/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.bcel.util;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import org.apache.bcel.Const;
import org.apache.bcel.generic.ClassGenException;
import org.apache.bcel.generic.InstructionHandle;
import org.apache.bcel.generic.InstructionList;
import org.apache.commons.lang3.StringUtils;

/**
 * InstructionFinder is a tool to search for given instructions patterns, that is, match sequences of instructions in an
 * instruction list via regular expressions. This can be used, for example, in order to implement a peep hole optimizer that
 * looks for code patterns and replaces them with faster equivalents.
 *
 * <p>
 * This class internally uses the java.util.regex package to search for regular expressions.
 * </p>
 * <p>
 * A typical application would look like this:
 * </p>
 * <pre>
 *   InstructionFinder f = new InstructionFinder(il);
 *   String pat = &quot;IfInstruction ICONST_0 GOTO ICONST_1 NOP (IFEQ|IFNE)&quot;;
 *
 *   for (Iterator i = f.search(pat, constraint); i.hasNext(); ) {
 *       InstructionHandle[] match = (InstructionHandle[])i.next();
 *       ...
 *       il.delete(match[1], match[5]);
 *       ...
 *   }

 * </pre>
 *
 * @see org.apache.bcel.generic.Instruction
 * @see InstructionList
 */
public class InstructionFinder {

    /**
     * Code patterns found may be checked using an additional user-defined constraint object whether they really match the
     * needed criterion. I.e., check constraints that cannot expressed with regular expressions.
     */
    public interface CodeConstraint {

        /**
         * Checks if the matched code area is really useful.
         *
         * @param match array of instructions matching the requested pattern.
         * @return true if the matched area is really useful.
         */
        boolean checkCode(InstructionHandle[] match);
    }

    private static final int OFFSET = 32767; // char + OFFSET is outside of LATIN-1
    private static final int NO_OPCODES = 256; // Potential number, some are not used
    private static final Map<String, String> map = new HashMap<>();

