var ExpressionPropertyInterface = (function () {

  var defaultUnidimensionalValue = {pv: 0, v: 0, mult: 1};
  var defaultMultidimensionalValue = {pv: [0, 0, 0], v: [0, 0, 0], mult: 1};

  function completeProperty(expressionValue, property, type) {
    Object.defineProperty(expressionValue, 'velocity', {
      get: function () {
        return property.getVelocityAtTime(property.comp.currentFrame);
      },
    });
    expressionValue.numKeys = property.keyframes ? property.keyframes.length : 0;
    expressionValue.key = function (pos) {
      if (!expressionValue.numKeys) {
        return 0;
      } else {
        var value = '';
        if ('s' in property.keyframes[pos - 1]) {
          value = property.keyframes[pos - 1].s;
        } else if ('e' in property.keyframes[pos - 2]) {
          value = property.keyframes[pos - 2].e;
        } else {
          value = property.keyframes[pos - 2].s;
        }
        var valueProp = type === 'unidimensional' ? new Number(value) : Object.assign({}, value);
        valueProp.time = property.keyframes[pos - 1].t / property.elem.comp.globalData.frameRate;
        valueProp.value = type === 'unidimensional' ? value[0] : value;
        return valueProp;
      }
    };
    expressionValue.valueAtTime = property.getValueAtTime;
    expressionValue.speedAtTime = property.getSpeedAtTime;
    expressionValue.velocityAtTime = property.getVelocityAtTime;
    expressionValue.propertyGroup = property.propertyGroup;
  }

  function UnidimensionalPropertyInterface(property) {
    if(!property || !('pv' in property)) {
      property = defaultUnidimensionalValue;
    }
    var mult = 1 / property.mult;
    var val = property.pv * mult;
    var expressionValue = new Number(val);
    expressionValue.value = val;
    completeProperty(expressionValue, property, 'unidimensional');

    return function () {
      if (property.k) {
        property.getValue();
      }
      val = property.v * mult;
      if(expressionValue.value !== val) {
        expressionValue = new Number(val);
        expressionValue.value = val;
        completeProperty(expressionValue, property, 'unidimensional');
      }
      return expressionValue;
    };
  }

  function MultidimensionalPropertyInterface(property) {
    if(!property || !('pv' in property)) {
      property = defaultMultidimensionalValue;
    }
    var mult = 1 / property.mult;
    var len = (property.data && property.data.l) || property.pv.length;
    var expressionValue = createTypedArray('float32', len);
    var arrValue = createTypedArray('float32', len);
    expressionValue.value = arrValue;
    completeProperty(expressionValue, property, 'multidimensional');

    return function () {
      if (property.k) {
        property.getValue();
      }
      for (var i = 0; i < len; i += 1) {
        expressionValue[i] = arrValue[i] = property.v[i] * mult;
      }
      return expressionValue;
    };
  }

  // TODO: try to avoid using this getter
  function defaultGetter() {
    return defaultUnidimensionalValue;
  }
    
  return function (property) {
    if(!property) {
      return defaultGetter;
    } else if (property.propType === 'unidimensional') {
      return UnidimensionalPropertyInterface(property);
    } else {
      return MultidimensionalPropertyInterface(property);
    }
  };
}());