Refactoring _deployToRegion()

Change to async/await style.
Prepare to change to SDK v3. GH-641

Author: abetomo

lib/main.js

@@ -973,115 +973,108 @@ they may not work as expected in the Lambda environment.
       !!err.message.match(/^Function not found:/)
   }
 
-  _deployToRegion (program, params, region, buffer) {
+  async _deployToRegion (program, params, region, buffer) {
     aws.updateConfig(program, region)
 
     console.log('=> Reading event source file to memory')
     const eventSourceList = this._eventSourceList(program)
 
-    return Promise.resolve().then(() => {
-      if (this._isUseS3(program)) {
-        const s3Deploy = new S3Deploy(aws.sdk, region)
-        return s3Deploy.putPackage(params, region, buffer)
-      }
-      return null
-    }).then((code) => {
-      if (code != null) params.Code = code
-    }).then(() => {
-      if (!this._isUseS3(program)) {
-        console.log(`=> Uploading zip file to AWS Lambda ${region} with parameters:`)
-      } else {
-        console.log(`=> Uploading AWS Lambda ${region} with parameters:`)
-      }
-      console.log(params)
-
-      const lambda = new aws.sdk.Lambda({
-        region,
-        apiVersion: '2015-03-31'
-      })
-      const scheduleEvents = new ScheduleEvents(aws.sdk, region)
-      const s3Events = new S3Events(aws.sdk, region)
-      const cloudWatchLogs = new CloudWatchLogs(aws.sdk, region)
+    if (this._isUseS3(program)) {
+      const s3Deploy = new S3Deploy(aws.sdk, region)
+      params.Code = await s3Deploy.putPackage(params, region, buffer)
+      console.log(`=> Uploading AWS Lambda ${region} with parameters:`)
+    } else {
+      console.log(`=> Uploading zip file to AWS Lambda ${region} with parameters:`)
+    }
+    console.log(params)
+    const lambda = new aws.sdk.Lambda({
+      region,
+      apiVersion: '2015-03-31'
+    })
+    const scheduleEvents = new ScheduleEvents(aws.sdk, region)
+    const s3Events = new S3Events(aws.sdk, region)
+    const cloudWatchLogs = new CloudWatchLogs(aws.sdk, region)
 
-      // Checking function
-      return lambda.getFunction({
-        FunctionName: params.FunctionName
-      }).promise().then(() => {
-        // Function exists
-        return this._listEventSourceMappings(lambda, {
+    const existsFunction = await (async () => {
+      try {
+        await lambda.getFunction({
           FunctionName: params.FunctionName
-        }).then((existingEventSourceList) => {
-          return Promise.all([
-            this._uploadExisting(lambda, params).then((results) => {
-              console.log('=> Done uploading. Results follow: ')
-              console.log(results)
-              return results
-            }).then(results => {
-              return Promise.all([
-                this._updateScheduleEvents(
-                  scheduleEvents,
-                  results.FunctionArn,
-                  eventSourceList.ScheduleEvents
-                ),
-                this._updateS3Events(
-                  s3Events,
-                  results.FunctionArn,
-                  eventSourceList.S3Events
-                ),
-                this._updateTags(
-                  lambda,
-                  results.FunctionArn,
-                  params.Tags)
-              ])
-            }),
-            this._updateEventSources(
-              lambda,
-              params.FunctionName,
-              existingEventSourceList,
-              eventSourceList.EventSourceMappings
-            ),
-            this._setLogsRetentionPolicy(
-              cloudWatchLogs,
-              program,
-              params.FunctionName
-            )
-          ])
-        })
-      }).catch((err) => {
+        }).promise()
+        return true
+      } catch (err) {
         if (!this._isFunctionDoesNotExist(err)) {
           throw err
         }
-        // Function does not exist
-        return this._uploadNew(lambda, params).then((results) => {
-          console.log('=> Done uploading. Results follow: ')
-          console.log(results)
-
-          return Promise.all([
-            this._updateEventSources(
-              lambda,
-              params.FunctionName,
-              [],
-              eventSourceList.EventSourceMappings
-            ),
-            this._updateScheduleEvents(
-              scheduleEvents,
-              results.FunctionArn,
-              eventSourceList.ScheduleEvents
-            ),
-            this._updateS3Events(
-              s3Events,
-              results.FunctionArn,
-              eventSourceList.S3Events
-            ),
-            this._setLogsRetentionPolicy(
-              cloudWatchLogs,
-              program,
-              params.FunctionName
-            )
-          ])
-        })
+        return false
+      }
+    })()
+
+    if (existsFunction) {
+      const existingEventSourceList = await this._listEventSourceMappings(lambda, {
+        FunctionName: params.FunctionName
       })
-    })
+      const results = await this._uploadExisting(lambda, params)
+      console.log('=> Done uploading. Results follow: ')
+      console.log(results)
+
+      return Promise.all([
+        Promise.all([
+          this._updateScheduleEvents(
+            scheduleEvents,
+            results.FunctionArn,
+            eventSourceList.ScheduleEvents
+          ),
+          this._updateS3Events(
+            s3Events,
+            results.FunctionArn,
+            eventSourceList.S3Events
+          ),
+          this._updateTags(
+            lambda,
+            results.FunctionArn,
+            params.Tags)
+        ]),
+        this._updateEventSources(
+          lambda,
+          params.FunctionName,
+          existingEventSourceList,
+          eventSourceList.EventSourceMappings
+        ),
+        this._setLogsRetentionPolicy(
+          cloudWatchLogs,
+          program,
+          params.FunctionName
+        )
+      ])
+    } else {
+      const results = await this._uploadNew(lambda, params)
+      console.log('=> Done uploading. Results follow: ')
+      console.log(results)
+
+      return Promise.all([
+        this._updateEventSources(
+          lambda,
+          params.FunctionName,
+          [],
+          eventSourceList.EventSourceMappings
+        ),
+        this._updateScheduleEvents(
+          scheduleEvents,
+          results.FunctionArn,
+          eventSourceList.ScheduleEvents
+        ),
+        this._updateS3Events(
+          s3Events,
+          results.FunctionArn,
+          eventSourceList.S3Events
+        ),
+        this._setLogsRetentionPolicy(
+          cloudWatchLogs,
+          program,
+          params.FunctionName
+        )
+      ])
+    }
   }
 
   _printDeployResults (results, isFirst) {