const negate = require('lodash/negate');
const Element = require('./Element');
const ArraySlice = require('../ArraySlice');

/**
 * @class
 *
 * @param {Element[]} content
 * @param meta
 * @param attributes
 */
class ArrayElement extends Element {
  constructor(content, meta, attributes) {
    super(content || [], meta, attributes);
    this.element = 'array';
  }

  primitive() {
    return 'array';
  }

  /**
   * @returns {Element}
   */
  get(index) {
    return this.content[index];
  }

  /**
   * Helper for returning the value of an item
   * This works for both ArrayElement and ObjectElement instances
   */
  getValue(indexOrKey) {
    const item = this.get(indexOrKey);

    if (item) {
      return item.toValue();
    }

    return undefined;
  }

  /**
   * @returns {Element}
   */
  getIndex(index) {
    return this.content[index];
  }

  set(index, value) {
    this.content[index] = this.refract(value);
    return this;
  }

  remove(index) {
    const removed = this.content.splice(index, 1);

    if (removed.length) {
      return removed[0];
    }

    return null;
  }

  /**
   * @param callback - Function to execute for each element
   * @param thisArg - Value to use as this (i.e the reference Object) when executing callback
   */
  map(callback, thisArg) {
    return this.content.map(callback, thisArg);
  }

  /**
   * Maps and then flattens the results.
   * @param callback - Function to execute for each element.
   * @param thisArg - Value to use as this (i.e the reference Object) when executing callback
   * @returns {array}
   */
  flatMap(callback, thisArg) {
    return this
      .map(callback, thisArg)
      .reduce((a, b) => a.concat(b), []);
  }

  /**
   * Returns an array containing the truthy results of calling the given transformation with each element of this sequence
   * @param transform - A closure that accepts an element of this array as its argument and returns an optional value.
   * @param thisArg - Value to use as this (i.e the reference Object) when executing callback
   * @memberof ArrayElement.prototype
   * @returns An array of the non-undefined results of calling transform with each element of the array
   */
  compactMap(transform, thisArg) {
    const results = [];

    this.forEach((element) => {
      const result = transform.bind(thisArg)(element);

      if (result) {
        results.push(result);
      }
    });

    return results;
  }

  /**
   * @param callback - Function to execute for each element
   * @param thisArg - Value to use as this (i.e the reference Object) when executing callback
   * @returns {ArraySlice}
   */
  filter(callback, thisArg) {
    return new ArraySlice(this.content.filter(callback, thisArg));
  }

  /**
   * @param callback - Function to execute for each element
   * @param thisArg - Value to use as this (i.e the reference Object) when executing callback
   * @returns {ArraySlice}
   */
  reject(callback, thisArg) {
    return this.filter(negate(callback), thisArg);
  }

  /**
   * This is a reduce function specifically for Minim arrays and objects. It
   * allows for returning normal values or Minim instances, so it converts any
   * primitives on each step.
   */
  reduce(callback, initialValue) {
    let startIndex;
    let memo;

    // Allows for defining a starting value of the reduce
    if (initialValue !== undefined) {
      startIndex = 0;
      memo = this.refract(initialValue);
    } else {
      startIndex = 1;
      // Object Element content items are member elements. Because of this,
      // the memo should start out as the member value rather than the
      // actual member itself.
      memo = this.primitive() === 'object' ? this.first.value : this.first;
    }

    // Sending each function call to the registry allows for passing Minim
    // instances through the function return. This means you can return
    // primitive values or return Minim instances and reduce will still work.
    for (let i = startIndex; i < this.length; i += 1) {
      const item = this.content[i];

      if (this.primitive() === 'object') {
        memo = this.refract(callback(memo, item.value, item.key, item, this));
      } else {
        memo = this.refract(callback(memo, item, i, this));
      }
    }

    return memo;
  }

  /**
   * @callback forEachCallback
   * @param {Element} currentValue
   * @param {NumberElement} index
   */

  /**
   * @param {forEachCallback} callback - Function to execute for each element
   * @param thisArg - Value to use as this (i.e the reference Object) when executing callback
   * @memberof ArrayElement.prototype
   */
  forEach(callback, thisArg) {
    this.content.forEach((item, index) => {
      callback.bind(thisArg)(item, this.refract(index));
    });
  }

