ParseRunner.java

/*
 * 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 com.github.fge.grappa.run;

import com.github.fge.grappa.Grappa;
import com.github.fge.grappa.buffers.CharSequenceInputBuffer;
import com.github.fge.grappa.buffers.InputBuffer;
import com.github.fge.grappa.exceptions.GrappaException;
import com.github.fge.grappa.internal.NonFinalForTesting;
import com.github.fge.grappa.matchers.base.Matcher;
import com.github.fge.grappa.rules.Rule;
import com.github.fge.grappa.run.context.DefaultMatcherContext;
import com.github.fge.grappa.run.context.MatcherContext;
import com.github.fge.grappa.run.events.MatchContextEvent;
import com.github.fge.grappa.run.events.MatchFailureEvent;
import com.github.fge.grappa.run.events.MatchSuccessEvent;
import com.github.fge.grappa.run.events.PostParseEvent;
import com.github.fge.grappa.run.events.PreMatchEvent;
import com.github.fge.grappa.run.events.PreParseEvent;
import com.github.fge.grappa.stack.ArrayValueStack;
import com.github.fge.grappa.stack.ValueStack;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.eventbus.EventBus;

import javax.annotation.Nonnull;
import java.util.Objects;

/**
 * Class to run a parser on an input, and retrieve a result
 *
 * <p>This is the class which is used when you want to actually run an instance
 * of a parser (created using {@link Grappa#createParser(Class, Object...)})
 * against a text input.</p>
 *
 * <p>The basic text input is a {@link CharSequence}; since {@link String}
 * implements this interface, this is the most direct way to run a parser.
 * If you wish to, however, you may implement your own {@link InputBuffer} and
 * pass is as an alternative.</p>
 *
 * <p>You can also register a number of listeners implementing {@link
 * ParseEventListener}. Such listeners have the ability to listen to the parse
 * events of your choice (before parsing, before matching, match failure
 * or success, after parsing), further extending the use of grappa.</p>
 *
 * @param <V> type parameter of the parser's stack values
 *
 * @see ParseEventListener
 */
@NonFinalForTesting
public class ParseRunner<V>
    implements MatchHandler
{
    // TODO: does it need to be volatile?
    private volatile Throwable throwable = null;

    private final EventBus bus = new EventBus((exception, context) -> {
        if (throwable == null)
            throwable = exception;
        else
            throwable.addSuppressed(exception);
    });


    protected final Matcher rootMatcher;
    protected ValueStack<V> valueStack;
    protected Object stackSnapshot;

    /**
     * Constructor
     *
     * @param rule the rule
     */
    public ParseRunner(@Nonnull final Rule rule)
    {
        rootMatcher = Objects.requireNonNull((Matcher) rule, "rule");
    }

    public final ParsingResult<V> run(final CharSequence input)
    {
        Objects.requireNonNull(input, "input");
        return run(new CharSequenceInputBuffer(input));
    }

    public final ParsingResult<V> run(final InputBuffer inputBuffer)
    {
        Objects.requireNonNull(inputBuffer, "inputBuffer");
        resetValueStack();

        final MatcherContext<V> context = createRootContext(inputBuffer, this);
        bus.post(new PreParseEvent<>(context));

        if (throwable != null)
            throw new GrappaException("parsing listener error (before parse)",
                throwable);

        final boolean matched = context.runMatcher();
        final ParsingResult<V> result
            = createParsingResult(matched, context);

        bus.post(new PostParseEvent<>(result));

        if (throwable != null)
            throw new GrappaException("parsing listener error (after parse)",
                throwable);

        return result;
    }

    private void resetValueStack()
    {
        // TODO: write a "memoizing" API
        valueStack = new ArrayValueStack<>();
        stackSnapshot = null;
    }

    @VisibleForTesting
    MatcherContext<V> createRootContext(
        final InputBuffer inputBuffer, final MatchHandler matchHandler)
    {
        return new DefaultMatcherContext<>(inputBuffer, valueStack,
            matchHandler, rootMatcher);
    }

    @VisibleForTesting
    ParsingResult<V> createParsingResult(final boolean matched,
        final MatcherContext<V> context)
    {
        return new ParsingResult<>(matched, valueStack, context);
    }

    public final void registerListener(final ParseEventListener<V> listener)
    {
        bus.register(listener);
    }

    /**
     * Internal method. DO NOT USE!
     *
     * @param context the MatcherContext
     * @param <T> type parameter of the values on the parser stack
     * @return true on a match; false otherwise
     */
    @Override
    public <T> boolean match(final MatcherContext<T> context)
    {
        final Matcher matcher = context.getMatcher();

        final PreMatchEvent<T> preMatchEvent = new PreMatchEvent<>(context);
        bus.post(preMatchEvent);

        if (throwable != null)
            throw new GrappaException("parsing listener error (before match)",
                throwable);

        // FIXME: is there any case at all where context.getMatcher() is null?
        @SuppressWarnings("ConstantConditions")
        final boolean match = matcher.match(context);

        final MatchContextEvent<T> postMatchEvent = match
            ? new MatchSuccessEvent<>(context)
            : new MatchFailureEvent<>(context);

        bus.post(postMatchEvent);

        if (throwable != null)
            throw new GrappaException("parsing listener error (after match)",
                throwable);

        return match;
    }
}