define(['summernote/core/func'], function (func) {
  /**
   * @class core.list
   *
   * list utils
   *
   * @singleton
   * @alternateClassName list
   */
  var list = (function () {
    /**
     * returns the first item of an array.
     *
     * @param {Array} array
     */
    var head = function (array) {
      return array[0];
    };

    /**
     * returns the last item of an array.
     *
     * @param {Array} array
     */
    var last = function (array) {
      return array[array.length - 1];
    };

    /**
     * returns everything but the last entry of the array.
     *
     * @param {Array} array
     */
    var initial = function (array) {
      return array.slice(0, array.length - 1);
    };

    /**
     * returns the rest of the items in an array.
     *
     * @param {Array} array
     */
    var tail = function (array) {
      return array.slice(1);
    };

    /**
     * returns item of array
     */
    var find = function (array, pred) {
      for (var idx = 0, len = array.length; idx < len; idx ++) {
        var item = array[idx];
        if (pred(item)) {
          return item;
        }
      }
    };

    /**
     * returns true if all of the values in the array pass the predicate truth test.
     */
    var all = function (array, pred) {
      for (var idx = 0, len = array.length; idx < len; idx ++) {
        if (!pred(array[idx])) {
          return false;
        }
      }
      return true;
    };

    /**
     * returns index of item
     */
    var indexOf = function (array, item) {
      return $.inArray(item, array);
    };

    /**
     * returns true if the value is present in the list.
     */
    var contains = function (array, item) {
      return indexOf(array, item) !== -1;
    };

    /**
     * get sum from a list
     *
     * @param {Array} array - array
     * @param {Function} fn - iterator
     */
    var sum = function (array, fn) {
      fn = fn || func.self;
      return array.reduce(function (memo, v) {
        return memo + fn(v);
      }, 0);
    };
  
    /**
     * returns a copy of the collection with array type.
     * @param {Collection} collection - collection eg) node.childNodes, ...
     */
    var from = function (collection) {
      var result = [], idx = -1, length = collection.length;
      while (++idx < length) {
        result[idx] = collection[idx];
      }
      return result;
    };
  
    /**
     * cluster elements by predicate function.
     *
     * @param {Array} array - array
     * @param {Function} fn - predicate function for cluster rule
     * @param {Array[]}
     */
    var clusterBy = function (array, fn) {
      if (!array.length) { return []; }
      var aTail = tail(array);
      return aTail.reduce(function (memo, v) {
        var aLast = last(memo);
        if (fn(last(aLast), v)) {
          aLast[aLast.length] = v;
        } else {
          memo[memo.length] = [v];
        }
        return memo;
      }, [[head(array)]]);
    };
  
    /**
     * returns a copy of the array with all falsy values removed
     *
     * @param {Array} array - array
     * @param {Function} fn - predicate function for cluster rule
     */
    var compact = function (array) {
      var aResult = [];
      for (var idx = 0, len = array.length; idx < len; idx ++) {
        if (array[idx]) { aResult.push(array[idx]); }
      }
      return aResult;
    };

    /**
     * produces a duplicate-free version of the array
     *
     * @param {Array} array
     */
    var unique = function (array) {
      var results = [];

      for (var idx = 0, len = array.length; idx < len; idx ++) {
        if (!contains(results, array[idx])) {
          results.push(array[idx]);
        }
      }

      return results;
    };

    /**
     * returns next item.
     * @param {Array} array
     */
    var next = function (array, item) {
      var idx = indexOf(array, item);
      if (idx === -1) { return null; }

      return array[idx + 1];
    };

    /**
     * returns prev item.
     * @param {Array} array
     */
    var prev = function (array, item) {
      var idx = indexOf(array, item);
      if (idx === -1) { return null; }

      return array[idx - 1];
    };
  
    return { head: head, last: last, initial: initial, tail: tail,
             prev: prev, next: next, find: find, contains: contains,
             all: all, sum: sum, from: from,
             clusterBy: clusterBy, compact: compact, unique: unique };
  })();

  return list;
});
