/**
* Tom Select v2.4.2
* Licensed under the Apache License, Version 2.0 (the "License");
*/

(function (global, factory) {
	typeof exports === 'object' && typeof module !== 'undefined' ? module.exports = factory() :
	typeof define === 'function' && define.amd ? define(factory) :
	(global = typeof globalThis !== 'undefined' ? globalThis : global || self, global.virtual_scroll = factory());
})(this, (function () { 'use strict';

	/**
	 * Converts a scalar to its best string representation
	 * for hash keys and HTML attribute values.
	 *
	 * Transformations:
	 *   'str'     -> 'str'
	 *   null      -> ''
	 *   undefined -> ''
	 *   true      -> '1'
	 *   false     -> '0'
	 *   0         -> '0'
	 *   1         -> '1'
	 *
	 */

	/**
	 * Iterates over arrays and hashes.
	 *
	 * ```
	 * iterate(this.items, function(item, id) {
	 *    // invoked for each item
	 * });
	 * ```
	 *
	 */
	const iterate = (object, callback) => {
	  if (Array.isArray(object)) {
	    object.forEach(callback);
	  } else {
	    for (var key in object) {
	      if (object.hasOwnProperty(key)) {
	        callback(object[key], key);
	      }
	    }
	  }
	};

	/**
	 * Add css classes
	 *
	 */
	const addClasses = (elmts, ...classes) => {
	  var norm_classes = classesArray(classes);
	  elmts = castAsArray(elmts);
	  elmts.map(el => {
	    norm_classes.map(cls => {
	      el.classList.add(cls);
	    });
	  });
	};

	/**
	 * Return arguments
	 *
	 */
	const classesArray = args => {
	  var classes = [];
	  iterate(args, _classes => {
	    if (typeof _classes === 'string') {
	      _classes = _classes.trim().split(/[\t\n\f\r\s]/);
	    }
	    if (Array.isArray(_classes)) {
	      classes = classes.concat(_classes);
	    }
	  });
	  return classes.filter(Boolean);
	};

	/**
	 * Create an array from arg if it's not already an array
	 *
	 */
	const castAsArray = arg => {
	  if (!Array.isArray(arg)) {
	    arg = [arg];
	  }
	  return arg;
	};

	/**
	 * Plugin: "restore_on_backspace" (Tom Select)
	 * Copyright (c) contributors
	 *
	 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this
	 * file except in compliance with the License. You may obtain a copy of the License at:
	 * http://www.apache.org/licenses/LICENSE-2.0
	 *
	 * Unless required by applicable law or agreed to in writing, software distributed under
	 * the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF
	 * ANY KIND, either express or implied. See the License for the specific language
	 * governing permissions and limitations under the License.
	 *
	 */

	function plugin () {
	  const self = this;
	  const orig_canLoad = self.canLoad;
	  const orig_clearActiveOption = self.clearActiveOption;
	  const orig_loadCallback = self.loadCallback;
	  var pagination = {};
	  var dropdown_content;
	  var loading_more = false;
	  var load_more_opt;
	  var default_values = [];
	  if (!self.settings.shouldLoadMore) {
	    // return true if additional results should be loaded
	    self.settings.shouldLoadMore = () => {
	      const scroll_percent = dropdown_content.clientHeight / (dropdown_content.scrollHeight - dropdown_content.scrollTop);
	      if (scroll_percent > 0.9) {
	        return true;
	      }
	      if (self.activeOption) {
	        var selectable = self.selectable();
	        var index = Array.from(selectable).indexOf(self.activeOption);
	        if (index >= selectable.length - 2) {
	          return true;
	        }
	      }
	      return false;
	    };
	  }
	  if (!self.settings.firstUrl) {
	    throw 'virtual_scroll plugin requires a firstUrl() method';
	  }

	  // in order for virtual scrolling to work,
	  // options need to be ordered the same way they're returned from the remote data source
	  self.settings.sortField = [{
	    field: '$order'
	  }, {
	    field: '$score'
	  }];

