podman/vendor/github.com/containers/common/libimage/image_tree.go

package libimage

import (
	"fmt"
	"strings"

	"github.com/disiqueira/gotree/v3"
	"github.com/docker/go-units"
)

// Tree generates a tree for the specified image and its layers.  Use
// `traverseChildren` to traverse the layers of all children.  By default, only
// layers of the image are printed.
func (i *Image) Tree(traverseChildren bool) (string, error) {
	// NOTE: a string builder prevents us from copying to much data around
	// and compile the string when and where needed.
	sb := &strings.Builder{}

	// First print the pretty header for the target image.
	size, err := i.Size()
	if err != nil {
		return "", err
	}
	repoTags, err := i.RepoTags()
	if err != nil {
		return "", err
	}

	fmt.Fprintf(sb, "Image ID: %s\n", i.ID()[:12])
	fmt.Fprintf(sb, "Tags:     %s\n", repoTags)
	fmt.Fprintf(sb, "Size:     %v\n", units.HumanSizeWithPrecision(float64(size), 4))
	if i.TopLayer() != "" {
		fmt.Fprintf(sb, "Image Layers")
	} else {
		fmt.Fprintf(sb, "No Image Layers")
	}

	layerTree, err := i.runtime.layerTree()
	if err != nil {
		return "", err
	}
	imageNode := layerTree.node(i.TopLayer())

	// Traverse the entire tree down to all children.
	if traverseChildren {
		tree := gotree.New(sb.String())
		if err := imageTreeTraverseChildren(imageNode, tree); err != nil {
			return "", err
		}
		return tree.Print(), nil
	}

	// Walk all layers of the image and assemlbe their data.  Note that the
	// tree is constructed in reverse order to remain backwards compatible
	// with Podman.
	contents := []string{}
	for parentNode := imageNode; parentNode != nil; parentNode = parentNode.parent {
		if parentNode.layer == nil {
			break // we're done
		}
		var tags string
		repoTags, err := parentNode.repoTags()
		if err != nil {
			return "", err
		}
		if len(repoTags) > 0 {
			tags = fmt.Sprintf(" Top Layer of: %s", repoTags)
		}
		content := fmt.Sprintf("ID: %s Size: %7v%s", parentNode.layer.ID[:12], units.HumanSizeWithPrecision(float64(parentNode.layer.UncompressedSize), 4), tags)
		contents = append(contents, content)
	}
	contents = append(contents, sb.String())

	tree := gotree.New(contents[len(contents)-1])
	for i := len(contents) - 2; i >= 0; i-- {
		tree.Add(contents[i])
	}

	return tree.Print(), nil
}

func imageTreeTraverseChildren(node *layerNode, parent gotree.Tree) error {
	var tags string
	repoTags, err := node.repoTags()
	if err != nil {
		return err
	}
	if len(repoTags) > 0 {
		tags = fmt.Sprintf(" Top Layer of: %s", repoTags)
	}

	content := fmt.Sprintf("ID: %s Size: %7v%s", node.layer.ID[:12], units.HumanSizeWithPrecision(float64(node.layer.UncompressedSize), 4), tags)

	var newTree gotree.Tree
	if node.parent == nil || len(node.parent.children) <= 1 {
		// No parent or no siblings, so we can go linear.
		parent.Add(content)
		newTree = parent
	} else {
		// Each siblings gets a new tree, so we can branch.
		newTree = gotree.New(content)
		parent.AddTree(newTree)
	}

	for i := range node.children {
		child := node.children[i]
		if err := imageTreeTraverseChildren(child, newTree); err != nil {
			return err
		}
	}

	return nil
}