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Simple library for generating code.
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/*
 * Copyright (c) "Neo4j"
 * Neo4j Sweden AB [https://neo4j.com]
 *
 * This file is part of Neo4j.
 *
 * Neo4j is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program 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 for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see .
 */
package org.neo4j.codegen;

import static org.objectweb.asm.Type.getType;

import java.io.PrintStream;
import java.io.PrintWriter;
import java.lang.reflect.Modifier;
import java.nio.ByteBuffer;
import java.util.Arrays;
import org.objectweb.asm.ClassReader;
import org.objectweb.asm.ClassVisitor;
import org.objectweb.asm.FieldVisitor;
import org.objectweb.asm.Handle;
import org.objectweb.asm.Label;
import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Opcodes;

public interface ByteCodeVisitor {
    interface Configurable {
        void addByteCodeVisitor(ByteCodeVisitor visitor);
    }

    ByteCodeVisitor DO_NOTHING = (name, bytes) -> {};

    void visitByteCode(String name, ByteBuffer bytes);

    class Multiplex implements ByteCodeVisitor {
        private final ByteCodeVisitor[] visitors;

        Multiplex(ByteCodeVisitor[] visitors) {
            this.visitors = visitors;
        }

        @Override
        public void visitByteCode(String name, ByteBuffer bytes) {
            for (ByteCodeVisitor visitor : visitors) {
                visitor.visitByteCode(name, bytes.duplicate());
            }
        }
    }

    static Printer printer(PrintWriter out) {
        return new Printer() {
            @Override
            void printf(String format, Object... args) {
                out.format(format, args);
            }

            @Override
            void println(CharSequence line) {
                out.println(line);
            }
        };
    }

    static Printer printer(PrintStream out) {
        return new Printer() {
            @Override
            void printf(String format, Object... args) {
                out.format(format, args);
            }

            @Override
            void println(CharSequence line) {
                out.println(line);
            }
        };
    }

    abstract class Printer extends ClassVisitor implements ByteCodeVisitor, CodeGeneratorOption {
        private Printer() {
            super(Opcodes.ASM4);
        }

        @Override
        public void applyTo(Object target) {
            if (target instanceof Configurable) {
                ((Configurable) target).addByteCodeVisitor(this);
            }
        }

        abstract void printf(String format, Object... args);

        abstract void println(CharSequence line);

        @Override
        public void visitByteCode(String name, ByteBuffer bytes) {
            new ClassReader(bytes.array()).accept(this, 0);
        }

        @Override
        public void visit(
                int version, int access, String name, String signature, String superName, String[] interfaces) {
            StringBuilder iFaces = new StringBuilder();
            String prefix = " implements ";
            for (String iFace : interfaces) {
                iFaces.append(prefix).append(iFace);
                prefix = ", ";
            }
            printf("%s class %s extends %s%s%n{%n", Modifier.toString(access), name, superName, iFaces);
        }

        @Override
        public FieldVisitor visitField(int access, String name, String desc, String signature, Object value) {
            printf(
                    "  %s %s %s%s;%n",
                    Modifier.toString(access),
                    getType(desc).getClassName(),
                    name,
                    value == null ? "" : (" = " + value));
            return super.visitField(access, name, desc, signature, value);
        }

        @Override
        public MethodVisitor visitMethod(int access, String name, String desc, String signature, String[] exceptions) {
            printf("  %s %s%s%n  {%n", Modifier.toString(access), name, desc);
            return new MethodVisitor(api) {
                int offset;

