kernel: Add notification interface

This commit is part of the libbitcoinkernel project and seeks to remove
the ChainstateManager's and, more generally, the kernel library's
dependency on interface_ui with options methods in this and the following
few commits. By removing interface_ui from the kernel library, its
dependency on boost is reduced to just boost::multi_index.

Define a new kernel notification class with virtual methods for
notifying about internal kernel events. Create a new file in the node
library for defining a function creating the default set of notification
methods such that these do not need to be re-defined all over the
codebase. As a first step, add a `blockTip` method, wrapping
`uiInterface.NotifyBlockTip`.

1 files changed, 26 insertions, 0 deletions

diff --git a/src/kernel/notifications_interface.h b/src/kernel/notifications_interface.h
new file mode 100644
index 0000000000..d90284fbea
--- /dev/null
+++ b/src/kernel/notifications_interface.h
@@ -0,0 +1,26 @@
+// Copyright (c) 2023 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_KERNEL_NOTIFICATIONS_INTERFACE_H
+#define BITCOIN_KERNEL_NOTIFICATIONS_INTERFACE_H
+
+class CBlockIndex;
+enum class SynchronizationState;
+
+namespace kernel {
+
+/**
+ * A base class defining functions for notifying about certain kernel
+ * events.
+ */
+class Notifications
+{
+public:
+    virtual ~Notifications(){};
+
+    virtual void blockTip(SynchronizationState state, CBlockIndex& index) {}
+};
+} // namespace kernel
+
+#endif // BITCOIN_KERNEL_NOTIFICATIONS_INTERFACE_H