From c1a8f2d0f0214e3a57ae1a77d60f02cf52fb7b75 Mon Sep 17 00:00:00 2001
From: Dmitriy Shilin <dshil@fastmail.com>
Date: Fri, 25 Sep 2026 17:47:11 +0200
Subject: [PATCH] Introduce functional value monitor

---
 components/ocs_core/func_value_monitor.h      | 50 +++++++++++
 components/ocs_core/test/CMakeLists.txt       |  1 +
 .../ocs_core/test/test_func_value_monitor.cpp | 88 +++++++++++++++++++
 3 files changed, 139 insertions(+)
 create mode 100644 components/ocs_core/func_value_monitor.h
 create mode 100644 components/ocs_core/test/test_func_value_monitor.cpp

diff --git a/components/ocs_core/func_value_monitor.h b/components/ocs_core/func_value_monitor.h
new file mode 100644
index 00000000..cd420c1d
--- /dev/null
+++ b/components/ocs_core/func_value_monitor.h
@@ -0,0 +1,50 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Tendry Lab
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#pragma once
+
+#include <functional>
+
+#include "ocs_core/ivalue_monitor.h"
+#include "ocs_core/noncopyable.h"
+#include "ocs_status/code.h"
+
+namespace ocs {
+namespace core {
+
+//! Value monitor that delegates the update to the provided function.
+template <typename T>
+class FuncValueMonitor : public IValueMonitor<T>, private NonCopyable<> {
+public:
+    //! Function to update the underlying monitor.
+    using Func = std::function<status::StatusCode()>;
+
+    //! Initialize.
+    //!
+    //! @params
+    //!  - @p monitor to get the latest sampled value.
+    //!  - @p func to update the @p monitor, e.g. asynchronously on a specific task.
+    FuncValueMonitor(IValueMonitor<T>& monitor, Func func)
+        : monitor_(monitor)
+        , func_(func) {
+    }
+
+    //! Get latest sampled value from the underlying monitor.
+    T get() const override {
+        return monitor_.get();
+    }
+
+    //! Call the function to update the underlying monitor.
+    status::StatusCode update() override {
+        return func_();
+    }
+
+private:
+    IValueMonitor<T>& monitor_;
+    Func func_;
+};
+
+} // namespace core
+} // namespace ocs
diff --git a/components/ocs_core/test/CMakeLists.txt b/components/ocs_core/test/CMakeLists.txt
index 31e18871..cc883484 100644
--- a/components/ocs_core/test/CMakeLists.txt
+++ b/components/ocs_core/test/CMakeLists.txt
@@ -9,6 +9,7 @@ idf_component_register(
     "test_byte_writer.cpp"
     "test_byte_reader.cpp"
     "test_byte_transceiver.cpp"
+    "test_func_value_monitor.cpp"
 
     REQUIRES
     "unity"
diff --git a/components/ocs_core/test/test_func_value_monitor.cpp b/components/ocs_core/test/test_func_value_monitor.cpp
new file mode 100644
index 00000000..2ea2386a
--- /dev/null
+++ b/components/ocs_core/test/test_func_value_monitor.cpp
@@ -0,0 +1,88 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Tendry Lab
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include "unity.h"
+
+#include "ocs_core/func_value_monitor.h"
+#include "ocs_core/noncopyable.h"
+
+namespace ocs {
+namespace core {
+
+namespace {
+
+class TestValueMonitor : public IValueMonitor<int>, private NonCopyable<> {
+public:
+    int get() const override {
+        return value;
+    }
+
+    status::StatusCode update() override {
+        ++update_call_count;
+
+        return status::StatusCode::OK;
+    }
+
+    int value { 0 };
+    size_t update_call_count { 0 };
+};
+
+} // namespace
+
+TEST_CASE("Func value monitor: get value from the underlying monitor",
+          "[func_value_monitor], [ocs_core]") {
+    TestValueMonitor monitor;
+    size_t func_call_count = 0;
+
+    FuncValueMonitor<int> func_monitor(monitor, [&func_call_count]() {
+        ++func_call_count;
+
+        return status::StatusCode::OK;
+    });
+
+    monitor.value = 42;
+    TEST_ASSERT_EQUAL(42, func_monitor.get());
+
+    monitor.value = -1;
+    TEST_ASSERT_EQUAL(-1, func_monitor.get());
+
+    TEST_ASSERT_EQUAL(0, func_call_count);
+    TEST_ASSERT_EQUAL(0, monitor.update_call_count);
+}
+
+TEST_CASE("Func value monitor: update calls the function",
+          "[func_value_monitor], [ocs_core]") {
+    TestValueMonitor monitor;
+    size_t func_call_count = 0;
+
+    FuncValueMonitor<int> func_monitor(monitor, [&func_call_count]() {
+        ++func_call_count;
+
+        return status::StatusCode::OK;
+    });
+
+    TEST_ASSERT_EQUAL(status::StatusCode::OK, func_monitor.update());
+    TEST_ASSERT_EQUAL(1, func_call_count);
+
+    TEST_ASSERT_EQUAL(status::StatusCode::OK, func_monitor.update());
+    TEST_ASSERT_EQUAL(2, func_call_count);
+
+    // The underlying monitor is only updated by the function.
+    TEST_ASSERT_EQUAL(0, monitor.update_call_count);
+}
+
+TEST_CASE("Func value monitor: update propagates the function failure",
+          "[func_value_monitor], [ocs_core]") {
+    TestValueMonitor monitor;
+
+    FuncValueMonitor<int> func_monitor(monitor, []() {
+        return status::StatusCode::Error;
+    });
+
+    TEST_ASSERT_EQUAL(status::StatusCode::Error, func_monitor.update());
+}
+
+} // namespace core
+} // namespace ocs