/*
 * Copyright (c) 2019, 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
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package com.sun.tools.javac.jvm;

import com.sun.tools.javac.code.Symbol.ClassSymbol;
import com.sun.tools.javac.code.Symbol.ModuleSymbol;
import com.sun.tools.javac.code.Symbol.PackageSymbol;
import com.sun.tools.javac.code.Symtab;
import com.sun.tools.javac.code.Type;
import com.sun.tools.javac.jvm.PoolConstant.NameAndType;
import com.sun.tools.javac.util.ByteBuffer;
import com.sun.tools.javac.util.Name;
import com.sun.tools.javac.util.Name.NameMapper;
import com.sun.tools.javac.util.Names;

import static com.sun.tools.javac.jvm.ClassFile.CONSTANT_Class;
import static com.sun.tools.javac.jvm.ClassFile.CONSTANT_Double;
import static com.sun.tools.javac.jvm.ClassFile.CONSTANT_Dynamic;
import static com.sun.tools.javac.jvm.ClassFile.CONSTANT_Fieldref;
import static com.sun.tools.javac.jvm.ClassFile.CONSTANT_Float;
import static com.sun.tools.javac.jvm.ClassFile.CONSTANT_Integer;
import static com.sun.tools.javac.jvm.ClassFile.CONSTANT_InterfaceMethodref;
import static com.sun.tools.javac.jvm.ClassFile.CONSTANT_InvokeDynamic;
import static com.sun.tools.javac.jvm.ClassFile.CONSTANT_Long;
import static com.sun.tools.javac.jvm.ClassFile.CONSTANT_MethodHandle;
import static com.sun.tools.javac.jvm.ClassFile.CONSTANT_Methodref;
import static com.sun.tools.javac.jvm.ClassFile.CONSTANT_MethodType;
import static com.sun.tools.javac.jvm.ClassFile.CONSTANT_Module;
import static com.sun.tools.javac.jvm.ClassFile.CONSTANT_NameandType;
import static com.sun.tools.javac.jvm.ClassFile.CONSTANT_Package;
import static com.sun.tools.javac.jvm.ClassFile.CONSTANT_String;
import static com.sun.tools.javac.jvm.ClassFile.CONSTANT_Utf8;
import static com.sun.tools.javac.jvm.ClassFile.internalize;

Pool interface towards ClassReader. Exposes methods to decode and read javac entities from the constant pool. 
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.
/**
 * Pool interface towards {@code ClassReader}. Exposes methods to decode and read javac entities
 * from the constant pool.
 *
 *  <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 PoolReader {

    private final ClassReader reader;
    private final ByteBuffer buf;
    private final Names names;
    private final Symtab syms;

    private ImmutablePoolHelper pool;

    PoolReader(ByteBuffer buf) {
        this(null, buf, null, null);
    }

    PoolReader(ClassReader reader, Names names, Symtab syms) {
        this(reader, reader.buf, names, syms);
    }

    PoolReader(ClassReader reader, ByteBuffer buf, Names names, Symtab syms) {
        this.reader = reader;
        this.buf = buf;
        this.names = names;
        this.syms = syms;
    }

    
Get a class symbol from the pool at given index.
/**
     * Get a class symbol from the pool at given index.
     */
    ClassSymbol getClass(int index) {
        return pool.readIfNeeded(index);
    }

    
Get class name without resolving
/**
     * Get class name without resolving
     */
    <Z> Z peekClassName(int index, NameMapper<Z> mapper) {
        return peekName(buf.getChar(pool.offset(index)), mapper);
    }

    
Get package name without resolving
/**
     * Get package name without resolving
     */
    <Z> Z peekPackageName(int index, NameMapper<Z> mapper) {
        return peekName(buf.getChar(pool.offset(index)), mapper);
    }

    
Get module name without resolving
/**
     * Get module name without resolving
     */
    <Z> Z peekModuleName(int index, NameMapper<Z> mapper) {
        return peekName(buf.getChar(pool.offset(index)), mapper);
    }

    
Get a module symbol from the pool at given index.
/**
     * Get a module symbol from the pool at given index.
     */
    ModuleSymbol getModule(int index) {
        return pool.readIfNeeded(index);
    }

    
Get a module symbol from the pool at given index.
/**
     * Get a module symbol from the pool at given index.
     */
    PackageSymbol getPackage(int index) {
        return pool.readIfNeeded(index);
    }

    
Peek a name from the pool at given index without resolving.
/**
     * Peek a name from the pool at given index without resolving.
     */
    <Z> Z peekName(int index, Name.NameMapper<Z> mapper) {
        return getUtf8(index, mapper);
    }

    
Get a name from the pool at given index.
/**
     * Get a name from the pool at given index.
     */
    Name getName(int index) {
        return pool.readIfNeeded(index);
    }

    
Get a type from the pool at given index.
/**
     * Get a type from the pool at given index.
     */
    Type getType(int index) {
        return getName(index).map(reader::sigToType);
    }

    
Get a name and type pair from the pool at given index.
/**
     * Get a name and type pair from the pool at given index.
     */
    NameAndType getNameAndType(int index) {
        return pool.readIfNeeded(index);
    }