    // Initialize pattern map
    static {
        map.put("arithmeticinstruction",
            "(irem|lrem|iand|ior|ineg|isub|lneg|fneg|fmul|ldiv|fadd|lxor|frem|idiv|land|ixor|ishr|fsub|lshl|fdiv|iadd|lor|dmul|lsub|ishl|imul|lmul|lushr|dneg|iushr|lshr|ddiv|drem|dadd|ladd|dsub)");
        map.put("invokeinstruction", "(invokevirtual|invokeinterface|invokestatic|invokespecial|invokedynamic)");
        map.put("arrayinstruction",
            "(baload|aastore|saload|caload|fastore|lastore|iaload|castore|iastore|aaload|bastore|sastore|faload|laload|daload|dastore)");
        map.put("gotoinstruction", "(goto|goto_w)");
        map.put("conversioninstruction", "(d2l|l2d|i2s|d2i|l2i|i2b|l2f|d2f|f2i|i2d|i2l|f2d|i2c|f2l|i2f)");
        map.put("localvariableinstruction", "(fstore|iinc|lload|dstore|dload|iload|aload|astore|istore|fload|lstore)");
        map.put("loadinstruction", "(fload|dload|lload|iload|aload)");
        map.put("fieldinstruction", "(getfield|putstatic|getstatic|putfield)");
        map.put("cpinstruction",
            "(ldc2_w|invokeinterface|invokedynamic|multianewarray|putstatic|instanceof|getstatic|checkcast|getfield|invokespecial|ldc_w|invokestatic|invokevirtual|putfield|ldc|new|anewarray)");
        map.put("stackinstruction", "(dup2|swap|dup2_x2|pop|pop2|dup|dup2_x1|dup_x2|dup_x1)");
        map.put("branchinstruction",
            "(ifle|if_acmpne|if_icmpeq|if_acmpeq|ifnonnull|goto_w|iflt|ifnull|if_icmpne|tableswitch|if_icmple|ifeq|if_icmplt|jsr_w|if_icmpgt|ifgt|jsr|goto|ifne|ifge|lookupswitch|if_icmpge)");
        map.put("returninstruction", "(lreturn|ireturn|freturn|dreturn|areturn|return)");
        map.put("storeinstruction", "(istore|fstore|dstore|astore|lstore)");
        map.put("select", "(tableswitch|lookupswitch)");
        map.put("ifinstruction",
            "(ifeq|ifgt|if_icmpne|if_icmpeq|ifge|ifnull|ifne|if_icmple|if_icmpge|if_acmpeq|if_icmplt|if_acmpne|ifnonnull|iflt|if_icmpgt|ifle)");
        map.put("jsrinstruction", "(jsr|jsr_w)");
        map.put("variablelengthinstruction", "(tableswitch|jsr|goto|lookupswitch)");
        map.put("unconditionalbranch", "(goto|jsr|jsr_w|athrow|goto_w)");
        map.put("constantpushinstruction", "(dconst|bipush|sipush|fconst|iconst|lconst)");
        map.put("typedinstruction",
            "(imul|lsub|aload|fload|lor|new|aaload|fcmpg|iand|iaload|lrem|idiv|d2l|isub|dcmpg|dastore|ret|f2d|f2i|drem|iinc|i2c|checkcast|frem|lreturn|astore|lushr|daload|dneg|fastore|istore|lshl|ldiv|lstore|areturn|ishr|ldc_w|invokeinterface|invokedynamic|aastore|lxor|ishl|l2d|i2f|return|faload|sipush|iushr|caload|instanceof|invokespecial|putfield|fmul|ireturn|laload|d2f|lneg|ixor|i2l|fdiv|lastore|multianewarray|i2b|getstatic|i2d|putstatic|fcmpl|saload|ladd|irem|dload|jsr_w|dconst|dcmpl|fsub|freturn|ldc|aconst_null|castore|lmul|ldc2_w|dadd|iconst|f2l|ddiv|dstore|land|jsr|anewarray|dmul|bipush|dsub|sastore|d2i|i2s|lshr|iadd|l2i|lload|bastore|fstore|fneg|iload|fadd|baload|fconst|ior|ineg|dreturn|l2f|lconst|getfield|invokevirtual|invokestatic|iastore)");
        map.put("popinstruction", "(fstore|dstore|pop|pop2|astore|putstatic|istore|lstore)");
        map.put("allocationinstruction", "(multianewarray|new|anewarray|newarray)");
        map.put("indexedinstruction",
            "(lload|lstore|fload|ldc2_w|invokeinterface|invokedynamic|multianewarray|astore|dload|putstatic|instanceof|getstatic|checkcast|getfield|invokespecial|dstore|istore|iinc|ldc_w|ret|fstore|invokestatic|iload|putfield|invokevirtual|ldc|new|aload|anewarray)");
        map.put("pushinstruction", "(dup|lload|dup2|bipush|fload|ldc2_w|sipush|lconst|fconst|dload|getstatic|ldc_w|aconst_null|dconst|iload|ldc|iconst|aload)");
        map.put("stackproducer",
            "(imul|lsub|aload|fload|lor|new|aaload|fcmpg|iand|iaload|lrem|idiv|d2l|isub|dcmpg|dup|f2d|f2i|drem|i2c|checkcast|frem|lushr|daload|dneg|lshl|ldiv|ishr|ldc_w|invokeinterface|invokedynamic|lxor|ishl|l2d|i2f|faload|sipush|iushr|caload|instanceof|invokespecial|fmul|laload|d2f|lneg|ixor|i2l|fdiv|getstatic|i2b|swap|i2d|dup2|fcmpl|saload|ladd|irem|dload|jsr_w|dconst|dcmpl|fsub|ldc|arraylength|aconst_null|tableswitch|lmul|ldc2_w|iconst|dadd|f2l|ddiv|land|jsr|anewarray|dmul|bipush|dsub|d2i|newarray|i2s|lshr|iadd|lload|l2i|fneg|iload|fadd|baload|fconst|lookupswitch|ior|ineg|lconst|l2f|getfield|invokevirtual|invokestatic)");
