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;
                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.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);
        }
    }
}());