/*
 * WorldEdit, a Minecraft world manipulation toolkit
 * Copyright (C) sk89q <http://www.sk89q.com>
 * Copyright (C) WorldEdit team and contributors
 *
 * This program 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.
 *
 * This program 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 this program. If not, see <http://www.gnu.org/licenses/>.
 */

package com.sk89q.worldedit.function.visitor;

import static com.google.common.base.Preconditions.checkNotNull;

import java.util.Collection;

import com.sk89q.worldedit.Vector;
import com.sk89q.worldedit.function.RegionFunction;
import com.sk89q.worldedit.function.mask.Mask;
import com.sk89q.worldedit.function.operation.Operations;

/**
 * Visits adjacent points on the same X-Z plane as long as the points
 * pass the given mask, and then executes the provided region
 * function on the entire column.
 *
 * <p>This is used by {@code //fill}.</p>
 */
public class DownwardVisitor extends RecursiveVisitor {
    
    private final int baseY;
    
    /**
     * Create a new visitor.
     *
     * @param mask the mask
     * @param function the function
     * @param baseY the base Y
     */
    public DownwardVisitor(final Mask mask, final RegionFunction function, final int baseY) {
        super(mask, function);
        checkNotNull(mask);
        
        this.baseY = baseY;
        
        final Collection<Vector> directions = getDirections();
        directions.clear();
        directions.add(new Vector(1, 0, 0));
        directions.add(new Vector(-1, 0, 0));
        directions.add(new Vector(0, 0, 1));
        directions.add(new Vector(0, 0, -1));
        directions.add(new Vector(0, -1, 0));
    }
    
    @Override
    protected boolean isVisitable(final Vector from, final Vector to) {
        final int fromY = from.getBlockY();
        return ((fromY == baseY) || (to.subtract(from).getBlockY() < 0)) && super.isVisitable(from, to);
    }
    
    public static Class<?> inject() {
        return Operations.class;
    }
}