import animateScrollTo from 'animated-scroll-to';

// It returns a promise which will be resolved when scroll animation is finished

animateScrollTo(500).then(hasScrolledToPosition => {
  // scroll animation is finished

  // "hasScrolledToPosition" indicates if page/element
  // was scrolled to a desired position
  // or if animation got interrupted
  if (hasScrolledToPosition) {
    // page is scrolled to a desired position
  } else {
    // scroll animation was interrupted by user
    // or by another call of "animateScrollTo"
  }
});

// "y" is a desired vertical scroll position to scroll to
function animateScrollTo(y, options);

// "coords" are an array "[x, y]"
// Where "x" and "y" are desired horizontal and vertical positions to scroll to
// Both "x" and "y" can be null
// which will result in keeping the current scroll position for that axis
function animateScrollTo(coords, options);

// If you pass a DOM element, page will be scrolled to it
function animateScrollTo(scrollToElement, options);

// Scrolls page vertically to 1000px
animateScrollTo(1000);

// Scrolls page horizontally to 1000px but keeps vertical scroll position
animateScrollTo([1000, null]);

// Scrolls page horizontally too 1000px and vertically to 500px
animateScrollTo([1000, 500]);

// Scrolls page both horizontally and vertically to ".my-element"
animateScrollTo(document.querySelector('.my-element'));

const defaultOptions = {
  // Indicated if scroll animation should be canceled on user action (scroll/keypress/touch)
  // if set to "false" user input will be disabled until scroll animation is complete
  cancelOnUserAction: true,
  
  // Animation easing function, with "easeOutCubic" as default
  easing: t => (--t) * t * t + 1,
  
  // DOM element that should be scrolled
  // Example: document.querySelector('#element-to-scroll'),
  elementToScroll: window,
  
  // Horizontal scroll offset
  // Practical when you are scrolling to a DOM element and want to add some padding
  horizontalOffset: 0,
  
  // Maximum duration of the scroll animation
  maxDuration: 3000,
  
  // Minimum duration of the scroll animation
  minDuration: 250,
  
  // Duration of the scroll per 1000px
  speed: 500,

  // Vertical scroll offset
  // Practical when you are scrolling to a DOM element and want to add some padding
  verticalOffset: 0,
};

/*
 * Easing Functions
 * https://gist.github.com/gre/1650294
 */
const EasingFunctions = {
  // no easing, no acceleration
  linear: (t) => { return t },
  // accelerating from zero velocity
  easeInQuad: (t) => { return t * t },
  // decelerating to zero velocity
  easeOutQuad: (t) => { return t * (2 - t) },
  // acceleration until halfway, then deceleration
  easeInOutQuad: (t) => { return t < 0.5 ? 2 * t * t : -1 + (4 - 2 * t) * t },
  // accelerating from zero velocity 
  easeInCubic: (t) => { return t * t * t },
  // decelerating to zero velocity 
  easeOutCubic: (t) => { return (--t) * t * t + 1 },
  // acceleration until halfway, then deceleration 
  easeInOutCubic: (t) => { return t < 0.5 ? 4 * t * t * t : (t - 1) * (2 * t - 2) * (2 * t - 2) + 1 },
  // accelerating from zero velocity 
  easeInQuart: (t) => { return t * t * t * t },
  // decelerating to zero velocity 
  easeOutQuart: (t) => { return 1 - (--t) * t * t * t },
  // acceleration until halfway, then deceleration
  easeInOutQuart: (t) => { return t < 0.5 ? 8 * t * t * t * t : 1 - 8 * (--t) * t * t * t },
  // accelerating from zero velocity
  easeInQuint: (t) => { return t * t * t * t * t },
  // decelerating to zero velocity
  easeOutQuint: (t) => { return 1 + (--t) * t * t * t * t },
  // acceleration until halfway, then deceleration 
  easeInOutQuint: (t) => { return t < 0.5 ? 16 * t * t * t * t * t : 1 + 16 * (--t) * t * t * t * t }
}