codechunk.h

/* ScummVM - Graphic Adventure Engine
 *
 * ScummVM is the legal property of its developers, whose names
 * are too numerous to list here. Please refer to the COPYRIGHT
 * file distributed with this source distribution.
 *
 * 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, 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 <http://www.gnu.org/licenses/>.
 *
 */

#ifndef MEDIASTATION_MEDIASCRIPT_CODECHUNK_H
#define MEDIASTATION_MEDIASCRIPT_CODECHUNK_H

#include "common/array.h"

#include "mediastation/datafile.h"
#include "mediastation/mediascript/scriptvalue.h"
#include "mediastation/mediascript/scriptconstants.h"

namespace MediaStation {

class CodeChunk {
public:
    CodeChunk(ParameterReadStream *bytecode) : _bytecode(bytecode) {};
    ~CodeChunk();

    ScriptValue executeNextBlock();
    ScriptValue executeWithArguments(Common::Array<ScriptValue> *args);

private:
    // This is not the number of recursive calls, it is as far is the script call stack is
    // ever allowed to get.
    static const uint MAX_CALL_DEPTH = 0x20;

    void skipNextBlock();

    ScriptValue evaluateExpression();
    ScriptValue evaluateExpression(ExpressionType expressionType);
    void evaluateLValue(ScriptValue *&targetPtr);
    ScriptValue evaluateOperation();
    ScriptValue evaluateValue();
    ScriptValue evaluateVariable();

    ScriptValue *readAndReturnVariable();

    void evaluateIf();
    void evaluateIfElse();
    ScriptValue evaluateAssign();
    ScriptValue evaluateBinaryOperation(Opcode op);
    ScriptValue evaluateUnaryOperation();
    ScriptValue evaluateFunctionCall(bool isIndirect = false);
    ScriptValue evaluateFunctionCall(uint functionId, uint paramCount);
    ScriptValue evaluateMethodCall(bool isIndirect = false);
    ScriptValue evaluateMethodCall(BuiltInMethod method, uint paramCount);
    void evaluateDeclareLocals();
    void evaluateReturn();
    void evaluateReturnNoValue();
    void evaluateWhileLoop();

    static const uint MAX_LOOP_ITERATION_COUNT = 1000;
    bool _returnImmediately = false;
    ScriptValue _returnValue;
    Common::Array<ScriptValue> _locals;
    Common::Array<ScriptValue> *_args = nullptr;
    ParameterReadStream *_bytecode = nullptr;

    // Debug output indentation tracking.
    uint _debugIndentLevel = 0;
};

// These decompilation methods are intended to directly mirror the relevant code chunk
// methods from the original. While this does duplicate some opcode parsing and such,
// given that this part of the engine is pretty stable, the additional complexity
// (and departure from the disassembly) of a full decoder/visitor pattern was judged
// to not be worth it.
//
// The decompiled script format is based on the scripts shipped as debug statements
// in If You Give a Mouse a Cookie, which debug-printed every script line before executing
// the bytecode.
class CodeChunkDecompiler {
public:
    CodeChunkDecompiler(ParameterReadStream *bytecode, uint indentLevel = 0);

    Common::String decompileNextBlock();

private:
    Common::String decompileExpression();
    Common::String decompileExpression(ExpressionType expressionType);
    Common::String decompileOperation();
    Common::String decompileValue();
    Common::String decompileVariable();

    Common::String decompileIf();
    Common::String decompileIfElse();
    Common::String decompileAssign();
    Common::String decompileBinaryOperation(Opcode op);
    Common::String decompileUnaryOperation();
    Common::String decompileFunctionCall(bool isIndirect = false);
    Common::String decompileFunctionCall(uint functionId, uint paramCount);
    Common::String decompileMethodCall(bool isIndirect = false);
    Common::String decompileMethodCall(BuiltInMethod method, uint paramCount);
    void appendDecompiledParameterList(Common::String &result, uint paramCount);
    Common::String decompileDeclareLocals();
    Common::String decompileReturn();
    Common::String decompileReturnNoValue();
    Common::String decompileWhileLoop();

    uint _indentLevel = 0;
    ParameterReadStream *_bytecode = nullptr;
};

} // End of namespace MediaStation

#endif