#include "pocketpy/vm.h"

static const char* OP_NAMES[] = {
    #define OPCODE(name) #name,
    #include "pocketpy/opcodes.h"
    #undef OPCODE
};

namespace pkpy{

    struct JsonSerializer{
        VM* vm;
        PyVar root;
        SStream ss;

        JsonSerializer(VM* vm, PyVar root) : vm(vm), root(root) {}

        template<typename T>
        void write_array(T& arr){
            ss << '[';
            for(int i=0; i<arr.size(); i++){
                if(i != 0) ss << ", ";
                write_object(arr[i]);
            }
            ss << ']';
        }

        void write_dict(Dict& dict){
            ss << '{';
            bool first = true;
            dict.apply([&](PyVar k, PyVar v){
                if(!first) ss << ", ";
                first = false;
                if(!is_type(k, VM::tp_str)){
                    vm->TypeError(_S("json keys must be string, got ", _type_name(vm, vm->_tp(k))));
                }
                ss << _CAST(Str&, k).escape(false) << ": ";
                write_object(v);
            });
            ss << '}';
        }

        void write_object(PyVar obj){
            Type obj_t = vm->_tp(obj);
            if(obj == vm->None){
                ss << "null";
            }else if(obj_t == vm->tp_int){
                ss << _CAST(i64, obj);
            }else if(obj_t == vm->tp_float){
                f64 val = _CAST(f64, obj);
                if(std::isinf(val) || std::isnan(val)) vm->ValueError("cannot jsonify 'nan' or 'inf'");
                ss << val;
            }else if(obj_t == vm->tp_bool){
                ss << (obj == vm->True ? "true" : "false");
            }else if(obj_t == vm->tp_str){
                _CAST(Str&, obj).escape_(ss, false);
            }else if(obj_t == vm->tp_list){
                write_array<List>(_CAST(List&, obj));
            }else if(obj_t == vm->tp_tuple){
                write_array<Tuple>(_CAST(Tuple&, obj));
            }else if(obj_t == vm->tp_dict){
                write_dict(_CAST(Dict&, obj));
            }else{
                vm->TypeError(_S("unrecognized type ", _type_name(vm, obj_t).escape()));
            }
        }

        Str serialize(){
            auto _lock = vm->heap.gc_scope_lock();
            write_object(root);
            return ss.str();
        }
    };

    VM::VM(bool enable_os) : heap(this), enable_os(enable_os) {
        this->vm = this;
        this->__c.error = nullptr;
        _ceval_on_step = nullptr;
        _stdout = [](const char* buf, int size) { std::cout.write(buf, size); };
        _stderr = [](const char* buf, int size) { std::cerr.write(buf, size); };
        _main = nullptr;
        __last_exception = nullptr;
        _import_handler = [](const char* name, int* out_size) -> unsigned char*{ return nullptr; };
        __init_builtin_types();
    }

    Str VM::py_str(PyVar obj){
        const PyTypeInfo* ti = _tp_info(obj);
        if(ti->m__str__) return ti->m__str__(this, obj);
        PyVar self;
        PyVar f = get_unbound_method(obj, __str__, &self, false);
        if(self != PY_NULL){
            PyVar retval = call_method(self, f);
            if(!is_type(retval, tp_str)){
                throw std::runtime_error("object.__str__ must return str");
            }
            return PK_OBJ_GET(Str, retval);
        }
        return py_repr(obj);
    }

    Str VM::py_repr(PyVar obj){
        const PyTypeInfo* ti = _tp_info(obj);
        if(ti->m__repr__) return ti->m__repr__(this, obj);
        PyVar retval = call_method(obj, __repr__);
        if(!is_type(retval, tp_str)){
            throw std::runtime_error("object.__repr__ must return str");
        }
        return PK_OBJ_GET(Str, retval);
    }

    Str VM::py_json(PyVar obj){
        auto j = JsonSerializer(this, obj);
        return j.serialize();
    }

    PyVar VM::py_iter(PyVar obj){
        const PyTypeInfo* ti = _tp_info(obj);
        if(ti->m__iter__) return ti->m__iter__(this, obj);
        PyVar self;
        PyVar iter_f = get_unbound_method(obj, __iter__, &self, false);
        if(self != PY_NULL) return call_method(self, iter_f);
        TypeError(_type_name(vm, _tp(obj)).escape() + " object is not iterable");
        return nullptr;
    }

    ArgsView VM::cast_array_view(PyVar obj){
        if(is_type(obj, VM::tp_list)){
            List& list = PK_OBJ_GET(List, obj);
            return ArgsView(list.begin(), list.end());
        }else if(is_type(obj, VM::tp_tuple)){
            Tuple& tuple = PK_OBJ_GET(Tuple, obj);
            return ArgsView(tuple.begin(), tuple.end());
        }
        TypeError(_S("expected list or tuple, got ", _type_name(this, _tp(obj)).escape()));
        PK_UNREACHABLE();
    }

    void VM::set_main_argv(int argc, char** argv){
        PyVar mod = vm->_modules["sys"];
        List argv_(argc);
        for(int i=0; i<argc; i++) argv_[i] = VAR(std::string_view(argv[i]));
        mod->attr().set("argv", VAR(std::move(argv_)));
    }

    PyVar VM::find_name_in_mro(Type cls, StrName name){
        PyVar val;
        do{
            val = _t(cls)->attr().try_get(name);
            if(val != nullptr) return val;
            cls = _all_types[cls].base;
            if(cls.index == -1) break;
        }while(true);
        return nullptr;
    }

    bool VM::isinstance(PyVar obj, Type base){
        return issubclass(_tp(obj), base);
    }

    bool VM::issubclass(Type cls, Type base){
        do{
            if(cls == base) return true;
            Type next = _all_types[cls].base;
            if(next.index == -1) break;
            cls = next;
        }while(true);
        return false;
    }

    PyVar VM::exec(std::string_view source, Str filename, CompileMode mode, PyVar _module){
        if(_module == nullptr) _module = _main;
        try {
#if PK_DEBUG_PRECOMPILED_EXEC == 1
            Str precompiled = vm->precompile(source, filename, mode);
            source = precompiled.sv();
#endif
            CodeObject_ code = compile(source, filename, mode);
            return _exec(code, _module);
        }catch (const Exception& e){
            stderr_write(e.summary() + "\n");
        }
        catch(const std::exception& e) {
            Str msg = "An std::exception occurred! It could be a bug.\n";
            msg = msg + e.what() + "\n";
            stderr_write(msg);
        }
        catch(NeedMoreLines){
            throw;
        }
        catch(...) {
            Str msg = "An unknown exception occurred! It could be a bug. Please report it to @blueloveTH on GitHub.\n";
            stderr_write(msg);
        }
        callstack.clear();
        s_data.clear();
        return nullptr;
    }

    PyVar VM::exec(std::string_view source){
        return exec(source, "main.py", EXEC_MODE);
    }

    PyVar VM::eval(std::string_view source){
        return exec(source, "<eval>", EVAL_MODE);
    }

    PyVar VM::new_type_object(PyVar mod, StrName name, Type base, bool subclass_enabled){
        PyVar obj = heap._new<Type>(tp_type, Type(_all_types.size()));
        const PyTypeInfo& base_info = _all_types[base];
        if(!base_info.subclass_enabled){
            Str error = _S("type ", base_info.name.escape(), " is not `subclass_enabled`");
            throw std::runtime_error(error.c_str());
        }
        PyTypeInfo info{
            obj,
            base,
            mod,
            name,
            subclass_enabled,
        };
        _all_types.push_back(info);
        return obj;
    }

    bool VM::py_eq(PyVar lhs, PyVar rhs){
        if(lhs == rhs) return true;
        const PyTypeInfo* ti = _tp_info(lhs);
        PyVar res;
        if(ti->m__eq__){
            res = ti->m__eq__(this, lhs, rhs);
            if(res != vm->NotImplemented) return res == vm->True;
        }
        res = call_method(lhs, __eq__, rhs);
        if(res != vm->NotImplemented) return res == vm->True;

        ti = _tp_info(rhs);
        if(ti->m__eq__){
            res = ti->m__eq__(this, rhs, lhs);
            if(res != vm->NotImplemented) return res == vm->True;
        }
        res = call_method(rhs, __eq__, lhs);
        if(res != vm->NotImplemented) return res == vm->True;
        return false;
    }

