Gamelib/src/main/java/uulm/teamname/marvelous/gamelibrary/gamelogic/GameLogic.java

package uulm.teamname.marvelous.gamelibrary.gamelogic;

import uulm.teamname.marvelous.gamelibrary.IntVector2;
import uulm.teamname.marvelous.gamelibrary.entities.*;
import uulm.teamname.marvelous.gamelibrary.entities.Character;
import uulm.teamname.marvelous.gamelibrary.events.*;
import uulm.teamname.marvelous.gamelibrary.events.Event;
import uulm.teamname.marvelous.gamelibrary.requests.CharacterRequest;
import uulm.teamname.marvelous.gamelibrary.requests.Request;
import uulm.teamname.marvelous.gamelibrary.requests.RequestType;

import java.awt.*;
import java.awt.geom.Line2D;
import java.util.*;

/** Contains game logic handling. */
class GameLogic {
    private static final Random rand = new Random();

    /**
     * Produces resulting {@link Event}s from a given {@link Request}.
     * @param state The game state to execute on
     * @param request The request to execute
     * @return The list of resulting events
     */
    public static ArrayList<Event> executeRequest(GameState state, Request request) {
        ArrayList<Event> result = new ArrayList<>();

        switch(request.type) {
            case MeleeAttackRequest, RangedAttackRequest -> {
                CharacterRequest data = (CharacterRequest)request;
                result.add(new EventBuilder(request.type == RequestType.MeleeAttackRequest ? EventType.MeleeAttackEvent : EventType.RangedAttackEvent)
                        .withOriginEntity(data.originEntity)
                        .withTargetEntity(data.targetEntity)
                        .withOriginField(data.originField)
                        .withTargetField(data.targetField)
                        .withAmount(data.value)
                        .buildCharacterEvent());
                result.add(new EventBuilder(EventType.ConsumedAPEvent)
                        .withTargetEntity(data.originEntity)
                        .withTargetField(data.originField)
                        .withAmount(1)
                        .buildEntityEvent());
                result.add(new EventBuilder(EventType.TakenDamageEvent)
                        .withTargetEntity(data.targetEntity)
                        .withTargetField(data.targetField)
                        .withAmount(data.value)
                        .buildEntityEvent());
            }
            case MoveRequest -> {
                CharacterRequest data = (CharacterRequest)request;
                result.add(new EventBuilder(EventType.MoveEvent)
                        .withOriginEntity(data.originEntity)
                        .withOriginField(data.originField)
                        .withTargetField(data.targetField)
                        .buildCharacterEvent());
                result.add(new EventBuilder(EventType.ConsumedMPEvent)
                        .withTargetEntity(data.originEntity)
                        .withTargetField(data.targetField) //when this event gets handled, the character already moved to the target field
                        .withAmount(1)
                        .buildEntityEvent());
                for(Entity entity: state.entities.findByPosition(data.targetField)) {
                    if(entity instanceof Character) {
                        result.add(new EventBuilder(EventType.MoveEvent)
                                .withOriginEntity(entity.id)
                                .withOriginField(data.targetField)
                                .withTargetField(data.originField)
                                .buildCharacterEvent());
                        break; //we should only have one character per field anyways
                    }
                }
            }
            case ExchangeInfinityStoneRequest, UseInfinityStoneRequest -> {
                CharacterRequest data = (CharacterRequest)request;
                result.add(new EventBuilder(request.type == RequestType.ExchangeInfinityStoneRequest ? EventType.ExchangeInfinityStoneEvent : EventType.UseInfinityStoneEvent)
                        .withOriginEntity(data.originEntity)
                        .withOriginField(data.originField)
                        .withTargetEntity(data.targetEntity)
                        .withTargetField(data.targetField)
                        .withStoneType(data.stoneType)
                        .buildCharacterEvent());
                result.add(new EventBuilder(EventType.ConsumedAPEvent)
                        .withTargetEntity(data.originEntity)
                        .withTargetField(data.originField)
                        .withAmount(1)
                        .buildEntityEvent());

