Merge pull request #3 from mrdck/feature/di

Introduce dependency injection

Author: ikhvost

README.md

@@ -8,6 +8,7 @@
     - [Lint](#lint)
     - [Deployment](#deployment)
     - [Project Structure](#project-structure)
+    - [Dependency Injection (IoC)](#dependency-injection-ioc)
   - [License](#license)
 
 <!-- END doctoc generated TOC please keep comment here to allow auto update -->
@@ -88,5 +89,29 @@ yarn deploy
 ├── tsconfig.json
 └── yarn.lock
 ```
+
+### Dependency Injection (IoC)
+Following template leverage Dependency Injection on inversify package that introduces Inversion of Control container.
+In `src/common/container` there is container component that serve purpose of Root Composite that hooks and instantiate all dependencies with container.
+
+This approach allow easy access on handler level
+```typescript
+// container with dependencies is available in context
+export async function handler(_: APIGatewayProxyEvent, { container }: Context): Promise<APIGatewayProxyResult> {
+  // get dependency bound to container
+  const config = container.get<Config>(Config)
+
+  if (config.foo) {
+    // some foo logic
+  }
+
+  return response(StatusCodes.OK, ReasonPhrases.OK)
+}
+
+// handler needs to be decorated with middleware otherwise container is not bound
+export const health = middleware(handler)
+```
+
+
 ## License
 MIT

package.json

@@ -24,6 +24,7 @@
     "aws-lambda": "^1.0.6",
     "doctoc": "^2.1.0",
     "dotenv": "^14.2.0",
+    "env-var": "^7.1.1",
     "eslint": "^7.32.0",
     "eslint-config-standard": "^16.0.3",
     "eslint-plugin-import": "^2.25.2",
@@ -32,8 +33,10 @@
     "eslint-plugin-standard": "^5.0.0",
     "http-status-codes": "^2.1.4",
     "husky": "^7.0.4",
+    "inversify": "^6.0.1",
     "jest": "^27.3.1",
     "lint-staged": "^11.2.4",
+    "reflect-metadata": "^0.1.13",
     "serverless": "^2.64.1",
     "serverless-bundle": "^5.0.2",
     "serverless-jest-plugin": "^0.4.0",

src/common/config.ts

@@ -0,0 +1,16 @@
+import * as env from 'env-var'
+import { ContainerModule } from 'inversify'
+
+export interface Config {
+  foo: string
+}
+
+export const Config = Symbol('Config')
+
+const resolve = (): Config => ({
+  foo: env.get('NODE_ENV').default('testing').asString(),
+})
+
+export default new ContainerModule(bind => {
+  bind<Config>(Config).toConstantValue(resolve())
+})

src/common/container.ts

@@ -0,0 +1,18 @@
+import 'reflect-metadata'
+
+import { Container } from 'inversify'
+
+import config from './config'
+
+/**
+ * Root Composite component that instantiate and hooks Inversion of Control container
+ */
+export const compositeRoot = () => {
+  const container = new Container()
+
+  container.load(config)
+
+  return container
+}
+
+export const container = compositeRoot()

src/common.ts src/common/http.tssrc/common.ts renamed to src/common/http.ts

@@ -0,0 +1,4 @@
+export * from './middleware'
+export * from './http'
+export * from './container'
+export * from './config'

src/common/index.ts

@@ -4,6 +4,8 @@ import errorHandler from '@middy/http-error-handler'
 
 import type { Handler } from 'aws-lambda'
 
+import { container } from './container'
+
 /**
  * No Operation logger
  */
@@ -16,4 +18,8 @@ export const middleware = <Event, Context>(handler: Handler<Event, Context>) =>
   return middy(handler)
     .use(bodyParser())
     .use(errorHandler({ logger: nullLogger }))
+    .before(request => {
+      // decorate context with container
+      Reflect.set(request.context, 'container', container)
+    })
 }

src/middleware.ts src/common/middleware.tssrc/middleware.ts renamed to src/common/middleware.ts

@@ -3,8 +3,7 @@ import validator from '@middy/validator'
 import type { APIGatewayProxyResult, APIGatewayProxyEvent } from 'aws-lambda'
 import { StatusCodes } from 'http-status-codes'
 
-import { response } from './common'
-import { middleware } from './middleware'
+import { response, middleware } from './common'
 
 const schema = {
   type:       'object',

src/foo.ts

@@ -1,8 +1,19 @@
-import type { APIGatewayProxyResult } from 'aws-lambda'
+import type { APIGatewayProxyEvent, APIGatewayProxyResult, Context } from 'aws-lambda'
 import { StatusCodes, ReasonPhrases } from 'http-status-codes'
 
-import { response } from './common'
+import { response, Config, middleware } from './common'
+
+export async function handler(_: APIGatewayProxyEvent, { container }: Context): Promise<APIGatewayProxyResult> {
+  const config = container.get<Config>(Config)
+
+  /**
+   * This code below serve example purpose for getting values out of container
+   */
+  if (config.foo) {
+    console.log('foo')
+  }
 
-export async function health(): Promise<APIGatewayProxyResult> {
   return response(StatusCodes.OK, ReasonPhrases.OK)
 }
+
+export const health = middleware(handler)

src/health.ts

@@ -0,0 +1,9 @@
+import 'typesafe-api-gateway'
+
+import { interfaces } from 'inversify'
+
+declare module 'aws-lambda' {
+  interface Context extends LambdaContext {
+    container: interfaces.Container
+  }
+}