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Core building blocks and API for the Metal library.
There is a newer version: 10.0.0
/*
 * Copyright 2013-2016 Netherlands Forensic Institute
 *
 * 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 io.parsingdata.metal.token;

import static io.parsingdata.metal.Util.checkNotNull;
import static io.parsingdata.metal.Util.failure;
import static io.parsingdata.metal.Util.success;

import java.util.Objects;
import java.util.Optional;

import io.parsingdata.metal.Util;
import io.parsingdata.metal.data.Environment;
import io.parsingdata.metal.data.ParseState;
import io.parsingdata.metal.encoding.Encoding;
import io.parsingdata.metal.expression.Expression;

/**
 * A {@link Token} that specifies a precondition for parsing a nested token.
 * 
 * A Pre consists of a token (a {@link Token}) and a
 * predicate (an {@link Expression}). First
 * predicate is evaluated. If it evaluates to true,
 * the token is parsed. Parsing this token will only succeed if the
 * predicate evaluates to true and if parsing the
 * nested token succeeds.
 *
 * @see Expression
 */
public class Pre extends Token {

    public final Token token;
    public final Expression predicate;

    public Pre(final String name, final Token token, final Expression predicate, final Encoding encoding) {
        super(name, encoding);
        this.token = checkNotNull(token, "token");
        this.predicate = checkNotNull(predicate, "predicate");
    }

    @Override
    protected Optional parseImpl(final Environment environment) {
        if (!predicate.eval(environment.parseState, environment.encoding)) {
            return failure();
        }
        return token
            .parse(environment.addBranch(this))
            .map(resultParseState -> success(resultParseState.closeBranch()))
            .orElseGet(Util::failure);
    }

    @Override
    public String toString() {
        return getClass().getSimpleName() + "(" + makeNameFragment() + token + "," + predicate + ")";
    }

    @Override
    public boolean equals(final Object obj) {
        return super.equals(obj)
            && Objects.equals(token, ((Pre)obj).token)
            && Objects.equals(predicate, ((Pre)obj).predicate);
    }

    @Override
    public int hashCode() {
        return Objects.hash(super.hashCode(), token, predicate);
    }

}