Flipdot-display/src/esp32/logic/stopwatch.h

#pragma once

#include <stdint.h>

// The stopwatch of the dynamic pages, started and stopped in the web UI and Home Assistant.
// Times are the real time in ms since 1970 (UTC), so it counts from a date, keeps counting
// while the display is off or restarting (system/stopwatch_store keeps it in NVS) and can
// run for years. Pure logic, tested in test/test_esp32.
class Stopwatch
{
public:
	// The state as it is stored
	struct State
	{
		bool running = false;
		int64_t started = 0; // when it was started (again)
		int64_t before = 0;  // ms counted before the last start
	};

	void start(int64_t now)
	{
		if (_state.running)
			return;
		_state.running = true;
		_state.started = now;
	}
	void stop(int64_t now)
	{
		if (!_state.running)
			return;
		_state.before = elapsed(now);
		_state.running = false;
	}
	// Back to 0, stopped
	void reset() { _state = State(); }
	// Counts from this moment (in the past) on, running; false (nothing changed) when it is
	// in the future
	bool setStart(int64_t start, int64_t now)
	{
		if (start > now)
			return false;
		_state.running = true;
		_state.started = start;
		_state.before = 0;
		return true;
	}
	bool running() const { return _state.running; }
	// Never negative (the clock set back)
	uint64_t elapsed(int64_t now) const
	{
		int64_t ms = _state.before;
		if (_state.running && now > _state.started)
			ms += now - _state.started;
		return ms > 0 ? (uint64_t)ms : 0;
	}

	const State &state() const { return _state; }
	void restore(const State &state) { _state = state; }

private:
	State _state;
};