    PyVar VM::py_op(std::string_view name){
        PyVar func;
        auto it = __cached_op_funcs.find(name);
        if(it == __cached_op_funcs.end()){
            func = py_import("operator")->attr(StrName::get(name));
            __cached_op_funcs[name] = func;
        }else{
            func = it->second;
        }
        return func;
    }

    i64 VM::normalized_index(i64 index, int size){
        if(index < 0) index += size;
        if(index < 0 || index >= size){
            IndexError(std::to_string(index) + " not in [0, " + std::to_string(size) + ")");
        }
        return index;
    }

    PyVar VM::_py_next(const PyTypeInfo* ti, PyVar obj){
        if(ti->m__next__){
            unsigned n = ti->m__next__(this, obj);
            return __pack_next_retval(n);
        }
        return call_method(obj, __next__);
    }

    PyVar VM::py_next(PyVar obj){
        const PyTypeInfo* ti = _tp_info(obj);
        return _py_next(ti, obj);
    }

    bool VM::py_callable(PyVar obj){
        Type cls = vm->_tp(obj);
        switch(cls.index){
            case VM::tp_function.index: return vm->True;
            case VM::tp_native_func.index: return vm->True;
            case VM::tp_bound_method.index: return vm->True;
            case VM::tp_type.index: return vm->True;
        }
        return vm->find_name_in_mro(cls, __call__) != nullptr;
    }

    PyVar VM::__minmax_reduce(bool (VM::*op)(PyVar, PyVar), PyVar args, PyVar key){
        auto _lock = heap.gc_scope_lock();
        const Tuple& args_tuple = PK_OBJ_GET(Tuple, args);  // from *args, it must be a tuple
        if(key==vm->None && args_tuple.size()==2){
            // fast path
            PyVar a = args_tuple[0];
            PyVar b = args_tuple[1];
            return (this->*op)(a, b) ? a : b;
        }

        if(args_tuple.size() == 0) TypeError("expected at least 1 argument, got 0");
        
        ArgsView view(nullptr, nullptr);
        if(args_tuple.size()==1){
            view = cast_array_view(args_tuple[0]);
        }else{
            view = ArgsView(args_tuple);
        }

        if(view.empty()) ValueError("arg is an empty sequence");
        PyVar res = view[0];

        if(key == vm->None){
            for(int i=1; i<view.size(); i++){
                if((this->*op)(view[i], res)) res = view[i];
            }
        }else{
            auto _lock = heap.gc_scope_lock();
            for(int i=1; i<view.size(); i++){
                PyVar a = call(key, view[i]);
                PyVar b = call(key, res);
                if((this->*op)(a, b)) res = view[i];
            }
        }
        return res;
    }

    PyVar VM::py_import(Str path, bool throw_err){
        if(path.empty()) vm->ValueError("empty module name");
        static auto f_join = [](const pod_vector<std::string_view>& cpnts){
            SStream ss;
            for(int i=0; i<cpnts.size(); i++){
                if(i != 0) ss << ".";
                ss << cpnts[i];
            }
            return ss.str();
        };

        if(path[0] == '.'){
            if(__import_context.pending.empty()){
                ImportError("relative import outside of package");
            }
            Str curr_path = __import_context.pending.back();
            bool curr_is_init = __import_context.pending_is_init.back();
            // convert relative path to absolute path
            pod_vector<std::string_view> cpnts = curr_path.split('.');
            int prefix = 0;     // how many dots in the prefix
            for(int i=0; i<path.length(); i++){
                if(path[i] == '.') prefix++;
                else break;
            }
            if(prefix > cpnts.size()) ImportError("attempted relative import beyond top-level package");
            path = path.substr(prefix);     // remove prefix
            for(int i=(int)curr_is_init; i<prefix; i++) cpnts.pop_back();
            if(!path.empty()) cpnts.push_back(path.sv());
            path = f_join(cpnts);
        }

        PK_ASSERT(path.begin()[0] != '.' && path.end()[-1] != '.');

        // check existing module
        StrName name(path);
        PyVar ext_mod = _modules.try_get(name);
        if(ext_mod != nullptr) return ext_mod;

        pod_vector<std::string_view> path_cpnts = path.split('.');
        // check circular import
        if(__import_context.pending.size() > 128){
            ImportError("maximum recursion depth exceeded while importing");
        }

        // try import
        Str filename = path.replace('.', PK_PLATFORM_SEP) + ".py";
        Str source;
        bool is_init = false;
        auto it = _lazy_modules.find(name);
        if(it == _lazy_modules.end()){
            int out_size;
            unsigned char* out = _import_handler(filename.c_str(), &out_size);
            if(out == nullptr){
                filename = path.replace('.', PK_PLATFORM_SEP).str() + PK_PLATFORM_SEP + "__init__.py";
                is_init = true;
                out = _import_handler(filename.c_str(), &out_size);
            }
            if(out == nullptr){
                if(throw_err) ImportError(_S("module ", path.escape(), " not found"));
                else return nullptr;
            }
            PK_ASSERT(out_size >= 0)
            source = Str(std::string_view((char*)out, out_size));
            free(out);
        }else{
            source = it->second;
            _lazy_modules.erase(it);
        }
        auto _ = __import_context.scope(path, is_init);
        CodeObject_ code = compile(source, filename, EXEC_MODE);

        Str name_cpnt = path_cpnts.back();
        path_cpnts.pop_back();
        PyVar new_mod = new_module(name_cpnt, f_join(path_cpnts));
        _exec(code, new_mod);
        return new_mod;
    }

    VM::~VM() {
        callstack.clear();
        s_data.clear();
        _all_types.clear();
        _modules.clear();
        _lazy_modules.clear();
    }

PyVar VM::py_negate(PyVar obj){
    const PyTypeInfo* ti = _tp_info(obj);
    if(ti->m__neg__) return ti->m__neg__(this, obj);
    return call_method(obj, __neg__);
}

bool VM::py_bool(PyVar obj){
    if(obj == vm->True) return true;
    if(obj == vm->False) return false;
    if(obj == None) return false;
    if(is_int(obj)) return _CAST(i64, obj) != 0;
    if(is_float(obj)) return _CAST(f64, obj) != 0.0;
    PyVar self;
    PyVar len_f = get_unbound_method(obj, __len__, &self, false);
    if(self != PY_NULL){
        PyVar ret = call_method(self, len_f);
        return CAST(i64, ret) > 0;
    }
    return true;
}

List VM::py_list(PyVar it){
    auto _lock = heap.gc_scope_lock();
    it = py_iter(it);
    List list;
    const PyTypeInfo* info = _tp_info(it);
    PyVar obj = _py_next(info, it);
    while(obj != StopIteration){
        list.push_back(obj);
        obj = _py_next(info, it);
    }
    return list;
}



void VM::parse_int_slice(const Slice& s, int length, int& start, int& stop, int& step){
    auto clip = [](int value, int min, int max){
        if(value < min) return min;
        if(value > max) return max;
        return value;
    };
    if(s.step == None) step = 1;
    else step = CAST(int, s.step);
    if(step == 0) ValueError("slice step cannot be zero");
    if(step > 0){
        if(s.start == None){
            start = 0;
        }else{
            start = CAST(int, s.start);
            if(start < 0) start += length;
            start = clip(start, 0, length);
        }
        if(s.stop == None){
            stop = length;
        }else{
            stop = CAST(int, s.stop);
            if(stop < 0) stop += length;
            stop = clip(stop, 0, length);
        }
    }else{
        if(s.start == None){
            start = length - 1;
        }else{
            start = CAST(int, s.start);
            if(start < 0) start += length;
            start = clip(start, -1, length - 1);
        }
        if(s.stop == None){
            stop = -1;
        }else{
            stop = CAST(int, s.stop);
            if(stop < 0) stop += length;
            stop = clip(stop, -1, length - 1);
        }
    }
}

i64 VM::py_hash(PyVar obj){
    // https://docs.python.org/3.10/reference/datamodel.html#object.__hash__
    const PyTypeInfo* ti = _tp_info(obj);
    if(ti->m__hash__) return ti->m__hash__(this, obj);

