backup: pre-hardening baseline

backend/internal/config/file/diff.go

@@ -0,0 +1,84 @@
+package file
+
+import (
+	"fmt"
+	"strings"
+)
+
+// UnifiedDiff returns a unified diff between old and new content
+func UnifiedDiff(filename, oldContent, newContent string) string {
+	if oldContent == newContent {
+		return ""
+	}
+	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]++
+	}
+	newSet := make(map[string]int)
+	for _, l := range newLines {
+		newSet[l]++
+	}
+
+	// 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)
+			}
+		}
+	}
+	return b.String()
+}
+
+func splitLines(s string) []string {
+	if s == "" {
+		return []string{}
+	}
+	// Normalize line endings
+	s = strings.ReplaceAll(s, "\r\n", "\n")
+	return strings.Split(s, "\n")
+}