package platform

import (
	"context"
	"fmt"
	"io"
	"net/http"
	"os"
)

// Download fetches url into destPath atomically (temp file + rename) with
// the given file mode. Any non-2xx response returns an error and leaves
// no file behind.
func Download(ctx context.Context, url, destPath string, mode os.FileMode) error {
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
	if err != nil {
		return err
	}
	resp, err := http.DefaultClient.Do(req)
	if err != nil {
		return err
	}
	defer resp.Body.Close()
	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		return fmt.Errorf("download %s: http %d", url, resp.StatusCode)
	}
	tmp := destPath + ".tmp"
	f, err := os.OpenFile(tmp, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, mode)
	if err != nil {
		return err
	}
	if _, err := io.Copy(f, resp.Body); err != nil {
		f.Close()
		os.Remove(tmp)
		return err
	}
	if err := f.Close(); err != nil {
		os.Remove(tmp)
		return err
	}
	return os.Rename(tmp, destPath)
}