Short-circuit defender water-crossing checks (#8779)

src/main/cpp/net/eagle0/shardok/ai/AIDefenderStrategySelector.cpp

@@ -4,9 +4,6 @@
 
 #include "AIDefenderStrategySelector.hpp"
 
-#include <algorithm>
-#include <ranges>
-
 #include "src/main/cpp/net/eagle0/shardok/ai/AIAttackGroups.hpp"
 #include "src/main/cpp/net/eagle0/shardok/ai/AIScoreUtilities.hpp"
 #include "src/main/cpp/net/eagle0/shardok/ai/AIWaterCrossingCalculator.hpp"
@@ -67,45 +64,15 @@ auto AIDefenderStrategySelector::BestDefenderStrategy(
             canFlee && roundsRemaining > 2 &&
             defenderTroops < MAXIMUM_RATIO_FOR_DEFENDER_TO_FLEE * attackerTroops &&
             attackerNonUndeadUnitCount >= criticalTileCoords.size();
-    if (waterCrossingCouldAffectStrategy) {
-        vector<UnitId> attackerUnitIdsRequiringWaterCrossing{};
-        attackerUnitIdsRequiringWaterCrossing.reserve(gameState->units()->size());
-        for (const auto& player : *gameState->player_infos()) {
-            if (!player->is_defender()) {
-                const auto& unitIdsRequiringWaterCrossing = UnitIdsRequiringWaterCrossing(
+    if (waterCrossingCouldAffectStrategy && HasEnoughNonUndeadAttackersWithoutWaterCrossing(
                                                     gameState,
-                        player->player_id(),
                                                     criticalTileCoords,
                                                     landRegions,
                                                     apdCache,
-                        battalionTypeGetter);
-                attackerUnitIdsRequiringWaterCrossing.insert(
-                        attackerUnitIdsRequiringWaterCrossing.end(),
-                        unitIdsRequiringWaterCrossing.begin(),
-                        unitIdsRequiringWaterCrossing.end());
-            }
-        }
-
-        uint32_t attackerNonUndeadUnitNotRequiringWaterCrossingCount = 0;
-        for (const Unit* unit : *gameState->units()) {
-            if (unit->status() != net::eagle0::shardok::storage::fb::UnitStatus_NORMAL_UNIT &&
-                unit->status() != net::eagle0::shardok::storage::fb::UnitStatus_RESERVE_UNIT) {
-                continue;
-            }
-
-            const auto* pi = PlayerInfoForPid(gameState, unit->player_id());
-            if (pi != nullptr && !pi->is_defender() &&
-                unit->battalion().type() !=
-                        net::eagle0::shardok::storage::fb::BattalionTypeId_UNDEAD &&
-                !std::ranges::contains(attackerUnitIdsRequiringWaterCrossing, unit->unit_id())) {
-                ++attackerNonUndeadUnitNotRequiringWaterCrossingCount;
-            }
-        }
-
-        if (attackerNonUndeadUnitNotRequiringWaterCrossingCount >= criticalTileCoords.size()) {
+                                                    battalionTypeGetter,
+                                                    criticalTileCoords.size())) {
         return FleeStrategy;
     }
-    }
 
     if (attackerNonUndeadUnitCount >= criticalTileCoords.size()) {
         chosenStrategy = HoldCastlesStrategy;

src/main/cpp/net/eagle0/shardok/ai/AIWaterCrossingCalculator.cpp

@@ -37,6 +37,15 @@ auto CanReachWithDistances(
     return distances->Distance(origin, destination) != ActionPointDistances::IMPOSSIBLE;
 }
 
+auto CanReachAllWithDistances(
+        const Coords &origin,
+        const CoordsSet &destinations,
+        const ActionPointDistances *distances) -> bool {
+    return std::ranges::all_of(destinations, [&](const Coords &destination) {
+        return CanReachWithDistances(origin, destination, distances);
+    });
+}
+
 auto DefinitelyReachesAllWithoutWater(
         const LandRegions &landRegions,
         const Coords &origin,
@@ -46,6 +55,58 @@ auto DefinitelyReachesAllWithoutWater(
     });
 }
 
