// Cheney style stop and copy garbage collector
#include "gc.h"

static cons_t *old, *new, *scanptr, *freeptr, *eom, *root;
static cons_t *the_empty_list = NULL;
size_t tos;

void init() {
  old = calloc(sizeof(cons_t), SIZE);
  freeptr = old;
  eom = old + (SIZE / 2);
  new = eom + 1;
  root = alloc();
}

cons_t *alloc() {
  if (freeptr < eom) {
    cons_t *retval = freeptr;
    freeptr++;
    return retval;
  } else {
    gc_run();
    return alloc();
  }
}

void gc_run() {
  freeptr = new;
  scanptr = new;
  // Relocate root
  relocate(root);
  // Enter the main GC loop
  gc_loop();
  // Flip old and new;
  cons_t *temp = old;
  old = new;
  new = temp;
}

void gc_loop() {
  while (scanptr < freeptr) {
    relocate(scanptr);
    scanptr++;
  }
}

void move(box_t box) {
  if (box.type == CONS && box.cons != the_empty_list) {
    if (box.cons->car.type == BROKEN_HEART) {
      box.cons = box.cons->cdr.cons;
    } else {
      memcpy(freeptr, box.cons, sizeof(cons_t));
      box.cons->car.type = BROKEN_HEART;
      box.cons->cdr.cons = freeptr;
      freeptr++;
    }
  }
}

void relocate(cons_t* cons) {
  move(cons->car);
  move(cons->cdr);
}

int main() {
  init();
  // Simulate running linear fibonnaci
  root->car.type = INTEGER;
  root->car.integer = 1;
  root->cdr.type = CONS;
  root->cdr.cons = alloc();
  root->cdr.cons->car.type = INTEGER;
  root->cdr.cons->car.integer = 0;
  root->cdr.cons->cdr.type = CONS;
  root->cdr.cons->cdr.cons = the_empty_list;
  for (size_t i = 0; i < 29; i++) {
    cons_t *cons = alloc();
    cons->car.type = INTEGER;
    cons->car.integer = root->car.integer + root->cdr.cons->car.integer;
    
    cons->cdr.type = CONS;
    cons->cdr.cons = root;
    root->cdr.cons = the_empty_list;
    root = cons;
  };
  printf("%d\n", root->car.integer); // 832040, and we've definitely run gc a few times
}