import Utils from './aria'

/**
 * @constructor
 * @desc Dialog object providing modal focus management.
 *
 * Assumptions: The element serving as the dialog container is present in the
 * DOM and hidden. The dialog container has role='dialog'.
 *
 * @param dialogId
 *          The ID of the element serving as the dialog container.
 * @param focusAfterClosed
 *          Either the DOM node or the ID of the DOM node to focus when the
 *          dialog closes.
 * @param focusFirst
 *          Optional parameter containing either the DOM node or the ID of the
 *          DOM node to focus when the dialog opens. If not specified, the
 *          first focusable element in the dialog will receive focus.
 */
let tabEvent: EventHandlerNonNull

class Dialog {
  public lastFocus: Nullable<Element> = null;
  constructor(public dialogNode: Nullable<HTMLElement>, public focusAfterClosed: HTMLElement, public focusFirst: HTMLElement | string) {
    if (this.dialogNode === null || this.dialogNode.getAttribute('role') !== 'dialog') {
      throw new Error('Dialog() requires a DOM element with ARIA role of dialog.')
    }

    if (typeof focusAfterClosed === 'string') {
      this.focusAfterClosed = document.getElementById(focusAfterClosed)
    } else if (typeof focusAfterClosed === 'object') {
      this.focusAfterClosed = focusAfterClosed
    } else {
      this.focusAfterClosed = null
    }

    if (typeof focusFirst === 'string') {
      this.focusFirst = document.getElementById(focusFirst)
    } else if (typeof focusFirst === 'object') {
      this.focusFirst = focusFirst
    } else {
      this.focusFirst = null
    }

    if (this.focusFirst) {
      (this.focusFirst as HTMLElement).focus()
    } else {
      Utils.focusFirstDescendant(this.dialogNode)
    }

    this.lastFocus = document.activeElement
    tabEvent = (e: KeyboardEvent) => {
      this.trapFocus(e)
    }
    this.addListeners()
  }

  addListeners(): void {
    document.addEventListener('focus', tabEvent, true)
  }

  removeListeners(): void {
    document.removeEventListener('focus', tabEvent, true)
  }

  closeDialog(): void {
    this.removeListeners()
    if (this.focusAfterClosed) {
      setTimeout(() => {
        this.focusAfterClosed.focus()
      })
    }
  }

  trapFocus(event: KeyboardEvent): void {
    if (Utils.IgnoreUtilFocusChanges) {
      return
    }
    if (this.dialogNode.contains(event.target as Node)) {
      this.lastFocus = event.target as HTMLElement
    } else {
      Utils.focusFirstDescendant(this.dialogNode)
      if (this.lastFocus === document.activeElement) {
        Utils.focusLastDescendant(this.dialogNode)
      }
      this.lastFocus = document.activeElement
    }
  }
}

export default Dialog