#include <stdarg.h>
#include <stdio.h>
#include <string.h>
#include <time.h>

#include "common.h"
#include "compiler.h"
#include "debug.h"
#include "object.h"
#include "memory.h"
#include "vm.h"

VM vm;

static Value clockNative(int argCount, Value* args)
{
    (void)argCount;
    (void)args;

    return NUMBER_VAL((double)clock() / CLOCKS_PER_SEC);
}

static void resetStack()
{
    vm.stackTop = vm.stack;
    vm.frameCount = 0;
    vm.openUpvalues = nullptr;
}

static void runtimeError(const char* format, ...)
{
    va_list args;
    va_start(args, format);
    vfprintf(stderr, format, args);
    va_end(args);
    fputs("\n", stderr);

    for (auto i = vm.frameCount - 1; i >= 0; i--) {
        CallFrame* frame = &vm.frames[i];
        ObjFunction* function = frame->closure->function;
        auto instruction = frame->ip - function->chunk.code - 1;
        fprintf(stderr, "[line %d] in ", function->chunk.lines[instruction]);
        if (function->name == nullptr) {
            fprintf(stderr, "script\n");
        } else {
            fprintf(stderr, "%s()\n", function->name->chars);
        }
    }

    resetStack();
}

static void defineNative(const char* name, NativeFn function)
{
    push(OBJ_VAL(copyString(name, (int)strlen(name))));
    push(OBJ_VAL(newNative(function)));
    tableSet(&vm.globals, AS_STRING(vm.stack[0]), vm.stack[1]);
    pop();
    pop();
}

void initVM()
{
    resetStack();
    vm.objects = nullptr;
    vm.bytesAllocated = 0;
    vm.nextGC = 1024 * 1024;

    vm.grayCount = 0;
    vm.grayCapacity = 0;
    vm.grayStack = nullptr;

    initTable(&vm.globals);
    initTable(&vm.strings);

    vm.initString = nullptr;
    vm.initString = copyString("init", 4);

    defineNative("clock", clockNative);
}

void freeVM()
{
    freeTable(&vm.globals);
    freeTable(&vm.strings);
    vm.initString = nullptr;
    freeObjects();
}

void push(Value value)
{
    *vm.stackTop = value;
    vm.stackTop++;
}

Value pop()
{
    vm.stackTop--;
    return *vm.stackTop;
}

static Value peek(int distance)
{
    return vm.stackTop[-1 - distance];
}

static bool call(ObjClosure* closure, int argCount)
{
    if (argCount != closure->function->arity) {
        runtimeError("Expected %d arguments but got %d.", closure->function->arity, argCount);
        return false;
    }

    if (vm.frameCount == FRAMES_MAX) {
        runtimeError("Stack overflow.");
        return false;
    }

    CallFrame* frame = &vm.frames[vm.frameCount++];
    frame->closure = closure;
    frame->ip = closure->function->chunk.code;
    frame->slots = vm.stackTop - argCount - 1;
    return true;
}

static bool callValue(Value callee, int argCount)
{
    if (IS_OBJ(callee)) {
        switch (OBJ_TYPE(callee)) {
        case OBJ_BOUND_METHOD:
            {
                ObjBoundMethod* bound = AS_BOUND_METHOD(callee);
                vm.stackTop[-argCount - 1] = bound->receiver;
                return call(bound->method, argCount);
            }
        case OBJ_CLASS:
            {
                ObjClass* klass = AS_CLASS(callee);
                vm.stackTop[-argCount - 1] = OBJ_VAL(newInstance(klass));
                Value initializer;
                if (tableGet(&klass->methods, vm.initString, &initializer)) {
                    return call(AS_CLOSURE(initializer), argCount);
                } else if (argCount != 0) {
                    runtimeError("Expected 0 arguments but got %d.", argCount);
                    return false;
                }
                return true;
            }
        case OBJ_CLOSURE:
            return call(AS_CLOSURE(callee), argCount);
        case OBJ_NATIVE:
            {
                auto native = AS_NATIVE(callee);
                auto result = native(argCount, vm.stackTop - argCount);
                vm.stackTop -= argCount + 1;
                push(result);
                return true;
            }
        default:
            break;
        }
    }
    runtimeError("Can only call functions and classes.");
    return false;
}

static bool invokeFromClass(ObjClass* klass, ObjString* name, int argCount)
{
    Value method;
    if (!tableGet(&klass->methods, name, &method)) {
        runtimeError("Undefined property '%s'.", name->chars);
        return false;
    }
    return call(AS_CLOSURE(method), argCount);
}

static bool invoke(ObjString* name, int argCount)
{
    auto receiver = peek(argCount);

    if (!IS_INSTANCE(receiver)) {
        runtimeError("Only instances have methods.");
        return false;
    }

