#include <stdio.h>
#include <stdlib.h>

#include "gc.h"
#include "vm.h"

struct virtualMachine *initVM() {
  struct virtualMachine *vm = malloc(sizeof(struct virtualMachine));
  vm->stackSize = 0;
  vm->refCount = 0;
  vm->refMax = GC_THRESHOLD;
  vm->head = NULL;
  return vm;
}

void push(struct virtualMachine *vm, struct garbageObject *value) {
  if (vm->stackSize >= STACK_MAX) {
    fprintf(stderr, "ERROR: push(): refusing to overflow the stack!\n");
    return;
  }
  vm->stack[vm->stackSize++] = value;
}

struct garbageObject *pop(struct virtualMachine *vm) {
  if (vm->stackSize < 0) {
    fprintf(stderr, "ERROR: pop(): Stack size cannot be negative!");
    return NULL;
  }

  return vm->stack[--vm->stackSize];
}

struct garbageObject *initGarbage(struct virtualMachine *vm,
                                  enum garbageData type) {

  if (vm->refCount >= vm->refMax) {
    collect(vm);
  }

  struct garbageObject *obj = malloc(sizeof(struct garbageObject));
  if (obj == NULL) {
    fprintf(stderr, "initGarbage(): Allocation failure!");
    return obj;
  }

  obj->type = type;
  obj->mark = 0;
  obj->next = vm->head;
  vm->head = obj;
  vm->refCount++;
  return obj;
}

void pushInt(struct virtualMachine *vm, int value) {
  struct garbageObject *obj = initGarbage(vm, GARBAGE_INT);
  if (obj == NULL) {
    fprintf(stderr, "pushInt(): Unable to create GARBAGE_INT - out of memory?");
  }

  obj->value = value;
  push(vm, obj);
}

struct garbageObject *pushPair(struct virtualMachine *vm) {
  struct garbageObject *obj = initGarbage(vm, GARBAGE_PAIR);
  if (obj == NULL) {
    fprintf(stderr,
            "pushPair(): Unable to create GARBAGE_PAIR - out of memory?");
  }

  obj->tail = pop(vm);
  obj->head = pop(vm);

  push(vm, obj);
  return obj;
}