/*

 * Copyright (c) 2009, 2013, 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.classfile;

import java.util.Locale;

/**

 * See JVMS, chapter 6.

 *

 *  <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>

 *

 * @see Code_attribute#getInstructions

 */

public class Instruction {

    /** The kind of an instruction, as determined by the position, size and

     *  types of its operands. */

    public static enum Kind {

        /** Opcode is not followed by any operands. */

        NO_OPERANDS(1),

        /** Opcode is followed by a byte indicating a type. */

        ATYPE(2),

        /** Opcode is followed by a 2-byte branch offset. */

        BRANCH(3),

        /** Opcode is followed by a 4-byte branch offset. */

        BRANCH_W(5),

        /** Opcode is followed by a signed byte value. */

        BYTE(2),

        /** Opcode is followed by a 1-byte index into the constant pool. */

        CPREF(2),

        /** Opcode is followed by a 2-byte index into the constant pool. */

        CPREF_W(3),

        /** Opcode is followed by a 2-byte index into the constant pool,

         *  an unsigned byte value. */

        CPREF_W_UBYTE(4),

        /** Opcode is followed by a 2-byte index into the constant pool.,

         *  an unsigned byte value, and a zero byte. */

        CPREF_W_UBYTE_ZERO(5),

        /** Opcode is followed by variable number of operands, depending

         * on the instruction.*/

        DYNAMIC(-1),

        /** Opcode is followed by a 1-byte reference to a local variable. */

        LOCAL(2),

        /** Opcode is followed by a 1-byte reference to a local variable,

         *  and a signed byte value. */

        LOCAL_BYTE(3),

        /** Opcode is followed by a signed short value. */

        SHORT(3),

        /** Wide opcode is not followed by any operands. */

        WIDE_NO_OPERANDS(2),

        /** Wide opcode is followed by a 2-byte index into the local variables array. */

        WIDE_LOCAL(4),

        /** Wide opcode is followed by a 2-byte index into the constant pool. */

        WIDE_CPREF_W(4),

        /** Wide opcode is followed by a 2-byte index into the constant pool,

         *  and a signed short value. */

        WIDE_CPREF_W_SHORT(6),

        /** Wide opcode is followed by a 2-byte reference to a local variable,

         *  and a signed short value. */

        WIDE_LOCAL_SHORT(6),

        /** Opcode was not recognized. */

        UNKNOWN(1);

        Kind(int length) {

            this.length = length;

        }

        /** The length, in bytes, of this kind of instruction, or -1 is the

         *  length depends on the specific instruction. */

        public final int length;

    /** A utility visitor to help decode the operands of an instruction.

     *  @see Instruction#accept */

    public interface KindVisitor<R,P> {

        /** See {@link Kind#NO_OPERANDS}, {@link Kind#WIDE_NO_OPERANDS}. */

        R visitNoOperands(Instruction instr, P p);

        /** See {@link Kind#ATYPE}. */

        R visitArrayType(Instruction instr, TypeKind kind, P p);

        /** See {@link Kind#BRANCH}, {@link Kind#BRANCH_W}. */

        R visitBranch(Instruction instr, int offset, P p);

        /** See {@link Kind#CPREF}, {@link Kind#CPREF_W}, {@link Kind#WIDE_CPREF_W}. */

        R visitConstantPoolRef(Instruction instr, int index, P p);

        /** See {@link Kind#CPREF_W_UBYTE}, {@link Kind#CPREF_W_UBYTE_ZERO}, {@link Kind#WIDE_CPREF_W_SHORT}. */

        R visitConstantPoolRefAndValue(Instruction instr, int index, int value, P p);

        /** See {@link Kind#LOCAL}, {@link Kind#WIDE_LOCAL}. */

        R visitLocal(Instruction instr, int index, P p);

        /** See {@link Kind#LOCAL_BYTE}. */

        R visitLocalAndValue(Instruction instr, int index, int value, P p);

        /** See {@link Kind#DYNAMIC}. */

        R visitLookupSwitch(Instruction instr, int default_, int npairs, int[] matches, int[] offsets, P p);

        /** See {@link Kind#DYNAMIC}. */

        R visitTableSwitch(Instruction instr, int default_, int low, int high, int[] offsets, P p);

        /** See {@link Kind#BYTE}, {@link Kind#SHORT}. */

        R visitValue(Instruction instr, int value, P p);

        /** Instruction is unrecognized. */

        R visitUnknown(Instruction instr, P p);

    }

    /** The kind of primitive array type to create.

     *  See JVMS chapter 6, newarray. */

    public static enum TypeKind {

        T_BOOLEAN(4, "boolean"),

        T_CHAR(5, "char"),

        T_FLOAT(6, "float"),

        T_DOUBLE(7, "double"),

        T_BYTE(8, "byte"),

        T_SHORT(9, "short"),

        T_INT (10, "int"),

        T_LONG (11, "long");

        TypeKind(int value, String name) {

            this.value = value;

            this.name = name;

        }

        public static TypeKind get(int value) {

            switch (value) {

                case  4: return T_BOOLEAN;

                case  5: return T_CHAR;

                case  6: return T_FLOAT;

                case  7: return T_DOUBLE;

                case  8: return T_BYTE;

                case  9: return T_SHORT;

                case  10: return T_INT;

                case  11: return T_LONG;

                default: return null;

            }

        }

        public final int value;

        public final String name;

    }

    /** An instruction is defined by its position in a bytecode array. */

    public Instruction(byte[] bytes, int pc) {

        this.bytes = bytes;

        this.pc = pc;

    }

    /** Get the position of the instruction within the bytecode array. */

    public int getPC() {

        return pc;

    }

    /** Get a byte value, relative to the start of this instruction. */

    public int getByte(int offset) {

        return bytes[pc + offset];