        map.put("stackconsumer",
            "(imul|lsub|lor|iflt|fcmpg|if_icmpgt|iand|ifeq|if_icmplt|lrem|ifnonnull|idiv|d2l|isub|dcmpg|dastore|if_icmpeq|f2d|f2i|drem|i2c|checkcast|frem|lreturn|astore|lushr|pop2|monitorexit|dneg|fastore|istore|lshl|ldiv|lstore|areturn|if_icmpge|ishr|monitorenter|invokeinterface|invokedynamic|aastore|lxor|ishl|l2d|i2f|return|iushr|instanceof|invokespecial|fmul|ireturn|d2f|lneg|ixor|pop|i2l|ifnull|fdiv|lastore|i2b|if_acmpeq|ifge|swap|i2d|putstatic|fcmpl|ladd|irem|dcmpl|fsub|freturn|ifgt|castore|lmul|dadd|f2l|ddiv|dstore|land|if_icmpne|if_acmpne|dmul|dsub|sastore|ifle|d2i|i2s|lshr|iadd|l2i|bastore|fstore|fneg|fadd|ior|ineg|ifne|dreturn|l2f|if_icmple|getfield|invokevirtual|invokestatic|iastore)");
        map.put("exceptionthrower",
            "(irem|lrem|laload|putstatic|baload|dastore|areturn|getstatic|ldiv|anewarray|iastore|castore|idiv|saload|lastore|fastore|putfield|lreturn|caload|getfield|return|aastore|freturn|newarray|instanceof|multianewarray|athrow|faload|iaload|aaload|dreturn|monitorenter|checkcast|bastore|arraylength|new|invokevirtual|sastore|ldc_w|ireturn|invokespecial|monitorexit|invokeinterface|invokedynamic|ldc|invokestatic|daload)");
        map.put("loadclass",
            "(multianewarray|invokeinterface|invokedynamic|instanceof|invokespecial|putfield|checkcast|putstatic|invokevirtual|new|getstatic|invokestatic|getfield|anewarray)");
        map.put("instructiontargeter",
            "(ifle|if_acmpne|if_icmpeq|if_acmpeq|ifnonnull|goto_w|iflt|ifnull|if_icmpne|tableswitch|if_icmple|ifeq|if_icmplt|jsr_w|if_icmpgt|ifgt|jsr|goto|ifne|ifge|lookupswitch|if_icmpge)");
        // Some aliases
        map.put("if_icmp", "(if_icmpne|if_icmpeq|if_icmple|if_icmpge|if_icmplt|if_icmpgt)");
        map.put("if_acmp", "(if_acmpeq|if_acmpne)");
        map.put("if", "(ifeq|ifne|iflt|ifge|ifgt|ifle)");
        // Precompile some aliases first
        map.put("iconst", precompile(Const.ICONST_0, Const.ICONST_5, Const.ICONST_M1));
        map.put("lconst", new String(new char[] {'(', makeChar(Const.LCONST_0), '|', makeChar(Const.LCONST_1), ')'}));
        map.put("dconst", new String(new char[] {'(', makeChar(Const.DCONST_0), '|', makeChar(Const.DCONST_1), ')'}));
        map.put("fconst", new String(new char[] {'(', makeChar(Const.FCONST_0), '|', makeChar(Const.FCONST_1), '|', makeChar(Const.FCONST_2), ')'}));
        map.put("lload", precompile(Const.LLOAD_0, Const.LLOAD_3, Const.LLOAD));
        map.put("iload", precompile(Const.ILOAD_0, Const.ILOAD_3, Const.ILOAD));
        map.put("dload", precompile(Const.DLOAD_0, Const.DLOAD_3, Const.DLOAD));
        map.put("fload", precompile(Const.FLOAD_0, Const.FLOAD_3, Const.FLOAD));
        map.put("aload", precompile(Const.ALOAD_0, Const.ALOAD_3, Const.ALOAD));
        map.put("lstore", precompile(Const.LSTORE_0, Const.LSTORE_3, Const.LSTORE));
        map.put("istore", precompile(Const.ISTORE_0, Const.ISTORE_3, Const.ISTORE));
        map.put("dstore", precompile(Const.DSTORE_0, Const.DSTORE_3, Const.DSTORE));
        map.put("fstore", precompile(Const.FSTORE_0, Const.FSTORE_3, Const.FSTORE));
        map.put("astore", precompile(Const.ASTORE_0, Const.ASTORE_3, Const.ASTORE));
        // Compile strings
        map.forEach((key, value) -> {
            final char ch = value.charAt(1); // Omit already precompiled patterns
            if (ch < OFFSET) {
                map.put(key, compilePattern(value)); // precompile all patterns
            }
        });
        // Add instruction alias to match anything
        final StringBuilder buf = new StringBuilder("(");
        for (short i = 0; i < NO_OPCODES; i++) {
            if (Const.getNoOfOperands(i) != Const.UNDEFINED) { // Not an invalid opcode
                buf.append(makeChar(i));
                if (i < NO_OPCODES - 1) {
                    buf.append('|');
                }
            }
        }
        buf.append(')');
        map.put("instruction", buf.toString());
    }

