feat(diff): диф-движок шаблон↔зона с Actionable и ReadOnly для NS/SOA

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/diff/diff.go

@@ -0,0 +1,79 @@
+package diff
+
+import "github.com/vasyakrg/dns-autoresolver/internal/model"
+
+type ChangeKind string
+
+const (
+	InSync ChangeKind = "in_sync"
+	Add    ChangeKind = "add"
+	Update ChangeKind = "update"
+	Delete ChangeKind = "delete"
+)
+
+// RecordDiff describes one RRset's deviation between template and zone.
+type RecordDiff struct {
+	Kind     ChangeKind
+	Type     model.RecordType
+	Name     string
+	Desired  *model.Record // nil for Delete
+	Actual   *model.Record // nil for Add
+	ReadOnly bool          // NS/SOA — shown but never applied
+}
+
+type Changeset struct {
+	Diffs []RecordDiff
+}
+
+// Actionable returns managed diffs that are not in sync.
+func (c Changeset) Actionable() []RecordDiff {
+	var out []RecordDiff
+	for _, d := range c.Diffs {
+		if d.ReadOnly || d.Kind == InSync {
+			continue
+		}
+		out = append(out, d)
+	}
+	return out
+}
+
+// Diff compares a template against the actual zone records.
+// Records present in the zone but absent from the template yield Delete.
+func Diff(template, actual []model.Record) Changeset {
+	current := index(actual)
+	seen := make(map[string]bool, len(template))
+	var diffs []RecordDiff
+
+	for _, t := range template {
+		tt := t
+		key := tt.Key()
+		seen[key] = true
+		ro := !tt.Type.Managed()
+		if a, ok := current[key]; ok {
+			ac := a
+			kind := Update
+			if tt.Equal(ac) {
+				kind = InSync
+			}
+			diffs = append(diffs, RecordDiff{Kind: kind, Type: tt.Type, Name: tt.Name, Desired: &tt, Actual: &ac, ReadOnly: ro})
+		} else {
+			diffs = append(diffs, RecordDiff{Kind: Add, Type: tt.Type, Name: tt.Name, Desired: &tt, ReadOnly: ro})
+		}
+	}
+	for _, a := range actual {
+		ac := a
+		if seen[ac.Key()] {
+			continue
+		}
+		diffs = append(diffs, RecordDiff{Kind: Delete, Type: ac.Type, Name: ac.Name, Actual: &ac, ReadOnly: !ac.Type.Managed()})
+	}
+	return Changeset{Diffs: diffs}
+}
+
+func index(recs []model.Record) map[string]model.Record {
+	m := make(map[string]model.Record, len(recs))
+	for _, r := range recs {
+		m[r.Key()] = r
+	}
+	return m
+}