    PyVar self;
    PyVar f = get_unbound_method(obj, __hash__, &self, false);
    if(f != nullptr){
        PyVar ret = call_method(self, f);
        return CAST(i64, ret);
    }
    // if it is trivial `object`, return PK_BITS
    if(ti == &_all_types[tp_object]) return PK_BITS(obj);
    // otherwise, we check if it has a custom __eq__ other than object.__eq__
    bool has_custom_eq = false;
    if(ti->m__eq__) has_custom_eq = true;
    else{
        f = get_unbound_method(obj, __eq__, &self, false);
        has_custom_eq = f != _t(tp_object)->attr(__eq__);
    }
    if(has_custom_eq){
        TypeError(_S("unhashable type: ", ti->name.escape()));
        PK_UNREACHABLE()
    }else{
        return PK_BITS(obj);
    }
}

PyVar VM::__py_exec_internal(const CodeObject_& code, PyVar globals, PyVar locals){
    Frame* frame = nullptr;
    if(!callstack.empty()) frame = &callstack.top();

    // fast path
    if(frame && globals == vm->None && locals == vm->None){
        return vm->_exec(code.get(), frame->_module, frame->_callable, frame->_locals);
    }

    auto _lock = heap.gc_scope_lock();  // for safety

    PyVar globals_obj = nullptr;
    Dict* globals_dict = nullptr;

    NameDict_ locals_closure = nullptr;
    Dict* locals_dict = nullptr;

    if(globals == vm->None){
        globals_obj = frame ? frame->_module : _main;
    }else{
        if(is_type(globals, VM::tp_mappingproxy)){
            globals_obj = PK_OBJ_GET(MappingProxy, globals).obj;
        }else{
            check_compatible_type(globals, VM::tp_dict);
            // make a temporary object and copy globals into it
            globals_obj = heap.gcnew<DummyInstance>(VM::tp_object);
            globals_obj->_enable_instance_dict();
            globals_dict = &PK_OBJ_GET(Dict, globals);
            globals_dict->apply([&](PyVar k, PyVar v){
                globals_obj->attr().set(CAST(Str&, k), v);
            });
        }
    }

    PyVar retval = nullptr;

    if(locals == vm->None){
        retval = vm->_exec(code, globals_obj);   // only globals
    }else{
        check_compatible_type(locals, VM::tp_dict);
        locals_dict = &PK_OBJ_GET(Dict, locals);
        locals_closure = std::make_shared<NameDict>();
        locals_dict->apply([&](PyVar k, PyVar v){
            locals_closure->set(CAST(Str&, k), v);
        });
        PyVar _callable = VAR(Function(__dynamic_func_decl, globals_obj, nullptr, locals_closure));
        retval = vm->_exec(code.get(), globals_obj, _callable, vm->s_data._sp);
    }

    if(globals_dict){
        globals_dict->clear();
        globals_obj->attr().apply([&](StrName k, PyVar v){
            globals_dict->set(VAR(k.sv()), v);
        });
    }

    if(locals_dict){
        locals_dict->clear();
        locals_closure->apply([&](StrName k, PyVar v){
            locals_dict->set(VAR(k.sv()), v);
        });
    }
    return retval;
}

void VM::py_exec(std::string_view source, PyVar globals, PyVar locals){
    CodeObject_ code = vm->compile(source, "<exec>", EXEC_MODE, true);
    __py_exec_internal(code, globals, locals);
}

PyVar VM::py_eval(std::string_view source, PyVar globals, PyVar locals){
    CodeObject_ code = vm->compile(source, "<eval>", EVAL_MODE, true);
    return __py_exec_internal(code, globals, locals);
}

PyVar VM::__format_object(PyVar obj, Str spec){
    if(spec.empty()) return VAR(py_str(obj));
    char type;
    switch(spec.end()[-1]){
        case 'f': case 'd': case 's':
            type = spec.end()[-1];
            spec = spec.substr(0, spec.length() - 1);
            break;
        default: type = ' '; break;
    }

    char pad_c = ' ';
    for(char c: std::string_view("0-=*#@!~")){
        if(spec[0] == c){
            pad_c = c;
            spec = spec.substr(1);
            break;
        }
    }
    char align;
    if(spec[0] == '^'){
        align = '^';
        spec = spec.substr(1);
    }else if(spec[0] == '>'){
        align = '>';
        spec = spec.substr(1);
    }else if(spec[0] == '<'){
        align = '<';
        spec = spec.substr(1);
    }else{
        if(is_int(obj) || is_float(obj)) align = '>';
        else align = '<';
    }

    int dot = spec.index(".");
    int width, precision;
    try{
        if(dot >= 0){
            if(dot == 0){
                width = -1;
            }else{
                width = std::stoi(spec.substr(0, dot).str());
            }
            precision = std::stoi(spec.substr(dot+1).str());
        }else{
            width = std::stoi(spec.str());
            precision = -1;
        }
    }catch(...){
        ValueError("invalid format specifer");
    }

    if(type != 'f' && dot >= 0) ValueError("precision not allowed in the format specifier");
    Str ret;
    if(type == 'f'){
        f64 val = CAST(f64, obj);
        if(precision < 0) precision = 6;
        SStream ss;
        ss.setprecision(precision);
        ss << val;
        ret = ss.str();
    }else if(type == 'd'){
        ret = std::to_string(CAST(i64, obj));
    }else if(type == 's'){
        ret = CAST(Str&, obj);
    }else{
        ret = py_str(obj);
    }
    if(width != -1 && width > ret.length()){
        int pad = width - ret.length();
        if(align == '>' || align == '<'){
            std::string padding(pad, pad_c);
            if(align == '>') ret = padding.c_str() + ret;
            else ret = ret + padding.c_str();
        }else{  // ^
            int pad_left = pad / 2;
            int pad_right = pad - pad_left;
            std::string padding_left(pad_left, pad_c);
            std::string padding_right(pad_right, pad_c);
            ret = padding_left.c_str() + ret + padding_right.c_str();
        }
    }
    return VAR(ret);
}

PyVar VM::new_module(Str name, Str package) {
    PyVar obj = heap._new<DummyModule>(tp_module);
    obj->attr().set(__name__, VAR(name));
    obj->attr().set(__package__, VAR(package));
    // convert to fullname
    if(!package.empty()) name = package + "." + name;
    obj->attr().set(__path__, VAR(name));

    // we do not allow override in order to avoid memory leak
    // it is because Module objects are not garbage collected
    if(_modules.contains(name)){
        throw std::runtime_error(_S("module ", name.escape(), " already exists").str());
    }
    // set it into _modules
    _modules.set(name, obj);
    return obj;
}

static std::string _opcode_argstr(VM* vm, Bytecode byte, const CodeObject* co){
    std::string argStr = std::to_string(byte.arg);
    switch(byte.op){
        case OP_LOAD_CONST: case OP_FORMAT_STRING: case OP_IMPORT_PATH:
            if(vm != nullptr){
                argStr += _S(" (", vm->py_repr(co->consts[byte.arg]), ")").sv();
            }
            break;
        case OP_LOAD_NAME: case OP_LOAD_GLOBAL: case OP_LOAD_NONLOCAL: case OP_STORE_GLOBAL:
        case OP_LOAD_ATTR: case OP_LOAD_METHOD: case OP_STORE_ATTR: case OP_DELETE_ATTR:
        case OP_BEGIN_CLASS: case OP_GOTO:
        case OP_DELETE_GLOBAL: case OP_INC_GLOBAL: case OP_DEC_GLOBAL: case OP_STORE_CLASS_ATTR: case OP_FOR_ITER_STORE_GLOBAL:
            argStr += _S(" (", StrName(byte.arg).sv(), ")").sv();
            break;
        case OP_LOAD_FAST: case OP_STORE_FAST: case OP_DELETE_FAST: case OP_INC_FAST: case OP_DEC_FAST:
        case OP_FOR_ITER_STORE_FAST: case OP_LOAD_SUBSCR_FAST: case OP_STORE_SUBSCR_FAST:
            argStr += _S(" (", co->varnames[byte.arg].sv(), ")").sv();
            break;
        case OP_LOAD_FUNCTION:
            argStr += _S(" (", co->func_decls[byte.arg]->code->name, ")").sv();
            break;
        case OP_LOAD_SMALL_INT: case OP_LOAD_SUBSCR_SMALL_INT:
            argStr += _S(" (", (int)(byte.arg >> 2), ")").sv();
    }
    return argStr;
}