                if(request.type == RequestType.UseInfinityStoneRequest) {
                    switch(((CharacterRequest) request).stoneType) {
                        case SpaceStone -> {
                            result.add(new EventBuilder(EventType.MoveEvent)
                                    .withOriginEntity(data.originEntity)
                                    .withOriginField(data.originField)
                                    .withTargetField(data.targetField)
                                    .buildCharacterEvent());
                        }
                        case MindStone -> {
                            EntityType target = data.originEntity.type == EntityType.P1 ? EntityType.P2 : EntityType.P1;
                            Line2D line = new Line2D.Float(data.originField.getX(), data.originField.getY(), data.targetField.getX(), data.targetField.getY());
                            for(int i = data.originField.getX(); i <= data.targetField.getX(); i++) {
                                for(int j = data.originField.getY(); j <= data.targetField.getY(); j++) {
                                    var cell = new Rectangle.Float(i - 0.5f, j - 0.5f, 1, 1);
                                    if(line.intersects(cell)) {
                                        for(Entity entity: state.entities.findByPosition(data.targetField)) {
                                            if(entity.id.isSameType(target)) {
                                                result.add(new EventBuilder(EventType.TakenDamageEvent)
                                                        .withTargetEntity(entity.id)
                                                        .withTargetField(new IntVector2(i, j))
                                                        .withAmount(data.value)
                                                        .buildEntityEvent());
                                            }
                                        }
                                    }
                                }
                            }
                        }
                        case RealityStone -> {
                            if(data.originEntity == data.targetEntity) { // => place stone
                                result.add(new EventBuilder(EventType.SpawnEntityEvent)
                                        .withTargetField(data.targetField)
                                        .withEntity(new Rock(new EntityID(EntityType.Rocks, state.entities.findFreeRockSlot()), data.targetField, 100))
                                        .buildEntityEvent());
                            }else { // => destroy stone
                                result.add(new EventBuilder(EventType.DestroyedEntityEvent)
                                        .withTargetField(data.targetField)
                                        .withTargetEntity(data.targetEntity)
                                        .buildEntityEvent());
                            }
                        }
                        case PowerStone -> {
                            Character origin = (Character)state.entities.findEntity(data.originEntity);
                            int dmg = (int)Math.round(origin.hp.getValue() * 0.1);
                            if(origin.hp.getValue() != 1 && dmg > 0) {
                                result.add(new EventBuilder(EventType.TakenDamageEvent)
                                        .withTargetEntity(data.originEntity)
                                        .withTargetField(data.originField)
                                        .withAmount(dmg)
                                        .buildEntityEvent());
                            }
                            result.add(new EventBuilder(EventType.TakenDamageEvent)
                                    .withTargetEntity(data.targetEntity)
                                    .withTargetField(data.targetField)
                                    .withAmount(data.value)
                                    .buildEntityEvent());
                        }
                        case TimeStone -> {
                            Character origin = (Character)state.entities.findEntity(data.originEntity);
                            int ap = origin.ap.max - origin.ap.getValue();
                            if(ap < 0) {
                                result.add(new EventBuilder(EventType.ConsumedAPEvent)
                                        .withTargetEntity(data.originEntity)
                                        .withTargetField(data.originField)
                                        .withAmount(ap)
                                        .buildEntityEvent());
                            }
                            int mp = origin.mp.max - origin.mp.getValue();
                            if(mp < 0) {
                                result.add(new EventBuilder(EventType.ConsumedMPEvent)
                                        .withTargetEntity(data.originEntity)
                                        .withTargetField(data.originField)
                                        .withAmount(mp)
                                        .buildEntityEvent());
                            }
                        }
                        case SoulStone -> {
                            Character target = (Character)state.entities.findEntity(data.targetEntity);
                            result.add(new EventBuilder(EventType.HealedEvent)
                                    .withTargetEntity(data.targetEntity)
                                    .withTargetField(data.targetField)
                                    .withAmount(target.hp.max)
                                    .buildEntityEvent());
                        }
                    }
                }
            }
            case EndRoundRequest -> {
                result.addAll(handleTurnEnd(state)); //why is it called end round request when it ends a turn...
            }
            case Req -> {
                result.add(buildGameStateEvent(state));
            }
        }

        return result;
    }

    /**
     * Builds a {@link EventType#GamestateEvent} for the given {@link GameState}.
     * @param state The game state to use
     * @return The resulting event
     */
    public static Event buildGameStateEvent(GameState state) {
        return new EventBuilder(EventType.GamestateEvent)
                .withEntities(state.entities.export())
                .withTurnOrder((EntityID[])state.turnOrder.toArray())
                .withMapSize(state.mapSize)
                .withActiveCharacter(state.activeCharacter)
                .withStoneCooldowns(state.stoneCooldown.export())
                .withWinCondition(state.won)
                .buildGameStateEvent();
    }

