package docker

import (
	"errors"
	"fmt"
	"os"
	"os/exec"
	"path/filepath"
)

type IClient interface {
	Save(imageName, dest string) (string, error)
}

var ErrDockerClientSave = errors.New("unable to save image into tar")

// Client is a simple Docker client wrapping the local Docker daemon.
// It does not use the Docker API but instead shell command and collect the output.
//
// NOTE: for now, it's ok, it only needs one command so, no need to add a fat dedicated
// library with full Docker client API.
type Client struct{}

var _ IClient = (*Client)(nil)

func NewClient() Client {
	return Client{}
}

// Save saves the `imageName` (tag included) in tar format in the target directory: `dest`.
// The `dest` directory must exist with correct permissions.
func (c *Client) Save(imageName, dest string) (string, error) {
	destInfo, err := os.Stat(dest)
	if err != nil {
		return "", fmt.Errorf("unable to stat file, dir=%s, err=%v", dest, err)
	}

	if !destInfo.IsDir() {
		return "", fmt.Errorf("dest file must be a directory, dir=%s, err=%v", dest, err)
	}

	tarFile := fmt.Sprintf("%s.tar", imageName)

	cmd := exec.Command("docker", "save", "-o", tarFile, imageName)
	cmd.Dir = dest
	if _, err := cmd.Output(); err != nil {
		return "", fmt.Errorf(
			"%w, dir=%s, image=%s, err=%v",
			ErrDockerClientSave,
			dest,
			imageName,
			err,
		)
	}

	return filepath.Join(dest, tarFile), nil
}