Add notifying parameter callbacks

inc/Helpers/NotifyParameter.hpp

+#ifndef ECSS_SERVICES_NOTIFYPARAMETER_HPP
+#define ECSS_SERVICES_NOTIFYPARAMETER_HPP
+
+#include <etl/optional.h>
+#include <functional>
+#include "Parameter.hpp"
+
+/**
+ * A Notifying parameter will call a function whenever its value is written to.
+ *
+ * This is useful for updating the state of things when a parameter is changed,
+ * for example to disable/enable peripherals, to make configuration changes etc.
+ *
+ * @warning Calling NotifyParameter::setValue will *not* call the notifier
+ * function. You should use setValueLoudly for this purpose instead.
+ *
+ * @tparam DataType The data type of the parameter's value
+ */
+template <typename DataType>
+class NotifyParameter : public Parameter<DataType> {
+public:
+	using Notifier = std::function<void(const DataType&)>;
+	using Parent = Parameter<DataType>;
+
+	/**
+	 * Constructor without a notifier function. Nothing will then happen when the parameter is updated.
+	 */
+	explicit NotifyParameter(DataType initialValue) : Parent(initialValue) {}
+
+	/**
+	 * Constructor with a default notifier function.
+	 */
+	NotifyParameter(DataType initialValue, const Notifier& notifier) : Parent(initialValue), notifier(notifier) {}
+
+	/**
+	 * Same as Parameter::setValue(), but also calls the NotifyParameter::notifier function, if it
+	 * exists.
+	 */
+	inline void setValueLoudly(DataType value) {
+		Parent::setValue(value);
+
+		if (notifier) {
+			(*notifier)(Parent::currentValue);
+		}
+	}
+
+	/**
+	 * Call the notifier if it exists, without updating the value
+	 */
+	inline void notify() {
+		if (notifier) {
+			(*notifier)(Parent::currentValue);
+		}
+	}
+
+	inline void setValueFromMessage(Message& message) override {
+		Parent::setValueFromMessage(message);
+
+		if (notifier) {
+			(*notifier)(Parent::currentValue);
+		}
+	}
+
+	/**
+	 * Set the notifier function, to be called whenever the value of this parameter is updated.
+	 *
+	 * @note This function will be called even when a _parameter update_ command is received, but the
+	 * new value is the same as the previous one. This is done so that there is an option to repair
+	 * systems with a weird or unknown state.
+	 * @param call Whether to also call the notifier function immediately, to ensure that a change is
+	 * made.
+	 */
+	void setNotifier(const Notifier& _notifier, bool call=true) {
+		notifier = _notifier;
+
+		if (call) {
+			_notifier(Parent::currentValue);
+		}
+	}
+
+	/**
+	 * Unset the notifier function, so that nothing is called when the value of this function is updated.
+	 */
+	void unsetNotifier() {
+		notifier.reset();
+	}
+
+private:
+	etl::optional<Notifier> notifier;
+};
+
+
+#endif //ECSS_SERVICES_NOTIFYPARAMETER_HPP

inc/Helpers/Parameter.hpp

@@ -58,7 +58,7 @@ public:
  */
 template <typename DataType>
 class Parameter : public ParameterBase {
-private:
+protected:
 	DataType currentValue;
 
 public:

test/Parameters/NotifyParameterTests.cpp

+#include "Helpers/NotifyParameter.hpp"
+#include "Message.hpp"
+#include "catch2/catch_all.hpp"
+
+TEST_CASE("Notify Parameter: Notifier") {
+	int counter = 0;
+
+	NotifyParameter<uint32_t> parameter(0);
+
+	SECTION("Notifier not set") {
+		parameter.setValueLoudly(1);
+		CHECK(counter == 0);
+	}
+
+	parameter.setNotifier([&counter](auto) -> auto{
+		counter++;
+	});
+	CHECK(counter == 1);
+
+	parameter.setValueLoudly(2);
+	CHECK(counter == 2);
+
+	parameter.setValueLoudly(2);
+	CHECK(counter == 3);
+
+	parameter.unsetNotifier();
+	parameter.setValueLoudly(3);
+	CHECK(counter == 3);
+}
+
+TEST_CASE("Notify Parameter: Messages") {
+	int16_t storage;
+
+	NotifyParameter<uint32_t> parameter(
+	    0, [&storage](auto v) -> auto{
+		    storage = v;
+	    });
+
+	Message message(0, 0, Message::TC);
+	message.appendUint32(184);
+
+	parameter.setValueFromMessage(message);
+
+	CHECK(storage == 184);
+}
+
+TEST_CASE("Notify Parameter: Extra functionality") {
+	int counter = 0;
+
+	NotifyParameter<uint32_t> parameter(0);
+	auto notifier = [&counter](auto) -> auto{
+		counter++;
+	};
+
+	parameter.setNotifier(notifier);
+	CHECK(counter == 1);
+
+	parameter.setNotifier(notifier, false);
+	CHECK(counter == 1);
+
+	parameter.notify();
+	CHECK(counter == 2);
+}
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