    /**
     * Checks a {@link Request} for validity for a {@link GameState}.
     * @param state The game state to check on
     * @param request The request to validate
     * @return Whether or not the request is valid
     */
    public static boolean checkRequest(GameState state, Request request) {
        try {
            switch(request.type) {
                case MeleeAttackRequest, RangedAttackRequest -> {
                    CharacterRequest data = (CharacterRequest)request;

                    Character origin = getCharacter(state, data.originField, data.originEntity);
                    Character target = getCharacter(state, data.targetField, data.targetEntity);

                    requireAlive(origin);
                    requireAlive(target);
                    requireAP(origin, 1);

                    if(request.type == RequestType.MeleeAttackRequest) {
                        if(origin.meleeDamage != data.value) {
                            throw new InvalidRequestException();
                        }
                        if(data.originField.distanceChebyshev(data.targetField) > 1) {
                            throw new InvalidRequestException();
                        }
                    }else if(request.type == RequestType.RangedAttackRequest) {
                        if(origin.rangedDamage != data.value) {
                            throw new InvalidRequestException();
                        }
                        if(data.originField.distanceChebyshev(data.targetField) > origin.attackRange) {
                            throw new InvalidRequestException();
                        }
                        if(data.originField.distanceChebyshev(data.targetField) <= 1) {
                            throw new InvalidRequestException();
                        }
                        requireLineOfSight(state, data.originField, data.targetField);
                    }

                    return true;
                }
                case MoveRequest -> {
                    CharacterRequest data = (CharacterRequest)request;

                    Character origin = getCharacter(state, data.originField, data.originEntity);

                    requireAlive(origin);
                    requireMP(origin, 1);
                    verifyCoordinates(state, data.targetField);

                    if(data.originField.distanceChebyshev(data.targetField) != 1) {
                        throw new InvalidRequestException();
                    }

                    if(state.entities.blocksMovement(data.targetField)) {
                        throw new InvalidRequestException();
                    }

                    return true;
                }
                case ExchangeInfinityStoneRequest -> {
                    CharacterRequest data = (CharacterRequest)request;

                    Character origin = getCharacter(state, data.originField, data.originEntity);
                    Character target = getCharacter(state, data.targetField, data.targetEntity);

                    requireAlive(origin);
                    requireAlive(target);
                    requireAP(origin, 1);
                    requireInfinityStone(origin, data.stoneType);

                    if(data.originField.distanceChebyshev(data.targetField) != 1) {
                        throw new InvalidRequestException();
                    }

                    return true;
                }
                case UseInfinityStoneRequest -> {
                    CharacterRequest data = (CharacterRequest)request;

                    Character origin = getCharacter(state, data.originField, data.originEntity);

                    requireAlive(origin);
                    requireAP(origin, 1);
                    requireInfinityStone(origin, data.stoneType);

                    if(state.stoneCooldown.onCooldown(data.stoneType)) {
                        throw new InvalidRequestException();
                    }

                    switch(((CharacterRequest) request).stoneType) {
                        case SpaceStone -> {
                            verifyCoordinates(state, data.targetField);

                            if(state.entities.blocksMovement(data.targetField)) {
                                throw new InvalidRequestException();
                            }
                        }
                        case MindStone -> {
                            if(data.originField == data.targetField) {
                                throw new InvalidRequestException();
                            }
                            if(data.value != state.partyConfig.mindStoneDMG) {
                                throw new InvalidRequestException();
                            }
                        }
                        case RealityStone -> {
                            if(data.originEntity == data.targetEntity) { // => place stone
                                if(state.entities.findByPosition(data.targetField).size() != 0) {
                                    throw new InvalidRequestException();
                                }
                            }else { // => destroy stone
                                boolean hasRock = false;
                                for(Entity entity: state.entities.findByPosition(data.targetField)) {
                                    if(entity.id.isSameType(EntityType.Rocks)) {
                                        hasRock = true;
                                        break;
                                    }
                                }
                                if(!hasRock) {
                                    throw new InvalidRequestException();
                                }
                            }
                        }
                        case PowerStone -> {
                            Character target = getCharacter(state, data.targetField, data.targetEntity);

