/*

Java 4 Browser Bytecode Translator

Copyright (C) 2012-2012 Jaroslav Tulach <jaroslav.tulach@apidesign.org>

This program 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, version 2 of the License.

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. Look for COPYING file in the top folder.

If not, see http://opensource.org/licenses/GPL-2.0.

*/

package org.apidesign.java4browser;

import java.io.IOException;

import java.io.InputStream;

import java.util.List;

import static org.netbeans.modules.classfile.ByteCodes.*;

import org.netbeans.modules.classfile.CPMethodInfo;

import org.netbeans.modules.classfile.ClassFile;

import org.netbeans.modules.classfile.Code;

import org.netbeans.modules.classfile.Method;

import org.netbeans.modules.classfile.Parameter;

/** Translator of the code inside class files to JavaScript.

 *

 * @author Jaroslav Tulach <jtulach@netbeans.org>

 */

public final class ByteCodeToJavaScript {

    private final ClassFile jc;

    private final Appendable out;

    private ByteCodeToJavaScript(ClassFile jc, Appendable out) {

        this.jc = jc;

        this.out = out;

    }

    /** Converts a given class file to a JavaScript version.

     * @param fileName the name of the file we are reading

     * @param classFile input stream with code of the .class file

     * @param out a {@link StringBuilder} or similar to generate the output to

     * @throws IOException if something goes wrong during read or write or translating

     */

    public static void compile(String fileName, InputStream classFile, Appendable out) throws IOException {

        ClassFile jc = new ClassFile(classFile, true);

        ByteCodeToJavaScript compiler = new ByteCodeToJavaScript(jc, out);

        for (Method m : jc.getMethods()) {

            if (m.isStatic()) {

                compiler.generateStaticMethod(m);

            }

        }

    }

    private void generateStaticMethod(Method m) throws IOException {

        out.append("\nfunction ").append(

            jc.getName().getExternalName().replace('.', '_')

        ).append('_').append(

            m.getName()

        );

        out.append(m.getReturnType());

        List<Parameter> args = m.getParameters();

        for (Parameter t : args) {

            out.append(t.getDescriptor());

        }

        out.append('(');

        String space = "";

        for (int index = 0, i = 0; i < args.size(); i++) {

            out.append(space);

            out.append("arg").append(String.valueOf(index));

            space = ",";

            final String desc = args.get(i).getDescriptor();

            if ("D".equals(desc) || "J".equals(desc)) {

                index += 2;

            } else {

                index++;

            }

        }

        out.append(") {").append("\n");

        final Code code = m.getCode();

        int len = code.getMaxLocals();

        for (int index = args.size(), i = args.size(); i < len; i++) {

            out.append("  var ");

            out.append("arg").append(String.valueOf(i)).append(";\n");

        }

        out.append(";\n  var stack = new Array(");

        out.append(Integer.toString(code.getMaxStack()));

        out.append(");\n");

        produceCode(code.getByteCodes());

        out.append("}");

    }

    private void produceCode(byte[] byteCodes) throws IOException {

        out.append("\nvar gt = 0;\nfor(;;) switch(gt) {\n");

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

            int prev = i;

            out.append("  case " + i).append(": ");

            final int c = (byteCodes[i] + 256) % 256;

            switch (c) {

                case bc_aload_0:

                case bc_iload_0:

                case bc_lload_0:

                case bc_fload_0:

                case bc_dload_0:

                    out.append("stack.push(arg0);");

                    break;

                case bc_aload_1:

                case bc_iload_1:

                case bc_lload_1:

                case bc_fload_1:

                case bc_dload_1:

                    out.append("stack.push(arg1);");

                    break;

                case bc_aload_2:

                case bc_iload_2:

                case bc_lload_2:

                case bc_fload_2:

                case bc_dload_2:

                    out.append("stack.push(arg2);");

                    break;

                case bc_aload_3:

                case bc_iload_3:

                case bc_lload_3:

                case bc_fload_3:

                case bc_dload_3:

                    out.append("stack.push(arg3);");

                    break;

                case bc_iload:

                case bc_lload:

                case bc_fload:

                case bc_dload:

                case bc_aload: {

                    final int indx = (byteCodes[++i] + 256) % 256;

                    out.append("stack.push(arg").append(indx + ");");

                    break;