    ObjInstance* instance = AS_INSTANCE(receiver);

    Value value;
    if (tableGet(&instance->fields, name, &value)) {
        vm.stackTop[-argCount - 1] = value;
        return callValue(value, argCount);
    }

    return invokeFromClass(instance->klass, name, argCount);
}

static bool bindMethod(ObjClass* klass, ObjString* name)
{
    Value method;
    if (!tableGet(&klass->methods, name, &method)) {
        runtimeError("Undefined property '%s'.", name->chars);
        return false;
    }

    ObjBoundMethod* bound = newBoundMethod(peek(0), AS_CLOSURE(method));
    pop();
    push(OBJ_VAL(bound));
    return true;
}

static ObjUpvalue* captureUpvalue(Value* local)
{
    ObjUpvalue* prevUpvalue = nullptr;
    ObjUpvalue* upvalue = vm.openUpvalues;
    while (upvalue != nullptr && upvalue->location > local) {
        prevUpvalue = upvalue;
        upvalue = upvalue->next;
    }

    if (upvalue != nullptr && upvalue->location == local) {
        return upvalue;
    }

    ObjUpvalue* createdUpvalue = newUpvalue(local);
    createdUpvalue->next = upvalue;

    if (prevUpvalue == nullptr) {
        vm.openUpvalues = createdUpvalue;
    } else {
        prevUpvalue->next = createdUpvalue;
    }

    return createdUpvalue;
}

static void closeUpvalues(Value* last)
{
    while (vm.openUpvalues != nullptr && vm.openUpvalues->location >= last) {
        ObjUpvalue* upvalue = vm.openUpvalues;
        upvalue->closed = *upvalue->location;
        upvalue->location = &upvalue->closed;
        vm.openUpvalues = upvalue->next;
    }
}

static void defineMethod(ObjString* name)
{
    auto method = peek(0);
    ObjClass* klass = AS_CLASS(peek(1));
    tableSet(&klass->methods, name, method);
    pop();
}

static bool isFalsey(Value value)
{
    return IS_NIL(value) || (IS_BOOL(value) && !AS_BOOL(value));
}

static void concatenate()
{
    ObjString* b = AS_STRING(peek(0));
    ObjString* a = AS_STRING(peek(1));

    auto length = a->length + b->length;
    char* chars = ALLOCATE(char, length + 1);
    memcpy(chars, a->chars, a->length);
    memcpy(chars + a->length, b->chars, b->length);
    chars[length] = '\0';

    ObjString* result = takeString(chars, length);
    pop();
    pop();
    push(OBJ_VAL(result));
}

static InterpretResult run()
{
    CallFrame* frame = &vm.frames[vm.frameCount - 1];

#define READ_BYTE() (*frame->ip++)
#define READ_SHORT() (frame->ip += 2, (uint16_t)((frame->ip[-2] << 8) | frame->ip[-1]))
#define READ_CONSTANT() (frame->closure->function->chunk.constants.values[READ_BYTE()])
#define READ_STRING() AS_STRING(READ_CONSTANT())

#define BINARY_OP(valueType, op)                          \
    do {                                                  \
        if (!IS_NUMBER(peek(0)) || !IS_NUMBER(peek(1))) { \
            runtimeError("Operands must be numbers.");    \
            return INTERPRET_RUNTIME_ERROR;               \
        }                                                 \
        auto b = AS_NUMBER(pop());                        \
        auto a = AS_NUMBER(pop());                        \
        push(valueType(a op b));                          \
    } while (false)

    for (;;) {
#ifdef DEBUG_TRACE_EXECUTION
        printf("          ");
        for (Value* slot = vm.stack; slot < vm.stackTop; slot++) {
            printf("[ ");
            printValue(*slot);
            printf(" ]");
        }
        printf("\n");
        disassembleInstruction(&frame->closure->function->chunk, (int)(frame->ip - frame->closure->function->chunk.code));
#endif

