Arakne / Araknemu

 * This file is part of Araknemu.

 *

 * Araknemu is free software: you can redistribute it and/or modify

 * it under the terms of the GNU Lesser General Public License as published by

 * the Free Software Foundation, either version 3 of the License, or

 * (at your option) any later version.

 *

 * Araknemu is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU Lesser General Public License for more details.

 *

 * You should have received a copy of the GNU Lesser General Public License

 * along with Araknemu.  If not, see <https://www.gnu.org/licenses/>.

 *

 * Copyright (c) 2017-2020 Vincent Quatrevieux

 */

package fr.quatrevieux.araknemu.game.fight.ai.action;

import fr.arakne.utils.maps.CoordinateCell;

import fr.quatrevieux.araknemu.game.fight.ai.AI;

import fr.quatrevieux.araknemu.game.fight.ai.simulation.CastSimulation;

import fr.quatrevieux.araknemu.game.fight.ai.simulation.Simulator;

import fr.quatrevieux.araknemu.game.fight.ai.util.AIHelper;

import fr.quatrevieux.araknemu.game.fight.fighter.ActiveFighter;

import fr.quatrevieux.araknemu.game.fight.map.FightCell;

import fr.quatrevieux.araknemu.game.fight.turn.action.Action;

import java.util.Collection;

import java.util.HashMap;

import java.util.Map;

import java.util.Optional;

import java.util.stream.Collectors;

/**

 * Try to move for perform an attack

 *

 * The nearest cell for perform an attack is selected.

 * If the current cell permit attacking, the fighter will not perform any move.

 *

 * For select the cell, the generator will iterate over all reachable cells

 * with the current amount of MPs, sort them by distance,

 * and check all spells on all available cells.

 * The first matching cell is selected.

 */

public final class MoveToAttack implements ActionGenerator {

    private final Movement movement;

    private final Simulator simulator;

    private final Attack attack;

    private final TargetSelectionStrategy strategy;

    private final Map<FightCell, Collection<CastSimulation>> possibleActionsCache = new HashMap<>();

    private ActiveFighter fighter;

    private AIHelper helper;

    private MoveToAttack(Simulator simulator, TargetSelectionStrategy strategy) {

        this.simulator = simulator;

        this.attack = new Attack(simulator);

        this.strategy = strategy;

        this.movement = new Movement(this::score, this::isValidCell);

    }

    @Override

    public void initialize(AI ai) {

        movement.initialize(ai);

        attack.initialize(ai);

        this.fighter = ai.fighter();

    }

    @Override

    public Optional<Action> generate(AI ai) {

        helper = ai.helper();

        // Cannot move or attack

        if (!helper.canCast() || !helper.canMove()) {

            return Optional.empty();

        }

        try {

            // Can attack, but there is at least 1 enemy : do not perform move because of potential tackle

            if (canAttackFromCell(fighter.cell()) && helper.enemies().adjacent().findFirst().isPresent()) {

                return Optional.empty();

            }

            return movement.generate(ai);

        } finally {

            possibleActionsCache.clear();

        }

    }

    /**

     * Simulate possible attacks from the given cell

     *

     * - List available spells

     * - Combine with all accessible cells

     * - Check if the action is valid

     * - Simulate the action

     * - Keep only simulation results with an effective attack

     *

     * Note: Because the fighter should be move to the tested cell, values cannot be computed lazily, like with a stream

     *

     * @param cell The cell from which spells will be casted

     *

     * @see Attack#valid(CastSimulation) To check if the attack is effective

     */

    /**

     * Check if there is at least one attack possible from the given cell

     */

    private boolean canAttackFromCell(FightCell cell) {

        return !computePossibleCasts(cell).isEmpty();

    }

    /**

     * Compute the score of a cell

     * The lowest value will be selected

     */

    private double score(CoordinateCell<FightCell> coordinate) {

        return strategy.score(this, coordinate);

    }

    /**

     * Check if the cell is a valid movement

     *

     * It must have at least one possible attack

     */

    private boolean isValidCell(Movement.ScoredCell scoredCell) {

        return canAttackFromCell(scoredCell.coordinates().cell());

    }

    /**

     * Select the nearest cell where a cast is possible

     *

     * Note: This selected cell is not the best cell for perform an attack, but the nearest cell.

     *       So, it do not perform the best move for maximize damage.

     */

    public static MoveToAttack nearest(Simulator simulator) {

        return new MoveToAttack(simulator, new NearestStrategy());

    }

    /**

     * Select the best target cell for cast a spell, and maximizing damage

     */

    public static MoveToAttack bestTarget(Simulator simulator) {

        return new MoveToAttack(simulator, new BestTargetStrategy());

    }

    public interface TargetSelectionStrategy {

        /**

         * Compute the score of a given target cell

         *

         * @param generator The action generator

         * @param target The cell to check

         *

         * @return The score as double. The highest value will be selected

         */

        public double score(MoveToAttack generator, CoordinateCell<FightCell> target);

    }

    public static final class BestTargetStrategy implements TargetSelectionStrategy {

        @Override

        public double score(MoveToAttack generator, CoordinateCell<FightCell> target) {

            return maxScore(generator, target.cell()) - target.distance(generator.fighter.cell());

        }

        /**

         * Compute the max spell score from the given cell

         */

        private static double maxScore(MoveToAttack generator, FightCell cell) {

            return generator.computePossibleCasts(cell).stream()

                .mapToDouble(generator.attack::score)

                .max().orElse(0)

            ;

        }

    }

    private static final class NearestStrategy implements TargetSelectionStrategy {

        @Override

        public double score(MoveToAttack generator, CoordinateCell<FightCell> target) {

            return -target.distance(generator.fighter.cell()) + sigmoid(BestTargetStrategy.maxScore(generator, target.cell()));

        }

        /**

         * Transform score value in interval [-inf; +inf] to bounded value [0; 1]

         *

         * @param value Score to transform

         */

        private double sigmoid(double value) {

            return 0.5 + value / (2 * (1 + Math.abs(value)));

        }

    }

}