package main

import (
	"context"
	"fmt"
	"github.com/aws/aws-sdk-go-v2/aws"
	"github.com/aws/aws-sdk-go-v2/config"
	"github.com/aws/aws-sdk-go-v2/feature/s3/manager"
	"github.com/aws/aws-sdk-go-v2/service/s3"
	"github.com/dustin/go-humanize"
	"io"
	"log"
	"sync"
	"sync/atomic"
)

type OrderedWriter struct {
	buffer   sync.Map
	writer   *io.PipeWriter
	written  uint64
	expected int64
	size     *uint64
	wg       sync.WaitGroup
	mu       sync.Mutex
}

func (o *OrderedWriter) WriteAt(p []byte, offset int64) (n int, err error) {
	o.wg.Add(1)
	writeBlockSize := len(p)
	if o.size != nil {
		atomic.AddUint64(&o.written, uint64(writeBlockSize))
		percentageDownloaded := float32(o.written*100) / float32(*o.size)
		log.Printf("File size: %s, downloaded: %s, percentage: %.2f%%\n", humanize.IBytes(*o.size), humanize.IBytes(o.written), percentageDownloaded)
	}
	buf := make([]byte, writeBlockSize)
	copy(buf, p)
	o.buffer.Store(offset, buf)
	o.flush()
	return writeBlockSize, nil
}

func (o *OrderedWriter) flush() {
	o.mu.Lock()
	defer func() {
		o.wg.Done()
		o.mu.Unlock()
	}()

	for {
		if data, ok := o.buffer.Load(o.expected); ok {
			buf := data.([]byte)
			flushBlockSize := len(buf)
			_, err := o.writer.Write(buf)
			if err != nil {
				panic("Error writing to buf: " + err.Error())
			}
			o.buffer.Delete(o.expected)
			atomic.AddInt64(&o.expected, int64(flushBlockSize))
		} else {
			break
		}
	}

}

func download(s3Client *s3.Client, orderedWriter *OrderedWriter, sourceBucket string, sourceKey string) {
	log.Println("Begin downloading...")
	downloader := manager.NewDownloader(s3Client, func(downloader *manager.Downloader) {
		// Define a strategy that will buffer 50 MiB in memory
		downloader.BufferProvider = manager.NewPooledBufferedWriterReadFromProvider(50 * 1024 * 1024)
		downloader.PartSize = 100 * 1024 * 1024 // 100MB
		downloader.Concurrency = 5
		downloader.PartBodyMaxRetries = 5
	})
	_, err := downloader.Download(context.TODO(), orderedWriter, &s3.GetObjectInput{
		Bucket: aws.String(sourceBucket),
		Key:    aws.String(sourceKey),
	})
	if err != nil {
		log.Fatalf("download failed due to: %v\n", err)
	}
	log.Println("Download Success!")
	orderedWriter.wg.Wait()
	defer func() {
		if err := orderedWriter.writer.Close(); err != nil {
			panic(fmt.Sprintf("close writer error: %v", err))
		}
	}()
}

func upload(s3Client *s3.Client, wg *sync.WaitGroup, destinationBucket string, destinationKey string, reader *io.PipeReader) {
	defer wg.Done()
	uploader := manager.NewUploader(s3Client, func(u *manager.Uploader) {
		// Define a strategy that will buffer 50 MiB in memory
		u.BufferProvider = manager.NewBufferedReadSeekerWriteToPool(50 * 1024 * 1024)
		u.PartSize = 100 * 1024 * 1024 // 100 MiB
		u.Concurrency = 5
	})

	log.Println("Begin uploading...")
	_, err := uploader.Upload(context.TODO(), &s3.PutObjectInput{
		Bucket: aws.String(destinationBucket),
		Key:    aws.String(destinationKey),
		Body:   reader,
	})
	if err != nil {
		log.Fatalf("upload failed due to: %v\n", err)
	}
	log.Println("Finish uploading...")
}

func getFileSize(s3Client s3.Client, sourceBucket string, sourceKey string) *uint64 {
	headObject, err := s3Client.HeadObject(context.TODO(), &s3.HeadObjectInput{
		Bucket: aws.String(sourceBucket),
		Key:    aws.String(sourceKey),
	})
	if err != nil {
		log.Fatalf("failed to get source object metadata, err: %v", err)
	}
	if headObject.ContentLength != nil {
		return aws.Uint64(uint64(*headObject.ContentLength))
	}
	return nil
}

func getS3Client(profile string) *s3.Client {
	// Using the SDK's default configuration, More about Configuring the AWS SDK
	// https://aws.github.io/aws-sdk-go-v2/docs/configuring-sdk/
	cfg, err := config.LoadDefaultConfig(context.TODO(), config.WithSharedConfigProfile(profile))
	if err != nil {
		log.Fatalf("failed to load aws config of profile: %s, err: %v", profile, err)
	}

	return s3.NewFromConfig(cfg, func(options *s3.Options) {
		options.RetryMaxAttempts = 5
	})
}

func main() {
	// REPLACE AS YOUR REQUIRED CONFIGURATION BEGIN
	sourceBucket := "source-bucket"
	destinationBucket := "destination-bucket"
	sourceKey := "source-key"
	destinationKey := "destination-key"
	sourceAccountProfile := "source-profile"
	destinationAccountProfile := "destination-profile"
	// REPLACE AS YOUR REQUIRED CONFIGURATION END

	sourceS3Client := getS3Client(sourceAccountProfile)
	destinationClient := getS3Client(destinationAccountProfile)

	reader, writer := io.Pipe()
	orderedWriter := &OrderedWriter{
		writer:   writer,
		expected: 0,
		size:     getFileSize(*sourceS3Client, sourceBucket, sourceKey),
	}
	var wg sync.WaitGroup
	wg.Add(1)
	go download(sourceS3Client, orderedWriter, sourceBucket, sourceKey)
	go upload(destinationClient, &wg, destinationBucket, destinationKey, reader)
	wg.Wait()

	log.Println("Download && Upload Success!")
}