Str VM::disassemble(CodeObject_ co){
    auto pad = [](const Str& s, const int n){
        if(s.length() >= n) return s.substr(0, n);
        return s + std::string(n - s.length(), ' ');
    };

    std::vector<int> jumpTargets;
    for(auto byte : co->codes){
        if(byte.op == OP_JUMP_ABSOLUTE || byte.op == OP_POP_JUMP_IF_FALSE || byte.op == OP_SHORTCUT_IF_FALSE_OR_POP || byte.op == OP_LOOP_CONTINUE){
            jumpTargets.push_back(byte.arg);
        }
        if(byte.op == OP_GOTO){
            // TODO: pre-compute jump targets for OP_GOTO
            int* target = co->labels.try_get_2_likely_found(StrName(byte.arg));
            if(target != nullptr) jumpTargets.push_back(*target);
        }
    }
    SStream ss;
    int prev_line = -1;
    for(int i=0; i<co->codes.size(); i++){
        const Bytecode& byte = co->codes[i];
        Str line = std::to_string(co->lines[i].lineno);
        if(co->lines[i].lineno == prev_line) line = "";
        else{
            if(prev_line != -1) ss << "\n";
            prev_line = co->lines[i].lineno;
        }

        std::string pointer;
        if(std::find(jumpTargets.begin(), jumpTargets.end(), i) != jumpTargets.end()){
            pointer = "-> ";
        }else{
            pointer = "   ";
        }
        ss << pad(line, 8) << pointer << pad(std::to_string(i), 3);
        std::string bc_name(OP_NAMES[byte.op]);
        if(co->lines[i].is_virtual) bc_name += '*';
        ss << " " << pad(bc_name, 25) << " ";
        // ss << pad(byte.arg == -1 ? "" : std::to_string(byte.arg), 5);
        std::string argStr = _opcode_argstr(this, byte, co.get());
        ss << argStr;
        // ss << pad(argStr, 40);      // may overflow
        // ss << co->blocks[byte.block].type;
        if(i != co->codes.size() - 1) ss << '\n';
    }

    for(auto& decl: co->func_decls){
        ss << "\n\n" << "Disassembly of " << decl->code->name << ":\n";
        ss << disassemble(decl->code);
    }
    ss << "\n";
    return Str(ss.str());
}

#if PK_DEBUG_CEVAL_STEP
void VM::__log_s_data(const char* title) {
    if(_main == nullptr) return;
    if(callstack.empty()) return;
    SStream ss;
    if(title) ss << title << " | ";
    std::map<PyVar*, int> sp_bases;
    for(Frame& f: callstack.data()){
        if(f._sp_base == nullptr) PK_FATAL_ERROR();
        sp_bases[f._sp_base] += 1;
    }
    Frame* frame = &callstack.top();
    int line = frame->co->lines[frame->_ip];
    ss << frame->co->name << ":" << line << " [";
    for(PyVar* p=s_data.begin(); p!=s_data.end(); p++){
        ss << std::string(sp_bases[p], '|');
        if(sp_bases[p] > 0) ss << " ";
        PyVar obj = *p;
        if(obj == nullptr) ss << "(nil)";
        else if(obj == PY_NULL) ss << "NULL";
        else if(is_int(obj)) ss << CAST(i64, obj);
        else if(is_float(obj)) ss << CAST(f64, obj);
        else if(is_type(obj, tp_str)) ss << CAST(Str, obj).escape();
        else if(obj == None) ss << "None";
        else if(obj == True) ss << "True";
        else if(obj == False) ss << "False";
        else if(is_type(obj, tp_function)){
            auto& f = CAST(Function&, obj);
            ss << f.decl->code->name << "(...)";
        } else if(is_type(obj, tp_type)){
            Type t = PK_OBJ_GET(Type, obj);
            ss << "<class " + _all_types[t].name.escape() + ">";
        } else if(is_type(obj, tp_list)){
            auto& t = CAST(List&, obj);
            ss << "list(size=" << t.size() << ")";
        } else if(is_type(obj, tp_tuple)){
            auto& t = CAST(Tuple&, obj);
            ss << "tuple(size=" << t.size() << ")";
        } else ss << "(" << _type_name(this, obj->type) << ")";
        ss << ", ";
    }
    std::string output = ss.str();
    if(!s_data.empty()) {
        output.pop_back(); output.pop_back();
    }
    output.push_back(']');
    Bytecode byte = frame->co->codes[frame->_ip];
    std::cout << output << " " << OP_NAMES[byte.op] << " " << _opcode_argstr(nullptr, byte, frame->co) << std::endl;
}
#endif

void VM::__init_builtin_types(){
    _all_types.push_back({heap._new<Type>(Type(1), Type(0)), Type(-1), nullptr, "object", true});
    _all_types.push_back({heap._new<Type>(Type(1), Type(1)), Type(0), nullptr, "type", false});

    auto _new_type = [this](const char* name, Type base=Type(0), bool subclass_enabled=false){
        PyVar obj = new_type_object(nullptr, name, base, subclass_enabled);
        return PK_OBJ_GET(Type, obj);
    };

    if(tp_int != _new_type("int")) exit(-3);
    if((tp_float != _new_type("float"))) exit(-3);

    if(tp_bool != _new_type("bool")) exit(-3);
    if(tp_str != _new_type("str")) exit(-3);
    if(tp_list != _new_type("list")) exit(-3);
    if(tp_tuple != _new_type("tuple")) exit(-3);

    if(tp_slice != _new_type("slice")) exit(-3);
    if(tp_range != _new_type("range")) exit(-3);
    if(tp_module != _new_type("module")) exit(-3);
    if(tp_function != _new_type("function")) exit(-3);
    if(tp_native_func != _new_type("native_func")) exit(-3);
    if(tp_bound_method != _new_type("bound_method")) exit(-3);

    if(tp_super != _new_type("super")) exit(-3);
    if(tp_exception != _new_type("Exception", Type(0), true)) exit(-3);
    if(tp_bytes != _new_type("bytes")) exit(-3);
    if(tp_mappingproxy != _new_type("mappingproxy")) exit(-3);
    if(tp_dict != _new_type("dict", Type(0), true)) exit(-3);  // dict can be subclassed
    if(tp_property != _new_type("property")) exit(-3);
    if(tp_star_wrapper != _new_type("_star_wrapper")) exit(-3);

    if(tp_staticmethod != _new_type("staticmethod")) exit(-3);
    if(tp_classmethod != _new_type("classmethod")) exit(-3);

    // SyntaxError and IndentationError must be created here
    Type tp_syntax_error = _new_type("SyntaxError", tp_exception, true);
    Type tp_indentation_error = _new_type("IndentationError", tp_syntax_error, true);

    this->None = heap._new<Dummy>(_new_type("NoneType"));
    this->NotImplemented = heap._new<Dummy>(_new_type("NotImplementedType"));
    this->Ellipsis = heap._new<Dummy>(_new_type("ellipsis"));
    this->True = heap._new<Dummy>(tp_bool);
    this->False = heap._new<Dummy>(tp_bool);
    this->StopIteration = _all_types[_new_type("StopIteration", tp_exception)].obj;

    this->builtins = new_module("builtins");
    
    // setup public types
    builtins->attr().set("type", _t(tp_type));
    builtins->attr().set("object", _t(tp_object));
    builtins->attr().set("bool", _t(tp_bool));
    builtins->attr().set("int", _t(tp_int));
    builtins->attr().set("float", _t(tp_float));
    builtins->attr().set("str", _t(tp_str));
    builtins->attr().set("list", _t(tp_list));
    builtins->attr().set("tuple", _t(tp_tuple));
    builtins->attr().set("range", _t(tp_range));
    builtins->attr().set("bytes", _t(tp_bytes));
    builtins->attr().set("dict", _t(tp_dict));
    builtins->attr().set("property", _t(tp_property));
    builtins->attr().set("StopIteration", StopIteration);
    builtins->attr().set("NotImplemented", NotImplemented);
    builtins->attr().set("slice", _t(tp_slice));
    builtins->attr().set("Exception", _t(tp_exception));
    builtins->attr().set("SyntaxError", _t(tp_syntax_error));
    builtins->attr().set("IndentationError", _t(tp_indentation_error));

