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

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

VM vm;

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

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

  CallFrame *frame = &vm.frames[vm.frameCount - 1];
  size_t instruction = frame->ip - frame->function->chunk.code - 1;
  int line = frame->function->chunk.lines[instruction];
  fprintf(stderr, "[line %d] in script\n", line);
  resetStack();
}

void initVM() {
  resetStack();
  vm.objects = NULL;

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

void freeVM() {
  freeTable(&vm.globals);
  freeTable(&vm.strings);
  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 isFalsey(Value value) {
  return IS_NIL(value) || (IS_BOOL(value) && !AS_BOOL(value));
}

static void concatenate() {
  ObjString *b = AS_STRING(pop());
  ObjString *a = AS_STRING(pop());

  int 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);
  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->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.");                               \
    }                                                                          \
    double b = AS_NUMBER(pop());                                               \
    double 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->function->chunk,
                           (int)(frame->ip - frame->function->chunk.code));
#endif

    uint8_t instruction;
    switch (instruction = READ_BYTE()) {
    case OP_CONSTANT: {
      Value 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: {
      uint8_t slot = READ_BYTE();
      push(frame->slots[slot]);
      break;
    }
    case OP_SET_LOCAL: {
      uint8_t 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_EQUAL: {
      Value b = pop();
      Value 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))) {
        double b = AS_NUMBER(pop());
        double 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: {
      uint16_t offset = READ_SHORT();
      frame->ip += offset;
      break;
    }
    case OP_JUMP_IF_FALSE: {
      uint16_t offset = READ_SHORT();
      if (isFalsey(peek(0)))
        frame->ip += offset;
      break;
    }
    case OP_LOOP: {
      uint16_t offset = READ_SHORT();
      frame->ip -= offset;
      break;
    }
    case OP_RETURN: {
      /* The book said to remove this, but when I do I get an infinite loop and
         then a segfault because it keeps trying to add the constant 1 to the
         stack. */
      printValue(pop());
      printf("\n");
      return INTERPRET_OK;
    }
    }
  }

#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 != NULL)
    return INTERPRET_COMPILE_ERROR;

  push(OBJ_VAL(function));
  CallFrame *frame = &vm.frames[vm.frameCount++];
  frame->function = function;
  frame->ip = function->chunk.code;
  frame->slots = vm.stack;

  return run();
}