Feature: Configurable subsidy duration

11 files changed, 70 insertions, 28 deletions

diff --git a/src/date_type.h b/src/date_type.h
index 4cbcfac4e..c0f005734 100644
--- a/src/date_type.h
+++ b/src/date_type.h
@@ -28,6 +28,7 @@ typedef uint8  Day;   ///< Type for the day of the month, note: 1 based, first d
 static const int DAY_TICKS         =  74; ///< ticks per day
 static const int DAYS_IN_YEAR      = 365; ///< days per year
 static const int DAYS_IN_LEAP_YEAR = 366; ///< sometimes, you need one day more...
+static const int MONTHS_IN_YEAR    =  12; ///< months per year
 
 static const int STATION_RATING_TICKS     = 185; ///< cycle duration for updating station rating
 static const int STATION_ACCEPTANCE_TICKS = 250; ///< cycle duration for updating station acceptance
diff --git a/src/lang/english.txt b/src/lang/english.txt
index 4a92eba89..206cc212f 100644
--- a/src/lang/english.txt
+++ b/src/lang/english.txt
@@ -883,11 +883,11 @@ STR_NEWS_STATION_NOW_ACCEPTS_CARGO_AND_CARGO                    :{WHITE}{STATION
 
 STR_NEWS_OFFER_OF_SUBSIDY_EXPIRED                               :{BIG_FONT}{BLACK}Offer of subsidy expired:{}{}{STRING} from {STRING2} to {STRING2} will now not attract a subsidy
 STR_NEWS_SUBSIDY_WITHDRAWN_SERVICE                              :{BIG_FONT}{BLACK}Subsidy withdrawn:{}{}{STRING} service from {STRING2} to {STRING2} is no longer subsidised
-STR_NEWS_SERVICE_SUBSIDY_OFFERED                                :{BIG_FONT}{BLACK}Service subsidy offered:{}{}First {STRING} service from {STRING2} to {STRING2} will attract a year's subsidy from the local authority!
-STR_NEWS_SERVICE_SUBSIDY_AWARDED_HALF                           :{BIG_FONT}{BLACK}Service subsidy awarded to {RAW_STRING}!{}{}{STRING} service from {STRING2} to {STRING2} will pay 50% extra for the next year!
-STR_NEWS_SERVICE_SUBSIDY_AWARDED_DOUBLE                         :{BIG_FONT}{BLACK}Service subsidy awarded to {RAW_STRING}!{}{}{STRING} service from {STRING2} to {STRING2} will pay double rates for the next year!
-STR_NEWS_SERVICE_SUBSIDY_AWARDED_TRIPLE                         :{BIG_FONT}{BLACK}Service subsidy awarded to {RAW_STRING}!{}{}{STRING} service from {STRING2} to {STRING2} will pay triple rates for the next year!
-STR_NEWS_SERVICE_SUBSIDY_AWARDED_QUADRUPLE                      :{BIG_FONT}{BLACK}Service subsidy awarded to {RAW_STRING}!{}{}{STRING} service from {STRING2} to {STRING2} will pay quadruple rates for the next year!
+STR_NEWS_SERVICE_SUBSIDY_OFFERED                                :{BIG_FONT}{BLACK}Service subsidy offered:{}{}First {STRING} service from {STRING2} to {STRING2} will attract a {NUM} year subsidy from the local authority!
+STR_NEWS_SERVICE_SUBSIDY_AWARDED_HALF                           :{BIG_FONT}{BLACK}Service subsidy awarded to {RAW_STRING}!{}{}{STRING} service from {STRING2} to {STRING2} will pay 50% extra for the next {NUM} year{P "" s}!
+STR_NEWS_SERVICE_SUBSIDY_AWARDED_DOUBLE                         :{BIG_FONT}{BLACK}Service subsidy awarded to {RAW_STRING}!{}{}{STRING} service from {STRING2} to {STRING2} will pay double rates for the next {NUM} year{P "" s}!
+STR_NEWS_SERVICE_SUBSIDY_AWARDED_TRIPLE                         :{BIG_FONT}{BLACK}Service subsidy awarded to {RAW_STRING}!{}{}{STRING} service from {STRING2} to {STRING2} will pay triple rates for the next {NUM} year{P "" s}!
+STR_NEWS_SERVICE_SUBSIDY_AWARDED_QUADRUPLE                      :{BIG_FONT}{BLACK}Service subsidy awarded to {RAW_STRING}!{}{}{STRING} service from {STRING2} to {STRING2} will pay quadruple rates for the next {NUM} year{P "" s}!
 
