Add consistent monotonic day counter - get_day_count()

I've written several experimental bits of code that revolve around the
need for a consistent calendar, but implementing one is extremely hard
in mods due to time changes and mods overriding core.get_timeofday(),
which will conflict.

The second part of the problem is that doing this from a mod requires
constant maintenance of a settings file.

An implementation in core is trivial, however, and solves all of
these problems at virtually no cost: No extra branches in server
steps, and a single branch when minetest.set_time_of_day(), which is
entirely reasonable.

We store the day_count value in env_meta.txt.

The use case is obvious: This change allows mods to create an actual
virtual calendar, or properly account for seasonal changes, etc..

We add a "/days" chatcommand that displays the current day count. No
permissions are needed. It can only retrieve the day count, not
modify it.

1 files changed, 19 insertions, 1 deletions

diff --git a/src/environment.cpp b/src/environment.cpp
index 6da376a15..0d00ed170 100644
--- a/src/environment.cpp
+++ b/src/environment.cpp
@@ -208,6 +208,8 @@ void Environment::setDayNightRatioOverride(bool enable, u32 value)
 void Environment::setTimeOfDay(u32 time)
 {
 	MutexAutoLock lock(this->m_time_lock);
+	if (m_time_of_day > time)
+		m_day_count++;
 	m_time_of_day = time;
 	m_time_of_day_f = (float)time / 24000.0;
 }
@@ -238,8 +240,10 @@ void Environment::stepTimeOfDay(float dtime)
 	bool sync_f = false;
 	if (units > 0) {
 		// Sync at overflow
-		if (m_time_of_day + units >= 24000)
+		if (m_time_of_day + units >= 24000) {
 			sync_f = true;
+			m_day_count++;
+		}
 		m_time_of_day = (m_time_of_day + units) % 24000;
 		if (sync_f)
 			m_time_of_day_f = (float)m_time_of_day / 24000.0;
@@ -256,6 +260,13 @@ void Environment::stepTimeOfDay(float dtime)
 	}
 }
 
+u32 Environment::getDayCount()
+{
+	// Atomic<u32> counter
+	return m_day_count;
+}
+
+
 /*
 	ABMWithState
 */
@@ -727,6 +738,7 @@ void ServerEnvironment::saveMeta()
 	args.setU64("lbm_introduction_times_version", 1);
 	args.set("lbm_introduction_times",
 		m_lbm_mgr.createIntroductionTimesString());
+	args.setU64("day_count", m_day_count);
 	args.writeLines(ss);
 	ss<<"EnvArgsEnd\n";
 
@@ -792,6 +804,12 @@ void ServerEnvironment::loadMeta()
 	}
 	m_lbm_mgr.loadIntroductionTimes(lbm_introduction_times, m_gamedef, m_game_time);
 
+	try {
+		m_day_count = args.getU64("day_count");
+	} catch (SettingNotFoundException &e) {
+		// If missing, start the day counter
+		m_day_count = 0;
+	}
 }
 
 void ServerEnvironment::loadDefaultMeta()