/*
 * Copyright (c) 1999, 2020, 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 com.sun.tools.javac.jvm;

import java.io.IOException;
import java.io.InputStream;
import java.nio.file.Files;
import java.nio.file.Path;

import javax.tools.JavaFileObject;

import com.sun.tools.javac.util.Convert;
import static com.sun.tools.javac.jvm.ClassFile.*;


Stripped down ClassReader, just sufficient to read module names from module-info.class files
while analyzing the module path.

This is NOT part of any supported API. If you write code that depends on this, you do so at
your own risk. This code and its internal interfaces are subject to change or deletion without
notice.
/**
 * Stripped down ClassReader, just sufficient to read module names from module-info.class files
 * while analyzing the module path.
 *
 * <p>
 * <b>This is NOT part of any supported API. If you write code that depends on this, you do so at
 * your own risk. This code and its internal interfaces are subject to change or deletion without
 * notice.</b>
 */
public class ModuleNameReader {
    public static class BadClassFile extends Exception {
        private static final long serialVersionUID = 0;
        BadClassFile(String msg) {
            super(msg);
        }
    }

    private static final int INITIAL_BUFFER_SIZE = 0x0fff0;

    
The buffer containing the currently read class file.
/** The buffer containing the currently read class file.
     */
    private byte[] buf = new byte[INITIAL_BUFFER_SIZE];

    
The current input pointer.
/** The current input pointer.
     */
    private int bp;

    
For every constant pool entry, an index into buf where the
 defining section of the entry is found.
/** For every constant pool entry, an index into buf where the
     *  defining section of the entry is found.
     */
    private int[] poolIdx;

    public ModuleNameReader() {
    }

    public String readModuleName(Path p) throws IOException, BadClassFile {
        try (InputStream in = Files.newInputStream(p)) {
            return readModuleName(in);
        }
    }

    public String readModuleName(JavaFileObject jfo) throws IOException, BadClassFile {
        try (InputStream in = jfo.openInputStream()) {
            return readModuleName(in);
        }
    }

    public String readModuleName(InputStream in) throws IOException, BadClassFile {
        bp = 0;
        buf = readInputStream(buf, in);

        int magic = nextInt();
        if (magic != JAVA_MAGIC)
            throw new BadClassFile("illegal.start.of.class.file");

        int minorVersion = nextChar();
        int majorVersion = nextChar();
        if (majorVersion < 53)
            throw new BadClassFile("bad major version number for module: " + majorVersion);

        indexPool();

        int access_flags = nextChar();
        if (access_flags != 0x8000)
            throw new BadClassFile("invalid access flags for module: 0x" + Integer.toHexString(access_flags));

        int this_class = nextChar();
        // could, should, check this_class == CONSTANT_Class("mdoule-info")
        checkZero(nextChar(), "super_class");
        checkZero(nextChar(), "interface_count");
        checkZero(nextChar(), "fields_count");
        checkZero(nextChar(), "methods_count");
        int attributes_count = nextChar();
        for (int i = 0; i < attributes_count; i++) {
            int attr_name = nextChar();
            int attr_length = nextInt();
            if (getUtf8Value(attr_name, false).equals("Module") && attr_length > 2) {
                return getModuleName(nextChar());
            } else {
                // skip over unknown attributes
                bp += attr_length;
            }
        }
        throw new BadClassFile("no Module attribute");
    }

    void checkZero(int count, String name) throws BadClassFile {
        if (count != 0)
            throw new BadClassFile("invalid " + name + " for module: " + count);
    }

    
Extract a character at position bp from buf.
/** Extract a character at position bp from buf.
     */
    char getChar(int bp) {
        return
            (char)(((buf[bp] & 0xFF) << 8) + (buf[bp+1] & 0xFF));
    }

    
Read a character.
/** Read a character.
     */
    char nextChar() {
        return (char)(((buf[bp++] & 0xFF) << 8) + (buf[bp++] & 0xFF));
    }

    
Read an integer.
/** Read an integer.
     */
    int nextInt() {
        return
            ((buf[bp++] & 0xFF) << 24) +
            ((buf[bp++] & 0xFF) << 16) +
            ((buf[bp++] & 0xFF) << 8) +
            (buf[bp++] & 0xFF);
    }

    
Index all constant pool entries, writing their start addresses into
 poolIdx.
/** Index all constant pool entries, writing their start addresses into
     *  poolIdx.
     */
    void indexPool() throws BadClassFile {
        poolIdx = new int[nextChar()];
        int i = 1;
        while (i < poolIdx.length) {
            poolIdx[i++] = bp;
            byte tag = buf[bp++];
            switch (tag) {
            case CONSTANT_Utf8: case CONSTANT_Unicode: {
                int len = nextChar();
                bp = bp + len;
                break;
            }
            case CONSTANT_Class:
            case CONSTANT_String:
            case CONSTANT_MethodType:
            case CONSTANT_Module:
            case CONSTANT_Package:
                bp = bp + 2;
                break;
            case CONSTANT_MethodHandle:
                bp = bp + 3;
                break;
            case CONSTANT_Fieldref:
            case CONSTANT_Methodref:
            case CONSTANT_InterfaceMethodref:
            case CONSTANT_NameandType:
            case CONSTANT_Integer:
            case CONSTANT_Float:
            case CONSTANT_InvokeDynamic:
                bp = bp + 4;
                break;
            case CONSTANT_Long:
            case CONSTANT_Double:
                bp = bp + 8;
                i++;
                break;
            default:
                throw new BadClassFile("malformed constant pool");
            }
        }
    }

    String getUtf8Value(int index, boolean internalize) throws BadClassFile {
        int utf8Index = poolIdx[index];
        if (buf[utf8Index] == CONSTANT_Utf8) {
            int len = getChar(utf8Index + 1);
            int start = utf8Index + 3;
            if (internalize) {
                return Convert.utf2string(ClassFile.internalize(buf, start, len));
            } else {
                return Convert.utf2string(buf, start, len);
            }
        }
        throw new BadClassFile("bad name at index " + index);
    }

    String getModuleName(int index) throws BadClassFile {
        int infoIndex = poolIdx[index];
        if (buf[infoIndex] == CONSTANT_Module) {
            return getUtf8Value(getChar(infoIndex + 1), true);
        } else {
            throw new BadClassFile("bad module name at index " + index);
        }
    }

    private static byte[] readInputStream(byte[] buf, InputStream s) throws IOException {
        try {
            buf = ensureCapacity(buf, s.available());
            int r = s.read(buf);
            int bp = 0;
            while (r != -1) {
                bp += r;
                buf = ensureCapacity(buf, bp);
                r = s.read(buf, bp, buf.length - bp);
            }
            return buf;
        } finally {
            try {
                s.close();
            } catch (IOException e) {
                /* Ignore any errors, as this stream may have already
                 * thrown a related exception which is the one that
                 * should be reported.
                 */
            }
        }
    }

    /*
     * ensureCapacity will increase the buffer as needed, taking note that
     * the new buffer will always be greater than the needed and never
     * exactly equal to the needed size or bp. If equal then the read (above)
     * will infinitely loop as buf.length - bp == 0.
     */
    private static byte[] ensureCapacity(byte[] buf, int needed) {
        if (buf.length <= needed) {
            byte[] old = buf;
            buf = new byte[Integer.highestOneBit(needed) << 1];
            System.arraycopy(old, 0, buf, 0, old.length);
        }
        return buf;
    }
}