                @Override
                public void visitFrame(int type, int nLocal, Object[] local, int nStack, Object[] stack) {
                    StringBuilder frame = new StringBuilder().append("    [FRAME:");
                    switch (type) {
                        case Opcodes.F_NEW:
                            frame.append("NEW");
                            break;
                        case Opcodes.F_FULL:
                            frame.append("FULL");
                            break;
                        case Opcodes.F_APPEND:
                            frame.append("APPEND");
                            break;
                        case Opcodes.F_CHOP:
                            frame.append("CHOP");
                            break;
                        case Opcodes.F_SAME:
                            frame.append("SAME");
                            break;
                        case Opcodes.F_SAME1:
                            frame.append("SAME1");
                            break;
                        default:
                            frame.append(type);
                    }
                    frame.append(", ").append(nLocal).append(" locals: [");
                    String prefix = "";
                    for (int i = 0; i < nLocal; i++) {
                        frame.append(prefix);
                        if (local[i] instanceof String) {
                            frame.append(local[i]);
                        } else if (local[i] == Opcodes.TOP) {
                            frame.append("TOP");
                        } else if (local[i] == Opcodes.INTEGER) {
                            frame.append("INTEGER");
                        } else if (local[i] == Opcodes.FLOAT) {
                            frame.append("FLOAT");
                        } else if (local[i] == Opcodes.DOUBLE) {
                            frame.append("DOUBLE");
                        } else if (local[i] == Opcodes.LONG) {
                            frame.append("LONG");
                        } else if (local[i] == Opcodes.NULL) {
                            frame.append("NULL");
                        } else if (local[i] == Opcodes.UNINITIALIZED_THIS) {
                            frame.append("UNINITIALIZED_THIS");
                        } else {
                            frame.append(local[i]);
                        }
                        prefix = ", ";
                    }
                    frame.append("], ").append(nStack).append(" items on stack: [");
                    prefix = "";
                    for (int i = 0; i < nStack; i++) {
                        frame.append(prefix).append(stack[i]);
                        prefix = ", ";
                    }
                    println(frame.append(']'));
                }

                @Override
                public void visitInsn(int opcode) {
                    printf("    @%03d: %s%n", offset, opcode(opcode));
                    offset += 1;
                }

                @Override
                public void visitIntInsn(int opcode, int operand) {
                    printf("    @%03d: %s %d%n", offset, opcode(opcode), operand);
                    offset += opcode == Opcodes.SIPUSH ? 3 : 2;
                }

                @Override
                public void visitVarInsn(int opcode, int var) {
                    printf("    @%03d: %s var:%d%n", offset, opcode(opcode), var);
                    // guessing the most efficient encoding was used:
                    if (var <= 0x3) {
                        offset += 1;
                    } else if (var <= 0xFF) {
                        offset += 2;
                    } else {
                        offset += 4;
                    }
                }

                @Override
                public void visitTypeInsn(int opcode, String type) {
                    printf("    @%03d: %s %s%n", offset, opcode(opcode), type);
                    offset += 3;
                }

                @Override
                public void visitFieldInsn(int opcode, String owner, String name, String desc) {
                    printf("    @%03d: %s %s.%s:%s%n", offset, opcode(opcode), owner, name, desc);
                    offset += 3;
                }

                @Override
                public void visitMethodInsn(int opcode, String owner, String name, String desc, boolean itf) {
                    printf("    @%03d: %s %s.%s%s%n", offset, opcode(opcode), owner, name, desc);
                    offset += opcode == Opcodes.INVOKEINTERFACE ? 5 : 3;
                }

                @Override
                public void visitInvokeDynamicInsn(String name, String desc, Handle bsm, Object... bsmArgs) {
                    printf(
                            "    @%03d: InvokeDynamic %s%s / bsm:%s%s%n",
                            offset, name, desc, bsm, Arrays.toString(bsmArgs));
                    offset += 5;
                }

                @Override
                public void visitJumpInsn(int opcode, Label label) {
                    printf("    @%03d: %s %s%n", offset, opcode(opcode), label);
                    offset += 3; // TODO: how do we tell if a wide (+=5) instruction (GOTO_W=200, JSR_W=201) was used?
                    // wide instructions get simplified to their basic counterpart, but are used for long jumps
                }

                @Override
                public void visitLabel(Label label) {
                    printf("   %s:%n", label);
                }

                @Override
                public void visitLdcInsn(Object cst) {
                    printf("    @%03d: LDC %s%n", offset, cst);
                    offset += 2; // TODO: how do we tell if the WIDE instruction prefix (+=3) was used?
                    // we don't know index of the constant in the pool, wide instructions are used for high indexes
                }

                @Override
                public void visitIincInsn(int var, int increment) {
                    printf("    @%03d: IINC %d += %d%n", offset, var, increment);
                    // guessing the most efficient encoding was used:
                    if (var <= 0xFF && increment <= 0xFF) {
                        offset += 3;
                    } else {
                        offset += 6;
                    }
                }