        uint8_t instruction;
        switch (instruction = READ_BYTE()) {
        case OP_CONSTANT:
            {
                auto constant = READ_CONSTANT();
                push(constant);
            }
            break;
        case OP_NIL:
            push(NIL_VAL);
            break;
        case OP_TRUE:
            push(BOOL_VAL(true));
            break;
        case OP_FALSE:
            push(BOOL_VAL(false));
            break;
        case OP_POP:
            pop();
            break;
        case OP_GET_LOCAL:
            {
                auto slot = READ_BYTE();
                push(frame->slots[slot]);
            }
            break;
        case OP_SET_LOCAL:
            {
                auto slot = READ_BYTE();
                frame->slots[slot] = peek(0);
            }
            break;
        case OP_GET_GLOBAL:
            {
                ObjString* name = READ_STRING();
                Value value;
                if (!tableGet(&vm.globals, name, &value)) {
                    runtimeError("Undefined variable '%s'.", name->chars);
                    return INTERPRET_RUNTIME_ERROR;
                }
                push(value);
            }
            break;
        case OP_DEFINE_GLOBAL:
            {
                ObjString* name = READ_STRING();
                tableSet(&vm.globals, name, peek(0));
                pop();
            }
            break;
        case OP_SET_GLOBAL:
            {
                ObjString* name = READ_STRING();
                if (tableSet(&vm.globals, name, peek(0))) {
                    tableDelete(&vm.globals, name);
                    runtimeError("Undefined variable '%s'.", name->chars);
                    return INTERPRET_RUNTIME_ERROR;
                }
            }
            break;
        case OP_GET_UPVALUE:
            {
                auto slot = READ_BYTE();
                push(*frame->closure->upvalues[slot]->location);
            }
            break;
        case OP_SET_UPVALUE:
            {
                auto slot = READ_BYTE();
                *frame->closure->upvalues[slot]->location = peek(0);
            }
            break;
        case OP_GET_PROPERTY:
            {
                if (!IS_INSTANCE(peek(0))) {
                    runtimeError("Only instances have properties.");
                    return INTERPRET_RUNTIME_ERROR;
                }

                ObjInstance* instance = AS_INSTANCE(peek(0));
                ObjString* name = READ_STRING();

                Value value;
                if (tableGet(&instance->fields, name, &value)) {
                    pop();
                    push(value);
                    break;
                }

                if (!bindMethod(instance->klass, name)) {
                    return INTERPRET_RUNTIME_ERROR;
                }
            }
            break;
        case OP_SET_PROPERTY:
            {
                if (!IS_INSTANCE(peek(1))) {
                    runtimeError("Only instances have fields.");
                    return INTERPRET_RUNTIME_ERROR;
                }

                ObjInstance* instance = AS_INSTANCE(peek(1));
                tableSet(&instance->fields, READ_STRING(), peek(0));
                auto value = pop();
                pop();
                push(value);
            }
            break;
        case OP_GET_SUPER:
            {
                ObjString* name = READ_STRING();
                ObjClass* superclass = AS_CLASS(pop());

