// history
( function( window, factory ) {
  // universal module definition
  if ( typeof module == 'object' && module.exports ) {
    // CommonJS
    module.exports = factory(
        window,
        require('./core'),
        require('fizzy-ui-utils'),
    );
  } else {
    // browser global
    factory(
        window,
        window.InfiniteScroll,
        window.fizzyUIUtils,
    );
  }

}( window, function factory( window, InfiniteScroll, utils ) {

let proto = InfiniteScroll.prototype;

Object.assign( InfiniteScroll.defaults, {
  history: 'replace',
  // historyTitle: false,
} );

let link = document.createElement('a');

// ----- create/destroy ----- //

InfiniteScroll.create.history = function() {
  if ( !this.options.history ) return;

  // check for same origin
  link.href = this.getAbsolutePath();
  // MS Edge does not have origin on link
  // https://developer.microsoft.com/en-us/microsoft-edge/platform/issues/12236493/
  let linkOrigin = link.origin || link.protocol + '//' + link.host;
  let isSameOrigin = linkOrigin == location.origin;
  if ( !isSameOrigin ) {
    console.error( '[InfiniteScroll] cannot set history with different origin: ' +
      `${link.origin} on ${location.origin} . History behavior disabled.` );
    return;
  }

  // two ways to handle changing history
  if ( this.options.append ) {
    this.createHistoryAppend();
  } else {
    this.createHistoryPageLoad();
  }
};

proto.createHistoryAppend = function() {
  this.updateMeasurements();
  this.updateScroller();
  // array of scroll positions of appended pages
  this.scrollPages = [
    // first page
    {
      top: 0,
      path: location.href,
      title: document.title,
    },
  ];
  this.scrollPage = this.scrollPages[0];
  // events
  this.scrollHistoryHandler = this.onScrollHistory.bind( this );
  this.unloadHandler = this.onUnload.bind( this );
  this.scroller.addEventListener( 'scroll', this.scrollHistoryHandler );
  this.on( 'append', this.onAppendHistory );
  this.bindHistoryAppendEvents( true );
};

proto.bindHistoryAppendEvents = function( isBind ) {
  let addRemove = isBind ? 'addEventListener' : 'removeEventListener';
  this.scroller[ addRemove ]( 'scroll', this.scrollHistoryHandler );
  window[ addRemove ]( 'unload', this.unloadHandler );
};

proto.createHistoryPageLoad = function() {
  this.on( 'load', this.onPageLoadHistory );
};

InfiniteScroll.destroy.history =
proto.destroyHistory = function() {
  let isHistoryAppend = this.options.history && this.options.append;
  if ( isHistoryAppend ) {
    this.bindHistoryAppendEvents( false );
  }
};

// ----- append history ----- //

proto.onAppendHistory = function( response, path, items ) {
  // do not proceed if no items. #779
  if ( !items || !items.length ) return;

  let firstItem = items[0];
  let elemScrollY = this.getElementScrollY( firstItem );
  // resolve path
  link.href = path;
  // add page data to hash
  this.scrollPages.push({
    top: elemScrollY,
    path: link.href,
    title: response.title,
  });
};

proto.getElementScrollY = function( elem ) {
  if ( this.options.elementScroll ) {
    return elem.offsetTop - this.top;
  } else {
    let rect = elem.getBoundingClientRect();
    return rect.top + window.scrollY;
  }
};

proto.onScrollHistory = function() {
  // cycle through positions, find biggest without going over
  let scrollPage = this.getClosestScrollPage();
  // set history if changed
  if ( scrollPage != this.scrollPage ) {
    this.scrollPage = scrollPage;
    this.setHistory( scrollPage.title, scrollPage.path );
  }
};

utils.debounceMethod( InfiniteScroll, 'onScrollHistory', 150 );

proto.getClosestScrollPage = function() {
  let scrollViewY;
  if ( this.options.elementScroll ) {
    scrollViewY = this.scroller.scrollTop + this.scroller.clientHeight / 2;
  } else {
    scrollViewY = window.scrollY + this.windowHeight / 2;
  }

  let scrollPage;
  for ( let page of this.scrollPages ) {
    if ( page.top >= scrollViewY ) break;

    scrollPage = page;
  }
  return scrollPage;
};

proto.setHistory = function( title, path ) {
  let optHistory = this.options.history;
  let historyMethod = optHistory && history[ optHistory + 'State' ];
  if ( !historyMethod ) return;

  history[ optHistory + 'State' ]( null, title, path );
  if ( this.options.historyTitle ) document.title = title;
  this.dispatchEvent( 'history', null, [ title, path ] );
};

// scroll to top to prevent initial scroll-reset after page refresh
// https://stackoverflow.com/a/18633915/182183
proto.onUnload = function() {
  if ( this.scrollPage.top === 0 ) return;

  // calculate where scroll position would be on refresh
  let scrollY = window.scrollY - this.scrollPage.top + this.top;
  // disable scroll event before setting scroll #679
  this.destroyHistory();
  scrollTo( 0, scrollY );
};

// ----- load history ----- //

// update URL
proto.onPageLoadHistory = function( response, path ) {
  this.setHistory( response.title, path );
};

// --------------------------  -------------------------- //

return InfiniteScroll;

} ) );