 STR_NEWS_ROAD_REBUILDING                                        :{BIG_FONT}{BLACK}Traffic chaos in {TOWN}!{}{}Road rebuilding programme funded by {RAW_STRING} brings 6 months of misery to motorists!
 STR_NEWS_EXCLUSIVE_RIGHTS_TITLE                                 :{BIG_FONT}{BLACK}Transport monopoly!
@@ -1203,6 +1203,10 @@ STR_CONFIG_SETTING_VEHICLE_BREAKDOWNS                           :Vehicle breakdo
 STR_CONFIG_SETTING_VEHICLE_BREAKDOWNS_HELPTEXT                  :Control how often inadequately serviced vehicles may break down
 STR_CONFIG_SETTING_SUBSIDY_MULTIPLIER                           :Subsidy multiplier: {STRING2}
 STR_CONFIG_SETTING_SUBSIDY_MULTIPLIER_HELPTEXT                  :Set how much is paid for subsidised connections
+STR_CONFIG_SETTING_SUBSIDY_DURATION                             :Subsidy duration: {STRING2}
+STR_CONFIG_SETTING_SUBSIDY_DURATION_HELPTEXT                    :Set the number of years for which a subsidy is awarded
+STR_CONFIG_SETTING_SUBSIDY_DURATION_VALUE                       :{NUM} year{P "" s}
+STR_CONFIG_SETTING_SUBSIDY_DURATION_DISABLED                    :No subsidies
 STR_CONFIG_SETTING_CONSTRUCTION_COSTS                           :Construction costs: {STRING2}
 STR_CONFIG_SETTING_CONSTRUCTION_COSTS_HELPTEXT                  :Set level of construction and purchase costs
 STR_CONFIG_SETTING_RECESSIONS                                   :Recessions: {STRING2}
diff --git a/src/saveload/saveload.h b/src/saveload/saveload.h
index 3a2427c93..28af1fd37 100644
--- a/src/saveload/saveload.h
+++ b/src/saveload/saveload.h
@@ -328,6 +328,7 @@ enum SaveLoadVersion : uint16 {
 	SLV_INDUSTRY_TEXT,                      ///< 289  PR#8576 v1.11.0-RC1  Additional GS text for industries.
 	SLV_MAPGEN_SETTINGS_REVAMP,             ///< 290  PR#8891 v1.11  Revamp of some mapgen settings (snow coverage, desert coverage, heightmap height, custom terrain type).
 	SLV_GROUP_REPLACE_WAGON_REMOVAL,        ///< 291  PR#7441 Per-group wagon removal flag.
+	SLV_CUSTOM_SUBSIDY_DURATION,            ///< 292  PR#9081 Configurable subsidy duration.
 
 	SL_MAX_VERSION,                         ///< Highest possible saveload version
 };
diff --git a/src/saveload/subsidy_sl.cpp b/src/saveload/subsidy_sl.cpp
index b17ae1f25..9ed65a04e 100644
--- a/src/saveload/subsidy_sl.cpp
+++ b/src/saveload/subsidy_sl.cpp
@@ -16,14 +16,15 @@
 