                            requireAlive(target);

                            if(origin.rangedDamage * 2 != data.value) {
                                throw new InvalidRequestException();
                            }
                        }
                        case TimeStone -> {
                            // "👍  i approve" - the server
                        }
                        case SoulStone -> {
                            Character target = getCharacter(state, data.targetField, data.targetEntity);

                            if(target.hp.getValue() != 0) {
                                throw new InvalidRequestException();
                            }
                        }
                    }

                    return true;
                }
                case EndRoundRequest, Req -> {
                    return true;
                }
            }
        }catch(Exception ignored) {
            return false;
        }

        return false;
    }

    /**
     * Retrieves a {@link Character} for a {@link Request}.
     * @param state The game state to use
     * @param position The requested position
     * @param entityID The requested {@link EntityID}
     * @return The found character
     * @throws InvalidRequestException if the character is invalid or not found
     */
    private static Character getCharacter(GameState state, IntVector2 position, EntityID entityID) throws InvalidRequestException {
        Entity entity = state.entities.findEntity(entityID);
        if(entity == null || entity.getPosition() != position || !(entity instanceof Character)) {
            throw new InvalidRequestException();
        }
        try {
            return (Character)entity;
        }catch(Exception ignored) {
            throw new InvalidRequestException();
        }
    }

    /**
     * Verifies that a {@link Character} is alive.
     */
    private static void requireAlive(Character entity) throws InvalidRequestException {
        //TODO: only characters are allowed here
        if(entity.hp.getValue() <= 0 || !entity.isActive()) {
            throw new InvalidRequestException();
        }
    }

    /**
     * Verifies that a {@link Character} has enough {@link StatType#AP}.
     */
    private static void requireAP(Character entity, int ap) throws InvalidRequestException {
        if(entity.ap.getValue() < ap) {
            throw new InvalidRequestException();
        }
    }

    /**
     * Verifies that a {@link Character} has enough {@link StatType#MP}.
     */
    private static void requireMP(Character entity, int mp) throws InvalidRequestException {
        if(entity.mp.getValue() < mp) {
            throw new InvalidRequestException();
        }
    }

    /**
     * Verifies that a {@link Character} has the required {@link StoneType}.
     */
    private static void requireInfinityStone(Character entity, StoneType stone) throws InvalidRequestException {
        if(stone == null || !entity.inventory.hasStone(stone)) {
            throw new InvalidRequestException();
        }
    }

    /**
     * Verifies that coordinates are within the playing area.
     */
    private static void verifyCoordinates(GameState state, IntVector2 position) throws InvalidRequestException {
        if(position.getX() < 0 || position.getX() >= state.mapSize.getX() || position.getY() < 0 || position.getY() >= state.mapSize.getY()) {
            throw new InvalidRequestException();
        }
    }

    /**
     * Verifies that there is a line of sight between two positions.
     */
    private static void requireLineOfSight(GameState state, IntVector2 start, IntVector2 end) throws InvalidRequestException {
        if(!checkLineOfSight(state, start, end)) {
            throw new InvalidRequestException();
        }
    }

    /**
     * Checks if a line of sight exists between the two positions
     * @param state The game state to work on
     * @param start The first position
     * @param end The second position
     * @return Whether or not the light of sight exists
     */
    private static boolean checkLineOfSight(GameState state, IntVector2 start, IntVector2 end) {
        //naive code for the win!!! \o/
        //at least its early exit and probably only O(ln(n*m))
        //TODO: implement proper line rasterization algorithm in GameLogic.checkLineOfSight
        Line2D line = new Line2D.Float(start.getX(), start.getY(), end.getX(), end.getY());
        for(int i = start.getX(); i <= end.getX(); i++) {
            for(int j = start.getY(); j <= end.getY(); j++) {
                var cell = new Rectangle.Float(i - 0.5f, j - 0.5f, 1, 1);
                if(line.intersects(cell)) {
                    if(state.entities.blocksVision(new IntVector2(i, j))) {
                        return false;
                    }
                }
            }
        }
        return true;
    }