    
Get a class symbol from the pool at given index.
/**
     * Get a class symbol from the pool at given index.
     */
    Object getConstant(int index) {
        return pool.readIfNeeded(index);
    }

    boolean hasTag(int index, int tag) {
        return pool.tag(index) == tag;
    }

    private <Z> Z getUtf8(int index, NameMapper<Z> mapper) {
        int tag = pool.tag(index);
        if (tag == CONSTANT_Utf8) {
            int offset = pool.offset(index);
            int len = pool.poolbuf.getChar(offset);
            return mapper.map(pool.poolbuf.elems, offset + 2, len);
        } else {
            throw new AssertionError("Unexpected constant tag: " + tag);
        }
    }

    private Object resolve(ByteBuffer poolbuf, int tag, int offset) {
        switch (tag) {
            case CONSTANT_Utf8: {
                int len = poolbuf.getChar(offset);
                return names.fromUtf(poolbuf.elems, offset + 2, len);
            }
            case CONSTANT_Class: {
                int index = poolbuf.getChar(offset);
                Name name = names.fromUtf(getName(index).map(ClassFile::internalize));
                return syms.enterClass(reader.currentModule, name);
            }
            case CONSTANT_NameandType: {
                Name name = getName(poolbuf.getChar(offset));
                Type type = getType(poolbuf.getChar(offset + 2));
                return new NameAndType(name, type);
            }
            case CONSTANT_Integer:
                return poolbuf.getInt(offset);
            case CONSTANT_Float:
                return poolbuf.getFloat(offset);
            case CONSTANT_Long:
                return poolbuf.getLong(offset);
            case CONSTANT_Double:
                return poolbuf.getDouble(offset);
            case CONSTANT_String:
                return getName(poolbuf.getChar(offset)).toString();
            case CONSTANT_Package: {
                Name name = getName(poolbuf.getChar(offset));
                return syms.enterPackage(reader.currentModule, names.fromUtf(internalize(name)));
            }
            case CONSTANT_Module: {
                Name name = getName(poolbuf.getChar(offset));
                return syms.enterModule(name);
            }
            default:
                throw new AssertionError("Unexpected constant tag: " + tag);
        }
    }

    
Parse all constant pool entries, and keep track of their offsets. For performance and laziness reasons, it would be unwise to eagerly turn all pool entries into corresponding javac entities. First, not all entries are actually going to be read/used by javac; secondly, there are cases where creating a symbol too early might result in issues (hence methods like peekClassName(int, NameMapper<Object>). /**
     * Parse all constant pool entries, and keep track of their offsets. For performance and laziness
     * reasons, it would be unwise to eagerly turn all pool entries into corresponding javac
     * entities. First, not all entries are actually going to be read/used by javac; secondly,
     * there are cases where creating a symbol too early might result in issues (hence methods like
     * {@link PoolReader#peekClassName(int, NameMapper)}.
     */
    int readPool(ByteBuffer poolbuf, int offset) {
        int poolSize = poolbuf.getChar(offset);
        int index = 1;
        offset += 2;
        int[] offsets = new int[poolSize];
        while (index < poolSize) {
            byte tag = poolbuf.getByte(offset++);
            offsets[index] = offset;
            switch (tag) {
                case CONSTANT_Utf8: {
                    int len = poolbuf.getChar(offset);
                    offset += 2 + len;
                    break;
                }
                case CONSTANT_Class:
                case CONSTANT_String:
                case CONSTANT_Module:
                case CONSTANT_Package:
                case CONSTANT_MethodType:
                    offset += 2;
                    break;
                case CONSTANT_MethodHandle:
                    offset += 3;
                    break;
                case CONSTANT_Fieldref:
                case CONSTANT_Methodref:
                case CONSTANT_InterfaceMethodref:
                case CONSTANT_NameandType:
                case CONSTANT_Integer:
                case CONSTANT_Float:
                case CONSTANT_Dynamic:
                case CONSTANT_InvokeDynamic:
                    offset += 4;
                    break;
                case CONSTANT_Long:
                case CONSTANT_Double:
                    offset += 8;
                    break;
                default:
                    throw reader.badClassFile("bad.const.pool.tag.at",
                            Byte.toString(tag),
                            Integer.toString(offset - 1));
            }
            index += sizeof(tag);
        }
        pool = new ImmutablePoolHelper(poolbuf, offsets);
        return offset;
    }

    private int sizeof(int tag) {
        switch (tag) {
            case ClassFile.CONSTANT_Double: case ClassFile.CONSTANT_Long:
                return 2;
            default:
                return 1;
        }
    }

    class ImmutablePoolHelper {

        final Object[] values;
        final int[] offsets;
        final ByteBuffer poolbuf;

        public ImmutablePoolHelper(ByteBuffer poolbuf, int[] offsets) {
            this.offsets = offsets;
            this.values = new Object[offsets.length];
            this.poolbuf = poolbuf;
        }

        private int checkIndex(int index) {
            if (index <= 0 || index >= offsets.length) {
                //pool index is outside valid range.
                throw reader.badClassFile("bad.const.pool.index", reader.currentClassFile,
                        index, offsets.length);
            } else {
                return index;
            }
        }

        int offset(int index) {
            return offsets[checkIndex(index)];
        }

        @SuppressWarnings("unchecked")
        <P> P readIfNeeded(int index) {
            Object v = values[checkIndex(index)];
            if (v != null) {
                return (P)v;
            } else {
                P p = (P)resolve(poolbuf, tag(index), offset(index));
                values[index] = p;
                return p;
            }
        }

        int tag(int index) {
            return poolbuf.elems[offset(index) - 1];
        }
    }
}