                }

                case bc_istore_0:

                case bc_lstore_0:

                case bc_fstore_0:

                case bc_dstore_0:

                    out.append("arg0 = stack.pop();");

                    break;

                case bc_istore_1:

                case bc_lstore_1:

                case bc_fstore_1:

                case bc_dstore_1:

                    out.append("arg1 = stack.pop();");

                    break;

                case bc_istore_2:

                case bc_lstore_2:

                case bc_fstore_2:

                case bc_dstore_2:

                    out.append("arg2 = stack.pop();");

                    break;

                case bc_istore_3:

                case bc_lstore_3:

                case bc_fstore_3:

                case bc_dstore_3:

                    out.append("arg3 = stack.pop();");

                    break;

                case bc_iadd:

                case bc_ladd:

                case bc_fadd:

                case bc_dadd:

                    out.append("stack.push(stack.pop() + stack.pop());");

                    break;

                case bc_isub:

                case bc_lsub:

                case bc_fsub:

                case bc_dsub:

                    out.append("{ var tmp = stack.pop(); stack.push(stack.pop() - tmp); }");

                    break;

                case bc_imul:

                case bc_lmul:

                case bc_fmul:

                case bc_dmul:

                    out.append("stack.push(stack.pop() * stack.pop());");

                    break;

                case bc_idiv:

                case bc_ldiv:

                    out.append("{ var tmp = stack.pop(); stack.push(Math.floor(stack.pop() / tmp)); }");

                    break;

                case bc_fdiv:

                case bc_ddiv:

                    out.append("{ var tmp = stack.pop(); stack.push(stack.pop() / tmp); }");

                    break;

                case bc_iand:

                case bc_land:

                    out.append("stack.push(stack.pop() & stack.pop());");

                    break;

                case bc_ior:

                case bc_lor:

                    out.append("stack.push(stack.pop() | stack.pop());");

                    break;

                case bc_ixor:

                case bc_lxor:

                    out.append("stack.push(stack.pop() ^ stack.pop());");

                    break;

                case bc_iinc: {

                    final int varIndx = (byteCodes[++i] + 256) % 256;

                    final int incrBy = (byteCodes[++i] + 256) % 256;

                    if (incrBy == 1) {

                        out.append("arg" + varIndx).append("++;");

                    } else {

                        out.append("arg" + varIndx).append(" += " + incrBy).append(";");

                    }

                    break;

                }

                case bc_ireturn:

                case bc_lreturn:

                case bc_freturn:

                case bc_dreturn:

                    out.append("return stack.pop();");

                    break;

                case bc_i2l:

                case bc_i2f:

                case bc_i2d:

                case bc_l2i:

                    // max int check?

                case bc_l2f:

                case bc_l2d:

                case bc_f2d:

                case bc_d2f:

                    out.append("/* number conversion */");

                    break;

                case bc_f2i:

                case bc_f2l:

                case bc_d2i:

                case bc_d2l:

                    out.append("stack.push(Math.floor(stack.pop()));");

                    break;

                case bc_i2b:

                case bc_i2c:

                case bc_i2s:

                    out.append("/* number conversion */");

                    break;

                case bc_iconst_0:

                case bc_dconst_0:

                case bc_lconst_0:

                case bc_fconst_0:

                    out.append("stack.push(0);");

                    break;

                case bc_iconst_1:

                case bc_lconst_1:

                case bc_fconst_1:

                case bc_dconst_1:

                    out.append("stack.push(1);");

                    break;

                case bc_iconst_2:

                case bc_fconst_2:

                    out.append("stack.push(2);");

                    break;

                case bc_iconst_3:

                    out.append("stack.push(3);");

                    break;

                case bc_iconst_4:

                    out.append("stack.push(4);");

                    break;

                case bc_iconst_5:

                    out.append("stack.push(5);");

                    break;

                case bc_if_icmpeq: {

                    i = generateIf(byteCodes, i, "==");

                    break;