	  // can we load more results for given query?
	  const canLoadMore = query => {
	    if (typeof self.settings.maxOptions === 'number' && dropdown_content.children.length >= self.settings.maxOptions) {
	      return false;
	    }
	    if (query in pagination && pagination[query]) {
	      return true;
	    }
	    return false;
	  };
	  const clearFilter = (option, value) => {
	    if (self.items.indexOf(value) >= 0 || default_values.indexOf(value) >= 0) {
	      return true;
	    }
	    return false;
	  };

	  // set the next url that will be
	  self.setNextUrl = (value, next_url) => {
	    pagination[value] = next_url;
	  };

	  // getUrl() to be used in settings.load()
	  self.getUrl = query => {
	    if (query in pagination) {
	      const next_url = pagination[query];
	      pagination[query] = false;
	      return next_url;
	    }

	    // if the user goes back to a previous query
	    // we need to load the first page again
	    self.clearPagination();
	    return self.settings.firstUrl.call(self, query);
	  };

	  // clear pagination
	  self.clearPagination = () => {
	    pagination = {};
	  };

	  // don't clear the active option (and cause unwanted dropdown scroll)
	  // while loading more results
	  self.hook('instead', 'clearActiveOption', () => {
	    if (loading_more) {
	      return;
	    }
	    return orig_clearActiveOption.call(self);
	  });

	  // override the canLoad method
	  self.hook('instead', 'canLoad', query => {
	    // first time the query has been seen
	    if (!(query in pagination)) {
	      return orig_canLoad.call(self, query);
	    }
	    return canLoadMore(query);
	  });

	  // wrap the load
	  self.hook('instead', 'loadCallback', (options, optgroups) => {
	    if (!loading_more) {
	      self.clearOptions(clearFilter);
	    } else if (load_more_opt) {
	      const first_option = options[0];
	      if (first_option !== undefined) {
	        load_more_opt.dataset.value = first_option[self.settings.valueField];
	      }
	    }
	    orig_loadCallback.call(self, options, optgroups);
	    loading_more = false;
	  });

	  // add templates to dropdown
	  //	loading_more if we have another url in the queue
	  //	no_more_results if we don't have another url in the queue
	  self.hook('after', 'refreshOptions', () => {
	    const query = self.lastValue;
	    var option;
	    if (canLoadMore(query)) {
	      option = self.render('loading_more', {
	        query: query
	      });
	      if (option) {
	        option.setAttribute('data-selectable', ''); // so that navigating dropdown with [down] keypresses can navigate to this node
	        load_more_opt = option;
	      }
	    } else if (query in pagination && !dropdown_content.querySelector('.no-results')) {
	      option = self.render('no_more_results', {
	        query: query
	      });
	    }
	    if (option) {
	      addClasses(option, self.settings.optionClass);
	      dropdown_content.append(option);
	    }
	  });

	  // add scroll listener and default templates
	  self.on('initialize', () => {
	    default_values = Object.keys(self.options);
	    dropdown_content = self.dropdown_content;

	    // default templates
	    self.settings.render = Object.assign({}, {
	      loading_more: () => {
	        return `<div class="loading-more-results">Loading more results ... </div>`;
	      },
	      no_more_results: () => {
	        return `<div class="no-more-results">No more results</div>`;
	      }
	    }, self.settings.render);

	    // watch dropdown content scroll position
	    dropdown_content.addEventListener('scroll', () => {
	      if (!self.settings.shouldLoadMore.call(self)) {
	        return;
	      }

	      // !important: this will get checked again in load() but we still need to check here otherwise loading_more will be set to true
	      if (!canLoadMore(self.lastValue)) {
	        return;
	      }

	      // don't call load() too much
	      if (loading_more) return;
	      loading_more = true;
	      self.load.call(self, self.lastValue);
	    });
	  });
	}

	return plugin;

}));
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