From 675b31887ab97a3bd851ec93da76c115ad16a886 Mon Sep 17 00:00:00 2001
From: Jonathan G Rennison <j.g.rennison@gmail.com>
Date: Wed, 21 Feb 2024 21:08:31 +0000
Subject: [PATCH] Saveload: Fix recalculation of _state_ticks

For XSLFI_VARIABLE_DAY_LENGTH versions 1 to 3
---
 src/date.cpp               |  6 +++---
 src/date_func.h            |  2 +-
 src/saveload/afterload.cpp | 14 ++++++++------
 3 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/src/date.cpp b/src/date.cpp
index 5ed74781a0..4f9aadf22b 100644
--- a/src/date.cpp
+++ b/src/date.cpp
@@ -110,14 +110,14 @@ EconTime::State EconTime::Detail::NewState(EconTime::Year year)
 	return state;
 }
 
-StateTicks GetStateTicksFromCurrentDateWithoutOffset()
+StateTicks GetStateTicksFromDateWithoutOffset(EconTime::Date date, EconTime::DateFract date_fract)
 {
-	return ((int64_t)(EconTime::DateToDateTicks(EconTime::CurDate(), EconTime::CurDateFract()).base()) * DayLengthFactor()) + TickSkipCounter();
+	return ((int64_t)(EconTime::DateToDateTicks(date, date_fract).base()) * DayLengthFactor()) + TickSkipCounter();
 }
 
 void RecalculateStateTicksOffset()
 {
-	DateDetail::_state_ticks_offset = _state_ticks - GetStateTicksFromCurrentDateWithoutOffset();
+	DateDetail::_state_ticks_offset = _state_ticks - GetStateTicksFromDateWithoutOffset(EconTime::CurDate(), EconTime::CurDateFract());
 }
 
 void UpdateEffectiveDayLengthFactor()
diff --git a/src/date_func.h b/src/date_func.h
index 7da63076a4..44b71ff4ab 100644
--- a/src/date_func.h
+++ b/src/date_func.h
@@ -24,7 +24,7 @@ namespace DateDetail {
 	extern uint8_t _effective_day_length;
 };
 
-StateTicks GetStateTicksFromCurrentDateWithoutOffset();
+StateTicks GetStateTicksFromDateWithoutOffset(EconTime::Date date, EconTime::DateFract date_fract);
 void RecalculateStateTicksOffset();
 
 inline uint8_t TickSkipCounter()
diff --git a/src/saveload/afterload.cpp b/src/saveload/afterload.cpp
index 12de639281..bb24ad3163 100644
--- a/src/saveload/afterload.cpp
+++ b/src/saveload/afterload.cpp
@@ -667,7 +667,12 @@ bool AfterLoadGame()
 
 	TileIndex map_size = MapSize();
 
+	/* Only new games can use wallclock units. */
+	if (SlXvIsFeatureMissing(XSLFI_VARIABLE_DAY_LENGTH, 5) && IsSavegameVersionBefore(SLV_ECONOMY_MODE_TIMEKEEPING_UNITS)) {
+		_settings_game.economy.timekeeping_units = TKU_CALENDAR;
+	}
 	UpdateEffectiveDayLengthFactor();
+
 	SetupTickRate();
 
 	extern TileIndex _cur_tileloop_tile; // From landscape.cpp.
@@ -865,18 +870,15 @@ bool AfterLoadGame()
 		_scaled_tick_counter = (uint64_t)((_tick_counter * DayLengthFactor()) + TickSkipCounter());
 	}
 	if (SlXvIsFeaturePresent(XSLFI_VARIABLE_DAY_LENGTH, 1, 3)) {
-		_state_ticks = GetStateTicksFromCurrentDateWithoutOffset() + DateDetail::_state_ticks_offset;
+		/* CalTime is used here because EconTime hasn't been set yet, but this needs to be done before setting EconTime::Detail::SetDate,
+		 * because that calls RecalculateStateTicksOffset which overwrites DateDetail::_state_ticks_offset which is an input here */
+		_state_ticks = GetStateTicksFromDateWithoutOffset(CalTime::CurDate().base(), CalTime::CurDateFract()) + DateDetail::_state_ticks_offset;
 	}
 
 	/* Update current year
 	 * must be done before loading sprites as some newgrfs check it */
 	CalTime::Detail::SetDate(CalTime::CurDate(), CalTime::CurDateFract());
 
-	/* Only new games can use wallclock units. */
-	if (SlXvIsFeatureMissing(XSLFI_VARIABLE_DAY_LENGTH, 5) && IsSavegameVersionBefore(SLV_ECONOMY_MODE_TIMEKEEPING_UNITS)) {
-		_settings_game.economy.timekeeping_units = TKU_CALENDAR;
-	}
-
 	if (SlXvIsFeaturePresent(XSLFI_VARIABLE_DAY_LENGTH, 5) || !IsSavegameVersionBefore(SLV_ECONOMY_DATE)) {
 		EconTime::Detail::SetDate(EconTime::CurDate(), EconTime::CurDateFract());
 	} else {