+auto DefinitelyReachesAllWithoutWater(
+        const GameStateW &gameState,
+        const net::eagle0::shardok::storage::fb::Unit *unit,
+        const CoordsSet &destinations,
+        const LandRegions &landRegions) -> bool {
+    if (unit->status() == net::eagle0::shardok::storage::fb::UnitStatus_NORMAL_UNIT) {
+        return DefinitelyReachesAllWithoutWater(landRegions, unit->location(), destinations);
+    }
+
+    const auto *startingPositions = gameState->hex_map()
+                                            ->attacker_starting_positions()
+                                            ->Get(unit->starting_position_index())
+                                            ->positions();
+    return std::ranges::all_of(*startingPositions, [&](const Coords *position) {
+        return DefinitelyReachesAllWithoutWater(landRegions, *position, destinations);
+    });
+}
+
+auto CanReachAllWithoutWater(
+        const GameStateW &gameState,
+        const net::eagle0::shardok::storage::fb::Unit *unit,
+        const CoordsSet &destinations,
+        const ActionPointDistances *distances) -> bool {
+    if (unit->status() == net::eagle0::shardok::storage::fb::UnitStatus_NORMAL_UNIT) {
+        return CanReachAllWithDistances(unit->location(), destinations, distances);
+    }
+
+    const auto *startingPositions = gameState->hex_map()
+                                            ->attacker_starting_positions()
+                                            ->Get(unit->starting_position_index())
+                                            ->positions();
+    return std::ranges::all_of(*startingPositions, [&](const Coords *position) {
+        return CanReachAllWithDistances(*position, destinations, distances);
+    });
+}
+
+auto IsActiveNonUndeadAttacker(
+        const GameStateW &gameState,
+        const net::eagle0::shardok::storage::fb::Unit *unit) -> bool {
+    if (unit->status() != net::eagle0::shardok::storage::fb::UnitStatus_NORMAL_UNIT &&
+        unit->status() != net::eagle0::shardok::storage::fb::UnitStatus_RESERVE_UNIT) {
+        return false;
+    }
+    if (unit->battalion().type() == net::eagle0::shardok::storage::fb::BattalionTypeId_UNDEAD) {
+        return false;
+    }
+
+    return std::ranges::any_of(*gameState->player_infos(), [&](const auto *playerInfo) {
+        return playerInfo->player_id() == unit->player_id() && !playerInfo->is_defender();
+    });
+}
+
 auto CanCreateWaterCrossing(
         const net::eagle0::shardok::storage::fb::Unit *unit,
         const BattalionTypeGetter &battalionTypeGetter) -> bool {
@@ -176,6 +237,73 @@ auto UnitIdsRequiringWaterCrossing(
     return unitIdsToReturn;
 }
 
+auto HasEnoughNonUndeadAttackersWithoutWaterCrossing(
+        const GameStateW &gameState,
+        const CoordsSet &destinations,
+        const LandRegions &landRegions,
+        const APDCache &apdCache,
+        const BattalionTypeGetter &battalionTypeGetter,
+        const std::size_t requiredUnitCount) -> bool {
+    if (requiredUnitCount == 0) return true;
+
+    std::size_t eligibleUnitCount = 0;
+    std::size_t reachableUnitCount = 0;
+    for (const auto *unit : *gameState->units()) {
+        if (!IsActiveNonUndeadAttacker(gameState, unit)) continue;
+
+        ++eligibleUnitCount;
+        if (DefinitelyReachesAllWithoutWater(gameState, unit, destinations, landRegions) &&
+            ++reachableUnitCount >= requiredUnitCount) {
+            return true;
+        }
+    }
+
+    if (eligibleUnitCount < requiredUnitCount) return false;
+
+    const HexMap *map = gameState->hex_map();
+    MapId mapId = ActionPointDistancesCache::GetMapId(map);
+
+    fb::HexMapW fireClearedMap;
+    if (HasNonWaterFire(map)) {
+        fireClearedMap = fb::CopyHexMap(map);
+        for (uint32_t index = 0; index < fireClearedMap->terrain()->size(); ++index) {
+            if (IsWater(fireClearedMap->terrain()->Get(index)->type())) continue;
+            // const_cast is safe because we own the mutable buffer (fireClearedMap)
+            const_cast<net::eagle0::shardok::storage::fb::Terrain *>(
+                    fireClearedMap->mutable_terrain()->GetMutableObject(index))
+                    ->mutable_modifier()
+                    .mutable_fire()
+                    .mutate_present(false);
+        }
+
+        map = fireClearedMap.Get();
+        mapId = RecomputeModifierHash(fireClearedMap.Get());
+    }
+
+    std::array<const ActionPointDistances *, BattalionTypeId::BattalionTypeId_MAX + 1>
+            distancesByBattalionType{};
+    const auto distancesFor = [&](const BattalionTypeSPtr &battalionType) {
+        auto &distances = distancesByBattalionType[battalionType->typeId];
+        if (distances == nullptr) {
+            distances = apdCache->GetRaw(map, mapId, battalionType, false);
+        }
+        return distances;
+    };
+
+    for (const auto *unit : *gameState->units()) {
+        if (!IsActiveNonUndeadAttacker(gameState, unit)) continue;
+        if (DefinitelyReachesAllWithoutWater(gameState, unit, destinations, landRegions)) continue;
+
+        const auto &battalionType = battalionTypeGetter(unit->battalion().type());
+        if (CanReachAllWithoutWater(gameState, unit, destinations, distancesFor(battalionType)) &&
+            ++reachableUnitCount >= requiredUnitCount) {
+            return true;
+        }
+    }
+
+    return false;
+}
+
 auto UnitIdsToCreateWaterCrossing(
         const GameStateW &gameState,
         const PlayerId pid,

