/*
 * This file is part of LibrePlan
 *
 * Copyright (C) 2009-2010 Fundación para o Fomento da Calidade Industrial e
 *                         Desenvolvemento Tecnolóxico de Galicia
 * Copyright (C) 2010-2011 Igalia, S.L.
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero 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 Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

package org.zkoss.ganttz.data;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import org.apache.commons.lang3.Validate;

/**
 * Represents a position for a task <br />
 * @author Óscar González Fernández <ogonzalez@igalia.com>
 */
public abstract class Position {

    /**
     * @param parents
     *            the list of ancestors from the parent to the more remote
     *            ancestor
     * @param positionInParent
     * @return a {@link Position} specified by the params
     */
    public static Position createPosition(List<? extends TaskContainer> parents, int positionInParent) {
        Validate.notEmpty(parents);
        Validate.noNullElements(parents);
        Validate.isTrue(positionInParent >= 0);
        Task firstParent = parents.get(0);
        Validate.isTrue(positionInParent < firstParent.getTasks().size());

        return new ChildPosition(parents, positionInParent);
    }

    public static Position createAtTopPosition(int position) {
        return new InsertInTopPosition(position);
    }

    public static Position createAppendToTopPosition() {
        return new AppendToTopPosition();
    }

    private final Integer position;

    protected Position(int position) {
        Validate.isTrue(position >= 0);
        this.position = position;
    }

    protected Position() {
        this.position = null;
    }

    public abstract boolean isAppendToTop();

    /**
     * From most near ancestor, to most remote, i.e., the first ancestor is the
     * parent and the last one is a top level task. It can return an empty list
     * if this {@link Position} is {@link #isAtTop()}
     */
    public abstract List<? extends TaskContainer> getAncestors();

    public abstract TaskContainer getParent();

    public boolean isAtTop() {
        return getAncestors().isEmpty();
    }

    public boolean specifiesPosition() {
        return position != null;
    }

    public Task getMostRemoteAncestor() {
        return getAncestors().get(getAncestors().size() - 1);
    }

    public Integer getInsertionPosition() {
        return position;
    }

    public abstract boolean canPop();

    /**
     * Removes the remotest ancestor
     * @return a new position
     * @throws UnsupportedOperationException
     *             if not {@link canPop}
     */
    public abstract Position pop() throws UnsupportedOperationException;

    /**
     * Creates a new position below the current one, with current being the
     * TaskContainer associated with the current {@link Position}.
     *
     * @param current
     * @param positionInParent
     * @return
     */
    public Position down(TaskContainer current, int positionInParent) {
        List<TaskContainer> ancestors = new ArrayList<>();
        ancestors.add(current);
        ancestors.addAll(getAncestors());

        return new ChildPosition(ancestors, positionInParent);
    }

    public abstract Position sameLevelAt(int positionInParent);


    private static class ChildPosition extends Position {

        private final List<? extends TaskContainer> parents;

        private TaskContainer parent;

        ChildPosition(List<? extends TaskContainer> parents, int positionInParent) {
            super(positionInParent);

            this.parents = parents;
            this.parent = parents.get(0);
        }

        @Override
        public boolean isAppendToTop() {
            return false;
        }

        @Override
        public TaskContainer getParent() {
            return parent;
        }

        @Override
        public List<? extends TaskContainer> getAncestors() {
            return parents;
        }

        @Override
        public Position pop() {
            return new ChildPosition(parents.subList(0, parents.size() - 1), getInsertionPosition());
        }

        @Override
        public boolean canPop() {
            return parents.size() > 1;
        }

        @Override
        public Position sameLevelAt(int positionInParent) {
            return new ChildPosition(parents, positionInParent);
        }
    }

    private static class AppendToTopPosition extends Position {
        @Override
        public boolean isAppendToTop() {
            return true;
        }

        @Override
        public TaskContainer getParent() {
            return null;
        }

        @Override
        public List<? extends TaskContainer> getAncestors() {
            return Collections.emptyList();
        }

        @Override
        public Position pop() {
            throw new UnsupportedOperationException();
        }

        @Override
        public boolean canPop() {
            return false;
        }

        @Override
        public Position sameLevelAt(int positionInParent) {
            return new InsertInTopPosition(positionInParent);
        }
    }

    private static class InsertInTopPosition extends Position {

        InsertInTopPosition(int position) {
            super(position);
        }

        @Override
        public boolean isAppendToTop() {
            return false;
        }

        @Override
        public TaskContainer getParent() {
            return null;
        }

        @Override
        public List<? extends TaskContainer> getAncestors() {
            return Collections.emptyList();
        }

        @Override
        public Position pop() {
            throw new UnsupportedOperationException();
        }

        @Override
        public boolean canPop() {
            return false;
        }

        @Override
        public Position sameLevelAt(int positionInParent) {
            return new InsertInTopPosition(positionInParent);
        }

    }

}