chainntfs: expand ChainNotifier interface

* The `NotificationTrigger` struct has been dropped. Instead we know
simply employ a non-blocking send over a chan struct. This moves the
responsibility of triggering callbacks a level above to the registering
client.

* Confirmation notifications also now have a counter part in order to
notify a caller of the scenario wherein a funding transaction drops out
of the chain due to a re-org. A “neagtiveConf” value will be sent to
the client over a channel in this case. This will allow a caller to
re-register for another confirmation notification. Note that due to
this scenario, callers should also register for notifications
concerning spends of the counterparty’s inputs to the funding
transaction. If a second spend (other than the funding) is detected,
the channel should be closed immediately.

* Notifications concerning spends now also include the spending
transaction, hash, and the input on the spending transaction at which
the outpoint is spent.

chainntfs/chainntfs.go

@@ -2,6 +2,7 @@ package chainntnfs
 
 import "github.com/btcsuite/btcd/wire"
 
+// ChainNotifier ...
 // TODO(roasbeef): finish
 //  * multiple backends for interface
 //   * btcd - websockets
@@ -12,14 +13,39 @@ import "github.com/btcsuite/btcd/wire"
 //   * SPV bloomfilter
 //   * other stuff maybe...
 type ChainNotifier interface {
-	RegisterConfirmationsNotification(txid *wire.ShaHash, numConfs uint32, trigger *NotificationTrigger) error
-	RegisterSpendNotification(outpoint *wire.OutPoint, trigger *NotificationTrigger) error
+	RegisterConfirmationsNtfn(txid *wire.ShaHash, numConfs uint32) (*ConfirmationEvent, error)
+	RegisterSpendNtfn(outpoint *wire.OutPoint) (*SpendEvent, error)
 
 	Start() error
 	Stop() error
 }
 
-type NotificationTrigger struct {
-	TriggerChan chan struct{}
-	Callback    func()
+// TODO(roasbeef): ln channels should request spend ntfns for counterparty's
+// inputs to funding tx also, consider channel closed if funding tx re-org'd
+// out and inputs double spent.
+
+// ConfirmationEvent ...
+type ConfirmationEvent struct {
+	Confirmed chan struct{} // MUST be buffered.
+
+	// TODO(roasbeef): all goroutines on ln channel updates should also
+	// have a struct chan that's closed if funding gets re-org out. Need
+	// to sync, to request another confirmation event ntfn, then re-open
+	// channel after confs.
+
+	NegativeConf chan uint32 // MUST be buffered.
+}
+
+// SpendDetail ...
+type SpendDetail struct {
+	SpentOutPoint *wire.OutPoint
+
+	SpendingTx        *wire.MsgTx
+	SpenderTxHash     *wire.ShaHash
+	SpenderInputIndex uint32
+}
+
+// SpendEvent ...
+type SpendEvent struct {
+	Spend chan *SpendDetail // MUST be buffered.
 }