Allow to omit large common parts in diff output

By default disabled, can be enabled and configured with `--context NUM`.

Author: njam

diff.go

@@ -4,38 +4,39 @@ import (
 	"fmt"
 	"io"
 	"strings"
+	"math"
 
 	"github.com/aryann/difflib"
 	"github.com/mgutz/ansi"
 
 	"github.com/databus23/helm-diff/manifest"
 )
 
-func diffManifests(oldIndex, newIndex map[string]*manifest.MappingResult, suppressedKinds []string, to io.Writer) {
+func diffManifests(oldIndex, newIndex map[string]*manifest.MappingResult, suppressedKinds []string, context int, to io.Writer) {
 	for key, oldContent := range oldIndex {
 		if newContent, ok := newIndex[key]; ok {
 			if oldContent.Content != newContent.Content {
 				// modified
 				fmt.Fprintf(to, ansi.Color("%s has changed:", "yellow")+"\n", key)
-				printDiff(suppressedKinds, oldContent.Kind, oldContent.Content, newContent.Content, to)
+				printDiff(suppressedKinds, oldContent.Kind, context, oldContent.Content, newContent.Content, to)
 			}
 		} else {
 			// removed
 			fmt.Fprintf(to, ansi.Color("%s has been removed:", "yellow")+"\n", key)
-			printDiff(suppressedKinds, oldContent.Kind, oldContent.Content, "", to)
+			printDiff(suppressedKinds, oldContent.Kind, context, oldContent.Content, "", to)
 		}
 	}
 
 	for key, newContent := range newIndex {
 		if _, ok := oldIndex[key]; !ok {
 			// added
 			fmt.Fprintf(to, ansi.Color("%s has been added:", "yellow")+"\n", key)
-			printDiff(suppressedKinds, newContent.Kind, "", newContent.Content, to)
+			printDiff(suppressedKinds, newContent.Kind, context, "", newContent.Content, to)
 		}
 	}
 }
 
-func printDiff(suppressedKinds []string, kind, before, after string, to io.Writer) {
+func printDiff(suppressedKinds []string, kind string, context int, before, after string, to io.Writer) {
 	diffs := difflib.Diff(strings.Split(before, "\n"), strings.Split(after, "\n"))
 
 	for _, ckind := range suppressedKinds {
@@ -46,16 +47,71 @@ func printDiff(suppressedKinds []string, kind, before, after string, to io.Write
 		}
 	}
 
-	for _, diff := range diffs {
-		text := diff.Payload
+	if context >= 0 {
+		distances := calculateDistances(diffs)
+		omitting := false
+		for i, diff := range diffs {
+			if distances[i] > context {
+				if !omitting {
+					fmt.Fprintln(to, "...")
+					omitting = true
+				}
+			} else {
+				omitting = false
+				printDiffRecord(diff, to)
+			}
+		}
+	} else {
+		for _, diff := range diffs {
+			printDiffRecord(diff, to)
+		}
+	}
+}
+
+func printDiffRecord(diff difflib.DiffRecord, to io.Writer) {
+	text := diff.Payload
+
+	switch diff.Delta {
+	case difflib.RightOnly:
+		fmt.Fprintf(to, "%s\n", ansi.Color("+ "+text, "green"))
+	case difflib.LeftOnly:
+		fmt.Fprintf(to, "%s\n", ansi.Color("- "+text, "red"))
+	case difflib.Common:
+		fmt.Fprintf(to, "%s\n", "  "+text)
+	}
+}
 
-		switch diff.Delta {
-		case difflib.RightOnly:
-			fmt.Fprintf(to, "%s\n", ansi.Color("+ "+text, "green"))
-		case difflib.LeftOnly:
-			fmt.Fprintf(to, "%s\n", ansi.Color("- "+text, "red"))
-		case difflib.Common:
-			fmt.Fprintf(to, "%s\n", "  "+text)
+// Calculate distance of every diff-line to the closest change
+func calculateDistances(diffs []difflib.DiffRecord) map[int]int {
+	distances := map[int]int{}
+
+	// Iterate forwards through diffs, set 'distance' based on closest 'change' before this line
+	change := -1
+	for i, diff := range diffs {
+		if diff.Delta != difflib.Common {
+			change = i
+		}
+		distance := math.MaxInt32
+		if change != -1 {
+			distance = i - change
+		}
+		distances[i] = distance
+	}
+
+	// Iterate backwards through diffs, reduce 'distance' based on closest 'change' after this line
+	change = -1
+	for i := len(diffs) - 1; i >= 0; i-- {
+		diff := diffs[i]
+		if diff.Delta != difflib.Common {
+			change = i
+		}
+		if change != -1 {
+			distance := change - i
+			if distance < distances[i] {
+				distances[i] = distance
+			}
 		}
 	}
+
+	return distances
 }

main.go

@@ -32,6 +32,7 @@ type diffCmd struct {
 	reuseValues     bool
 	resetValues     bool
 	suppressedKinds []string
+	outputContext   int
 }
 
 func main() {
@@ -77,6 +78,7 @@ func main() {
 	f.BoolVar(&diff.reuseValues, "reuse-values", false, "reuse the last release's values and merge in any new values")
 	f.BoolVar(&diff.resetValues, "reset-values", false, "reset the values to the ones built into the chart and merge in any new values")
 	f.StringArrayVar(&diff.suppressedKinds, "suppress", []string{}, "allows suppression of the values listed in the diff output")
+	f.IntVarP(&diff.outputContext, "context", "C", -1, "output NUM lines of context around changes")
 
 	if err := cmd.Execute(); err != nil {
 		os.Exit(1)
@@ -115,7 +117,7 @@ func (d *diffCmd) run() error {
 	currentSpecs := manifest.Parse(releaseResponse.Release.Manifest)
 	newSpecs := manifest.Parse(upgradeResponse.Release.Manifest)
 
-	diffManifests(currentSpecs, newSpecs, d.suppressedKinds, os.Stdout)
+	diffManifests(currentSpecs, newSpecs, d.suppressedKinds, d.outputContext, os.Stdout)
 
 	return nil
 }