src/main/cpp/net/eagle0/shardok/ai/AIWaterCrossingCalculator.hpp

@@ -5,6 +5,8 @@
 #ifndef EAGLE0_SHARDOK_AI_AI_WATER_CROSSING_CALCULATOR_HPP
 #define EAGLE0_SHARDOK_AI_AI_WATER_CROSSING_CALCULATOR_HPP
 
+#include <cstddef>
+
 #include "src/main/cpp/net/eagle0/shardok/ai/AICommonTypes.hpp"
 #include "src/main/cpp/net/eagle0/shardok/library/GameStateW.hpp"
 #include "src/main/cpp/net/eagle0/shardok/library/action_point_distances/ActionPointDistancesCache.hpp"
@@ -40,6 +42,16 @@ static inline void AssertValid(const Coords& c, const HexMap* hexMap) {
         const APDCache& apdCache,
         const BattalionTypeGetter& battalionTypeGetter) -> vector<UnitId>;
 
+// Whether at least requiredUnitCount active, non-undead attacker units can reach every destination
+// without crossing water.
+[[nodiscard]] auto HasEnoughNonUndeadAttackersWithoutWaterCrossing(
+        const GameStateW& gameState,
+        const CoordsSet& destinations,
+        const LandRegions& landRegions,
+        const APDCache& apdCache,
+        const BattalionTypeGetter& battalionTypeGetter,
+        std::size_t requiredUnitCount) -> bool;
+
 // Units belonging to the player that are capable of creating water crossings
 [[nodiscard]] auto UnitIdsToCreateWaterCrossing(
         const GameStateW& gameState,

src/test/cpp/net/eagle0/shardok/ai/AIWaterCrossingCalculator_test.cpp

@@ -32,6 +32,10 @@ class AIWaterCrossingCalculatorTest : public ::testing::Test {
                 AddGenericUnit(0, 1, Coords(4, 0))};
 
         const auto unitsOffset = fbb.CreateVectorOfSortedStructs(&unitsVec);
+        const auto playerInfoOffset = fbb.CreateVector(
+                std::vector<flatbuffers::Offset<net::eagle0::shardok::storage::fb::PlayerInfo>>{
+                        AddPlayerInfo(fbb, 0, false, 1000),
+                        AddPlayerInfo(fbb, 1, true, 1000)});
 
         auto terrainTypes = TERRAIN_VALUES_FB;
         terrainTypes[0 * 6 + 3] = net::eagle0::shardok::storage::fb::Terrain_::Type_RIVER;
@@ -52,6 +56,7 @@ class AIWaterCrossingCalculatorTest : public ::testing::Test {
         net::eagle0::shardok::storage::fb::GameStateBuilder gsb(fbb);
         gsb.add_units(unitsOffset);
         gsb.add_hex_map(hexMapOffset);
+        gsb.add_player_infos(playerInfoOffset);
 
         fbb.Finish(gsb.Finish());
         gameState = GameStateW(fbb);
@@ -235,6 +240,94 @@ TEST_F(AIWaterCrossingCalculatorTest,
     EXPECT_EQ(1, ActionPointDistancesCache::GetThreadLocalCacheSize());
 }
 
