package media

import (
	"bytes"
	"context"
	"fmt"
	"log"

	"github.com/aws/aws-sdk-go-v2/aws"
	"github.com/aws/aws-sdk-go-v2/service/s3"
	"github.com/aws/aws-sdk-go-v2/service/s3/types"
)

// multipartUploadWriter is a Writer that uploads transparently to an S3 bucket
// in 5MB parts. It buffers data internally until a part is ready to send over
// the network. Parts are sent as soon as they exceed the minimum part size of
// 5MB.
//
// The caller must call either Complete() or Abort() after finishing writing.
// Failure to do so will leave S3 in an inconsistent state.
type multipartUploadWriter struct {
	ctx                      context.Context
	s3                       S3Client
	buf                      *bytes.Buffer
	bucket, key, contentType string
	uploadID                 string
	completedParts           []types.CompletedPart
	bytesUploaded            int64
}

const targetPartSizeBytes = 5 * 1024 * 1024 // 5MB

// newMultipartUploadWriter creates a new multipart upload writer, including
// creating the upload on S3. Either Complete or Abort must be called after
// calling this function.
func newMultipartUploadWriter(ctx context.Context, s3Client S3Client, bucket, key, contentType string) (*multipartUploadWriter, error) {
	input := s3.CreateMultipartUploadInput{
		Bucket:      aws.String(bucket),
		Key:         aws.String(key),
		ContentType: aws.String(contentType),
	}

	output, err := s3Client.CreateMultipartUpload(ctx, &input)
	if err != nil {
		return nil, fmt.Errorf("error creating multipart upload: %v", err)
	}

	const bufferOverflowSize = 16_384
	b := make([]byte, 0, targetPartSizeBytes+bufferOverflowSize)

	return &multipartUploadWriter{
		ctx:         ctx,
		s3:          s3Client,
		buf:         bytes.NewBuffer(b),
		bucket:      bucket,
		key:         key,
		contentType: contentType,
		uploadID:    *output.UploadId,
	}, nil
}

func (u *multipartUploadWriter) Write(p []byte) (int, error) {
	n, err := u.buf.Write(p)
	if err != nil {
		return n, fmt.Errorf("error writing to buffer: %v", err)
	}

	if u.buf.Len() >= targetPartSizeBytes {
		partLen := u.buf.Len()
		log.Printf("uploading part num = %d, len = %d", u.partNum(), partLen)

		input := s3.UploadPartInput{
			Body:          u.buf,
			Bucket:        aws.String(u.bucket),
			Key:           aws.String(u.key),
			PartNumber:    u.partNum(),
			UploadId:      aws.String(u.uploadID),
			ContentLength: int64(partLen),
		}

		output, uploadErr := u.s3.UploadPart(u.ctx, &input)
		if uploadErr != nil {
			// TODO: retry on failure
			return n, fmt.Errorf("error uploading part: %v", uploadErr)
		}

		log.Printf("uploaded part num = %d, etag = %s, bytes = %d", u.partNum(), *output.ETag, partLen)

		u.completedParts = append(u.completedParts, types.CompletedPart{ETag: output.ETag, PartNumber: u.partNum()})
		u.bytesUploaded += int64(partLen)
	}

	return n, err
}

func (u *multipartUploadWriter) partNum() int32 {
	return int32(len(u.completedParts) + 1)
}

// Abort aborts the upload process, cancelling the upload on S3. It accepts a
// separate context to the associated writer in case it is called during
// cleanup after the original context was killed.
func (u *multipartUploadWriter) Abort(ctx context.Context) error {
	input := s3.AbortMultipartUploadInput{
		Bucket:   aws.String(u.bucket),
		Key:      aws.String(u.key),
		UploadId: aws.String(u.uploadID),
	}

	_, err := u.s3.AbortMultipartUpload(ctx, &input)
	if err != nil {
		return fmt.Errorf("error aborting upload: %v", err)
	}

	log.Printf("aborted upload, key = %s, bytesUploaded = %d", u.key, u.bytesUploaded)

	return nil
}

// Complete completes the upload process, finalizing the upload on S3.
// If no parts have been successfully uploaded, then Abort() will be called
// transparently.
func (u *multipartUploadWriter) Complete() error {
	if len(u.completedParts) == 0 {
		return u.Abort(u.ctx)
	}

	input := s3.CompleteMultipartUploadInput{
		Bucket:   aws.String(u.bucket),
		Key:      aws.String(u.key),
		UploadId: aws.String(u.uploadID),
		MultipartUpload: &types.CompletedMultipartUpload{
			Parts: u.completedParts,
		},
	}

	_, err := u.s3.CompleteMultipartUpload(u.ctx, &input)
	if err != nil {
		return fmt.Errorf("error completing upload: %v", err)
	}

	log.Printf("completed upload, key = %s, bytesUploaded = %d", u.key, u.bytesUploaded)
	return nil
}