package storage

import (
	"context"
	"fmt"
	"io"
)

// WriterDownloader is implemented by storage backends that stream an object
// into a caller-owned file handle.
type WriterDownloader interface {
	DownloadTo(ctx context.Context, key string, destination io.Writer) error
}

// DownloadTo streams one object into destination. Destination-confined callers
// require this capability rather than granting a backend a mutable pathname.
func DownloadTo(ctx context.Context, store ObjectStore, key string, destination io.Writer) error {
	writer, ok := store.(WriterDownloader)
	if !ok {
		return fmt.Errorf("object store does not support handle-confined downloads")
	}
	return writer.DownloadTo(ctx, key, destination)
}