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/*
 * Copyright (C) 2009-2011 Mathias Doenitz
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.parboiled.support;

import com.github.parboiled1.grappa.matchers.base.Matcher;
import com.google.common.base.Preconditions;
import org.parboiled.Context;

import javax.annotation.Nullable;

/**
 * Holds a snapshot of the current {@link Matcher} stack at a certain point
 * during the parsing process.
 * Implemented as a specialized, immutable single-linked list of Element objects
 * with the deepest stack Element in the first position and the root at the end.
 */
public final class MatcherPath
{
    public static final class Element
    {
        private final Matcher matcher;
        private final int startIndex;
        private final int level;

        public Element(final Matcher matcher, final int startIndex,
            final int level)
        {
            this.matcher = matcher;
            this.startIndex = startIndex;
            this.level = level;
        }

        public Matcher getMatcher()
        {
            return matcher;
        }

        public int getStartIndex()
        {
            return startIndex;
        }

        public int getLevel()
        {
            return level;
        }
    }

    private final Element element;
    private final MatcherPath parent;

    /**
     * Constructs a new MatcherPath wrapping the given elements.
     * Normally you don't construct a MatcherPath directly but rather call
     * {@link Context#getPath()} to get one.
     *
     * @param element the last element of this path
     * @param parent the parent path
     */
    // TODO: get rid of null parent!
    public MatcherPath(final Element element,
        @Nullable final MatcherPath parent)
    {
        this.element = Preconditions.checkNotNull(element, "element");
        this.parent = parent;
    }

    /**
     * @return the length of this path, i.e. the number of matchers contained in it
     */
    public int length()
    {
        return element.getLevel() + 1;
    }

    /**
     * Determines whether this path is a prefix of the given other path.
     *
     * @param that the other path
     * @return true if this path is a prefix of the given other path
     */
    public boolean isPrefixOf(final MatcherPath that)
    {
        Preconditions.checkNotNull(that, "that");
        if (element.getLevel() <= that.element.getLevel() && this == that)
            return true;
        if (!that.hasParent())
            return false;
        return isPrefixOf(that.parent);
    }

    public Element getElement()
    {
        return element;
    }

    public MatcherPath getParent()
    {
        return parent;
    }

    public boolean hasParent()
    {
        return parent != null;
    }

    /**
     * Returns the Element at the given level.
     *
     * @param level the level to get the element from
     * @return the element
     */
    @Nullable
    public Element getElementAtLevel(final int level)
    {
        Preconditions.checkArgument(level >= 0);
        if (level > element.getLevel())
            return null;
        if (level < element.getLevel())
            return parent.getElementAtLevel(level);
        return element;
    }

    /**
     * Returns the common prefix of this MatcherPath and the given other one.
     *
     * @param that the other path
     * @return the common prefix or null
     */
    @Nullable // TODO! Remove that null!
    public MatcherPath commonPrefix(final MatcherPath that)
    {
        Preconditions.checkNotNull(that, "that");
        if (element.getLevel() > that.element.getLevel())
            return parent.commonPrefix(that);
        if (element.getLevel() < that.element.getLevel())
            return commonPrefix(that.parent);
        if (this == that)
            return this;
        return hasParent() && that.hasParent()
            ? parent.commonPrefix(that.parent)
            : null;
    }

    /**
     * Determines whether the given matcher is contained in this path.
     *
     * @param matcher the matcher
     * @return true if contained
     */
    public boolean contains(final Matcher matcher)
    {
        if (element.getMatcher() == matcher)
            return true;
        if (parent == null)
            return false;
        return parent.contains(matcher);
    }

    @Override
    public String toString()
    {
        // TODO: get rid of that null!
        return toString(null);
    }

    public String toString(final MatcherPath skipPrefix)
    {
        return print(new StringBuilder(), skipPrefix).toString();
    }

    private StringBuilder print(final StringBuilder sb,
        final MatcherPath skipPrefix)
    {
        return (parent == skipPrefix ? sb
            : parent.print(sb, skipPrefix).append('/'))
                .append(element.getMatcher());
    }
}