let createQueryWrapper = require('query-ast')
let $ = createQueryWrapper(ast, options)

let ast = {
  type: 'program',
  value: [{
    type: 'item_container',
    value: [{
      type: 'item',
      value: 'a'
    }]
  }, {
    type: 'item_container',
    value: []
  }, {
    type: 'item',
    value: 'b'
  }]
}

// Create a QueryWrapper that will be used to traverse/modify an AST
let $ = createQueryWrapper(ast)

// By default, the QueryWrapper is scoped to the root node
$('item').length() // 2

// The QueryWrapper can also be scoped to a NodeWrapper or array of NodeWrappers
$('item_container').filter((n) => {
  return $(n).has('item')
}).length() // 1

let ast = {
  type: 'program',
  value: [{
    type: 'item_container',
    value: [{
      type: 'item',
      value: 'a'
    }]
  }, {
    type: 'item',
    value: 'b'
  }]
}

let $ = createQueryWrapper(ast)

// String
$('item').length() // 2

// RegExp
$(/item/).length() // 3

// Function
$((n) => n.node.value === 'a').length() // 1

let ast = {
  type: 'program',
  value: [{
    type: 'item',
    value: 'a'
  }]
}

let options = {
  /**
   * Return true if the node has children
   *
   * @param {object} node
   * @returns {boolean}
   */
  hasChildren: (node) => Array.isArray(node.value),
  /**
   * Return an array of child nodes
   *
   * @param {object} node
   * @returns {object[]}
   */
  getChildren: (node) => node.value,
  /**
   * Return a string representation of the node's type
   *
   * @param {object} node
   * @returns {string}
   */
  getType: (node) => node.type,
  /**
   * Convert the node back to JSON. This usually just means merging the
   * children back into the node
   *
   * @param {object} node
   * @param {object[]} [children]
   * @returns {string}
   */
  toJSON: (node, children) => {
    return Object.assign({}, node, {
      value: children ? children : node.value
    })
  },
  /**
   * Convert the node to a string
   *
   * @param {object} node
   * @returns {string}
   */
  toString: (node) => {
    return typeof node.value === 'string' ? node.value : ''
  }
}