    }

    /** Get an unsigned byte value, relative to the start of this instruction. */

    public int getUnsignedByte(int offset) {

        return getByte(offset) & 0xff;

    }

    /** Get a 2-byte value, relative to the start of this instruction. */

    public int getShort(int offset) {

        return (getByte(offset) << 8) | getUnsignedByte(offset + 1);

    }

    /** Get a unsigned 2-byte value, relative to the start of this instruction. */

    public int getUnsignedShort(int offset) {

        return getShort(offset) & 0xFFFF;

    }

    /** Get a 4-byte value, relative to the start of this instruction. */

    public int getInt(int offset) {

        return (getShort(offset) << 16) | (getUnsignedShort(offset + 2));

    }

    /** Get the Opcode for this instruction, or null if the instruction is

     * unrecognized. */

    public Opcode getOpcode() {

        int b = getUnsignedByte(0);

        switch (b) {

            case Opcode.NONPRIV:

            case Opcode.PRIV:

            case Opcode.WIDE:

                return Opcode.get(b, getUnsignedByte(1));

        }

        return Opcode.get(b);

    }

    /** Get the mnemonic for this instruction, or a default string if the

     * instruction is unrecognized. */

    public String getMnemonic() {

        Opcode opcode = getOpcode();

        if (opcode == null)

            return "bytecode " + getUnsignedByte(0);

        else

            return opcode.toString().toLowerCase(Locale.US);

    }

    /** Get the length, in bytes, of this instruction, including the opcode

     * and all its operands. */

    public int length() {

        Opcode opcode = getOpcode();

        if (opcode == null)

            return 1;

        switch (opcode) {

            case TABLESWITCH: {

                int pad = align(pc + 1) - pc;

                int low = getInt(pad + 4);

                int high = getInt(pad + 8);

                return pad + 12 + 4 * (high - low + 1);

            }

            case LOOKUPSWITCH: {

                int pad = align(pc + 1) - pc;

                int npairs = getInt(pad + 4);

                return pad + 8 + 8 * npairs;

            }

            default:

                return opcode.kind.length;

        }

    }

    /** Get the {@link Kind} of this instruction. */

    public Kind getKind() {

        Opcode opcode = getOpcode();

        return (opcode != null ? opcode.kind : Kind.UNKNOWN);

    }

    /** Invoke a method on the visitor according to the kind of this

     * instruction, passing in the decoded operands for the instruction. */

    public <R,P> R accept(KindVisitor<R,P> visitor, P p) {

        switch (getKind()) {

            case NO_OPERANDS:

                return visitor.visitNoOperands(this, p);

            case ATYPE:

                return visitor.visitArrayType(

                        this, TypeKind.get(getUnsignedByte(1)), p);

            case BRANCH:

                return visitor.visitBranch(this, getShort(1), p);

            case BRANCH_W:

                return visitor.visitBranch(this, getInt(1), p);

            case BYTE:

                return visitor.visitValue(this, getByte(1), p);

            case CPREF:

                return visitor.visitConstantPoolRef(this, getUnsignedByte(1), p);

            case CPREF_W:

                return visitor.visitConstantPoolRef(this, getUnsignedShort(1), p);

            case CPREF_W_UBYTE:

            case CPREF_W_UBYTE_ZERO:

                return visitor.visitConstantPoolRefAndValue(

                        this, getUnsignedShort(1), getUnsignedByte(3), p);

            case DYNAMIC: {

                switch (getOpcode()) {

                    case TABLESWITCH: {

                        int pad = align(pc + 1) - pc;

                        int default_ = getInt(pad);

                        int low = getInt(pad + 4);

                        int high = getInt(pad + 8);

                        int[] values = new int[high - low + 1];

                        for (int i = 0; i < values.length; i++)

                            values[i] = getInt(pad + 12 + 4 * i);

                        return visitor.visitTableSwitch(

                                this, default_, low, high, values, p);

                    }

                    case LOOKUPSWITCH: {

                        int pad = align(pc + 1) - pc;

                        int default_ = getInt(pad);

                        int npairs = getInt(pad + 4);

                        int[] matches = new int[npairs];

                        int[] offsets = new int[npairs];

                        for (int i = 0; i < npairs; i++) {

                            matches[i] = getInt(pad +  8 + i * 8);

                            offsets[i] = getInt(pad + 12 + i * 8);

                        }

                        return visitor.visitLookupSwitch(

                                this, default_, npairs, matches, offsets, p);

                    }

                    default:

                        throw new IllegalStateException();

                }

            }

            case LOCAL:

                return visitor.visitLocal(this, getUnsignedByte(1), p);

            case LOCAL_BYTE:

                return visitor.visitLocalAndValue(

                        this, getUnsignedByte(1), getByte(2), p);

            case SHORT:

                return visitor.visitValue(this, getShort(1), p);

            case WIDE_NO_OPERANDS:

                return visitor.visitNoOperands(this, p);

            case WIDE_LOCAL:

                return visitor.visitLocal(this, getUnsignedShort(2), p);

            case WIDE_CPREF_W:

                return visitor.visitConstantPoolRef(this, getUnsignedShort(2), p);

            case WIDE_CPREF_W_SHORT:

                return visitor.visitConstantPoolRefAndValue(

                        this, getUnsignedShort(2), getUnsignedByte(4), p);

            case WIDE_LOCAL_SHORT:

                return visitor.visitLocalAndValue(

                        this, getUnsignedShort(2), getShort(4), p);

            case UNKNOWN:

                return visitor.visitUnknown(this, p);

            default:

                throw new IllegalStateException();

        }

    }

    private static int align(int n) {

        return (n + 3) & ~3;

    }

    private byte[] bytes;

    private int pc;

}