 static const SaveLoad _subsidies_desc[] = {
 	    SLE_VAR(Subsidy, cargo_type, SLE_UINT8),
-	    SLE_VAR(Subsidy, remaining,  SLE_UINT8),
-	SLE_CONDVAR(Subsidy, awarded,    SLE_UINT8,                 SLV_125, SL_MAX_VERSION),
-	SLE_CONDVAR(Subsidy, src_type,   SLE_UINT8,                 SLV_125, SL_MAX_VERSION),
-	SLE_CONDVAR(Subsidy, dst_type,   SLE_UINT8,                 SLV_125, SL_MAX_VERSION),
-	SLE_CONDVAR(Subsidy, src,        SLE_FILE_U8 | SLE_VAR_U16,   SL_MIN_VERSION, SLV_5),
-	SLE_CONDVAR(Subsidy, src,        SLE_UINT16,                  SLV_5, SL_MAX_VERSION),
-	SLE_CONDVAR(Subsidy, dst,        SLE_FILE_U8 | SLE_VAR_U16,   SL_MIN_VERSION, SLV_5),
-	SLE_CONDVAR(Subsidy, dst,        SLE_UINT16,                  SLV_5, SL_MAX_VERSION),
+	SLE_CONDVAR(Subsidy, remaining,  SLE_FILE_U8 | SLE_VAR_U16, SL_MIN_VERSION, SLV_CUSTOM_SUBSIDY_DURATION),
+	SLE_CONDVAR(Subsidy, remaining,  SLE_UINT16,                SLV_CUSTOM_SUBSIDY_DURATION, SL_MAX_VERSION),
+	SLE_CONDVAR(Subsidy, awarded,    SLE_UINT8,                                     SLV_125, SL_MAX_VERSION),
+	SLE_CONDVAR(Subsidy, src_type,   SLE_UINT8,                                     SLV_125, SL_MAX_VERSION),
+	SLE_CONDVAR(Subsidy, dst_type,   SLE_UINT8,                                     SLV_125, SL_MAX_VERSION),
+	SLE_CONDVAR(Subsidy, src,        SLE_FILE_U8 | SLE_VAR_U16,                       SL_MIN_VERSION, SLV_5),
+	SLE_CONDVAR(Subsidy, src,        SLE_UINT16,                                      SLV_5, SL_MAX_VERSION),
+	SLE_CONDVAR(Subsidy, dst,        SLE_FILE_U8 | SLE_VAR_U16,                       SL_MIN_VERSION, SLV_5),
+	SLE_CONDVAR(Subsidy, dst,        SLE_UINT16,                                      SLV_5, SL_MAX_VERSION),
 };
 
 static void Save_SUBS()
diff --git a/src/settings_gui.cpp b/src/settings_gui.cpp
index 1bd58c13b..b17b343c7 100644
--- a/src/settings_gui.cpp
+++ b/src/settings_gui.cpp
@@ -1691,6 +1691,7 @@ static SettingsContainer &GetSettingsTree()
 			accounting->Add(new SettingEntry("difficulty.initial_interest"));
 			accounting->Add(new SettingEntry("difficulty.max_loan"));
 			accounting->Add(new SettingEntry("difficulty.subsidy_multiplier"));
+			accounting->Add(new SettingEntry("difficulty.subsidy_duration"));
 			accounting->Add(new SettingEntry("economy.feeder_payment_share"));
 			accounting->Add(new SettingEntry("economy.infrastructure_maintenance"));
 			accounting->Add(new SettingEntry("difficulty.vehicle_costs"));
diff --git a/src/settings_type.h b/src/settings_type.h
index 802368384..05efc11e5 100644
--- a/src/settings_type.h
+++ b/src/settings_type.h
@@ -72,7 +72,8 @@ struct DifficultySettings {
 	byte   vehicle_costs;                    ///< amount of money spent on vehicle running cost
 	byte   competitor_speed;                 ///< the speed at which the AI builds
 	byte   vehicle_breakdowns;               ///< likelihood of vehicles breaking down
-	byte   subsidy_multiplier;               ///< amount of subsidy
+	byte   subsidy_multiplier;               ///< payment multiplier for subsidized deliveries
+	uint16 subsidy_duration;                 ///< duration of subsidies
 	byte   construction_cost;                ///< how expensive is building
 	byte   terrain_type;                     ///< the mountainousness of the landscape
 	byte   quantity_sea_lakes;               ///< the amount of seas/lakes
diff --git a/src/subsidy.cpp b/src/subsidy.cpp
index 14679e4dc..8800da1bd 100644
--- a/src/subsidy.cpp
+++ b/src/subsidy.cpp
@@ -41,7 +41,7 @@ void Subsidy::AwardTo(CompanyID company)
 	assert(!this->IsAwarded());
 
 	this->awarded = company;
-	this->remaining = SUBSIDY_CONTRACT_MONTHS;
+	this->remaining = _settings_game.difficulty.subsidy_duration * MONTHS_IN_YEAR;
 
 	char company_name[MAX_LENGTH_COMPANY_NAME_CHARS * MAX_CHAR_LENGTH];
 	SetDParam(0, company);
@@ -50,7 +50,7 @@ void Subsidy::AwardTo(CompanyID company)
 	char *cn = stredup(company_name);
 
