From efe01c75cefc8a398dfa64ddbb41dfcd632f5016 Mon Sep 17 00:00:00 2001
From: Stein Fletcher <steindfletcher@gmail.com>
Date: Fri, 24 Jan 2020 13:58:10 +0000
Subject: [PATCH] Add cloudwatch handler

---
 cloudwatch_handler.go      | 71 ++++++++++++++++++++++++++++++++++++++
 cloudwatch_handler_test.go | 49 ++++++++++++++++++++++++++
 2 files changed, 120 insertions(+)
 create mode 100644 cloudwatch_handler.go
 create mode 100644 cloudwatch_handler_test.go

diff --git a/cloudwatch_handler.go b/cloudwatch_handler.go
new file mode 100644
index 0000000..29674f1
--- /dev/null
+++ b/cloudwatch_handler.go
@@ -0,0 +1,71 @@
+package g8
+
+import (
+	"context"
+
+	"github.com/aws/aws-lambda-go/events"
+	"github.com/aws/aws-lambda-go/lambda"
+	"github.com/google/uuid"
+	newrelic "github.com/newrelic/go-agent"
+	"github.com/newrelic/go-agent/_integrations/nrlambda"
+	"github.com/rs/zerolog"
+)
+
+type CloudWatchContext struct {
+	Context       context.Context
+	Event         events.CloudWatchEvent
+	Logger        zerolog.Logger
+	NewRelicTx    newrelic.Transaction
+	CorrelationID string
+}
+
+type CloudWatchHandlerFunc func(c *CloudWatchContext) error
+
+func CloudWatchHandler(h CloudWatchHandlerFunc, conf HandlerConfig) func(context.Context, events.CloudWatchEvent) error {
+	return func(ctx context.Context, event events.CloudWatchEvent) error {
+		correlationID := uuid.New().String()
+
+		// the resource that triggered the event, e.g. "arn:aws:events:us-east-1:123456789012:rule/MyScheduledRule"
+		var cloudWatchResource string
+		if len(event.Resources) > 0 {
+			cloudWatchResource = event.Resources[0]
+		}
+
+		logger := configureLogger(conf).
+			Str("cloud_watch_resource", cloudWatchResource).
+			Str("correlation_id", correlationID).
+			Logger()
+
+		c := &CloudWatchContext{
+			Context:       ctx,
+			Event:         event,
+			Logger:        logger,
+			NewRelicTx:    newrelic.FromContext(ctx),
+			CorrelationID: correlationID,
+		}
+
+		c.AddNewRelicAttribute("functionName", conf.FunctionName)
+		c.AddNewRelicAttribute("buildVersion", conf.BuildVersion)
+		c.AddNewRelicAttribute("correlationID", correlationID)
+		c.AddNewRelicAttribute("cloudWatchResource", cloudWatchResource)
+
+		if err := h(c); err != nil {
+			logUnhandledError(c.Logger, err)
+			return err
+		}
+		return nil
+	}
+}
+
+func CloudWatchHandlerWithNewRelic(h CloudWatchHandlerFunc, conf HandlerConfig) lambda.Handler {
+	return nrlambda.Wrap(CloudWatchHandler(h, conf), conf.NewRelicApp)
+}
+
+func (c *CloudWatchContext) AddNewRelicAttribute(key string, val interface{}) {
+	if c.NewRelicTx == nil {
+		return
+	}
+	if err := c.NewRelicTx.AddAttribute(key, val); err != nil {
+		c.Logger.Error().Msgf("failed to add attr '%s' to new relic tx: %+v", key, err)
+	}
+}
diff --git a/cloudwatch_handler_test.go b/cloudwatch_handler_test.go
new file mode 100644
index 0000000..1a13cc3
--- /dev/null
+++ b/cloudwatch_handler_test.go
@@ -0,0 +1,49 @@
+package g8_test
+
+import (
+	"context"
+	"io/ioutil"
+	"testing"
+
+	"github.com/aws/aws-lambda-go/events"
+	"github.com/rs/zerolog"
+	"github.com/stretchr/testify/assert"
+
+	"github.com/JSainsburyPLC/g8"
+)
+
+func TestCloudWatchHandler_SingleMessage(t *testing.T) {
+	timesCalled := 0
+	resourceArn := "arn:aws:events:us-east-1:123456789012:rule/MyScheduledRule"
+	h := g8.CloudWatchHandler(func(c *g8.CloudWatchContext) error {
+		timesCalled++
+
+		assert.Equal(t, resourceArn, c.Event.Resources[0])
+		assert.NotEmpty(t, c.CorrelationID)
+
+		return nil
+	}, g8.HandlerConfig{Logger: zerolog.New(ioutil.Discard)})
+
+	err := h(context.Background(), events.CloudWatchEvent{
+		Resources: []string{resourceArn},
+	})
+
+	assert.Nil(t, err)
+	assert.Equal(t, 1, timesCalled)
+}
+
+func TestCloudWatchHandler_HandlerError(t *testing.T) {
+	timesCalled := 0
+	handlerFunc := func(c *g8.CloudWatchContext) error {
+		timesCalled++
+		return assert.AnError
+	}
+
+	h := g8.CloudWatchHandler(handlerFunc, g8.HandlerConfig{
+		Logger: zerolog.New(ioutil.Discard),
+	})
+	err := h(context.Background(), events.CloudWatchEvent{})
+
+	assert.Equal(t, assert.AnError, err)
+	assert.Equal(t, 1, timesCalled)
+}