    __post_init_builtin_types();
    this->_main = new_module("__main__");
}

// `heap.gc_scope_lock();` needed before calling this function
void VM::__unpack_as_list(ArgsView args, List& list){
    for(PyVar obj: args){
        if(is_type(obj, tp_star_wrapper)){
            const StarWrapper& w = _CAST(StarWrapper&, obj);
            // maybe this check should be done in the compile time
            if(w.level != 1) TypeError("expected level 1 star wrapper");
            PyVar _0 = py_iter(w.obj);
            const PyTypeInfo* info = _tp_info(_0);
            PyVar _1 = _py_next(info, _0);
            while(_1 != StopIteration){
                list.push_back(_1);
                _1 = _py_next(info, _0);
            }
        }else{
            list.push_back(obj);
        }
    }
}

// `heap.gc_scope_lock();` needed before calling this function
void VM::__unpack_as_dict(ArgsView args, Dict& dict){
    for(PyVar obj: args){
        if(is_type(obj, tp_star_wrapper)){
            const StarWrapper& w = _CAST(StarWrapper&, obj);
            // maybe this check should be done in the compile time
            if(w.level != 2) TypeError("expected level 2 star wrapper");
            const Dict& other = CAST(Dict&, w.obj);
            dict.update(other);
        }else{
            const Tuple& t = CAST(Tuple&, obj);
            if(t.size() != 2) TypeError("expected tuple of length 2");
            dict.set(t[0], t[1]);
        }
    }
}


void VM::__prepare_py_call(PyVar* buffer, ArgsView args, ArgsView kwargs, const FuncDecl_& decl){
    const CodeObject* co = decl->code.get();
    int co_nlocals = co->varnames.size();
    int decl_argc = decl->args.size();

    if(args.size() < decl_argc){
        vm->TypeError(_S(
            co->name, "() takes ", decl_argc, " positional arguments but ", args.size(), " were given"
        ));
    }

    int i = 0;
    // prepare args
    for(int index: decl->args) buffer[index] = args[i++];
    // set extra varnames to PY_NULL
    for(int j=i; j<co_nlocals; j++) buffer[j] = PY_NULL;
    // prepare kwdefaults
    for(auto& kv: decl->kwargs) buffer[kv.index] = kv.value;
    
    // handle *args
    if(decl->starred_arg != -1){
        ArgsView vargs(args.begin() + i, args.end());
        buffer[decl->starred_arg] = VAR(vargs.to_tuple());
        i += vargs.size();
    }else{
        // kwdefaults override
        for(auto& kv: decl->kwargs){
            if(i >= args.size()) break;
            buffer[kv.index] = args[i++];
        }
        if(i < args.size()) TypeError(_S("too many arguments", " (", decl->code->name, ')'));
    }
    
    PyVar vkwargs;
    if(decl->starred_kwarg != -1){
        vkwargs = VAR(Dict(this));
        buffer[decl->starred_kwarg] = vkwargs;
    }else{
        vkwargs = nullptr;
    }

    for(int j=0; j<kwargs.size(); j+=2){
        StrName key(_CAST(uint16_t, kwargs[j]));
        int index = decl->kw_to_index.try_get_likely_found(key);
        // if key is an explicit key, set as local variable
        if(index >= 0){
            buffer[index] = kwargs[j+1];
        }else{
            // otherwise, set as **kwargs if possible
            if(vkwargs == nullptr){
                TypeError(_S(key.escape(), " is an invalid keyword argument for ", co->name, "()"));
            }else{
                Dict& dict = _CAST(Dict&, vkwargs);
                dict.set(VAR(key.sv()), kwargs[j+1]);
            }
        }
    }
}

PyVar VM::vectorcall(int ARGC, int KWARGC, bool op_call){
    PyVar* p1 = s_data._sp - KWARGC*2;
    PyVar* p0 = p1 - ARGC - 2;
    // [callable, <self>, args..., kwargs...]
    //      ^p0                    ^p1      ^_sp
    PyVar callable = p1[-(ARGC + 2)];
    Type callable_t = _tp(callable);

    int method_call = p0[1] != PY_NULL;

    // handle boundmethod, do a patch
    if(callable_t == tp_bound_method){
        if(method_call) PK_FATAL_ERROR();
        BoundMethod& bm = PK_OBJ_GET(BoundMethod, callable);
        callable = bm.func;      // get unbound method
        callable_t = _tp(callable);
        p1[-(ARGC + 2)] = bm.func;
        p1[-(ARGC + 1)] = bm.self;
        method_call = 1;
        // [unbound, self, args..., kwargs...]
    }

    ArgsView args(p1 - ARGC - method_call, p1);
    ArgsView kwargs(p1, s_data._sp);

    PyVar* _base = args.begin();
    PyVar buffer[PK_MAX_CO_VARNAMES];

    if(callable_t == tp_function){
        /*****************_py_call*****************/
        // check stack overflow
        if(s_data.is_overflow()) StackOverflowError();

        const Function& fn = PK_OBJ_GET(Function, callable);
        const CodeObject* co = fn.decl->code.get();
        int co_nlocals = co->varnames.size();

        switch(fn.decl->type){
            case FuncType::UNSET: PK_FATAL_ERROR(); break;
            case FuncType::NORMAL:
                __prepare_py_call(buffer, args, kwargs, fn.decl);
                // copy buffer back to stack
                s_data.reset(_base + co_nlocals);
                for(int j=0; j<co_nlocals; j++) _base[j] = buffer[j];
                break;
            case FuncType::SIMPLE:
                if(args.size() != fn.decl->args.size()) TypeError(_S(co->name, "() takes ", fn.decl->args.size(), " positional arguments but ", args.size(), " were given"));
                if(!kwargs.empty()) TypeError(_S(co->name, "() takes no keyword arguments"));
                // [callable, <self>, args..., local_vars...]
                //      ^p0                    ^p1      ^_sp
                s_data.reset(_base + co_nlocals);
                // initialize local variables to PY_NULL
                for(PyVar* p=p1; p!=s_data._sp; p++) *p = PY_NULL;
                break;
            case FuncType::EMPTY:
                if(args.size() != fn.decl->args.size()) TypeError(_S(co->name, "() takes ", fn.decl->args.size(), " positional arguments but ", args.size(), " were given"));
                if(!kwargs.empty()) TypeError(_S(co->name, "() takes no keyword arguments"));
                s_data.reset(p0);
                return None;
            case FuncType::GENERATOR:
                __prepare_py_call(buffer, args, kwargs, fn.decl);
                s_data.reset(p0);
                return __py_generator(
                    Frame(nullptr, co, fn._module, callable, nullptr),
                    ArgsView(buffer, buffer + co_nlocals)
                );
        };

        // simple or normal
        callstack.emplace(p0, co, fn._module, callable, args.begin());
        if(op_call) return PY_OP_CALL;
        return __run_top_frame();
        /*****************_py_call*****************/
    }

    if(callable_t == tp_native_func){
        const auto& f = PK_OBJ_GET(NativeFunc, callable);
        PyVar ret;
        if(f.decl != nullptr){
            int co_nlocals = f.decl->code->varnames.size();
            __prepare_py_call(buffer, args, kwargs, f.decl);
            // copy buffer back to stack
            s_data.reset(_base + co_nlocals);
            for(int j=0; j<co_nlocals; j++) _base[j] = buffer[j];
            ret = f.call(vm, ArgsView(s_data._sp - co_nlocals, s_data._sp));
        }else{
            if(f.argc != -1){
                if(KWARGC != 0) TypeError("old-style native_func does not accept keyword arguments");
                f.check_size(this, args);
            }
            ret = f.call(this, args);
        }
        s_data.reset(p0);
        return ret;
    }

    if(callable_t == tp_type){
        // [type, NULL, args..., kwargs...]
        PyVar new_f = find_name_in_mro(PK_OBJ_GET(Type, callable), __new__);
        PyVar obj;
        PK_DEBUG_ASSERT(new_f != nullptr && !method_call);
        if(new_f == __cached_object_new) {
            // fast path for object.__new__
            obj = vm->heap.gcnew<DummyInstance>(PK_OBJ_GET(Type, callable));
        }else{
            PUSH(new_f);
            PUSH(PY_NULL);
            PUSH(callable);    // cls
            for(PyVar o: args) PUSH(o);
            for(PyVar o: kwargs) PUSH(o);
            // if obj is not an instance of `cls`, the behavior is undefined
            obj = vectorcall(ARGC+1, KWARGC);
        }

