menu-string/index.js

Generate a menu with selectable menu items as a string

'use strict'

const inherits = require('util').inherits
const EventEmitter = require('events')
const BUFFER = 3

inherits(Menu, EventEmitter)

module.exports = Menu

function Menu (opts) {
  if (!(this instanceof Menu)) return new Menu(opts)

  EventEmitter.call(this)

  if (Array.isArray(opts)) opts = { items: opts }
  this.items = normalizeItems(opts.items)
  this._render = opts.render || render
  this._selected = opts.selected || 0
  this._height = opts.height
  this._offset = 0

  // If the selected item is a separator try to first find the next
  // non-separator going down. If none is found, try to go up. If none
  // is found up either, set the selected item to null
  if (this.items[this._selected].separator && !this.down() && !this.up()) this._selected = null

  this._viewportSync()
}

Menu.prototype.up = function () {
  let i = this._selected
  while (--i >= 0 && this.items[i].separator) {}
  if (i < 0) return false
  this._selected = i
  this._viewportUp()
  this.emit('update')
  return true
}

Menu.prototype.down = function () {
  let i = this._selected
  while (++i < this.items.length && this.items[i].separator) {}
  if (i === this.items.length) return false
  this._selected = i
  this._viewportDownCursorBottom()
  this.emit('update')
  return true
}

Menu.prototype.select = function (index) {
  if (!Number.isFinite(index) ||
    index < 0 ||
    index >= this.items.length ||
    this.items[index].separator) return false
  this._selected = index
  this._viewportSync()
  this.emit('update')
  return true
}

Menu.prototype.selected = function () {
  // in case the menu is empty or only consists of separators
  if (this._selected === null) return null
  return this.items[this._selected]
}

Menu.prototype.toggleMark = function () {
  if (this._selected === null) return
  this.items[this._selected].marked = !this.items[this._selected].marked
  this.emit('update')
}

Menu.prototype.toString = function () {
  const self = this
  return this.items
    .slice(this._offset, this._height && this._offset + this._height)
    .map(function (item, index) {
      return self._render(item, index + self._offset === self._selected)
    })
    .join('\n')
}

Menu.prototype._viewportSync = function () {
  if (this._height) {
    if (this._selected < this._offset) this._viewportUp()
    else if (this._selected >= (this._offset + this._height) - BUFFER) this._viewportDownCursorTop()
  }
}

Menu.prototype._viewportUp = function () {
  while (
    this._height && // if the menu have a max height
    this._offset > 0 && // and we haven't already reached the top
    this._selected - this._offset < BUFFER // and we are close the top edge
  ) this._offset-- // then move the viewport one up
}

Menu.prototype._viewportDownCursorTop = function () {
  while (
    this._offset + BUFFER < this._selected && // if the viewport is too far up related to the cursor
    this._height + this._offset < this.items.length // and we haven't yet reached the bottom
  ) this._offset++ // then move the viewport one down
}

Menu.prototype._viewportDownCursorBottom = function () {
  while (
    this._height && // if the menu have a max height
    this._selected >= (this._offset + this._height) - BUFFER && // and the viewport is too far up related to the cursor
    this._height + this._offset < this.items.length // but we haven't yet reached the bottom
  ) this._offset++ // then move the viewport one down
}

function render (item, selected) {
  return (selected ? '> ' : '  ') + item.text
}

function normalizeItems (items) {
  return items.map(function (item, index) {
    if (typeof item === 'string') item = { text: item }
    item.index = index
    return item
  })
}