 	/* Add a news item */
-	std::pair<NewsReferenceType, NewsReferenceType> reftype = SetupSubsidyDecodeParam(this, false);
+	std::pair<NewsReferenceType, NewsReferenceType> reftype = SetupSubsidyDecodeParam(this, SubsidyDecodeParamType::NewsAwarded);
 	InjectDParam(1);
 
 	SetDParamStr(0, cn);
@@ -69,17 +69,21 @@ void Subsidy::AwardTo(CompanyID company)
 /**
  * Setup the string parameters for printing the subsidy at the screen, and compute the news reference for the subsidy.
  * @param s %Subsidy being printed.
- * @param mode Unit of cargo used, \c true means general name, \c false means singular form.
+ * @param mode Type of subsidy news message to decide on parameter format.
  * @return Reference of the subsidy in the news system.
  */
-std::pair<NewsReferenceType, NewsReferenceType> SetupSubsidyDecodeParam(const Subsidy *s, bool mode)
+std::pair<NewsReferenceType, NewsReferenceType> SetupSubsidyDecodeParam(const Subsidy *s, SubsidyDecodeParamType mode)
 {
 	NewsReferenceType reftype1 = NR_NONE;
 	NewsReferenceType reftype2 = NR_NONE;
 
-	/* if mode is false, use the singular form */
+	/* Choose whether to use the singular or plural form of the cargo name based on how we're printing the subsidy */
 	const CargoSpec *cs = CargoSpec::Get(s->cargo_type);
-	SetDParam(0, mode ? cs->name : cs->name_single);
+	if (mode == SubsidyDecodeParamType::Gui || mode == SubsidyDecodeParamType::NewsWithdrawn) {
+		SetDParam(0, cs->name);
+	} else {
+		SetDParam(0, cs->name_single);
+	}
 
 	switch (s->src_type) {
 		case ST_INDUSTRY:
@@ -107,6 +111,11 @@ std::pair<NewsReferenceType, NewsReferenceType> SetupSubsidyDecodeParam(const Su
 	}
 	SetDParam(5, s->dst);
 
+	/* If the subsidy is being offered or awarded, the news item mentions the subsidy duration. */
+	if (mode == SubsidyDecodeParamType::NewsOffered || mode == SubsidyDecodeParamType::NewsAwarded) {
+		SetDParam(7, _settings_game.difficulty.subsidy_duration);
+	}
+
 	return std::pair<NewsReferenceType, NewsReferenceType>(reftype1, reftype2);
 }
 
@@ -216,7 +225,7 @@ void CreateSubsidy(CargoID cid, SourceType src_type, SourceID src, SourceType ds
 	s->remaining = SUBSIDY_OFFER_MONTHS;
 	s->awarded = INVALID_COMPANY;
 
