//go:build example
// +build example

package main

import (
	"flag"
	"fmt"
	"os"

	"github.com/aws/aws-sdk-go/aws"
	"github.com/aws/aws-sdk-go/aws/session"
	"github.com/aws/aws-sdk-go/service/dynamodb"
	"github.com/aws/aws-sdk-go/service/dynamodb/dynamodbattribute"
)

func exitWithError(err error) {
	fmt.Fprintln(os.Stderr, err)
	os.Exit(1)
}

func main() {
	cfg := Config{}
	if err := cfg.Load(); err != nil {
		exitWithError(fmt.Errorf("failed to load config, %v", err))
	}

	// Create the config specifying the Region for the DynamoDB table.
	// If Config.Region is not set the region must come from the shared
	// config or AWS_REGION environment variable.
	awscfg := &aws.Config{}
	if len(cfg.Region) > 0 {
		awscfg.WithRegion(cfg.Region)
	}

	// Create the session that the DynamoDB service will use.
	sess := session.Must(session.NewSession(awscfg))

	// Create the DynamoDB service client to make the query request with.
	svc := dynamodb.New(sess)

	// Build the query input parameters
	params := &dynamodb.ScanInput{
		TableName: aws.String(cfg.Table),
	}
	if cfg.Limit > 0 {
		params.Limit = aws.Int64(cfg.Limit)
	}

	// Make the DynamoDB Query API call
	result, err := svc.Scan(params)
	if err != nil {
		exitWithError(fmt.Errorf("failed to make Query API call, %v", err))
	}

	items := []Item{}

	// Unmarshal the Items field in the result value to the Item Go type.
	err = dynamodbattribute.UnmarshalListOfMaps(result.Items, &items)
	if err != nil {
		exitWithError(fmt.Errorf("failed to unmarshal Query result items, %v", err))
	}

	// Print out the items returned
	for i, item := range items {
		fmt.Printf("%d: Key: %d, Desc: %s\n", i, item.Key, item.Desc)
		fmt.Printf("\tNum Data Values: %d\n", len(item.Data))
		for k, v := range item.Data {
			fmt.Printf("\t- %q: %v\n", k, v)
		}
	}
}

type Item struct {
	Key  int
	Desc string
	Data map[string]interface{}
}

type Config struct {
	Table  string // required
	Region string // optional
	Limit  int64  // optional

}

func (c *Config) Load() error {
	flag.Int64Var(&c.Limit, "limit", 0, "Limit is the max items to be returned, 0 is no limit")
	flag.StringVar(&c.Table, "table", "", "Table to Query on")
	flag.StringVar(&c.Region, "region", "", "AWS Region the table is in")
	flag.Parse()

	if len(c.Table) == 0 {
		flag.PrintDefaults()
		return fmt.Errorf("table name is required.")
	}

	return nil
}
