helper.js

'use strict'
var React = require('react-native');

var {
   Animated,
   Easing
} = React;


module.exports = function (screen_height ) {
   var module = {};
   var initialUsedSpace;
   var tension;
   var friction;
   var initialPosition;
   var callbackPositionUpdated;

   module.calculateInitialPosition = function ( initial_used_space ){
      initialUsedSpace = Math.abs(initial_used_space);
      initialPosition = (screen_height * ( 1 - initialUsedSpace ));
      return initialPosition;
   };

   module.getInitialUsedSpace = function(){
      return initialUsedSpace;
   };

   module.getInitialPosition = function(){
      return initialPosition;
   };


   module.setupAnimation = function ( higher_tension, friction, callbackPositionUpdated ){
      this.tension = higher_tension;
      this.friction = friction;
      this.callbackPositionUpdated = callbackPositionUpdated;

   };


   module.isAValidMovement = function(distanceX, distanceY){
      var moveTravelledFarEnough =  Math.abs(distanceY) > Math.abs(distanceX) && Math.abs(distanceY) > 2;
      return moveTravelledFarEnough;
   };


   module.startAnimation = function (velocityY, positionY,initialPositon,id ){
      console.log('creating animation ');
      var isGoingToUp = ( velocityY < 0 )? true : false;
      var speed = Math.abs(velocityY);
      var currentPosition = Math.abs(positionY / screen_height);
      var endPosition = isGoingToUp? 0 : initialPositon;

      var position = new Animated.Value(positionY);
      position.removeAllListeners();

      console.log('configuration : '+endPosition)

      Animated.timing(position, {
         toValue: endPosition,
         tension: 30,
         friction: 1,
         //easing:Easing.elastic,
         velocity: velocityY
      }).start();

      position.addListener((position)=>{console.log('position by',position,endPosition);});
      position.addListener(this.callbackPositionUpdated);
   };

   return module;
};