Add pure secret-diff logic (kctl.DiffSecretValues) with unit tests

internal/kctl/diff.go

@@ -0,0 +1,51 @@
+package kctl
+
+import "sort"
+
+// SecretDiffEntry represents the comparison of one key between two secret
+// sources (e.g. AWS Secrets Manager vs. a Kubernetes Secret).
+type SecretDiffEntry struct {
+	Key   string
+	Left  string // e.g. the AWS Secrets Manager value
+	Right string // e.g. the decoded Kubernetes secret value
+	Match bool
+}
+
+// DiffSecretValues compares two key/value maps and returns a sorted list of
+// diff entries covering the union of keys present in either map. A key that
+// only exists on one side is still reported, with the missing side left as
+// an empty string and Match set to false (unless both sides happen to be
+// empty strings).
+func DiffSecretValues(left, right map[string]string) []SecretDiffEntry {
+	seen := map[string]bool{}
+	for k := range left {
+		seen[k] = true
+	}
+	for k := range right {
+		seen[k] = true
+	}
+
+	keys := make([]string, 0, len(seen))
+	for k := range seen {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+
+	result := make([]SecretDiffEntry, 0, len(keys))
+	for _, k := range keys {
+		l := left[k]
+		r := right[k]
+		result = append(result, SecretDiffEntry{Key: k, Left: l, Right: r, Match: l == r})
+	}
+	return result
+}
+
+// AnyMismatch reports whether at least one diff entry does not match.
+func AnyMismatch(entries []SecretDiffEntry) bool {
+	for _, e := range entries {
+		if !e.Match {
+			return true
+		}
+	}
+	return false
+}