        // __init__
        PyVar self;
        callable = get_unbound_method(obj, __init__, &self, false);
        if (callable != nullptr) {
            callable_t = _tp(callable);
            // replace `NULL` with `self`
            p1[-(ARGC + 2)] = callable;
            p1[-(ARGC + 1)] = self;
            // [init_f, self, args..., kwargs...]
            vectorcall(ARGC, KWARGC);
            // We just discard the return value of `__init__`
            // in cpython it raises a TypeError if the return value is not None
        }else{
            // manually reset the stack
            s_data.reset(p0);
        }
        return obj;
    }

    // handle `__call__` overload
    PyVar self;
    PyVar call_f = get_unbound_method(callable, __call__, &self, false);
    if(self != PY_NULL){
        p1[-(ARGC + 2)] = call_f;
        p1[-(ARGC + 1)] = self;
        // [call_f, self, args..., kwargs...]
        return vectorcall(ARGC, KWARGC, op_call);
    }
    TypeError(_type_name(vm, callable_t).escape() + " object is not callable");
    PK_UNREACHABLE()
}

void VM::delattr(PyVar _0, StrName _name){
    const PyTypeInfo* ti = _tp_info(_0);
    if(ti->m__delattr__ && ti->m__delattr__(this, _0, _name)) return;
    if(is_tagged(_0) || !_0->is_attr_valid()) TypeError("cannot delete attribute");
    if(!_0->attr().del(_name)) AttributeError(_0, _name);
}

// https://docs.python.org/3/howto/descriptor.html#invocation-from-an-instance
PyVar VM::getattr(PyVar obj, StrName name, bool throw_err){
    Type objtype(0);
    // handle super() proxy
    if(is_type(obj, tp_super)){
        const Super& super = PK_OBJ_GET(Super, obj);
        obj = super.first;
        objtype = super.second;
    }else{
        objtype = _tp(obj);
    }
    PyVar cls_var = find_name_in_mro(objtype, name);
    if(cls_var != nullptr){
        // handle descriptor
        if(is_type(cls_var, tp_property)){
            const Property& prop = PK_OBJ_GET(Property, cls_var);
            return call(prop.getter, obj);
        }
    }
    // handle instance __dict__
    if(!is_tagged(obj) && obj->is_attr_valid()){
        PyVar val;
        if(obj->type == tp_type){
            val = find_name_in_mro(PK_OBJ_GET(Type, obj), name);
            if(val != nullptr){
                if(is_tagged(val)) return val;
                if(val->type == tp_staticmethod) return PK_OBJ_GET(StaticMethod, val).func;
                if(val->type == tp_classmethod) return VAR(BoundMethod(obj, PK_OBJ_GET(ClassMethod, val).func));
                return val;
            }
        }else{
            val = obj->attr().try_get_likely_found(name);
            if(val != nullptr) return val;
        }
    }
    if(cls_var != nullptr){
        // bound method is non-data descriptor
        if(!is_tagged(cls_var)){
            switch(cls_var->type){
                case tp_function.index:
                    return VAR(BoundMethod(obj, cls_var));
                case tp_native_func.index:
                    return VAR(BoundMethod(obj, cls_var));
                case tp_staticmethod.index:
                    return PK_OBJ_GET(StaticMethod, cls_var).func;
                case tp_classmethod.index:
                    return VAR(BoundMethod(_t(objtype), PK_OBJ_GET(ClassMethod, cls_var).func));
            }
        }
        return cls_var;
    }

    const PyTypeInfo* ti = &_all_types[objtype];
    if(ti->m__getattr__){
        PyVar ret = ti->m__getattr__(this, obj, name);
        if(ret) return ret;
    }

    if(throw_err) AttributeError(obj, name);
    return nullptr;
}

// used by OP_LOAD_METHOD
// try to load a unbound method (fallback to `getattr` if not found)
PyVar VM::get_unbound_method(PyVar obj, StrName name, PyVar* self, bool throw_err, bool fallback){
    *self = PY_NULL;
    Type objtype(0);
    // handle super() proxy
    if(is_type(obj, tp_super)){
        const Super& super = PK_OBJ_GET(Super, obj);
        obj = super.first;
        objtype = super.second;
    }else{
        objtype = _tp(obj);
    }
    PyVar cls_var = find_name_in_mro(objtype, name);

    if(fallback){
        if(cls_var != nullptr){
            // handle descriptor
            if(is_type(cls_var, tp_property)){
                const Property& prop = PK_OBJ_GET(Property, cls_var);
                return call(prop.getter, obj);
            }
        }
        // handle instance __dict__
        if(!is_tagged(obj) && obj->is_attr_valid()){
            PyVar val;
            if(obj->type == tp_type){
                val = find_name_in_mro(PK_OBJ_GET(Type, obj), name);
                if(val != nullptr){
                    if(is_tagged(val)) return val;
                    if(val->type == tp_staticmethod) return PK_OBJ_GET(StaticMethod, val).func;
                    if(val->type == tp_classmethod) return VAR(BoundMethod(obj, PK_OBJ_GET(ClassMethod, val).func));
                    return val;
                }
            }else{
                val = obj->attr().try_get_likely_found(name);
                if(val != nullptr) return val;
            }
        }
    }

    if(cls_var != nullptr){
        if(!is_tagged(cls_var)){
            switch(cls_var->type){
                case tp_function.index:
                    *self = obj;
                    break;
                case tp_native_func.index:
                    *self = obj;
                    break;
                case tp_staticmethod.index:
                    *self = PY_NULL;
                    return PK_OBJ_GET(StaticMethod, cls_var).func;
                case tp_classmethod.index:
                    *self = _t(objtype);
                    return PK_OBJ_GET(ClassMethod, cls_var).func;
            }
        }
        return cls_var;
    }

    const PyTypeInfo* ti = &_all_types[objtype];
    if(fallback && ti->m__getattr__){
        PyVar ret = ti->m__getattr__(this, obj, name);
        if(ret) return ret;
    }

    if(throw_err) AttributeError(obj, name);
    return nullptr;
}

void VM::setattr(PyVar obj, StrName name, PyVar value){
    Type objtype(0);
    // handle super() proxy
    if(is_type(obj, tp_super)){
        Super& super = PK_OBJ_GET(Super, obj);
        obj = super.first;
        objtype = super.second;
    }else{
        objtype = _tp(obj);
    }
    PyVar cls_var = find_name_in_mro(objtype, name);
    if(cls_var != nullptr){
        // handle descriptor
        if(is_type(cls_var, tp_property)){
            const Property& prop = _CAST(Property&, cls_var);
            if(prop.setter != vm->None){
                call(prop.setter, obj, value);
            }else{
                TypeError(_S("readonly attribute: ", name.escape()));
            }
            return;
        }
    }

    const PyTypeInfo* ti = &_all_types[objtype];
    if(ti->m__setattr__){
        ti->m__setattr__(this, obj, name, value);
        return;
    }

    // handle instance __dict__
    if(is_tagged(obj) || !obj->is_attr_valid()) TypeError("cannot set attribute");
    obj->attr().set(name, value);
}

PyVar VM::bind_func(PyVar obj, StrName name, int argc, NativeFuncC fn, any userdata, BindType bt) {
    PyVar nf = VAR(NativeFunc(fn, argc, std::move(userdata)));
    switch(bt){
        case BindType::DEFAULT: break;
        case BindType::STATICMETHOD: nf = VAR(StaticMethod(nf)); break;
        case BindType::CLASSMETHOD: nf = VAR(ClassMethod(nf)); break;
    }
    if(obj != nullptr) obj->attr().set(name, nf);
    return nf;
}

PyVar VM::bind(PyVar obj, const char* sig, NativeFuncC fn, any userdata, BindType bt){
    return bind(obj, sig, nullptr, fn, std::move(userdata), bt);
}

PyVar VM::bind(PyVar obj, const char* sig, const char* docstring, NativeFuncC fn, any userdata, BindType bt){
    CodeObject_ co;
    try{
        // fn(a, b, *c, d=1) -> None
        co = compile(_S("def ", sig, " : pass"), "<bind>", EXEC_MODE);
    }catch(const Exception&){
        throw std::runtime_error("invalid signature: " + std::string(sig));
    }
    if(co->func_decls.size() != 1){
        throw std::runtime_error("expected 1 function declaration");
    }
    FuncDecl_ decl = co->func_decls[0];
    decl->docstring = docstring;
    PyVar f_obj = VAR(NativeFunc(fn, decl, std::move(userdata)));

    switch(bt){
        case BindType::STATICMETHOD:
            f_obj = VAR(StaticMethod(f_obj));
            break;
        case BindType::CLASSMETHOD:
            f_obj = VAR(ClassMethod(f_obj));
            break;
        case BindType::DEFAULT:
            break;
    }
    if(obj != nullptr) obj->attr().set(decl->code->name, f_obj);
    return f_obj;
}