                @Override
                public void visitTableSwitchInsn(int min, int max, Label dflt, Label... labels) {
                    printf("    @%03d: TABLE_SWITCH(min=%d, max=%d)%n    {%n", offset, min, max);
                    for (int i = 0, val = min; i < labels.length; i++, val++) {
                        printf("      case %d goto %s%n", val, labels[i]);
                    }
                    printf("      default goto %s%n    }%n", dflt);
                    offset += 4 - (offset & 3); // padding bytes, table starts at aligned offset
                    offset += 12; // default, min, max
                    offset += 4 * labels.length; // table of offsets
                }

                @Override
                public void visitLookupSwitchInsn(Label dflt, int[] keys, Label[] labels) {
                    printf("    @%03d: LOOKUP_SWITCH%n    {%n", offset);
                    for (int i = 0; i < labels.length; i++) {
                        printf("      case %d goto %s%n", keys[i], labels[i]);
                    }
                    printf("      default goto %s%n    }%n", dflt);
                    offset += 4 - (offset & 3); // padding bytes, table starts at aligned offset
                    offset += 8; // default, length
                    offset += 8 * labels.length; // table of key+offset
                }

                @Override
                public void visitMultiANewArrayInsn(String desc, int dims) {
                    printf("    @%03d: MULTI_ANEW_ARRAY %s, dims:%d%n", offset, desc, dims);
                    offset += 4;
                }

                @Override
                public void visitTryCatchBlock(Label start, Label end, Label handler, String type) {
                    printf("    [try/catch %s start@%s, end@%s, handler@%s]%n", type, start, end, handler);
                }

                @Override
                public void visitLocalVariable(
                        String name, String desc, String signature, Label start, Label end, int index) {
                    printf("    [local %s:%s, from %s to %s @offset=%d]%n", name, desc, start, end, index);
                }

                @Override
                public void visitLineNumber(int line, Label start) {
                    printf("    [line %d @ %s]%n", line, start);
                }

                @Override
                public void visitEnd() {
                    println("  }");
                }
            };
        }