                if (!bindMethod(superclass, name)) {
                    return INTERPRET_RUNTIME_ERROR;
                }
            }
            break;
        case OP_EQUAL:
            {
                auto b = pop();
                auto a = pop();
                push(BOOL_VAL(valuesEqual(a, b)));
            }
            break;
        case OP_GREATER:
            BINARY_OP(BOOL_VAL, >);
            break;
        case OP_LESS:
            BINARY_OP(BOOL_VAL, <);
            break;
        case OP_ADD:
            {
                if (IS_STRING(peek(0)) && IS_STRING(peek(1))) {
                    concatenate();
                } else if (IS_NUMBER(peek(0)) && IS_NUMBER(peek(1))) {
                    auto b = AS_NUMBER(pop());
                    auto a = AS_NUMBER(pop());
                    push(NUMBER_VAL(a + b));
                } else {
                    runtimeError("Operands must be two numbers or two strings.");
                    return INTERPRET_RUNTIME_ERROR;
                }
            }
            break;
        case OP_SUBTRACT:
            BINARY_OP(NUMBER_VAL, -);
            break;
        case OP_MULTIPLY:
            BINARY_OP(NUMBER_VAL, *);
            break;
        case OP_DIVIDE:
            BINARY_OP(NUMBER_VAL, /);
            break;
        case OP_NOT:
            push(BOOL_VAL(isFalsey(pop())));
            break;
        case OP_NEGATE:
            if (!IS_NUMBER(peek(0))) {
                runtimeError("Operand must be a number.");
                return INTERPRET_RUNTIME_ERROR;
            }
            push(NUMBER_VAL(-AS_NUMBER(pop())));
            break;
        case OP_PRINT:
            printValue(pop());
            printf("\n");
            break;
        case OP_JUMP:
            {
                auto offset = READ_SHORT();
                frame->ip += offset;
            }
            break;
        case OP_JUMP_IF_FALSE:
            {
                auto offset = READ_SHORT();
                if (isFalsey(peek(0))) {
                    frame->ip += offset;
                }
            }
            break;
        case OP_LOOP:
            {
                auto offset = READ_SHORT();
                frame->ip -= offset;
            }
            break;
        case OP_CALL:
            {
                auto argCount = READ_BYTE();
                if (!callValue(peek(argCount), argCount)) {
                    return INTERPRET_RUNTIME_ERROR;
                }
                frame = &vm.frames[vm.frameCount - 1];
            }
            break;
        case OP_INVOKE:
            {
                ObjString* method = READ_STRING();
                auto argCount = READ_BYTE();
                if (!invoke(method, argCount)) {
                    return INTERPRET_RUNTIME_ERROR;
                }
                frame = &vm.frames[vm.frameCount - 1];
            }
            break;
        case OP_SUPER_INVOKE:
            {
                ObjString* method = READ_STRING();
                auto argCount = READ_BYTE();
                ObjClass* superclass = AS_CLASS(pop());
                if (!invokeFromClass(superclass, method, argCount)) {
                    return INTERPRET_RUNTIME_ERROR;
                }
                frame = &vm.frames[vm.frameCount - 1];
            }
            break;
        case OP_CLOSURE:
            {
                ObjFunction* function = AS_FUNCTION(READ_CONSTANT());
                ObjClosure* closure = newClosure(function);
                push(OBJ_VAL(closure));
                for (auto i = 0; i < closure->upvalueCount; i++) {
                    auto isLocal = READ_BYTE();
                    auto index = READ_BYTE();
                    if (isLocal) {
                        closure->upvalues[i] = captureUpvalue(frame->slots + index);
                    } else {
                        closure->upvalues[i] = frame->closure->upvalues[index];
                    }
                }
            }
            break;
        case OP_CLOSE_UPVALUE:
            closeUpvalues(vm.stackTop - 1);
            pop();
            break;
        case OP_RETURN:
            {
                auto result = pop();
                closeUpvalues(frame->slots);
                vm.frameCount--;
                if (vm.frameCount == 0) {
                    pop();
                    return INTERPRET_OK;
                }

                vm.stackTop = frame->slots;
                push(result);
                frame = &vm.frames[vm.frameCount - 1];
            }
            break;
        case OP_CLASS:
            push(OBJ_VAL(newClass(READ_STRING())));
            break;
        case OP_INHERIT:
            {
                auto superClass = peek(1);
                if (!IS_CLASS(superClass)) {
                    runtimeError("Superclass must be a class.");
                    return INTERPRET_RUNTIME_ERROR;
                }
                ObjClass* subClass = AS_CLASS(peek(0));
                tableAddAll(&AS_CLASS(superClass)->methods, &subClass->methods);
                pop();
            }
            break;
        case OP_METHOD:
            defineMethod(READ_STRING());
            break;
        }
    }

#undef READ_BYTE
#undef READ_SHORT
#undef READ_CONSTANT
#undef READ_STRING

#undef BINARY_OP
}

InterpretResult interpret(const char* source)
{
    ObjFunction* function = compile(source);
    if (function == nullptr) {
        return INTERPRET_COMPILE_ERROR;
    }

    push(OBJ_VAL(function));
    ObjClosure* closure = newClosure(function);
    pop();
    push(OBJ_VAL(closure));
    call(closure, 0);

    return run();
}