Support configuring loggers as described in issue actions-on-google#413

(actions-on-google#413).

With that change, a client application that uses Firebase cloud functions would simply need to do the following to improve substantially the readability of log entries in the cloud functions logs console:

const app = smarthome({
  debug: true,
  logs: {
    debug: functions.logger.debug,
    info: functions.logger.info,
    // 'warn' maps to 'error' in firebase logs.
    // If set to functions.logger.warn, there is no level associated with the log entry.
    warn: functions.logger.error,
    error: functions.logger.error
  }
});

src/assistant.ts

@@ -20,10 +20,24 @@ import * as common from './common'
 /** @public */
 export type AppHandler = OmniHandler & BaseApp
 
+/** @public */
+export interface LogFn {
+  (params: any[]): void;
+}
+
+/** @public */
+export interface AppLogs {
+  debug: LogFn,
+  info: LogFn,
+  warn: LogFn,
+  error: LogFn
+}
+
 /** @public */
 export interface AppOptions {
   /** @public */
-  debug?: boolean
+  debug?: boolean,
+  logs?: AppLogs
 }
 
 /** @hidden */
@@ -50,6 +64,7 @@ export interface BaseApp extends ServiceBaseApp {
 
   /** @public */
   debug: boolean
+  logs?: AppLogs
 }
 
 /** @hidden */
@@ -60,6 +75,7 @@ const create = (options?: AppOptions): BaseApp => ({
     return plugin(this) || this
   },
   debug: !!(options && options.debug),
+  logs: (typeof (options) === 'undefined' || typeof (options.logs) === 'undefined') ? undefined : options.logs
 })
 
 /** @hidden */
@@ -78,6 +94,12 @@ export const attach = <TService>(
     return app.handler(args[0], args[1])
   }
   app = Object.assign(omni, app)
+
+  if (app.logs) {
+    // Redefine debug, warn, error, info according to app definitions of logs.
+    common.setLogs(app.logs)
+  }
+
   const handler: typeof app.handler = app.handler.bind(app)
   const standard: StandardHandler = async (body, headers, metadata) => {
     const log = app.debug ? common.info : common.debug

src/common.ts

@@ -16,22 +16,27 @@
 
 import * as Debug from 'debug'
 import * as https from 'https'
+import { AppLogs } from './assistant'
 
 const name = 'actions-on-google'
 
 /** @hidden */
-export const debug = Debug(`${name}:debug`)
+let debug = Debug(`${name}:debug`)
+export { debug }
 
 /** @hidden */
-export const warn = Debug(`${name}:warn`)
+let warn = Debug(`${name}:warn`)
+export { warn }
 
 /** @hidden */
 // tslint:disable-next-line:no-console Allow console binding
-export const error = console.error.bind(console) as typeof console.error
+let error = console.error.bind(console) as typeof console.error
+export { error }
 
 /** @hidden */
 // tslint:disable-next-line:no-console Allow console binding
-export const info = console.log.bind(console) as typeof console.log
+let info = console.log.bind(console) as typeof console.log
+export { info }
 
 warn.log = error
 debug.log = info
@@ -52,6 +57,13 @@ export const values = <T>(o: { [key: string]: T }) => Object.keys(o).map(k => o[
 /** @hidden */
 export const clone = <T>(o: T): T => JSON.parse(JSON.stringify(o))
 
+export const setLogs = (logs: AppLogs) => {
+  debug.log = logs.debug
+  info = logs.info
+  warn.log = logs.warn
+  error = logs.error
+}
+
 /** @hidden */
 // tslint:disable-next-line:no-any root can be anything
 export const stringify = (root: any, ...exclude: string[]) => {