  /**
   * @returns {Element}
   */
  shift() {
    return this.content.shift();
  }

  /**
   * @param value
   */
  unshift(value) {
    this.content.unshift(this.refract(value));
  }

  /**
   * @param value
   */
  push(value) {
    this.content.push(this.refract(value));
    return this;
  }

  /**
   * @param value
   */
  add(value) {
    this.push(value);
  }

  /**
   * Recusively search all descendents using a condition function.
   * @returns {Element[]}
   */
  findElements(condition, givenOptions) {
    const options = givenOptions || {};
    const recursive = !!options.recursive;
    const results = options.results === undefined ? [] : options.results;

    // The forEach method for Object Elements returns value, key, and member.
    // This passes those along to the condition function below.
    this.forEach((item, keyOrIndex, member) => {
      // We use duck-typing here to support any registered class that
      // may contain other elements.
      if (recursive && (item.findElements !== undefined)) {
        item.findElements(condition, {
          results,
          recursive,
        });
      }

      if (condition(item, keyOrIndex, member)) {
        results.push(item);
      }
    });

    return results;
  }

  /**
   * Recusively search all descendents using a condition function.
   * @param condition
   * @returns {ArraySlice}
   */
  find(condition) {
    return new ArraySlice(this.findElements(condition, { recursive: true }));
  }

  /**
   * @param {string} element
   * @returns {ArraySlice}
   */
  findByElement(element) {
    return this.find(item => item.element === element);
  }

  /**
   * @param {string} className
   * @returns {ArraySlice}
   * @memberof ArrayElement.prototype
   */
  findByClass(className) {
    return this.find(item => item.classes.includes(className));
  }

  /**
   * Search the tree recursively and find the element with the matching ID
   * @param {string} id
   * @returns {Element}
   * @memberof ArrayElement.prototype
   */
  getById(id) {
    return this.find(item => item.id.toValue() === id).first;
  }

  /**
   * Looks for matching children using deep equality
   * @param value
   * @returns {boolean}
   */
  includes(value) {
    return this.content.some(element => element.equals(value));
  }

  /**
   * Looks for matching children using deep equality
   * @param value
   * @returns {boolean}
   * @see includes
   * @deprecated method was replaced by includes
   */
  contains(value) {
    return this.includes(value);
  }

  // Fantasy Land

  /**
   * @returns {ArrayElement} An empty array element
   */
  empty() {
    return new this.constructor([]);
  }

  ['fantasy-land/empty']() {
    return this.empty();
  }

  /**
   * @param {ArrayElement} other
   * @returns {ArrayElement}
   */
  concat(other) {
    return new this.constructor(this.content.concat(other.content));
  }

  ['fantasy-land/concat'](other) {
    return this.concat(other);
  }

  ['fantasy-land/map'](transform) {
    return new this.constructor(this.map(transform));
  }

  ['fantasy-land/chain'](transform) {
    return this
      .map(element => transform(element), this)
      .reduce((a, b) => a.concat(b), this.empty());
  }

  ['fantasy-land/filter'](callback) {
    return new this.constructor(this.content.filter(callback));
  }

  ['fantasy-land/reduce'](transform, initialValue) {
    return this.content.reduce(transform, initialValue);
  }

  /**
   * Returns the length of the collection
   * @type number
   */
  get length() {
    return this.content.length;
  }

  /**
   * Returns whether the collection is empty
   * @type boolean
   */
  get isEmpty() {
    return this.content.length === 0;
  }

  /**
   * Return the first item in the collection
   * @type Element
   */
  get first() {
    return this.getIndex(0);
  }

  /**
   * Return the second item in the collection
   * @type Element
   */
  get second() {
    return this.getIndex(1);
  }

  /**
   * Return the last item in the collection
   * @type Element
   */
  get last() {
    return this.getIndex(this.length - 1);
  }
}

/**
 * @returns {ArrayElement} An empty array element
 */
ArrayElement.empty = function empty() {
  return new this();
};

ArrayElement['fantasy-land/empty'] = ArrayElement.empty;

if (typeof Symbol !== 'undefined') {
  ArrayElement.prototype[Symbol.iterator] = function symbol() {
    return this.content[Symbol.iterator]();
  };
}

module.exports = ArrayElement;