From 2712c1017e0a6d82ca2e1b48044bb1189faf7634 Mon Sep 17 00:00:00 2001
From: Alex Goodman <wagoodman@gmail.com>
Date: Mon, 7 Oct 2019 12:41:57 -0400
Subject: [PATCH] remove reverse iteration for layer display and processing

---
 dive/image/docker/image_archive.go   | 16 ++++++----------
 dive/image/podman/image_directory.go | 28 ++++++++++++----------------
 dive/image/podman/layer.go           | 10 +++++++---
 runtime/ui/layer_controller.go       |  4 +---
 4 files changed, 26 insertions(+), 32 deletions(-)

diff --git a/dive/image/docker/image_archive.go b/dive/image/docker/image_archive.go
index 106bd4a..8d93301 100644
--- a/dive/image/docker/image_archive.go
+++ b/dive/image/docker/image_archive.go
@@ -147,16 +147,13 @@ func (img *ImageArchive) ToImage() (*image.Image, error) {
 	}
 
 	// build the layers array
-	layers := make([]*image.Layer, len(trees))
+	layers := make([]*image.Layer, 0)
 
 	// note that the resolver config stores images in reverse chronological order, so iterate backwards through layers
 	// as you iterate chronologically through history (ignoring history items that have no layer contents)
 	// Note: history is not required metadata in a docker image!
-	tarPathIdx := 0
 	histIdx := 0
-	for layerIdx := len(trees) - 1; layerIdx >= 0; layerIdx-- {
-		tree := trees[(len(trees)-1)-layerIdx]
-
+	for idx, tree := range trees {
 		// ignore empty layers, we are only observing layers with content
 		historyObj := historyEntry{
 			CreatedBy: "(missing)",
@@ -176,14 +173,13 @@ func (img *ImageArchive) ToImage() (*image.Image, error) {
 
 		dockerLayer := layer{
 			history: historyObj,
-			index:   tarPathIdx,
-			tree:    trees[layerIdx],
+			index:   idx,
+			tree:    tree,
 		}
-		layers[layerIdx] = dockerLayer.ToLayer()
-
-		tarPathIdx++
+		layers = append(layers, dockerLayer.ToLayer())
 	}
 
+
 	return &image.Image{
 		Trees: trees,
 		Layers: layers,
diff --git a/dive/image/podman/image_directory.go b/dive/image/podman/image_directory.go
index 4e2d1d5..333e967 100644
--- a/dive/image/podman/image_directory.go
+++ b/dive/image/podman/image_directory.go
@@ -99,29 +99,25 @@ func processLayer(name, rootDir string) (*filetree.FileTree, error)  {
 
 func (img *ImageDirectoryRef) ToImage() (*image.Image, error) {
 	trees := make([]*filetree.FileTree, 0)
+	layers := make([]*image.Layer, 0)
+
 	// build the content tree
-	// todo: this isn't needed!
-	for _, id := range img.layerOrder {
-		tr, exists := img.treeMap[id]
-		if exists {
-			trees = append(trees, tr)
-			continue
-		}
-		return nil, fmt.Errorf("could not find '%s' in parsed trees", id)
-	}
-
-	layers := make([]*image.Layer, len(trees))
-
-	// note that the resolver config stores images in reverse chronological order, so iterate backwards through layers
-	// as you iterate chronologically through history (ignoring history items that have no layer contents)
-	// Note: history is not required metadata in an OCI image!
 	for layerIdx, id := range img.layerOrder {
+		tr, exists := img.treeMap[id]
+		if !exists {
+			return nil, fmt.Errorf("could not find '%s' in parsed trees", id)
+		}
+		trees = append(trees, tr)
+
+		// note that the resolver config stores images in reverse chronological order, so iterate backwards through layers
+		// as you iterate chronologically through history (ignoring history items that have no layer contents)
+		// Note: history is not required metadata in an OCI image!
 		podmanLayer := layer{
 			obj:     img.layerMap[id],
 			index:   layerIdx,
 			tree:    trees[layerIdx],
 		}
-		layers[layerIdx] = podmanLayer.ToLayer()
+		layers = append(layers, podmanLayer.ToLayer())
 	}
 
 	return &image.Image{
diff --git a/dive/image/podman/layer.go b/dive/image/podman/layer.go
index de173a5..daad3d3 100644
--- a/dive/image/podman/layer.go
+++ b/dive/image/podman/layer.go
@@ -1,6 +1,7 @@
 package podman
 
 import (
+	"context"
 	podmanImage "github.com/containers/libpod/libpod/image"
 	"github.com/wagoodman/dive/dive/filetree"
 	"github.com/wagoodman/dive/dive/image"
@@ -16,9 +17,12 @@ type layer struct {
 
 // ShortId returns the truncated id of the current layer.
 func (l *layer) Command() string {
-	if len(l.obj.ImageData.History) > 0 {
-		hist := l.obj.ImageData.History
-		return strings.TrimPrefix(hist[len(hist)-1].CreatedBy, "/bin/sh -c ")
+	history, err := l.obj.History(context.TODO())
+	if err != nil {
+		return "error: " + err.Error()
+	}
+	if len(history) > 0 {
+		return strings.TrimPrefix(history[0].CreatedBy, "/bin/sh -c ")
 	}
 	return "unknown"
 }
diff --git a/runtime/ui/layer_controller.go b/runtime/ui/layer_controller.go
index b1868c9..56cce36 100644
--- a/runtime/ui/layer_controller.go
+++ b/runtime/ui/layer_controller.go
@@ -291,9 +291,7 @@ func (controller *LayerController) Render() error {
 
 		// update contents
 		controller.view.Clear()
-		for revIdx := len(controller.Layers) - 1; revIdx >= 0; revIdx-- {
-			layer := controller.Layers[revIdx]
-			idx := (len(controller.Layers) - 1) - revIdx
+		for idx, layer := range controller.Layers {
 
 			layerStr := layer.String()
 			compareBar := controller.renderCompareBar(idx)