-	std::pair<NewsReferenceType, NewsReferenceType> reftype = SetupSubsidyDecodeParam(s, false);
+	std::pair<NewsReferenceType, NewsReferenceType> reftype = SetupSubsidyDecodeParam(s, SubsidyDecodeParamType::NewsOffered);
 	AddNewsItem(STR_NEWS_SERVICE_SUBSIDY_OFFERED, NT_SUBSIDIES, NF_NORMAL, reftype.first, s->src, reftype.second, s->dst);
 	SetPartOfSubsidyFlag(s->src_type, s->src, POS_SRC);
 	SetPartOfSubsidyFlag(s->dst_type, s->dst, POS_DST);
@@ -491,13 +500,13 @@ void SubsidyMonthlyLoop()
 	for (Subsidy *s : Subsidy::Iterate()) {
 		if (--s->remaining == 0) {
 			if (!s->IsAwarded()) {
-				std::pair<NewsReferenceType, NewsReferenceType> reftype = SetupSubsidyDecodeParam(s, true);
+				std::pair<NewsReferenceType, NewsReferenceType> reftype = SetupSubsidyDecodeParam(s, SubsidyDecodeParamType::NewsWithdrawn);
 				AddNewsItem(STR_NEWS_OFFER_OF_SUBSIDY_EXPIRED, NT_SUBSIDIES, NF_NORMAL, reftype.first, s->src, reftype.second, s->dst);
 				AI::BroadcastNewEvent(new ScriptEventSubsidyOfferExpired(s->index));
 				Game::NewEvent(new ScriptEventSubsidyOfferExpired(s->index));
 			} else {
 				if (s->awarded == _local_company) {
-					std::pair<NewsReferenceType, NewsReferenceType> reftype = SetupSubsidyDecodeParam(s, true);
+					std::pair<NewsReferenceType, NewsReferenceType> reftype = SetupSubsidyDecodeParam(s, SubsidyDecodeParamType::NewsWithdrawn);
 					AddNewsItem(STR_NEWS_SUBSIDY_WITHDRAWN_SERVICE, NT_SUBSIDIES, NF_NORMAL, reftype.first, s->src, reftype.second, s->dst);
 				}
 				AI::BroadcastNewEvent(new ScriptEventSubsidyExpired(s->index));
@@ -510,6 +519,9 @@ void SubsidyMonthlyLoop()
 
 	if (modified) {
 		RebuildSubsidisedSourceAndDestinationCache();
+	} else if (_settings_game.difficulty.subsidy_duration == 0) {
+		/* If subsidy duration is set to 0, subsidies are disabled, so bail out. */
+		return;
 	} else if (_settings_game.linkgraph.distribution_pax != DT_MANUAL &&
 			   _settings_game.linkgraph.distribution_mail != DT_MANUAL &&
 			   _settings_game.linkgraph.distribution_armoured != DT_MANUAL &&
diff --git a/src/subsidy_base.h b/src/subsidy_base.h
index ef9276433..120c5cece 100644
--- a/src/subsidy_base.h
+++ b/src/subsidy_base.h
@@ -21,7 +21,7 @@ extern SubsidyPool _subsidy_pool;
 /** Struct about subsidies, offered and awarded */
 struct Subsidy : SubsidyPool::PoolItem<&_subsidy_pool> {
 	CargoID cargo_type;  ///< Cargo type involved in this subsidy, CT_INVALID for invalid subsidy
-	byte remaining;      ///< Remaining months when this subsidy is valid
+	uint16 remaining;    ///< Remaining months when this subsidy is valid
 	CompanyID awarded;   ///< Subsidy is awarded to this company; INVALID_COMPANY if it's not awarded to anyone
 	SourceType src_type; ///< Source of subsidised path (ST_INDUSTRY or ST_TOWN)
 	SourceType dst_type; ///< Destination of subsidised path (ST_INDUSTRY or ST_TOWN)
@@ -52,11 +52,18 @@ struct Subsidy : SubsidyPool::PoolItem<&_subsidy_pool> {
 
 /** Constants related to subsidies */
 static const uint SUBSIDY_OFFER_MONTHS         =  12; ///< Duration of subsidy offer
-static const uint SUBSIDY_CONTRACT_MONTHS      =  12; ///< Duration of subsidy after awarding
 static const uint SUBSIDY_PAX_MIN_POPULATION   = 400; ///< Min. population of towns for subsidised pax route
 static const uint SUBSIDY_CARGO_MIN_POPULATION = 900; ///< Min. population of destination town for cargo route
 static const uint SUBSIDY_MAX_PCT_TRANSPORTED  =  42; ///< Subsidy will be created only for towns/industries with less % transported
 static const uint SUBSIDY_MAX_DISTANCE         =  70; ///< Max. length of subsidised route (DistanceManhattan)
 static const uint SUBSIDY_TOWN_CARGO_RADIUS    =   6; ///< Extent of a tile area around town center when scanning for town cargo acceptance and production (6 ~= min catchmement + min station / 2)
 
