package s3store

import (
	"io"
	"io/ioutil"
	"os"
)

// s3PartProducer converts a stream of bytes from the reader into a stream of files on disk
type s3PartProducer struct {
	store *S3Store
	files chan<- *os.File
	done  chan struct{}
	err   error
	r     io.Reader
}

func (spp *s3PartProducer) produce(partSize int64) {
	for {
		file, err := spp.nextPart(partSize)
		if err != nil {
			spp.err = err
			close(spp.files)
			return
		}
		if file == nil {
			close(spp.files)
			return
		}
		select {
		case spp.files <- file:
		case <-spp.done:
			close(spp.files)
			return
		}
	}
}

func (spp *s3PartProducer) nextPart(size int64) (*os.File, error) {
	// Create a temporary file to store the part
	file, err := ioutil.TempFile(spp.store.TemporaryDirectory, "tusd-s3-tmp-")
	if err != nil {
		return nil, err
	}

	limitedReader := io.LimitReader(spp.r, size)
	n, err := io.Copy(file, limitedReader)
	if err != nil {
		return nil, err
	}

	// If the entire request body is read and no more data is available,
	// io.Copy returns 0 since it is unable to read any bytes. In that
	// case, we can close the s3PartProducer.
	if n == 0 {
		cleanUpTempFile(file)
		return nil, nil
	}

	// Seek to the beginning of the file
	file.Seek(0, 0)

	return file, nil
}