PyVar VM::bind_property(PyVar obj, const char* name, NativeFuncC fget, NativeFuncC fset){
    PK_ASSERT(is_type(obj, tp_type));
    std::string_view name_sv(name); int pos = name_sv.find(':');
    if(pos > 0) name_sv = name_sv.substr(0, pos);
    PyVar _0 = heap.gcnew<NativeFunc>(tp_native_func, fget, 1);
    PyVar _1 = vm->None;
    if(fset != nullptr) _1 = heap.gcnew<NativeFunc>(tp_native_func, fset, 2);
    PyVar prop = VAR(Property(_0, _1));
    obj->attr().set(StrName(name_sv), prop);
    return prop;
}

void VM::__builtin_error(StrName type){ _error(call(builtins->attr(type))); }
void VM::__builtin_error(StrName type, PyVar arg){ _error(call(builtins->attr(type), arg)); }
void VM::__builtin_error(StrName type, const Str& msg){ __builtin_error(type, VAR(msg)); }

void VM::BinaryOptError(const char* op, PyVar _0, PyVar _1) {
    StrName name_0 = _type_name(vm, _tp(_0));
    StrName name_1 = _type_name(vm, _tp(_1));
    TypeError(_S("unsupported operand type(s) for ", op, ": ", name_0.escape(), " and ", name_1.escape()));
}

void VM::AttributeError(PyVar obj, StrName name){
    if(isinstance(obj, vm->tp_type)){
        __builtin_error("AttributeError", _S("type object ", _type_name(vm, PK_OBJ_GET(Type, obj)).escape(), " has no attribute ", name.escape()));
    }else{
        __builtin_error("AttributeError", _S(_type_name(vm, _tp(obj)).escape(), " object has no attribute ", name.escape()));
    }
}

void VM::_error(PyVar e_obj){
    PK_ASSERT(isinstance(e_obj, tp_exception))
    Exception& e = PK_OBJ_GET(Exception, e_obj);
    if(callstack.empty()){
        e.is_re = false;
        throw e;
    }
    PUSH(e_obj);
    __raise_exc();
}

void VM::__raise_exc(bool re_raise){
    Frame* frame = &callstack.top();
    Exception& e = PK_OBJ_GET(Exception, s_data.top());
    if(!re_raise){
        e._ip_on_error = frame->_ip;
        e._code_on_error = (void*)frame->co;
    }
    bool ok = frame->jump_to_exception_handler(&s_data);

    int actual_ip = frame->_ip;
    if(e._ip_on_error >= 0 && e._code_on_error == (void*)frame->co) actual_ip = e._ip_on_error;
    int current_line = frame->co->lines[actual_ip].lineno;         // current line
    auto current_f_name = frame->co->name.sv();             // current function name
    if(frame->_callable == nullptr) current_f_name = "";    // not in a function
    e.st_push(frame->co->src, current_line, nullptr, current_f_name);

    if(ok) throw HandledException();
    else throw UnhandledException();
}

void ManagedHeap::mark() {
    for(PyVar obj: _no_gc) PK_OBJ_MARK(obj);
    vm->callstack.apply([](Frame& frame){ frame._gc_mark(); });
    for(PyVar obj: vm->s_data) PK_OBJ_MARK(obj);
    for(auto [_, co]: vm->__cached_codes) co->_gc_mark();
    if(vm->__last_exception) PK_OBJ_MARK(vm->__last_exception);
    if(vm->__curr_class) PK_OBJ_MARK(vm->__curr_class);
    if(vm->__c.error != nullptr) PK_OBJ_MARK(vm->__c.error);
    if(_gc_marker_ex) _gc_marker_ex(vm);
}

StrName _type_name(VM *vm, Type type){
    return vm->_all_types[type].name;
}

void _gc_mark_namedict(NameDict* t){
    t->apply([](StrName name, PyVar obj){
        PK_OBJ_MARK(obj);
    });
}

void VM::bind__getitem__(Type type, PyVar (*f)(VM*, PyVar, PyVar)){
    _all_types[type].m__getitem__ = f;
    bind_func(type, __getitem__, 2, [](VM* vm, ArgsView args){
        return lambda_get_userdata<PyVar(*)(VM*, PyVar, PyVar)>(args.begin())(vm, args[0], args[1]);
    }, f);
}

void VM::bind__setitem__(Type type, void (*f)(VM*, PyVar, PyVar, PyVar)){
    _all_types[type].m__setitem__ = f;
    bind_func(type, __setitem__, 3, [](VM* vm, ArgsView args){
        lambda_get_userdata<void(*)(VM* vm, PyVar, PyVar, PyVar)>(args.begin())(vm, args[0], args[1], args[2]);
        return vm->None;
    }, f);
}

void VM::bind__delitem__(Type type, void (*f)(VM*, PyVar, PyVar)){
    _all_types[type].m__delitem__ = f;
    bind_func(type, __delitem__, 2, [](VM* vm, ArgsView args){
        lambda_get_userdata<void(*)(VM*, PyVar, PyVar)>(args.begin())(vm, args[0], args[1]);
        return vm->None;
    }, f);
}

PyVar VM::__pack_next_retval(unsigned n){
    if(n == 0) return StopIteration;
    if(n == 1) return s_data.popx();
    PyVar retval = VAR(s_data.view(n).to_tuple());
    s_data._sp -= n;
    return retval;
}

void VM::bind__next__(Type type, unsigned (*f)(VM*, PyVar)){
    _all_types[type].m__next__ = f;
    bind_func(type, __next__, 1, [](VM* vm, ArgsView args){
        int n = lambda_get_userdata<unsigned(*)(VM*, PyVar)>(args.begin())(vm, args[0]);
        return vm->__pack_next_retval(n);
    }, f);
}

void VM::bind__next__(Type type, PyVar (*f)(VM*, PyVar)){
    bind_func(type, __next__, 1, [](VM* vm, ArgsView args){
        auto f = lambda_get_userdata<PyVar(*)(VM*, PyVar)>(args.begin());
        return f(vm, args[0]);
    }, f);
}

#define BIND_UNARY_SPECIAL(name)                                                        \
    void VM::bind##name(Type type, PyVar (*f)(VM*, PyVar)){                     \
        _all_types[type].m##name = f;                                                   \
        bind_func(type, name, 1, [](VM* vm, ArgsView args){                             \
            return lambda_get_userdata<PyVar(*)(VM*, PyVar)>(args.begin())(vm, args[0]);    \
        }, f);                                                                          \
    }
    BIND_UNARY_SPECIAL(__iter__)
    BIND_UNARY_SPECIAL(__neg__)
    BIND_UNARY_SPECIAL(__invert__)
#undef BIND_UNARY_SPECIAL

void VM::bind__str__(Type type, Str (*f)(VM*, PyVar)){
    _all_types[type].m__str__ = f;
    bind_func(type, __str__, 1, [](VM* vm, ArgsView args){
        Str s = lambda_get_userdata<decltype(f)>(args.begin())(vm, args[0]);
        return VAR(s);
    }, f);
}

void VM::bind__repr__(Type type, Str (*f)(VM*, PyVar)){
    _all_types[type].m__repr__ = f;
    bind_func(type, __repr__, 1, [](VM* vm, ArgsView args){
        Str s = lambda_get_userdata<decltype(f)>(args.begin())(vm, args[0]);
        return VAR(s);
    }, f);
}

void VM::bind__hash__(Type type, i64 (*f)(VM*, PyVar)){
    _all_types[type].m__hash__ = f;
    bind_func(type, __hash__, 1, [](VM* vm, ArgsView args){
        i64 ret = lambda_get_userdata<decltype(f)>(args.begin())(vm, args[0]);
        return VAR(ret);
    }, f);
}

void VM::bind__len__(Type type, i64 (*f)(VM*, PyVar)){
    _all_types[type].m__len__ = f;
    bind_func(type, __len__, 1, [](VM* vm, ArgsView args){
        i64 ret = lambda_get_userdata<decltype(f)>(args.begin())(vm, args[0]);
        return VAR(ret);
    }, f);
}