                }

                case bc_ifeq: {

                    int indx = i + readIntArg(byteCodes, i);

                    out.append("if (stack.pop() == 0) { gt = " + indx);

                    out.append("; continue; }");

                    i += 2;

                    break;

                }

                case bc_if_icmpne:

                    i = generateIf(byteCodes, i, "!=");

                    break;

                case bc_if_icmplt:

                    i = generateIf(byteCodes, i, ">");

                    break;

                case bc_if_icmple:

                    i = generateIf(byteCodes, i, ">=");

                    break;

                case bc_if_icmpgt:

                    i = generateIf(byteCodes, i, "<");

                    break;

                case bc_if_icmpge:

                    i = generateIf(byteCodes, i, "<=");

                    break;

                case bc_goto: {

                    int indx = i + readIntArg(byteCodes, i);

                    out.append("gt = " + indx).append("; continue;");

                    i += 2;

                    break;

                }

                case bc_invokestatic: {

                    int methodIndex = readIntArg(byteCodes, i);

                    CPMethodInfo mi = (CPMethodInfo) jc.getConstantPool().get(methodIndex);

                    boolean[] hasReturn = { false };

                    StringBuilder signature = new StringBuilder();

                    int cnt = countArgs(mi.getDescriptor(), hasReturn, signature);

                    if (hasReturn[0]) {

                        out.append("stack.push(");

                    }

                    out.append(mi.getClassName().getInternalName().replace('/', '_'));

                    out.append('_');

                    out.append(mi.getName());

                    out.append(signature.toString());

                    out.append('(');

                    String sep = "";

                    for (int j = 0; j < cnt; j++) {

                        out.append(sep);

                        out.append("stack.pop()");

                        sep = ", ";

                    }

                    out.append(")");

                    if (hasReturn[0]) {

                        out.append(")");

                    }

                    out.append(";");

                    i += 2;

                    break;

                }

            }

            out.append(" /*");

            for (int j = prev; j <= i; j++) {

                out.append(" ");

                final int cc = (byteCodes[j] + 256) % 256;

                out.append(Integer.toString(cc));

            }

            out.append("*/\n");

        }

        out.append("}\n");

    }

    private int generateIf(byte[] byteCodes, int i, final String test) throws IOException {

        int indx = i + readIntArg(byteCodes, i);

        out.append("if (stack.pop() ").append(test).append(" stack.pop()) { gt = " + indx);

        out.append("; continue; }");

        return i + 2;

    }

    private int readIntArg(byte[] byteCodes, int offsetInstruction) {

        final int indxHi = byteCodes[offsetInstruction + 1] << 8;

        final int indxLo = byteCodes[offsetInstruction + 2];

        return (indxHi & 0xffffff00) | (indxLo & 0xff);

    }

    private static int countArgs(String descriptor, boolean[] hasReturnType, StringBuilder sig) {

        int cnt = 0;

        int i = 0;

        Boolean count = null;

        while (i < descriptor.length()) {

            char ch = descriptor.charAt(i++);

            switch (ch) {

                case '(':

                    count = true;

                    continue;

                case ')':

                    count = false;

                    continue;

                case 'B': 

                case 'C': 

                case 'D': 

                case 'F': 

                case 'I': 

                case 'J': 

                case 'S': 

                case 'Z': 

                    if (count) {

                        cnt++;

                        sig.append(ch);

                    } else {

                        hasReturnType[0] = true;

                        sig.insert(0, ch);

                    }

                    continue;

                case 'V': 

                    assert !count;

                    hasReturnType[0] = false;

                    sig.insert(0, 'V');

                    continue;

                case 'L':

                    i = descriptor.indexOf(';', i);

                    if (count) {

                        cnt++;

                    } else {

                        hasReturnType[0] = true;

                    }

                    continue;

                case '[':

                    //arrays++;

                    continue;

                default:

                    break; // invalid character

            }

        }

        return cnt;

    }

}