Decorators (#42)

Adds decorator functionality to BaseService

packages/medusa-interfaces/src/__tests__/base-service.js

@@ -0,0 +1,66 @@
+import BaseService from "../base-service"
+
+describe("BaseService", () => {
+  describe("addDecorator", () => {
+    const baseService = new BaseService()
+
+    it("successfully adds decorator", () => {
+      baseService.addDecorator(obj => {
+        return (obj.decorator1 = true)
+      })
+
+      expect(baseService.decorators_.length).toEqual(1)
+    })
+
+    it("throws if decorator is not a function", () => {
+      expect(() => baseService.addDecorator("not a function")).toThrow(
+        "Decorators must be of type function"
+      )
+    })
+  })
+
+  describe("runDecorators_", () => {
+    it("returns success when passwords match", async () => {
+      const baseService = new BaseService()
+
+      baseService.addDecorator(obj => {
+        obj.decorator1 = true
+        return obj
+      })
+      baseService.addDecorator(obj => {
+        obj.decorator2 = true
+        return obj
+      })
+
+      const result = await baseService.runDecorators_({ data: "initial" })
+      expect(result).toEqual({
+        data: "initial",
+        decorator1: true,
+        decorator2: true,
+      })
+    })
+
+    it("skips failing decorator", async () => {
+      const baseService = new BaseService()
+
+      baseService.addDecorator(obj => {
+        obj.decorator1 = true
+        return obj
+      })
+      baseService.addDecorator(obj => {
+        return Promise.reject("fail")
+      })
+      baseService.addDecorator(obj => {
+        obj.decorator3 = true
+        return Promise.resolve(obj)
+      })
+
+      const result = await baseService.runDecorators_({ data: "initial" })
+      expect(result).toEqual({
+        data: "initial",
+        decorator1: true,
+        decorator3: true,
+      })
+    })
+  })
+})

packages/medusa-interfaces/src/base-service.js

@@ -2,5 +2,35 @@
  * Common functionality for Services
  * @interface
  */
-class BaseService {}
+class BaseService {
+  constructor() {
+    this.decorators_ = []
+  }
+
+  /**
+   * Adds a decorator to a service. The decorator must be a function and should
+   * return a decorated object.
+   * @param {function} fn - the decorator to add to the service
+   */
+  addDecorator(fn) {
+    if (typeof fn !== "function") {
+      throw Error("Decorators must be of type function")
+    }
+
+    this.decorators_.push(fn)
+  }
+
+  /**
+   * Runs the decorators registered on the service. The decorators are run in
+   * the order they have been registered in. Failing decorators will be skipped
+   * in order to ensure deliverability in spite of breaking code.
+   * @param {object} obj - the object to decorate.
+   * @return {object} the decorated object.
+   */
+  runDecorators_(obj) {
+    return this.decorators_.reduce(async (acc, next) => {
+      return acc.then(res => next(res)).catch(() => acc)
+    }, Promise.resolve(obj))
+  }
+}
 export default BaseService