//
// Host GC integration library, see gc.h.
//

addToLibrary({
  $gcMap: 'new Map()',
  $gcWeakRefMap: 'new Map()',

  $gcFinalizer: null,

  gc_alloc__deps: ['$gcMap', '$gcWeakRefMap', '$gcFinalizer'],
  gc_alloc: (self, onCollect) => {
    if (!gcFinalizer) {
      gcFinalizer = new FinalizationRegistry((held) => {
        const [self, onCollect] = held;
        {{{ makeDynCall('vii', 'onCollect') }}}(self);
      });
    }

    const mirror = {
      self,
      onCollect,
      links: [],
      // Start at one root, until we are linked to.
      roots: 1,
      linkedTo: false,
    };

    gcMap.set(self, mirror);
    gcWeakRefMap.set(self, new WeakRef(mirror));
    gcFinalizer.register(mirror, [self, onCollect]);
  },

  gc_set__deps: ['gc_unroot'],
  gc_set: (self, index, value) => {
    // The value written may be null.
    const valueMirror = gcWeakRefMap.get(value)?.deref();
    gcWeakRefMap.get(self).deref().links[index] = valueMirror;
    if (valueMirror && !valueMirror.linkedTo) {
      valueMirror.linkedTo = true;
      _gc_unroot(value);
    }
  },

  gc_root: (self) => {
    const mirror = gcWeakRefMap.get(self).deref();
    mirror.roots++;
    if (mirror.roots == 1) {
      gcMap.set(self, mirror);
    }
  },

  gc_unroot: (self) => {
    const mirror = gcWeakRefMap.get(self).deref();
    mirror.roots--;
    if (mirror.roots == 0) {
      gcMap.delete(self);
    }
    if (mirror.roots < 0) {
      throw new Error('bad unroot');
    }
  },
});