff --git a/behavioral/registry/registry.go b/behavioral/registry/registry.go
new file mode 100644
index 0000000..6ea3f8f
--- /dev/null
+++ b/behavioral/registry/registry.go
@@ -0,0 +1,99 @@
+package registry
+
+import (
+	"fmt"
+
+	"github.com/google/uuid"
+)
+
+// IDNotFound is an error thrown when an id is not found in a Registry
+type IDNotFound struct {
+	id string
+}
+
+func (e IDNotFound) Error() string {
+	return fmt.Sprintf("ID not found in registry: %s", e.id)
+}
+
+// NameAlreadyRegistered is an error thrown when a duplicate id is found durring registration
+type NameAlreadyRegistered struct {
+	id string
+}
+
+func (e NameAlreadyRegistered) Error() string {
+	return fmt.Sprintf("Identifier was already in registry: %s", e.id)
+}
+
+// Registry acts a generic data registry
+// Objects are registered with the underlying struct, which returns an ID string
+// The ID string can then be used to retreive the object, or to remove it from the registry
+type Registry interface {
+
+	// Deregister removes an item identified by the passed id
+	Deregister(id string) error
+
+	// Get retreives an item identified by the passed id from the registry
+	Get(id string) (interface{}, error)
+
+	// Prune removes nil entries from the registry
+	Prune()
+
+	// Register adds an item to the registry and returns an identifying string
+	Register(data interface{}) string
+
+	// RegisterName adds an item to the registry under the suppplied identifier and returns an identifying string
+	// Returns a NameAlreadyRegistered error if the identifier has already been registered
+	RegisterName(data interface{}, identifier string) error
+}
+
+type registry struct {
+	registry map[string]interface{}
+}
+
+func (reg *registry) Deregister(id string) error {
+	if _, ok := reg.registry[id]; ok {
+		delete(reg.registry, id)
+		return nil
+	}
+	return IDNotFound{id}
+}
+
+func (reg *registry) Get(id string) (interface{}, error) {
+	if data, ok := reg.registry[id]; ok {
+		return data, nil
+	}
+	return nil, IDNotFound{id}
+}
+
+func (reg *registry) Prune() {
+	for key, value := range reg.registry {
+		if value == nil {
+			delete(reg.registry, key)
+		}
+	}
+}
+
+func (reg *registry) Register(data interface{}) string {
+	// Just in case the impossible happens and there is an id colision
+	for {
+		newUUID, _ := uuid.NewRandom()
+		id := newUUID.String()
+		if _, ok := reg.registry[id]; !ok {
+			reg.registry[id] = data
+			return id
+		}
+	}
+}
+
+func (reg *registry) RegisterName(data interface{}, identifier string) error {
+	if _, ok := reg.registry[identifier]; !ok {
+		reg.registry[identifier] = data
+		return nil
+	}
+	return NameAlreadyRegistered{identifier}
+}
+
+// New returns a new Registry interface
+func New() Registry {
+	return &registry{}
+}