+/** Types of subsidy news messages, which determine how the date is printed and whether to use singular or plural cargo names */
+enum class SubsidyDecodeParamType {
+	NewsOffered   = 0, ///< News item for an offered subsidy
+	NewsAwarded   = 1, ///< News item for an awarded subsidy
+	NewsWithdrawn = 2, ///< News item for a subsidy offer withdrawn, or expired subsidy
+	Gui           = 3, ///< Subsidies listed in the Subsidy GUI
+};
+
 #endif /* SUBSIDY_BASE_H */
diff --git a/src/subsidy_func.h b/src/subsidy_func.h
index cc63577d3..5cd7a3118 100644
--- a/src/subsidy_func.h
+++ b/src/subsidy_func.h
@@ -15,8 +15,9 @@
 #include "company_type.h"
 #include "cargo_type.h"
 #include "news_type.h"
+#include "subsidy_base.h"
 
-std::pair<NewsReferenceType, NewsReferenceType> SetupSubsidyDecodeParam(const struct Subsidy *s, bool mode);
+std::pair<NewsReferenceType, NewsReferenceType> SetupSubsidyDecodeParam(const struct Subsidy *s, SubsidyDecodeParamType mode);
 void DeleteSubsidyWith(SourceType type, SourceID index);
 bool CheckSubsidised(CargoID cargo_type, CompanyID company, SourceType src_type, SourceID src, const Station *st);
 void RebuildSubsidisedSourceAndDestinationCache();
diff --git a/src/subsidy_gui.cpp b/src/subsidy_gui.cpp
index fe3c55c11..b46ca4da2 100644
--- a/src/subsidy_gui.cpp
+++ b/src/subsidy_gui.cpp
@@ -161,7 +161,7 @@ struct SubsidyListWindow : Window {
 			if (!s->IsAwarded()) {
 				if (IsInsideMM(pos, 0, cap)) {
 					/* Displays the two offered towns */
-					SetupSubsidyDecodeParam(s, true);
+					SetupSubsidyDecodeParam(s, SubsidyDecodeParamType::Gui);
 					SetDParam(7, _date - ymd.day + s->remaining * 32);
 					DrawString(x, right, y + pos * FONT_HEIGHT_NORMAL, STR_SUBSIDIES_OFFERED_FROM_TO);
 				}
@@ -184,7 +184,7 @@ struct SubsidyListWindow : Window {
 		for (const Subsidy *s : Subsidy::Iterate()) {
 			if (s->IsAwarded()) {
 				if (IsInsideMM(pos, 0, cap)) {
-					SetupSubsidyDecodeParam(s, true);
+					SetupSubsidyDecodeParam(s, SubsidyDecodeParamType::Gui);
 					SetDParam(7, s->awarded);
 					SetDParam(8, _date - ymd.day + s->remaining * 32);
 
diff --git a/src/table/settings/settings.ini b/src/table/settings/settings.ini
index f9f1cb87b..17a4b3025 100644
--- a/src/table/settings/settings.ini
+++ b/src/table/settings/settings.ini
@@ -232,6 +232,19 @@ strhelp  = STR_CONFIG_SETTING_SUBSIDY_MULTIPLIER_HELPTEXT
 strval   = STR_SUBSIDY_X1_5
 
 [SDT_VAR]
+var      = difficulty.subsidy_duration
+type     = SLE_UINT16
+from     = SLV_CUSTOM_SUBSIDY_DURATION
+flags    = SF_GUI_0_IS_SPECIAL
+def      = 1
+min      = 0
+max      = 5000
+interval = 1
+str      = STR_CONFIG_SETTING_SUBSIDY_DURATION
+strhelp  = STR_CONFIG_SETTING_SUBSIDY_DURATION_HELPTEXT
+strval   = STR_CONFIG_SETTING_SUBSIDY_DURATION_VALUE
+
+[SDT_VAR]
 var      = difficulty.construction_cost
 type     = SLE_UINT8
 from     = SLV_97