        @Override
        public void visitEnd() {
            println("}");
        }

        private static String opcode(int opcode) {
            switch (opcode) {
                    // visitInsn
                case Opcodes.NOP:
                    return "NOP";
                case Opcodes.ACONST_NULL:
                    return "ACONST_NULL";
                case Opcodes.ICONST_M1:
                    return "ICONST_M1";
                case Opcodes.ICONST_0:
                    return "ICONST_0";
                case Opcodes.ICONST_1:
                    return "ICONST_1";
                case Opcodes.ICONST_2:
                    return "ICONST_2";
                case Opcodes.ICONST_3:
                    return "ICONST_3";
                case Opcodes.ICONST_4:
                    return "ICONST_4";
                case Opcodes.ICONST_5:
                    return "ICONST_5";
                case Opcodes.LCONST_0:
                    return "LCONST_0";
                case Opcodes.LCONST_1:
                    return "LCONST_1";
                case Opcodes.FCONST_0:
                    return "FCONST_0";
                case Opcodes.FCONST_1:
                    return "FCONST_1";
                case Opcodes.FCONST_2:
                    return "FCONST_2";
                case Opcodes.DCONST_0:
                    return "DCONST_0";
                case Opcodes.DCONST_1:
                    return "DCONST_1";
                case Opcodes.IALOAD:
                    return "IALOAD";
                case Opcodes.LALOAD:
                    return "LALOAD";
                case Opcodes.FALOAD:
                    return "FALOAD";
                case Opcodes.DALOAD:
                    return "DALOAD";
                case Opcodes.AALOAD:
                    return "AALOAD";
                case Opcodes.BALOAD:
                    return "BALOAD";
                case Opcodes.CALOAD:
                    return "CALOAD";
                case Opcodes.SALOAD:
                    return "SALOAD";
                case Opcodes.IASTORE:
                    return "IASTORE";
                case Opcodes.LASTORE:
                    return "LASTORE";
                case Opcodes.FASTORE:
                    return "FASTORE";
                case Opcodes.DASTORE:
                    return "DASTORE";
                case Opcodes.AASTORE:
                    return "AASTORE";
                case Opcodes.BASTORE:
                    return "BASTORE";
                case Opcodes.CASTORE:
                    return "CASTORE";
                case Opcodes.SASTORE:
                    return "SASTORE";
                case Opcodes.POP:
                    return "POP";
                case Opcodes.POP2:
                    return "POP2";
                case Opcodes.DUP:
                    return "DUP";
                case Opcodes.DUP_X1:
                    return "DUP_X1";
                case Opcodes.DUP_X2:
                    return "DUP_X2";
                case Opcodes.DUP2:
                    return "DUP2";
                case Opcodes.DUP2_X1:
                    return "DUP2_X1";
                case Opcodes.DUP2_X2:
                    return "DUP2_X2";
                case Opcodes.SWAP:
                    return "SWAP";
                case Opcodes.IADD:
                    return "IADD";
                case Opcodes.LADD:
                    return "LADD";
                case Opcodes.FADD:
                    return "FADD";
                case Opcodes.DADD:
                    return "DADD";
                case Opcodes.ISUB:
                    return "ISUB";
                case Opcodes.LSUB:
                    return "LSUB";
                case Opcodes.FSUB:
                    return "FSUB";
                case Opcodes.DSUB:
                    return "DSUB";
                case Opcodes.IMUL:
                    return "IMUL";
                case Opcodes.LMUL:
                    return "LMUL";
                case Opcodes.FMUL:
                    return "FMUL";
                case Opcodes.DMUL:
                    return "DMUL";
                case Opcodes.IDIV:
                    return "IDIV";
                case Opcodes.LDIV:
                    return "LDIV";
                case Opcodes.FDIV:
                    return "FDIV";
                case Opcodes.DDIV:
                    return "DDIV";
                case Opcodes.IREM:
                    return "IREM";
                case Opcodes.LREM:
                    return "LREM";
                case Opcodes.FREM:
                    return "FREM";
                case Opcodes.DREM:
                    return "DREM";
                case Opcodes.INEG:
                    return "INEG";
                case Opcodes.LNEG:
                    return "LNEG";
                case Opcodes.FNEG:
                    return "FNEG";
                case Opcodes.DNEG:
                    return "DNEG";
                case Opcodes.ISHL:
                    return "ISHL";
                case Opcodes.LSHL:
                    return "LSHL";
                case Opcodes.ISHR:
                    return "ISHR";
                case Opcodes.LSHR:
                    return "LSHR";
                case Opcodes.IUSHR:
                    return "IUSHR";
                case Opcodes.LUSHR:
                    return "LUSHR";
                case Opcodes.IAND:
                    return "IAND";
                case Opcodes.LAND:
                    return "LAND";
                case Opcodes.IOR:
                    return "IOR";
                case Opcodes.LOR:
                    return "LOR";
                case Opcodes.IXOR:
                    return "IXOR";
                case Opcodes.LXOR:
                    return "LXOR";
                case Opcodes.I2L:
                    return "I2L";
                case Opcodes.I2F:
                    return "I2F";
                case Opcodes.I2D:
                    return "I2D";
                case Opcodes.L2I:
                    return "L2I";
                case Opcodes.L2F:
                    return "L2F";
                case Opcodes.L2D:
                    return "L2D";
                case Opcodes.F2I:
                    return "F2I";
                case Opcodes.F2L:
                    return "F2L";
                case Opcodes.F2D:
                    return "F2D";
                case Opcodes.D2I:
                    return "D2I";
                case Opcodes.D2L:
                    return "D2L";
                case Opcodes.D2F:
                    return "D2F";
                case Opcodes.I2B:
                    return "I2B";
                case Opcodes.I2C:
                    return "I2C";
                case Opcodes.I2S:
                    return "I2S";
                case Opcodes.LCMP:
                    return "LCMP";
                case Opcodes.FCMPL:
                    return "FCMPL";
                case Opcodes.FCMPG:
                    return "FCMPG";
                case Opcodes.DCMPL:
                    return "DCMPL";
                case Opcodes.DCMPG:
                    return "DCMPG";
                case Opcodes.IRETURN:
                    return "IRETURN";
                case Opcodes.LRETURN:
                    return "LRETURN";
                case Opcodes.FRETURN:
                    return "FRETURN";
                case Opcodes.DRETURN:
                    return "DRETURN";
                case Opcodes.ARETURN:
                    return "ARETURN";
                case Opcodes.RETURN:
                    return "RETURN";
                case Opcodes.ARRAYLENGTH:
                    return "ARRAYLENGTH";
                case Opcodes.ATHROW:
                    return "ATHROW";
                case Opcodes.MONITORENTER:
                    return "MONITORENTER";
                case Opcodes.MONITOREXIT:
                    return "MONITOREXIT";
                    // visitIntInsn
                case Opcodes.BIPUSH:
                    return "BIPUSH";
                case Opcodes.SIPUSH:
                    return "SIPUSH";
                case Opcodes.NEWARRAY:
                    return "NEWARRAY";
                    // visitVarInsn
                case Opcodes.ILOAD:
                    return "ILOAD";
                case Opcodes.LLOAD:
                    return "LLOAD";
                case Opcodes.FLOAD:
                    return "FLOAD";
                case Opcodes.DLOAD:
                    return "DLOAD";
                case Opcodes.ALOAD:
                    return "ALOAD";
                case Opcodes.ISTORE:
                    return "ISTORE";
                case Opcodes.LSTORE:
                    return "LSTORE";
                case Opcodes.FSTORE:
                    return "FSTORE";
                case Opcodes.DSTORE:
                    return "DSTORE";
                case Opcodes.ASTORE:
                    return "ASTORE";
                case Opcodes.RET:
                    return "RET";
                    // visitTypeInsn
                case Opcodes.NEW:
                    return "NEW";
                case Opcodes.ANEWARRAY:
                    return "ANEWARRAY";
                case Opcodes.CHECKCAST:
                    return "CHECKCAST";
                case Opcodes.INSTANCEOF:
                    return "INSTANCEOF";
                    // visitFieldInsn
                case Opcodes.GETSTATIC:
                    return "GETSTATIC";
                case Opcodes.PUTSTATIC:
                    return "PUTSTATIC";
                case Opcodes.GETFIELD:
                    return "GETFIELD";
                case Opcodes.PUTFIELD:
                    return "PUTFIELD";
                    // visitMethodInsn
                case Opcodes.INVOKEVIRTUAL:
                    return "INVOKEVIRTUAL";
                case Opcodes.INVOKESPECIAL:
                    return "INVOKESPECIAL";
                case Opcodes.INVOKESTATIC:
                    return "INVOKESTATIC";
                case Opcodes.INVOKEINTERFACE:
                    return "INVOKEINTERFACE";
                    // visitJumpInsn
                case Opcodes.IFEQ:
                    return "IFEQ";
                case Opcodes.IFNE:
                    return "IFNE";
                case Opcodes.IFLT:
                    return "IFLT";
                case Opcodes.IFGE:
                    return "IFGE";
                case Opcodes.IFGT:
                    return "IFGT";
                case Opcodes.IFLE:
                    return "IFLE";
                case Opcodes.IF_ICMPEQ:
                    return "IF_ICMPEQ";
                case Opcodes.IF_ICMPNE:
                    return "IF_ICMPNE";
                case Opcodes.IF_ICMPLT:
                    return "IF_ICMPLT";
                case Opcodes.IF_ICMPGE:
                    return "IF_ICMPGE";
                case Opcodes.IF_ICMPGT:
                    return "IF_ICMPGT";
                case Opcodes.IF_ICMPLE:
                    return "IF_ICMPLE";
                case Opcodes.IF_ACMPEQ:
                    return "IF_ACMPEQ";
                case Opcodes.IF_ACMPNE:
                    return "IF_ACMPNE";
                case Opcodes.GOTO:
                    return "GOTO";
                case Opcodes.JSR:
                    return "JSR";
                case Opcodes.IFNULL:
                    return "IFNULL";
                case Opcodes.IFNONNULL:
                    return "IFNONNULL";
                default:
                    throw new IllegalArgumentException("unknown opcode: " + opcode);
            }
        }
    }
}