    /**
     * Finds free neighbour options from a starting field.
     * @param state The game state to work on
     * @param start The starting position
     * @return A list of free neighbour field options
     */
    private static ArrayList<IntVector2> getFreeNeighbour(GameState state, IntVector2 start) {
        ArrayList<IntVector2> options = new ArrayList<>();

        if(start.getX() < 0 || start.getX() >= state.mapSize.getX() || start.getY() < 0 || start.getY() >= state.mapSize.getY()) {
            return options;
        }

        for(IntVector2 dir: IntVector2.CardinalDirections) {
            if(state.entities.findByPosition(start.add(dir)).size() == 0) {
                options.add(start.add(dir));
            }
        }

        if(options.size() == 0) {
            return getFreeNeighbour(state, start.add(IntVector2.CardinalDirections[rand.nextInt(IntVector2.CardinalDirections.length)]));
        }else {
            return options;
        }
    }

    /**
     * Applies an {@link Event} to a {@link GameState}.
     * @param state The game state to apply to
     * @param event The event to apply
     */
    public static void applyEvent(GameState state, Event event) {
        switch(event.type) {
            case DestroyedEntityEvent -> {
                state.entities.removeEntity(((EntityEvent)event).targetEntity);
            }
            case TakenDamageEvent -> {
                Character target = (Character)state.entities.findEntity(((CharacterEvent)event).targetEntity);
                target.hp.decreaseValue(((CharacterEvent)event).amount);

                EntityType opposing = target.id.type == EntityType.P1 ? EntityType.P2 : EntityType.P1;
                state.winConditions.increaseValue(opposing, WinCondition.TotalDamage, ((CharacterEvent)event).amount);
                if(target.hp.getValue() == 0) {
                    state.winConditions.increaseValue(opposing, WinCondition.TotalKnockouts, 1);
                }
            }
            case ConsumedAPEvent -> {
                ((Character)state.entities.findEntity(((CharacterEvent)event).targetEntity)).ap.decreaseValue(((CharacterEvent)event).amount);
            }
            case ConsumedMPEvent -> {
                ((Character)state.entities.findEntity(((CharacterEvent)event).targetEntity)).mp.decreaseValue(((CharacterEvent)event).amount);
            }
            case SpawnEntityEvent -> {
                state.entities.addEntity(((EntityEvent)event).entity);
            }
            case HealedEvent -> {
                ((Character)state.entities.findEntity(((CharacterEvent)event).targetEntity)).hp.increaseValue(((CharacterEvent)event).amount);
            }
            case MoveEvent -> {
                Character target = (Character)state.entities.findEntity(((CharacterEvent)event).originEntity);
                for(Entity entity: state.entities.findByPosition(((CharacterEvent)event).targetField)) {
                    if(entity instanceof InfinityStone) {
                        target.inventory.addStone(((InfinityStone)entity).type);

                        state.winConditions.updateValue(target.id.type, WinCondition.MaxStones, target.inventory.getSize());
                    }
                }
                target.setPosition(((CharacterEvent)event).targetField);
            }
            case UseInfinityStoneEvent -> {
                state.stoneCooldown.setCooldown(((CharacterEvent)event).stoneType);
            }
            case ExchangeInfinityStoneEvent -> {
                ((Character)state.entities.findEntity(((CharacterEvent)event).originEntity)).inventory.removeStone(((CharacterEvent)event).stoneType);
                Character target = (Character)state.entities.findEntity(((CharacterEvent)event).targetEntity);
                target.inventory.addStone(((CharacterEvent)event).stoneType);

                state.winConditions.updateValue(target.id.type, WinCondition.MaxStones, target.inventory.getSize());
            }
        }
    }

