From 163ad879f94a137fb566f7bef11c77885bbf4615 Mon Sep 17 00:00:00 2001
From: Steve Hoeksema <steve@kotiri.com>
Date: Fri, 5 Nov 2021 10:02:27 +1300
Subject: [PATCH] kv: Conditional delete and purge

---
 kv.go           | 76 ++++++++++++++++++++++++++++++++++++++-----------
 test/kv_test.go |  6 +++-
 2 files changed, 64 insertions(+), 18 deletions(-)

diff --git a/kv.go b/kv.go
index deaefde2a..765ab41a2 100644
--- a/kv.go
+++ b/kv.go
@@ -45,14 +45,18 @@ type KeyValue interface {
 	Put(key string, value []byte) (revision uint64, err error)
 	// PutString will place the string for the key into the store.
 	PutString(key string, value string) (revision uint64, err error)
-	// Create will add the key/value pair iff it does not exist.
+	// Create will add the key/value pair if it does not exist.
 	Create(key string, value []byte) (revision uint64, err error)
-	// Update will update the value iff the latest revision matches.
+	// Update will update the value if the latest revision matches.
 	Update(key string, value []byte, last uint64) (revision uint64, err error)
 	// Delete will place a delete marker and leave all revisions.
 	Delete(key string) error
+	// DeleteCond will place a delete marker and leave all revision if the latest revision matches.
+	DeleteCond(key string, last uint64) error
 	// Purge will place a delete marker and remove all previous revisions.
 	Purge(key string) error
+	// PurgeCond will place a delete marker and remove all previous revisions if the latest revision matches.
+	PurgeCond(key string, last uint64) error
 	// Watch for any updates to keys that match the keys argument which could include wildcards.
 	// Watch will send a nil entry when it has received all initial values.
 	Watch(keys string, opts ...WatchOpt) (KeyWatcher, error)
@@ -437,7 +441,7 @@ func (kv *kvs) PutString(key string, value string) (revision uint64, err error)
 	return kv.Put(key, []byte(value))
 }
 
-// Create will add the key/value pair iff it does not exist.
+// Create will add the key/value pair if it does not exist.
 func (kv *kvs) Create(key string, value []byte) (revision uint64, err error) {
 	v, err := kv.Update(key, value, 0)
 	if err == nil {
@@ -453,7 +457,7 @@ func (kv *kvs) Create(key string, value []byte) (revision uint64, err error) {
 	return 0, err
 }
 
-// Update will update the value iff the latest revision matches.
+// Update will update the value if the latest revision matches.
 func (kv *kvs) Update(key string, value []byte, revision uint64) (uint64, error) {
 	if !keyValid(key) {
 		return 0, ErrInvalidKey
@@ -475,17 +479,63 @@ func (kv *kvs) Update(key string, value []byte, revision uint64) (uint64, error)
 
 // Delete will place a delete marker and leave all revisions.
 func (kv *kvs) Delete(key string) error {
-	return kv.delete(key, false)
+	m, err := kv.buildDelete(key)
+	if err != nil {
+		return err
+	}
+
+	m.Header.Set(kvop, kvdel)
+
+	_, err = kv.js.PublishMsg(m)
+	return err
+}
+
+// DeleteCond will place a delete marker and leave all revisions if the latest revision matches.
+func (kv *kvs) DeleteCond(key string, revision uint64) error {
+	m, err := kv.buildDelete(key)
+	if err != nil {
+		return err
+	}
+
+	m.Header.Set(kvop, kvdel)
+	m.Header.Set(ExpectedLastSubjSeqHdr, strconv.FormatUint(revision, 10))
+
+	_, err = kv.js.PublishMsg(m)
+	return err
 }
 
 // Purge will remove the key and all revisions.
 func (kv *kvs) Purge(key string) error {
-	return kv.delete(key, true)
+	m, err := kv.buildDelete(key)
+	if err != nil {
+		return err
+	}
+
+	m.Header.Set(kvop, kvpurge)
+	m.Header.Set(MsgRollup, MsgRollupSubject)
+
+	_, err = kv.js.PublishMsg(m)
+	return err
 }
 
-func (kv *kvs) delete(key string, purge bool) error {
+// PurgeCond will remove the key and all revisions if the latest revision matches.
+func (kv *kvs) PurgeCond(key string, revision uint64) error {
+	m, err := kv.buildDelete(key)
+	if err != nil {
+		return err
+	}
+
+	m.Header.Set(kvop, kvpurge)
+	m.Header.Set(MsgRollup, MsgRollupSubject)
+	m.Header.Set(ExpectedLastSubjSeqHdr, strconv.FormatUint(revision, 10))
+
+	_, err = kv.js.PublishMsg(m)
+	return err
+}
+
+func (kv *kvs) buildDelete(key string) (*Msg, error) {
 	if !keyValid(key) {
-		return ErrInvalidKey
+		return nil, ErrInvalidKey
 	}
 
 	var b strings.Builder
@@ -494,15 +544,7 @@ func (kv *kvs) delete(key string, purge bool) error {
 
 	// DEL op marker. For watch functionality.
 	m := NewMsg(b.String())
-
-	if purge {
-		m.Header.Set(kvop, kvpurge)
-		m.Header.Set(MsgRollup, MsgRollupSubject)
-	} else {
-		m.Header.Set(kvop, kvdel)
-	}
-	_, err := kv.js.PublishMsg(m)
-	return err
+	return m, nil
 }
 
 // PurgeDeletes will remove all current delete markers.
diff --git a/test/kv_test.go b/test/kv_test.go
index 6c8602603..02c62ced7 100644
--- a/test/kv_test.go
+++ b/test/kv_test.go
@@ -66,9 +66,13 @@ func TestKeyValueBasics(t *testing.T) {
 	if r != 3 {
 		t.Fatalf("Expected 3 for the revision, got %d", r)
 	}
+	err = kv.DeleteCond("name", 4)
+	expectErr(t, err)
+	err = kv.DeleteCond("name", 3)
+	expectOk(t, err)
 
 	// Conditional Updates.
-	r, err = kv.Update("name", []byte("rip"), 3)
+	r, err = kv.Update("name", []byte("rip"), 4)
 	expectOk(t, err)
 	_, err = kv.Update("name", []byte("ik"), 3)
 	expectErr(t, err)