import { IAccessibilityComponent, IAccessibilityKeyboardHandlers } from './interfaces'

class HSAccessibilityObserver {
  private components: IAccessibilityComponent[] = []
  private currentlyOpenedComponents: IAccessibilityComponent[] = []
  private activeComponent: IAccessibilityComponent | null = null

  private readonly allowedKeybindings = new Set([
    'Escape',
    'Enter',
    ' ',
    'Space',
    'ArrowDown',
    'ArrowUp',
    'ArrowLeft',
    'ArrowRight',
    'Tab',
    'Home',
    'End'
  ])

  constructor() {
    this.initGlobalListeners()
  }

  private initGlobalListeners(): void {
    document.addEventListener('keydown', evt => this.handleGlobalKeydown(evt))

    document.addEventListener('focusin', evt => this.handleGlobalFocusin(evt))
  }

  private isAllowedKeybinding(evt: KeyboardEvent): boolean {
    if (this.allowedKeybindings.has(evt.key)) {
      return true
    }

    if (
      evt.key.length === 1 &&
      /^[a-zA-Z]$/.test(evt.key) &&
      !evt.metaKey &&
      !evt.ctrlKey &&
      !evt.altKey &&
      !evt.shiftKey
    ) {
      return true
    }

    return false
  }

  private getActiveComponent(el: HTMLElement) {
    if (!el) return null

    const containingComponents = this.components.filter(
      comp => comp.wrapper.contains(el) || (comp.context && comp.context.contains(el))
    )

    if (containingComponents.length === 0) return null
    if (containingComponents.length === 1) return containingComponents[0]

    let closestComponent = null
    let minDistance = Number.MAX_SAFE_INTEGER

    for (const comp of containingComponents) {
      let distance = 0
      let current = el

      while (current && current !== comp.wrapper && current !== comp.context) {
        distance++
        current = current.parentElement
      }

      if (distance < minDistance) {
        minDistance = distance
        closestComponent = comp
      }
    }

    return closestComponent
  }

  private handleGlobalFocusin(evt: FocusEvent): void {
    const target = evt.target as HTMLElement
    this.activeComponent = this.getActiveComponent(target)
  }

  private handleGlobalKeydown(evt: KeyboardEvent): void {
    const target = evt.target as HTMLElement
    this.activeComponent = this.getActiveComponent(target)

    if (!this.activeComponent) return

    if (!this.isAllowedKeybinding(evt)) {
      return
    }

    switch (evt.key) {
      case 'Escape':
        if (!this.activeComponent.isOpened) {
          const closestOpenParent = this.findClosestOpenParent(target)

          if (closestOpenParent?.handlers.onEsc) {
            closestOpenParent.handlers.onEsc()
            evt.preventDefault()
            evt.stopPropagation()
          }
        } else if (this.activeComponent.handlers.onEsc) {
          this.activeComponent.handlers.onEsc()
          evt.preventDefault()
          evt.stopPropagation()
        }
        break
      case 'Enter':
        if (this.activeComponent.handlers.onEnter) {
          this.activeComponent.handlers.onEnter()
          evt.preventDefault()
          evt.stopPropagation()
        }
        break
      case ' ':
      case 'Space':
        if (target.tagName === 'INPUT' || target.tagName === 'TEXTAREA') {
          return
        }

        if (this.activeComponent.handlers.onSpace) {
          this.activeComponent.handlers.onSpace()
          evt.preventDefault()
          evt.stopPropagation()
        }
        break
      case 'ArrowDown':
      case 'ArrowUp':
      case 'ArrowLeft':
      case 'ArrowRight':
        if (this.activeComponent.handlers.onArrow) {
          if (evt.metaKey || evt.ctrlKey || evt.altKey || evt.shiftKey) {
            return
          }

          this.activeComponent.handlers.onArrow(evt)
          evt.preventDefault()
          evt.stopPropagation()
        }
        break
      case 'Tab': {
        if (!this.activeComponent.handlers.onTab) break
        const handler = evt.shiftKey ? this.activeComponent.handlers.onShiftTab : this.activeComponent.handlers.onTab
        if (handler) handler()
        break
      }
      case 'Home':
        if (this.activeComponent.handlers.onHome) {
          this.activeComponent.handlers.onHome()
          evt.preventDefault()
          evt.stopPropagation()
        }
        break
      case 'End':
        if (this.activeComponent.handlers.onEnd) {
          this.activeComponent.handlers.onEnd()
          evt.preventDefault()
          evt.stopPropagation()
        }
        break
      default:
        if (target.tagName === 'INPUT' || target.tagName === 'TEXTAREA' || target.isContentEditable) {
          return
        }
        if (this.activeComponent.handlers.onFirstLetter && evt.key.length === 1 && /^[a-zA-Z]$/.test(evt.key)) {
          this.activeComponent.handlers.onFirstLetter(evt.key)
          evt.preventDefault()
          evt.stopPropagation()
        }
        break
    }
  }

  private findClosestOpenParent(target: HTMLElement): IAccessibilityComponent | null {
    let current = target.parentElement

    while (current) {
      const parentComponent = this.currentlyOpenedComponents.find(
        comp => comp.wrapper === current && comp !== this.activeComponent
      )

      if (parentComponent) {
        return parentComponent
      }

      current = current.parentElement
    }

    return null
  }

  public registerComponent(
    wrapper: HTMLElement,
    handlers: IAccessibilityKeyboardHandlers,
    isOpened: boolean = true,
    name: string = '',
    selector: string = '',
    context?: HTMLElement
  ): IAccessibilityComponent {
    const component: IAccessibilityComponent = {
      wrapper,
      handlers,
      isOpened,
      name,
      selector,
      context,
      isRegistered: true
    }

    this.components.push(component)
    return component
  }

  public updateComponentState(component: IAccessibilityComponent, isOpened: boolean): void {
    component.isOpened = isOpened

    if (isOpened) {
      if (!this.currentlyOpenedComponents.includes(component)) {
        this.currentlyOpenedComponents.push(component)
      }
    } else {
      this.currentlyOpenedComponents = this.currentlyOpenedComponents.filter(comp => comp !== component)
    }
  }

  public unregisterComponent(component: IAccessibilityComponent): void {
    this.components = this.components.filter(comp => comp !== component)
    this.currentlyOpenedComponents = this.currentlyOpenedComponents.filter(comp => comp !== component)
  }

  public addAllowedKeybinding(key: string): void {
    this.allowedKeybindings.add(key)
  }

  public removeAllowedKeybinding(key: string): void {
    this.allowedKeybindings.delete(key)
  }

  public getAllowedKeybindings(): string[] {
    return Array.from(this.allowedKeybindings)
  }
}

export default HSAccessibilityObserver