function mixinProperties<T extends MixinLike>(mixinsMeta: Meta, mixin: T): MixinLike {
  if (mixin instanceof Mixin) {
    if (mixinsMeta.hasMixin(mixin)) {
      return CONTINUE;
    }
    mixinsMeta.addMixin(mixin);
    return mixin.properties!;
  } else {
    return mixin; // apply anonymous mixin properties
  }
}

function finishChains(meta: Meta): void {
  // finish any current chains node watchers that reference obj
  let chainWatchers = meta.readableChainWatchers();
  if (chainWatchers !== undefined) {
    chainWatchers.revalidateAll();
  }
  // ensure that if we have inherited any chains they have been
  // copied onto our own meta.
  if (meta.readableChains() !== undefined) {
    meta.writableChains(makeChainNode);
  }
}

function iterDeps(
  method: (obj: object, key: string, meta: Meta) => void,
  obj: object,
  depKey: string,
  seen: Map<object, Set<string>>,
  meta: Meta
) {
  let current = seen.get(obj);

  if (current === undefined) {
    current = new Set();
    seen.set(obj, current);
  }

  if (current.has(depKey)) {
    return;
  }

  let possibleDesc;
  meta.forEachInDeps(depKey, (key: string) => {
    possibleDesc = descriptorFor(obj, key, meta);

    if (possibleDesc !== undefined && possibleDesc._suspended === obj) {
      return;
    }

    method(obj, key, meta);
  });
}

function notifyObservers(obj: object, keyName: string, meta: Meta) {
  if (meta.isSourceDestroying()) {
    return;
  }

  let eventName = changeEvent(keyName);
  if (deferred > 0) {
    observerSet.add(obj, keyName, eventName);
  } else {
    sendEvent(obj, eventName, [obj, keyName]);
  }
}

export function markObjectAsDirty(obj: object, propertyKey: string, meta: Meta): void {
  let objectTag = meta.readableTag();

  if (objectTag !== undefined) {
    if (isProxy(obj)) {
      (objectTag.inner! as any).first.inner.dirty();
    } else {
      (objectTag.inner! as any).dirty();
    }
  }

  let tags = meta.readableTags();
  let propertyTag = tags !== undefined ? tags[propertyKey] : undefined;

  if (propertyTag !== undefined) {
    dirty(propertyTag);
  }

  if (objectTag !== undefined || propertyTag !== undefined) {
    ensureRunloop();
  }
}

// called whenever a property has just changed to update dependent keys
function dependentKeysDidChange(obj: object, depKey: string, meta: Meta) {
  if (meta.isSourceDestroying() || !meta.hasDeps(depKey)) {
    return;
  }
  let seen = SEEN_MAP;
  let isTop = IS_TOP_SEEN_MAP;

  if (isTop) {
    IS_TOP_SEEN_MAP = false;
  }

  iterDeps(notifyPropertyChange, obj, depKey, seen, meta);

  if (isTop) {
    SEEN_MAP.clear();
    IS_TOP_SEEN_MAP = true;
  }
}

export function removeDependentKeys(
  desc: DescriptorWithDependentKeys,
  obj: object,
  keyName: string,
  meta: Meta
): void {
  // the descriptor has a list of dependent keys, so
  // remove all of its dependent keys.
  let depKeys = desc._dependentKeys;
  if (depKeys === null || depKeys === undefined) {
    return;
  }

  for (let idx = 0; idx < depKeys.length; idx++) {
    let depKey = depKeys[idx];
    // Decrement the number of times depKey depends on keyName.
    meta.writeDeps(depKey, keyName, meta.peekDeps(depKey, keyName) - 1);
    // Unwatch the depKey
    unwatch(obj, depKey, meta);
  }
}

export function defineProperty(
  obj: object,
  keyName: string,
  desc: Descriptor | undefined | null,
  data?: any | undefined | null,
  meta?: Meta
) {
  if (meta === undefined) {
    meta = metaFor(obj);
  }

  let watching = meta.peekWatching(keyName) > 0;
  let previousDesc = descriptorFor(obj, keyName, meta);
  let wasDescriptor = previousDesc !== undefined;

  if (wasDescriptor) {
    previousDesc.teardown(obj, keyName, meta);
    meta.removeDescriptors(keyName);
  }

  // used to track if the the property being defined be enumerable
  let enumerable = true;

  // Ember.NativeArray is a normal Ember.Mixin that we mix into `Array.prototype` when prototype extensions are enabled
  // mutating a native object prototype like this should _not_ result in enumerable properties being added (or we have significant
  // issues with things like deep equality checks from test frameworks, or things like jQuery.extend(true, [], [])).
  //
  // this is a hack, and we should stop mutating the array prototype by default 😫
  if (obj === Array.prototype) {
    enumerable = false;
  }

  let value;
  if (desc instanceof Descriptor) {
    value = desc;

    Object.defineProperty(obj, keyName, {
      configurable: true,
      enumerable,
      get: DESCRIPTOR_GETTER_FUNCTION(keyName, value),
    });

    meta.writeDescriptors(keyName, value);

    desc.setup(obj, keyName);
  } else if (desc === undefined || desc === null) {
    value = data;

    if (DEBUG && watching) {
      meta.writeValues(keyName, data);

      let defaultDescriptor = {
        configurable: true,
        enumerable,
        set: MANDATORY_SETTER_FUNCTION(keyName),
        get: DEFAULT_GETTER_FUNCTION(keyName),
      };

      Object.defineProperty(obj, keyName, defaultDescriptor);
    } else if (wasDescriptor || enumerable === false) {
      Object.defineProperty(obj, keyName, {
        configurable: true,
        enumerable,
        writable: true,
        value,
      });
    } else {
      obj[keyName] = data;
    }
  } else {
    value = desc;

    // fallback to ES5
    Object.defineProperty(obj, keyName, desc);
  }

  // if key is being watched, override chains that
  // were initialized with the prototype
  if (watching) {
    overrideChains(obj, keyName, meta);
  }

  // The `value` passed to the `didDefineProperty` hook is
  // either the descriptor or data, whichever was passed.
  if (typeof (obj as ExtendedObject).didDefineProperty === 'function') {
    (obj as ExtendedObject).didDefineProperty!(obj, keyName, value);
  }
}

function overrideChains(_obj: object, keyName: string, meta: Meta) {
  let chainWatchers = meta.readableChainWatchers();
  if (chainWatchers !== undefined) {
    chainWatchers.revalidate(keyName);
  }
}

function chainsDidChange(_obj: object, keyName: string, meta: Meta) {
  let chainWatchers = meta.readableChainWatchers();
  if (chainWatchers !== undefined) {
    chainWatchers.notify(keyName, true, notifyPropertyChange);
  }
}