package main

import (
	"encoding/json"
	"fmt"
	"log"
	"os"

	"github.com/aws/aws-cdk-go/awscdk/v2"

	"github.com/aws/aws-cdk-go/awscdk/v2/awsdynamodb"
	"github.com/aws/aws-cdk-go/awscdk/v2/awslogs"
	"github.com/aws/aws-cdk-go/awscdk/v2/awslogsdestinations"
	"github.com/aws/aws-cdk-go/awscdklambdagoalpha/v2"
	"github.com/aws/constructs-go/constructs/v10"
	"github.com/aws/jsii-runtime-go"
)

type CloudwatchLogAlertsStackProps struct {
	awscdk.StackProps
	SlackWebhook        string
	LambdaFunctionNames []string
}

func NewCloudwatchLogAlertsStack(scope constructs.Construct, id string, props *CloudwatchLogAlertsStackProps) awscdk.Stack {
	var sprops awscdk.StackProps
	if props != nil {
		sprops = props.StackProps
	}
	stack := awscdk.NewStack(scope, &id, &sprops)

	table := awsdynamodb.NewTableV2(stack, jsii.String("CloudwatchLogAlertsTable"), &awsdynamodb.TablePropsV2{
		PartitionKey: &awsdynamodb.Attribute{
			Name: jsii.String("fingerprint"),
			Type: awsdynamodb.AttributeType_STRING,
		},
		TableClass:          awsdynamodb.TableClass_STANDARD,
		Billing:             awsdynamodb.Billing_OnDemand(),
		Encryption:          awsdynamodb.TableEncryptionV2_DynamoOwnedKey(),
		PointInTimeRecovery: jsii.Bool(true),
		TimeToLiveAttribute: jsii.String("expires"),
	})

	lambda_fn := awscdklambdagoalpha.NewGoFunction(stack, jsii.String("CloudwatchLogAlertsLambda"),
		&awscdklambdagoalpha.GoFunctionProps{
			Description: jsii.String("CloudWatch Log Alerts"),
			Environment: &map[string]*string{
				"SLACK_WEBHOOK": jsii.String(props.SlackWebhook),
				"DDB_TABLE":     table.TableName(),
			},
			LogRetention: awslogs.RetentionDays_ONE_MONTH,
			MemorySize:   jsii.Number(512),
			Timeout:      awscdk.Duration_Seconds(jsii.Number(5)),
			Entry:        jsii.String("./lambda-fn/main.go"),
		},
	)

	table.GrantWriteData(lambda_fn)

	for _, functionName := range props.LambdaFunctionNames {
		awslogs.NewSubscriptionFilter(
			stack,
			jsii.String(fmt.Sprintf("SubscriptionFilter_%s", functionName)),
			&awslogs.SubscriptionFilterProps{
				LogGroup: awslogs.LogGroup_FromLogGroupName(
					stack,
					jsii.String(fmt.Sprintf("LogGroup_%s", functionName)),
					jsii.String(fmt.Sprintf("/aws/lambda/%s", functionName)),
				),
				Destination: awslogsdestinations.NewLambdaDestination(
					lambda_fn,
					nil,
				),
				FilterPattern: awslogs.FilterPattern_StringValue(
					jsii.String("$.level"),
					jsii.String("="),
					jsii.String("error"),
				),
			},
		)
	}

	return stack
}

func main() {
	defer jsii.Close()

	var props CloudwatchLogAlertsStackProps
	f, err := os.Open("properties.json")
	if err != nil {
		log.Fatalf("Error opening properties.json: %v", err)
	}
	defer f.Close()
	if err := json.NewDecoder(f).Decode(&props); err != nil {
		log.Fatalf("Error parsing properties.json: %v", err)
	}
	props.StackProps = awscdk.StackProps{
		Env: env(),
	}

	app := awscdk.NewApp(nil)

	NewCloudwatchLogAlertsStack(app, "CloudwatchLogAlertsStack", &props)

	app.Synth(nil)
}

// env determines the AWS environment (account+region) in which our stack is to
// be deployed. For more information see: https://docs.aws.amazon.com/cdk/latest/guide/environments.html
func env() *awscdk.Environment {
	// If unspecified, this stack will be "environment-agnostic".
	// Account/Region-dependent features and context lookups will not work, but a
	// single synthesized template can be deployed anywhere.
	//---------------------------------------------------------------------------
	//return nil

	// Uncomment if you know exactly what account and region you want to deploy
	// the stack to. This is the recommendation for production stacks.
	//---------------------------------------------------------------------------
	// return &awscdk.Environment{
	// 	Account: jsii.String("111111111111"),
	// 	Region:  jsii.String("eu-west-1"),
	// }

	// Uncomment to specialize this stack for the AWS Account and Region that are
	// implied by the current CLI configuration. This is recommended for dev
	// stacks.
	//---------------------------------------------------------------------------
	return &awscdk.Environment{
		Account: jsii.String(os.Getenv("CDK_DEFAULT_ACCOUNT")),
		Region:  jsii.String(os.Getenv("CDK_DEFAULT_REGION")),
	}
}