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An unofficial backport of the JDK Classfile API to Java 17
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/*
 * Copyright (c) 2022, 2024, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code 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 General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package io.github.dmlloyd.classfile.impl;

import io.github.dmlloyd.classfile.*;
import io.github.dmlloyd.classfile.constantpool.Utf8Entry;
import java.lang.constant.MethodTypeDesc;
import java.util.function.Consumer;

import static java.util.Objects.requireNonNull;

public final class DirectMethodBuilder
        extends AbstractDirectBuilder
        implements TerminalMethodBuilder, Util.Writable {

    final Utf8Entry name;
    final Utf8Entry desc;
    int flags;
    int[] parameterSlots;

    public DirectMethodBuilder(SplitConstantPool constantPool,
                               ClassFileImpl context,
                               Utf8Entry nameInfo,
                               Utf8Entry typeInfo,
                               int flags,
                               MethodModel original) {
        super(constantPool, context);
        setOriginal(original);
        this.name = requireNonNull(nameInfo);
        this.desc = requireNonNull(typeInfo);
        this.flags = flags;
    }

    @Override
    public MethodBuilder withFlags(int flags) {
        setFlags(flags);
        return this;
    }

    void setFlags(int flags) {
        boolean wasStatic = (this.flags & ClassFile.ACC_STATIC) != 0;
        boolean isStatic = (flags & ClassFile.ACC_STATIC) != 0;
        if (wasStatic != isStatic)
            throw new IllegalArgumentException("Cannot change ACC_STATIC flag of method");
        this.flags = flags;
    }

    @Override
    public Utf8Entry methodName() {
        return name;
    }

    @Override
    public Utf8Entry methodType() {
        return desc;
    }

    @Override
    public MethodTypeDesc methodTypeSymbol() {
        return Util.methodTypeSymbol(methodType());
    }

    @Override
    public int methodFlags() {
        return flags;
    }

    @Override
    public int parameterSlot(int paramNo) {
        if (paramNo == 0) {
            return ((flags & ClassFile.ACC_STATIC) != 0) ? 0 : 1;
        }
        if (parameterSlots == null)
            parameterSlots = Util.parseParameterSlots(methodFlags(), methodTypeSymbol());
        return parameterSlots[paramNo];
    }

    @Override
    public BufferedCodeBuilder bufferedCodeBuilder(CodeModel original) {
        return new BufferedCodeBuilder(this, constantPool, context, original);
    }

    @Override
    public MethodBuilder with(MethodElement element) {
        if (element instanceof AbstractElement ae) {
            ae.writeTo(this);
        } else {
            writeAttribute((CustomAttribute) requireNonNull(element));
        }
        return this;
    }

    private MethodBuilder withCode(CodeModel original,
                                  Consumer handler) {
        var cb = DirectCodeBuilder.build(this, handler, constantPool, context, original);
        writeAttribute(cb);
        return this;
    }

    @Override
    public MethodBuilder withCode(Consumer handler) {
        return withCode(null, handler);
    }

    @Override
    public MethodBuilder transformCode(CodeModel code, CodeTransform transform) {
        return withCode(code, new Consumer<>() {
            @Override
            public void accept(CodeBuilder builder) {
                builder.transform(code, transform);
            }
        });
    }

    public DirectMethodBuilder run(Consumer handler) {
        handler.accept(this);
        return this;
    }

    @Override
    public void writeTo(BufWriterImpl buf) {
        buf.writeU2U2U2(flags, buf.cpIndex(name), buf.cpIndex(desc));
        attributes.writeTo(buf);
    }
}