#define BIND_BINARY_SPECIAL(name)                                                       \
    void VM::bind##name(Type type, BinaryFuncC f){                                      \
        _all_types[type].m##name = f;                                                   \
        bind_func(type, name, 2, [](VM* vm, ArgsView args){                             \
            return lambda_get_userdata<BinaryFuncC>(args.begin())(vm, args[0], args[1]);\
        }, f);                                                                          \
    }

    BIND_BINARY_SPECIAL(__eq__)
    BIND_BINARY_SPECIAL(__lt__)
    BIND_BINARY_SPECIAL(__le__)
    BIND_BINARY_SPECIAL(__gt__)
    BIND_BINARY_SPECIAL(__ge__)
    BIND_BINARY_SPECIAL(__contains__)

    BIND_BINARY_SPECIAL(__add__)
    BIND_BINARY_SPECIAL(__sub__)
    BIND_BINARY_SPECIAL(__mul__)
    BIND_BINARY_SPECIAL(__truediv__)
    BIND_BINARY_SPECIAL(__floordiv__)
    BIND_BINARY_SPECIAL(__mod__)
    BIND_BINARY_SPECIAL(__pow__)
    BIND_BINARY_SPECIAL(__matmul__)

    BIND_BINARY_SPECIAL(__lshift__)
    BIND_BINARY_SPECIAL(__rshift__)
    BIND_BINARY_SPECIAL(__and__)
    BIND_BINARY_SPECIAL(__or__)
    BIND_BINARY_SPECIAL(__xor__)

#undef BIND_BINARY_SPECIAL


void Dict::_probe_0(PyVar key, bool &ok, int &i) const{
    ok = false;
    i64 hash = vm->py_hash(key);
    i = hash & _mask;
    for(int j=0; j<_capacity; j++) {
        if(_items[i].first != nullptr){
            if(vm->py_eq(_items[i].first, key)) { ok = true; break; }
        }else{
            if(_items[i].second == nullptr) break;
        }
        // https://github.com/python/cpython/blob/3.8/Objects/dictobject.c#L166
        i = ((5*i) + 1) & _mask;
    }
}

void Dict::_probe_1(PyVar key, bool &ok, int &i) const{
    ok = false;
    i = vm->py_hash(key) & _mask;
    while(_items[i].first != nullptr) {
        if(vm->py_eq(_items[i].first, key)) { ok = true; break; }
        // https://github.com/python/cpython/blob/3.8/Objects/dictobject.c#L166
        i = ((5*i) + 1) & _mask;
    }
}

void NativeFunc::check_size(VM* vm, ArgsView args) const{
    if(args.size() != argc && argc != -1) {
        vm->TypeError(_S("expected ", argc, " arguments, got ", args.size()));
    }
}

#if PK_ENABLE_PROFILER
void NextBreakpoint::_step(VM* vm){
    int curr_callstack_size = vm->callstack.size();
    int curr_lineno = vm->callstack.top().curr_lineno();
    if(should_step_into){
        if(curr_callstack_size != callstack_size || curr_lineno != lineno){
            vm->__breakpoint();
        }
    }else{
        if(curr_callstack_size == callstack_size) {
            if(curr_lineno != lineno) vm->__breakpoint();
        }else if(curr_callstack_size < callstack_size){
            // returning
            vm->__breakpoint();
        }
    }
}
#endif

void VM::__pop_frame(){
    s_data.reset(callstack.top()._sp_base);
    callstack.pop();

#if PK_ENABLE_PROFILER
    if(!_next_breakpoint.empty() && callstack.size()<_next_breakpoint.callstack_size){
        _next_breakpoint = NextBreakpoint();
    }
#endif
}

void VM::__breakpoint(){
#if PK_ENABLE_PROFILER
    _next_breakpoint = NextBreakpoint();

    bool show_where = false;
    bool show_headers = true;
    
    while(true){
        std::vector<LinkedFrame*> frames;
        LinkedFrame* lf = callstack._tail;
        while(lf != nullptr){
            frames.push_back(lf);
            lf = lf->f_back;
            if(frames.size() >= 4) break;
        }

        if(show_headers){
            for(int i=frames.size()-1; i>=0; i--){
                if(!show_where && i!=0) continue;

                SStream ss;
                Frame* frame = &frames[i]->frame;
                int lineno = frame->curr_lineno();
                ss << "File \"" << frame->co->src->filename << "\", line " << lineno;
                if(frame->_callable){
                    ss << ", in ";
                    ss << PK_OBJ_GET(Function, frame->_callable).decl->code->name;
                }
                ss << '\n';
                ss << "-> " << frame->co->src->get_line(lineno) << '\n';
                stdout_write(ss.str());
            }
            show_headers = false;
        }

        vm->stdout_write("(Pdb) ");
        Frame* frame_0 = &frames[0]->frame;

        std::string line;
        if(!std::getline(std::cin, line)){
            stdout_write("--KeyboardInterrupt--\n");
            continue;
        }

        if(line == "h" || line == "help"){
            stdout_write("h, help: show this help message\n");
            stdout_write("q, quit: exit the debugger\n");
            stdout_write("n, next: execute next line\n");
            stdout_write("s, step: step into\n");
            stdout_write("w, where: show current stack frame\n");
            stdout_write("c, continue: continue execution\n");
            stdout_write("a, args: show local variables\n");
            stdout_write("p, print <expr>: evaluate expression\n");
            stdout_write("l, list: show lines around current line\n");
            stderr_write("ll, longlist: show all lines\n");
            stdout_write("!: execute statement\n");
            continue;
        }
        if(line == "q" || line == "quit") {
            vm->RuntimeError("pdb quit");
            PK_UNREACHABLE()
        }
        if(line == "n" || line == "next"){
            vm->_next_breakpoint = NextBreakpoint(vm->callstack.size(), frame_0->curr_lineno(), false);
            break;
        }
        if(line == "s" || line == "step"){
            vm->_next_breakpoint = NextBreakpoint(vm->callstack.size(), frame_0->curr_lineno(), true);
            break;
        }
        if(line == "w" || line == "where"){
            show_where = !show_where;
            show_headers = true;
            continue;
        }
        if(line == "c" || line == "continue") break;
        if(line == "a" || line == "args"){
            int i = 0;
            for(PyVar obj: frame_0->_locals){
                if(obj == PY_NULL) continue;
                StrName name = frame_0->co->varnames[i++];
                stdout_write(_S(name.sv(), " = ", vm->py_repr(obj), '\n'));
            }
            continue;
        }

        bool is_list = line == "l" || line == "list";
        bool is_longlist = line == "ll" || line == "longlist";

        if(is_list || is_longlist){
            if(frame_0->co->src->is_precompiled) continue;
            int lineno = frame_0->curr_lineno();
            int start, end;

            if(is_list){
                int max_line = frame_0->co->src->line_starts.size() + 1;
                start = std::max(1, lineno-5);
                end = std::min(max_line, lineno+5);
            }else{
                start = frame_0->co->start_line;
                end = frame_0->co->end_line;
                if(start == -1 || end == -1) continue;
            }
            
            SStream ss;
            int max_width = std::to_string(end).size();
            for(int i=start; i<=end; i++){
                int spaces = max_width - std::to_string(i).size();
                ss << std::string(spaces, ' ') << std::to_string(i);
                if(i == lineno) ss << "  -> ";
                else ss << "     ";
                ss << frame_0->co->src->get_line(i) << '\n';
            }
            stdout_write(ss.str());
            continue;
        }
        
        int space = line.find_first_of(' ');
        if(space != -1){
            std::string cmd = line.substr(0, space);
            std::string arg = line.substr(space+1);
            if(arg.empty()) continue;   // ignore empty command
            if(cmd == "p" || cmd == "print"){
                CodeObject_ code = compile(arg, "<stdin>", EVAL_MODE, true);
                PyVar retval = vm->_exec(code.get(), frame_0->_module, frame_0->_callable, frame_0->_locals);
                stdout_write(vm->py_repr(retval));
                stdout_write("\n");
            }else if(cmd == "!"){
                CodeObject_ code = compile(arg, "<stdin>", EXEC_MODE, true);
                vm->_exec(code.get(), frame_0->_module, frame_0->_callable, frame_0->_locals);
            }
            continue;
        }
    }
#endif
}

}   // namespace pkpy