feat: ETLng loader basics (#1808)

For #1597

src/etlng/impl/AmendmentBlockHandler.cpp

@@ -0,0 +1,56 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2024, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#include "etlng/impl/AmendmentBlockHandler.hpp"
+
+#include "etl/SystemState.hpp"
+#include "util/async/AnyExecutionContext.hpp"
+#include "util/log/Logger.hpp"
+
+#include <chrono>
+#include <functional>
+#include <utility>
+
+namespace etlng::impl {
+
+AmendmentBlockHandler::ActionType const AmendmentBlockHandler::kDEFAULT_AMENDMENT_BLOCK_ACTION = []() {
+    static util::Logger const log{"ETL"};  // NOLINT(readability-identifier-naming)
+    LOG(log.fatal()) << "Can't process new ledgers: The current ETL source is not compatible with the version of "
+                     << "the libxrpl Clio is currently using. Please upgrade Clio to a newer version.";
+};
+
+AmendmentBlockHandler::AmendmentBlockHandler(
+    util::async::AnyExecutionContext&& ctx,
+    etl::SystemState& state,
+    std::chrono::steady_clock::duration interval,
+    ActionType action
+)
+    : state_{std::ref(state)}, interval_{interval}, ctx_{std::move(ctx)}, action_{std::move(action)}
+{
+}
+
+void
+AmendmentBlockHandler::notifyAmendmentBlocked()
+{
+    state_.get().isAmendmentBlocked = true;
+    if (not operation_.has_value())
+        operation_.emplace(ctx_.executeRepeatedly(interval_, action_));
+}
+
+}  // namespace etlng::impl