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Core building blocks and API for the Metal library.
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/*
 * Copyright 2013-2024 Netherlands Forensic Institute
 * Copyright 2021-2024 Infix Technologies B.V.
 *
 * 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 java.math.BigInteger.ZERO;

import static io.parsingdata.metal.Util.checkNotEmpty;
import static io.parsingdata.metal.Util.checkNotNull;
import static io.parsingdata.metal.Util.success;
import static io.parsingdata.metal.expression.value.NotAValue.NOT_A_VALUE;

import java.math.BigInteger;
import java.util.Objects;
import java.util.Optional;

import io.parsingdata.metal.data.Environment;
import io.parsingdata.metal.data.ParseState;
import io.parsingdata.metal.data.ParseValue;
import io.parsingdata.metal.encoding.Encoding;
import io.parsingdata.metal.expression.value.SingleValueExpression;

/**
 * A {@link Token} that specifies a value to parse in the input.
 * 
 * A Def consists of a size (a {@link SingleValueExpression}.
 * 
 * Parsing will succeed if size evaluates to a value and if
 * that many bytes are available in the input. This means that a size of zero
 * will lead to a successful parse, but will not produce a value.
 *
 * @see SingleValueExpression
 */
public class Def extends Token {

    public final SingleValueExpression size;

    public Def(final String name, final SingleValueExpression size, final Encoding encoding) {
        super(checkNotEmpty(name, "name"), encoding);
        this.size = checkNotNull(size, "size");
    }

    @Override
    protected Optional parseImpl(final Environment environment) {
        return size.evalSingle(environment.parseState, environment.encoding)
            .filter(sizeValue -> !sizeValue.equals(NOT_A_VALUE))
            .flatMap(sizeValue -> sizeValue.asNumeric().compareTo(ZERO) != 0 ? slice(environment, sizeValue.asNumeric()) : success(environment.parseState));
    }

    private Optional slice(final Environment environment, final BigInteger dataSize) {
        return environment.parseState
            .slice(dataSize)
            .flatMap(slice -> environment.parseState.add(new ParseValue(environment.scope, this, slice, environment.encoding)).seek(dataSize.add(environment.parseState.offset)));
    }

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

    @Override
    public boolean equals(final Object obj) {
        return super.equals(obj)
            && Objects.equals(size, ((Def)obj).size);
    }

    @Override
    public int immutableHashCode() {
        return Objects.hash(super.immutableHashCode(), size);
    }

}