    /**
     * Replace symbolic names of instructions with the appropriate character and remove all white space from string. Meta
     * characters such as +, * are ignored.
     *
     * @param pattern The pattern to compile.
     * @return translated regular expression string.
     */
    private static String compilePattern(final String pattern) {
        // Bug: BCEL-77 - Instructions are assumed to be english, to avoid odd Locale issues
        final String lower = StringUtils.toRootLowerCase(pattern);
        final StringBuilder buf = new StringBuilder();
        final int size = pattern.length();
        for (int i = 0; i < size; i++) {
            char ch = lower.charAt(i);
            if (Character.isLetterOrDigit(ch)) {
                final StringBuilder name = new StringBuilder();
                while ((Character.isLetterOrDigit(ch) || ch == '_') && i < size) {
                    name.append(ch);
                    if (++i >= size) {
                        break;
                    }
                    ch = lower.charAt(i);
                }
                i--;
                buf.append(mapName(name.toString()));
            } else if (!Character.isWhitespace(ch)) {
                buf.append(ch);
            }
        }
        return buf.toString();
    }

    /**
     * Convert opcode number to char.
     */
    private static char makeChar(final short opcode) {
        return (char) (opcode + OFFSET);
    }

    /**
     * Map symbolic instruction names like "getfield" to a single character.
     *
     * @param pattern instruction pattern in lower case.
     * @return encoded string for a pattern such as "BranchInstruction".
     */
    private static String mapName(final String pattern) {
        final String result = map.get(pattern);
        if (result != null) {
            return result;
        }
        for (short i = 0; i < NO_OPCODES; i++) {
            if (pattern.equals(Const.getOpcodeName(i))) {
                return String.valueOf(makeChar(i));
            }
        }
        throw new IllegalArgumentException("Instruction unknown: " + pattern);
    }

    private static String precompile(final short from, final short to, final short extra) {
        final StringBuilder buf = new StringBuilder("(");
        for (short i = from; i <= to; i++) {
            buf.append(makeChar(i));
            buf.append('|');
        }
        buf.append(makeChar(extra));
        buf.append(")");
        return buf.toString();
    }

    private final InstructionList il;

    private String ilString; // instruction list as string

    private InstructionHandle[] handles; // map instruction

    // list to array

    /**
     * Constructs an InstructionFinder.
     *
     * @param il instruction list to search for given patterns.
     */
    public InstructionFinder(final InstructionList il) {
        this.il = il;
        reread();
    }

    /**
     * Gets the inquired instruction list.
     *
     * @return the inquired instruction list.
     */
    public final InstructionList getInstructionList() {
        return il;
    }

    /**
     * @return the matched piece of code as an array of instruction (handles).
     */
    private InstructionHandle[] getMatch(final int matchedFrom, final int matchLength) {
        return Arrays.copyOfRange(handles, matchedFrom, matchedFrom + matchLength);
    }

    /**
     * Reread the instruction list, for example, after you've altered the list upon a match.
     */
    public final void reread() {
        final int size = il.getLength();
        final char[] buf = new char[size]; // Create a string with length equal to il length
        handles = il.getInstructionHandles();
        // Map opcodes to characters
        for (int i = 0; i < size; i++) {
            buf[i] = makeChar(handles[i].getInstruction().getOpcode());
        }
        ilString = new String(buf);
    }