+TEST_F(AIWaterCrossingCalculatorTest,
+       EnoughAttackersWithoutWaterCrossing_staticRegionsShortCircuitWithoutDistances) {
+    unit0->mutable_location() = Coords(0, 4);
+    unit1->mutable_location() = Coords(0, 5);
+
+    CoordsSet destinations(hexMap);
+    destinations.Add(acrossDestination);
+
+    int battalionTypeLookups = 0;
+    EXPECT_TRUE(HasEnoughNonUndeadAttackersWithoutWaterCrossing(
+            gameState,
+            destinations,
+            alCache->GetLandRegions(),
+            apdCache,
+            [&](BattalionTypeId typeId) {
+                ++battalionTypeLookups;
+                return GetGameSettings()->GetGetter().GetBattalionType(typeId);
+            },
+            1));
+    EXPECT_EQ(0, battalionTypeLookups);
+    EXPECT_EQ(0, ActionPointDistancesCache::GetThreadLocalCacheSize());
+}
+
+TEST_F(AIWaterCrossingCalculatorTest,
+       EnoughAttackersWithoutWaterCrossing_exactDistancesShortCircuitAtThreshold) {
+    auto& bridgeModifier = MutableTerrain(hexMap, Coords(1, 3))->mutable_modifier();
+    bridgeModifier.mutable_bridge().mutate_present(true);
+    bridgeModifier.mutable_bridge().mutate_integrity(100.0);
+    hexMap->mutate_modifier_hash(0);
+    hexMap->mutate_modifier_hash(ActionPointDistancesCache::GetMapId(hexMap).modifierId);
+
+    CoordsSet destinations(hexMap);
+    destinations.Add(acrossDestination);
+
+    int battalionTypeLookups = 0;
+    EXPECT_TRUE(HasEnoughNonUndeadAttackersWithoutWaterCrossing(
+            gameState,
+            destinations,
+            alCache->GetLandRegions(),
+            apdCache,
+            [&](BattalionTypeId typeId) {
+                ++battalionTypeLookups;
+                return GetGameSettings()->GetGetter().GetBattalionType(typeId);
+            },
+            1));
+    EXPECT_EQ(1, battalionTypeLookups);
+    EXPECT_EQ(1, ActionPointDistancesCache::GetThreadLocalCacheSize());
+}
+
+TEST_F(AIWaterCrossingCalculatorTest, EnoughAttackersWithoutWaterCrossing_noLandPathReturnsFalse) {
+    CoordsSet destinations(hexMap);
+    destinations.Add(acrossDestination);
+
+    EXPECT_FALSE(HasEnoughNonUndeadAttackersWithoutWaterCrossing(
+            gameState,
+            destinations,
+            alCache->GetLandRegions(),
+            apdCache,
+            [](BattalionTypeId typeId) {
+                return GetGameSettings()->GetGetter().GetBattalionType(typeId);
+            },
+            1));
+    EXPECT_EQ(1, ActionPointDistancesCache::GetThreadLocalCacheSize());
+}
+
+TEST_F(AIWaterCrossingCalculatorTest,
+       EnoughAttackersWithoutWaterCrossing_ignoresDefendersAndUndead) {
+    unit0->mutate_player_id(1);
+    unit0->mutable_location() = Coords(0, 4);
+    unit1->mutable_battalion().mutate_type(
+            net::eagle0::shardok::storage::fb::BattalionTypeId_UNDEAD);
+    unit1->mutable_location() = Coords(0, 5);
+
+    CoordsSet destinations(hexMap);
+    destinations.Add(acrossDestination);
+
+    EXPECT_FALSE(HasEnoughNonUndeadAttackersWithoutWaterCrossing(
+            gameState,
+            destinations,
+            alCache->GetLandRegions(),
+            apdCache,
+            [](BattalionTypeId typeId) {
+                return GetGameSettings()->GetGetter().GetBattalionType(typeId);
+            },
+            1));
+    EXPECT_EQ(0, ActionPointDistancesCache::GetThreadLocalCacheSize());
+}
+
 TEST_F(AIWaterCrossingCalculatorTest, CanReach_sameSide_returnsTrue) {
     EXPECT_TRUE(CanReach(origin, sameSideDestination, hexMap, mapId, apdCache, heavyCavalry));
 }