A computed property that chains all given computed properties

computed-chain.js

/**
 A computed property that chains all given computed properties
 Example

  ```javascript
  Ember.computed.chain('content', [
    [Ember.computed.mapBy, 'key'],
    [Ember.computed.filter, callback], //e.g. remove undefined/null
    [Ember.computed.sum],
    [customComputed]
  ]);

  //or
  //looks up on Ember.computed
  Ember.computed.chain('content', [
    ['mapBy', 'key'],
    ['filter', callback],
    ['sum'],
    ['toFixed', 2]
  ]);
  ```

 @method computed.chain
 @for Ember
 @param {String} dependentKey
 @return {Ember.ComputedProperty} a chain of computed properties
*/
export function chain (dependentKey, computedChains) {
  var func, cp, dependantCPs = {};
  forEach(computedChains, function (item) {
    cp = item[0];
    var args = [dependentKey].concat(item.slice(1));
    if (typeof  cp == "string") {
      cp = Ember.computed[cp];
    }
    cp = cp.apply(null, args);
    dependentKey = guidFor(cp) + '-chain';
    dependantCPs[dependentKey] = cp;
  }, this);
  func = cp.func;
  cp.func = function (propertyName) {
    if (!this.__ember_meta__.cacheMeta[propertyName+'-chain']) {
      for (var k in dependantCPs) {
        var cp = dependantCPs[k];
        Ember.defineProperty(this, k, cp);
      }
      this.__ember_meta__.cacheMeta[propertyName+'-chain'] = true;
    }
    return func.apply(this, arguments);
  };
  return cp;
}