    /**
     * Starts end of round handling if necessary.
     * @param state The game state to work on
     * @return The list of resulting {@link Event}s
     */
    public static ArrayList<Event> checkTurnEnd(GameState state) {
        if(
            ((Character) state.entities.findEntity(state.activeCharacter)).ap.getValue() <= 0 &&
            ((Character) state.entities.findEntity(state.activeCharacter)).mp.getValue() <= 0
        ) {
            return handleTurnEnd(state);
        }

        return new ArrayList<>();
    }

    /**
     * Handles everything that happens at the end of a turn, including new rounds.
     * @param state The game state to work on
     * @return The list of resulting {@link Event}s
     */
    public static ArrayList<Event> handleTurnEnd(GameState state) {
        ArrayList<Event> result = new ArrayList<>();

        ArrayList<EntityID> alive = new ArrayList<>();

        for (EntityID id: state.turnOrder) {
            Character character = ((Character)state.entities.findEntity(id));

            if(character.hp.getValue() > 0){
                alive.add(id);
            }

            if(character.inventory.getFreeSlots() == 0) { // no slots => has all infinity stones
                result.addAll(handlePlayerWin(state, character.id.type));
                return result;
            }
        }

        if(alive.isEmpty()) {
            EntityType winner = state.winConditions.getWinner();
            if(winner == EntityType.None) {
                winner = rand.nextBoolean() ? EntityType.P1 : EntityType.P2;
            }
            result.addAll(handlePlayerWin(state, winner));
            return result;
        }

        int index = alive.indexOf(state.activeCharacter);
        if(index == alive.size() - 1) {
            result.addAll(handleRoundStart(state));
        }else {
            state.activeCharacter = alive.get(index + 1);
        }

        result.addAll(handleTurnStart(state));

        return result;
    }

    /**
     * Handles everything that happens at the beginning of new rounds.
     * @param state The game state to work on
     * @return The list of resulting {@link Event}s
     */
    public static ArrayList<Event> handleRoundStart(GameState state) {
        ArrayList<Event> result = new ArrayList<>();

        state.roundNumber++;
        state.turnNumber = 0;

        if(state.roundNumber >= 1 && state.roundNumber <= 6) {
            result.addAll(handleGoose(state));
        }

        HashSet<EntityID> revived = new HashSet<>();
        if(state.roundNumber == 7) {
            result.addAll(handleStan(state, revived));
        }

        //TODO: add handling for thanos

        Collections.shuffle(state.turnOrder);

        for (EntityID id: state.turnOrder) {
            if(revived.contains(id) || ((Character)state.entities.findEntity(id)).hp.getValue() > 0){
                state.activeCharacter = id;
                break;
            }
        }

        state.stoneCooldown.update();

        result.add(new EventBuilder(EventType.RoundSetupEvent)
                .withRoundCount(state.roundNumber)
                .withCharacterOrder(state.turnOrder.toArray(new EntityID[0]))
                .buildGameEvent());

        return result;
    }

    /**
     * Handles the actions of Goose at rounds 1-6.
     * @param state The game state to work on
     * @return The list of resulting {@link Event}s
     */
    public static ArrayList<Event> handleGoose(GameState state) {
        ArrayList<Event> result = new ArrayList<>();

        StoneType[] available = state.unvomitedStones.toArray(new StoneType[0]);
        StoneType stone = available[rand.nextInt(available.length)];
        state.unvomitedStones.remove(stone);

        ArrayList<IntVector2> free = new ArrayList<>();
        for(int x = 0; x < state.mapSize.getX(); x++) {
            for(int y = 0; y < state.mapSize.getY(); y++) {
                IntVector2 pos = new IntVector2(x, y);
                if(state.entities.findByPosition(pos).size() == 0) {
                    free.add(pos);
                }
            }
        }
        IntVector2 position = free.get(rand.nextInt(free.size()));

        EntityID goose = new EntityID(EntityType.NPC, 0);
        result.add(new EventBuilder(EventType.SpawnEntityEvent)
                .withEntity(new NPC(goose, position))
                .buildEntityEvent());
        result.add(new EventBuilder(EventType.SpawnEntityEvent)
                .withEntity(new InfinityStone(new EntityID(EntityType.InfinityStones, stone.getID()), position, stone))
                .buildEntityEvent());
        result.add(new EventBuilder(EventType.DestroyedEntityEvent)
                .withTargetEntity(goose)
                .withTargetField(position)
                .buildEntityEvent());

        return result;
    }

    /**
     * Handles the actions of Stan at round 7.
     * @param state The game state to work on
     * @return The list of resulting {@link Event}s
     */
    public static ArrayList<Event> handleStan(GameState state, HashSet<EntityID> revived) {
        ArrayList<Event> result = new ArrayList<>();

