Merge 708e69df88 into f978e42036

README.md

@@ -28,7 +28,7 @@ A curated collection of idiomatic design & application patterns for Go language.
 | [Bridge](/structural/bridge.md) | Decouples an interface from its implementation so that the two can vary independently | ✘ |
 | [Composite](/structural/composite.md) | Encapsulates and provides access to a number of different objects | ✘ |
 | [Decorator](/structural/decorator.md) | Adds behavior to an object, statically or dynamically | ✔ |
-| [Facade](/structural/facade.md) | Uses one type as an API to a number of others | ✘ |
+| [Facade](/structural/facade.md) | Uses one type as an API to a number of others | ✔ |
 | [Flyweight](/structural/flyweight.md) | Reuses existing instances of objects with similar/identical state to minimize resource usage | ✘ |
 | [Proxy](/structural/proxy.md) | Provides a surrogate for an object to control it's actions | ✔ |
 

structural/facade.md

@@ -0,0 +1,81 @@
+# Facade Pattern
+
+Facade design pattern provides a unified interface to a set
+of interfaces in a subsystem. Facade defines a higher-level
+interface that makes the subsystem easier to use
+
+## Implementation
+
+```go
+package facade
+
+// Models
+type Product struct {
+    name string
+    cost float64
+    discount float64
+}
+
+type User struct {
+    name string
+    discount float64
+}
+
+// Storages
+type ProductStorage struct {
+    storageMap map[string]Product
+}
+
+func (storage ProductStorage) GetProductByName(name string) Product{
+    product, ok := storage.storageMap[name]
+    if (!ok){
+        panic("Product is absent")
+    }
+
+    return product
+}
+
+type UserStorage struct {
+    storageMap map[string]User
+}
+
+func (storage UserStorage) GetUserByName(name string) User{
+    user, ok := storage.storageMap[name]
+    if (!ok){
+        panic("User is absent")
+    }
+
+    return user
+}
+
+// Facade
+type ProductFacade struct {
+    productStorage ProductStorage
+    userStorage UserStorage
+}
+
+func (productFacade ProductFacade) GetDiscountedCost(userName string, productName string) float64 {
+    product := productFacade.productStorage.GetProductByName(productName)
+    user := productFacade.userStorage.GetUserByName(userName)
+
+    return product.cost * (1 - product.discount) * (1 - user.discount)
+}
+
+```
+
+## Usage
+
+```go
+    user := User{name: "Alex", discount: 0.2}
+    product := Product{name: "Car", cost:10.50, discount: 0.1 }
+
+    userStorage := UserStorage{storageMap: make(map[string]User)}
+    userStorage.storageMap[user.name] = user
+
+    productStorage := ProductStorage{storageMap: make(map[string]Product)}
+    productStorage.storageMap[product.name] = product
+
+    facade := ProductFacade{productStorage: productStorage, userStorage: userStorage}
+    discount := facade.GetDiscountedCost("Alex", "Car")
+    fmt.Printf("Cost with discount is: %f", discount)
+```