    /**
     * Start search beginning from the start of the given instruction list.
     *
     * @param pattern the instruction pattern to search for, where case is ignored.
     * @return iterator of matches where e.nextElement() returns an array of instruction handles describing the matched area.
     */
    public final Iterator<InstructionHandle[]> search(final String pattern) {
        return search(pattern, il.getStart(), null);
    }

    /**
     * Start search beginning from the start of the given instruction list. Check found matches with the constraint object.
     *
     * @param pattern the instruction pattern to search for, case is ignored.
     * @param constraint constraints to be checked on matching code.
     * @return instruction handle or 'null' if the match failed.
     */
    public final Iterator<InstructionHandle[]> search(final String pattern, final CodeConstraint constraint) {
        return search(pattern, il.getStart(), constraint);
    }

    /**
     * Start search beginning from 'from'.
     *
     * @param pattern the instruction pattern to search for, where case is ignored.
     * @param from where to start the search in the instruction list.
     * @return iterator of matches where e.nextElement() returns an array of instruction handles describing the matched area.
     */
    public final Iterator<InstructionHandle[]> search(final String pattern, final InstructionHandle from) {
        return search(pattern, from, null);
    }

    /**
     * Search for the given pattern in the instruction list. You can search for any valid opcode via its symbolic name, for example
     * "istore". You can also use a super class or an interface name to match a whole set of instructions, for example
     * "BranchInstruction" or "LoadInstruction". "istore" is also an alias for all "istore_x" instructions. Additional
     * aliases are "if" for "ifxx", "if_icmp" for "if_icmpxx", "if_acmp" for "if_acmpxx".
     *
     * Consecutive instruction names must be separated by white space which will be removed during the compilation of the
     * pattern.
     *
     * For the rest the usual pattern matching rules for regular expressions apply.
     * <p>
     * Example pattern:
     * </p>
     * <pre>
     * search(&quot;BranchInstruction NOP ((IfInstruction|GOTO)+ ISTORE Instruction)*&quot;);
     * </pre>
     *
     * <p>
     * If you alter the instruction list upon a match such that other matching areas are affected, you should call reread()
     * to update the finder and call search() again, because the matches are cached.
     * </p>
     *
     * @param pattern the instruction pattern to search for, where case is ignored.
     * @param from where to start the search in the instruction list.
     * @param constraint optional CodeConstraint to check the found code pattern for user-defined constraints.
     * @return iterator of matches where e.nextElement() returns an array of instruction handles describing the matched area.
     */
    public final Iterator<InstructionHandle[]> search(final String pattern, final InstructionHandle from, final CodeConstraint constraint) {
        final String search = compilePattern(pattern);
        int start = -1;
        for (int i = 0; i < handles.length; i++) {
            if (handles[i] == from) {
                start = i; // Where to start search from (index)
                break;
            }
        }
        if (start == -1) {
            throw new ClassGenException("Instruction handle " + from + " not found in instruction list.");
        }
        final Pattern regex = Pattern.compile(search);
        final List<InstructionHandle[]> matches = new ArrayList<>();
        final Matcher matcher = regex.matcher(ilString);
        while (start < ilString.length() && matcher.find(start)) {
            final int startExpr = matcher.start();
            final int endExpr = matcher.end();
            final int lenExpr = endExpr - startExpr;
            final InstructionHandle[] match = getMatch(startExpr, lenExpr);
            if (constraint == null || constraint.checkCode(match)) {
                matches.add(match);
            }
            start = endExpr;
        }
        return matches.iterator();
    }

    /*
     * Internal debugging routines.
     */
//    private static final String pattern2string( String pattern ) {
//        return pattern2string(pattern, true);
//    }

//    private static final String pattern2string( String pattern, boolean make_string ) {
//        StringBuilder buf = new StringBuilder();
//        for (int i = 0; i < pattern.length(); i++) {
//            char ch = pattern.charAt(i);
//            if (ch >= OFFSET) {
//                if (make_string) {
//                    buf.append(Constants.getOpcodeName(ch - OFFSET));
//                } else {
//                    buf.append((ch - OFFSET));
//                }
//            } else {
//                buf.append(ch);
//            }
//        }
//        return buf.toString();
//    }
}