        ArrayList<Character> characters = new ArrayList<>();

        ArrayList<IntVector2> targetOptions = new ArrayList<>();
        int lowest = -1;
        for(EntityID id: state.turnOrder) {
            Character character = (Character)state.entities.findEntity(id);
            characters.add(character);

            if(lowest == -1 || character.hp.getValue() < lowest) {
                lowest = character.hp.getValue();
                targetOptions.clear();
            }
            if(lowest == character.hp.getValue()) {
                targetOptions.add(character.getPosition());
            }
        }
        IntVector2 targetPosition = targetOptions.get(rand.nextInt(targetOptions.size()));

        ArrayList<IntVector2> spawnOptions = getFreeNeighbour(state, targetPosition);
        if(spawnOptions.size() == 0) {
            return result;
        }
        IntVector2 spawnPosition = spawnOptions.get(rand.nextInt(spawnOptions.size()));

        EntityID stan = new EntityID(EntityType.NPC, 1);
        result.add(new EventBuilder(EventType.SpawnEntityEvent)
                .withEntity(new NPC(stan, spawnPosition))
                .buildEntityEvent());

        for(Character character: characters) {
            if(checkLineOfSight(state, spawnPosition, character.getPosition())) {
                if(character.hp.getValue() == 0) {
                    revived.add(character.id);
                }
                if(character.hp.getValue() != character.hp.max) {
                    result.add(new EventBuilder(EventType.HealedEvent)
                            .withTargetEntity(character.id)
                            .withTargetField(character.getPosition())
                            .withAmount(character.hp.max - character.hp.getValue())
                            .buildEntityEvent());
                }
            }
        }

        result.add(new EventBuilder(EventType.DestroyedEntityEvent)
                .withTargetEntity(stan)
                .withTargetField(spawnPosition)
                .buildEntityEvent());

        return result;
    }

    /**
     * Handles everything that happens at the beginning of a turn.
     * @param state The game state to work on
     * @return The list of resulting {@link Event}s
     */
    public static ArrayList<Event> handleTurnStart(GameState state) {
        ArrayList<Event> result = new ArrayList<>();

        state.turnNumber++;

        Character activeCharacter = (Character)state.entities.findEntity(state.activeCharacter);

        if(activeCharacter.ap.getValue() != activeCharacter.ap.max) {
            result.add(new EventBuilder(EventType.ConsumedAPEvent)
                    .withTargetEntity(state.activeCharacter)
                    .withTargetField(activeCharacter.getPosition())
                    .withAmount(activeCharacter.ap.getValue() - activeCharacter.ap.max)
                    .buildGameEvent());
        }
        if(activeCharacter.mp.getValue() != activeCharacter.mp.max) {
            result.add(new EventBuilder(EventType.ConsumedMPEvent)
                    .withTargetEntity(state.activeCharacter)
                    .withTargetField(activeCharacter.getPosition())
                    .withAmount(activeCharacter.mp.getValue() - activeCharacter.mp.max)
                    .buildGameEvent());
        }
        result.add(new EventBuilder(EventType.TurnEvent)
                .withTurnCount(state.turnOrder.size())
                .withNextCharacter(state.activeCharacter)
                .buildGameEvent());

        return result;
    }

    /**
     * Handles the victory of a player through one character.
     * @param state The game state to work on
     * @param winner The winning character
     * @return The list of resulting {@link Event}s
     */
    public static ArrayList<Event> handlePlayerWin(GameState state, EntityType winner) {
        ArrayList<Event> result = new ArrayList<>();

        state.won = true;

        result.add(new EventBuilder(EventType.WinEvent)
                .withPlayerWon(winner == EntityType.P1 ? 1 : 2)
                .buildGameEvent());

        return result;
    }
}