Add Certificates page and Traefik API frontend client

backend/internal/config/file/diff.go

@@ -1,11 +1,13 @@
 package file
 
 import (
-	"fmt"
 	"strings"
+
+	"github.com/pmezard/go-difflib/difflib"
 )
 
-// UnifiedDiff returns a unified diff between old and new content
+// UnifiedDiff returns a proper unified diff between old and new content using LCS (Myers via difflib).
+// It handles insertions, deletions, replacements, moved blocks, empty and new files.
 func UnifiedDiff(filename, oldContent, newContent string) string {
 	if oldContent == newContent {
 		return ""
@@ -13,72 +15,45 @@ func UnifiedDiff(filename, oldContent, newContent string) string {
 	oldLines := splitLines(oldContent)
 	newLines := splitLines(newContent)
 
-	// Simple line-based diff: collect added/removed
-	// Use LCS-style? For MVP use simple prefix diff
-	var b strings.Builder
-	fmt.Fprintf(&b, "--- a/%s\n+++ b/%s\n", filename, filename)
-
-	// Find common prefix/suffix for brevity
-	// Instead do full: show removed then added
-	oldSet := make(map[string]int)
-	for _, l := range oldLines {
-		oldSet[l]++
+	diff := difflib.UnifiedDiff{
+		A:        difflib.SplitLines(oldContent),
+		B:        difflib.SplitLines(newContent),
+		FromFile: "a/" + filename,
+		ToFile:   "b/" + filename,
+		Context:  3,
 	}
-	newSet := make(map[string]int)
-	for _, l := range newLines {
-		newSet[l]++
+	// difflib.SplitLines handles trailing newlines correctly, but we also keep oldLines/newLines for
+	// fallback when one side is empty to ensure diff is still produced.
+	if len(oldLines) == 0 && len(newLines) == 0 {
+		return ""
 	}
-
-	// Very simple: if old empty (new file), show all as +
-	if len(oldLines) == 0 || (len(oldLines) == 1 && oldLines[0] == "") {
-		for _, l := range newLines {
-			fmt.Fprintf(&b, "+%s\n", l)
-		}
-		return b.String()
-	}
-	if len(newLines) == 0 {
-		for _, l := range oldLines {
-			fmt.Fprintf(&b, "-%s\n", l)
-		}
-		return b.String()
-	}
-
-	// For MVP, do line-by-line with +/- for changed lines
-	// Use diff library would be better, but avoid extra dep: implement simple
-	max := len(oldLines)
-	if len(newLines) > max {
-		max = len(newLines)
-	}
-	// Show hunks: 3 context lines? Simple: show all
-	for i := 0; i < max; i++ {
-		var o, n string
-		hasO := i < len(oldLines)
-		hasN := i < len(newLines)
-		if hasO {
-			o = oldLines[i]
-		}
-		if hasN {
-			n = newLines[i]
-		}
-		if hasO && hasN && o == n {
-			fmt.Fprintf(&b, " %s\n", o)
-		} else {
-			if hasO {
-				fmt.Fprintf(&b, "-%s\n", o)
-			}
-			if hasN {
-				fmt.Fprintf(&b, "+%s\n", n)
+	text, _ := difflib.GetUnifiedDiffString(diff)
+	// difflib returns empty string when no diff; ensure header is present for new/deleted files
+	if text == "" {
+		// Fallback minimal diff for edge cases difflib might consider empty
+		var b strings.Builder
+		b.WriteString("--- a/" + filename + "\n+++ b/" + filename + "\n")
+		if len(oldLines) == 0 {
+			for _, l := range newLines {
+				b.WriteString("+" + l + "\n")
 			}
+			return b.String()
 		}
+		if len(newLines) == 0 {
+			for _, l := range oldLines {
+				b.WriteString("-" + l + "\n")
+			}
+			return b.String()
+		}
+		return ""
 	}
-	return b.String()
+	return text
 }
 
 func splitLines(s string) []string {
 	if s == "" {
 		return []string{}
 	}
-	// Normalize line endings
 	s = strings.ReplaceAll(s, "\r\n", "\n")
 	return strings.Split(s, "\n")
 }