export enum Key {
  Backspace = 8,
  Tab = 9,
  Enter = 13,
  Shift = 16,
  Ctrl = 17,
  Alt = 18,
  PauseBreak = 19,
  CapsLock = 20,
  Escape = 27,
  Space = 32,
  PageUp = 33,
  PageDown = 34,
  End = 35,
  Home = 36,

  LeftArrow = 37,
  UpArrow = 38,
  RightArrow = 39,
  DownArrow = 40,

  Insert = 45,
  Delete = 46,

  Zero = 48,
  ClosedParen = Zero,
  One = 49,
  ExclamationMark = One,
  Two = 50,
  AtSign = Two,
  Three = 51,
  PoundSign = Three,
  Hash = PoundSign,
  Four = 52,
  DollarSign = Four,
  Five = 53,
  PercentSign = Five,
  Six = 54,
  Caret = Six,
  Hat = Caret,
  Seven = 55,
  Ampersand = Seven,
  Eight = 56,
  Star = Eight,
  Asterik = Star,
  Nine = 57,
  OpenParen = Nine,

  A = 65,
  B = 66,
  C = 67,
  D = 68,
  E = 69,
  F = 70,
  G = 71,
  H = 72,
  I = 73,
  J = 74,
  K = 75,
  L = 76,
  M = 77,
  N = 78,
  O = 79,
  P = 80,
  Q = 81,
  R = 82,
  S = 83,
  T = 84,
  U = 85,
  V = 86,
  W = 87,
  X = 88,
  Y = 89,
  Z = 90,

  LeftWindowKey = 91,
  RightWindowKey = 92,
  SelectKey = 93,

  Numpad0 = 96,
  Numpad1 = 97,
  Numpad2 = 98,
  Numpad3 = 99,
  Numpad4 = 100,
  Numpad5 = 101,
  Numpad6 = 102,
  Numpad7 = 103,
  Numpad8 = 104,
  Numpad9 = 105,

  Multiply = 106,
  Add = 107,
  Subtract = 109,
  DecimalPoint = 110,
  Divide = 111,

  F1 = 112,
  F2 = 113,
  F3 = 114,
  F4 = 115,
  F5 = 116,
  F6 = 117,
  F7 = 118,
  F8 = 119,
  F9 = 120,
  F10 = 121,
  F11 = 122,
  F12 = 123,

  NumLock = 144,
  ScrollLock = 145,

  SemiColon = 186,
  Equals = 187,
  Comma = 188,
  Dash = 189,
  Period = 190,
  UnderScore = Dash,
  PlusSign = Equals,
  ForwardSlash = 191,
  Tilde = 192,
  GraveAccent = Tilde,

  OpenBracket = 219,
  ClosedBracket = 221,
  Quote = 222
}

type KeyCombo = Array<Key>

/**
 * @param {KeyboardEvent} event - pressed key event, in case of multi-key combos
 *  the last pressed key event is passed to this handler
 */
type Handler = (event: KeyboardEvent) => void

export class Keyboard {
  private mapCombosToHandlers = new Map<number[], Handler[]>();
  private pressedKeys = new Set<Key>();

  constructor(
      private domNode: Element | Document
  ) {
      this.startListening()
  }

  on(keys: Key[] | KeyCombo[], callback: Handler) {
      const combos = this.toCombos(keys)

      combos.forEach(combo => {
          this.registerComboCallback(combo, callback)
      })
  }

  startListening() {
      this.domNode.addEventListener('keydown', this.handleKeyDown)
      this.domNode.addEventListener('keyup', this.handleKeyUp)
  }

  stopListening() {
      this.domNode.removeEventListener('keydown', this.handleKeyDown)
      this.domNode.removeEventListener('keyup', this.handleKeyUp)
  }

  clear() {
      this.stopListening()
      this.mapCombosToHandlers.clear()
      this.pressedKeys.clear()
  }

  private handleKeyDown = (event: KeyboardEvent) => {
      this.pressedKeys.add(event.keyCode)

      this.mapCombosToHandlers.forEach((handlers, combo) => {
          if (this.isComboPressed(combo)) {
              handlers.forEach(handler => handler(event))
          }
      })
  }

  private handleKeyUp = (event: KeyboardEvent) => {
      this.pressedKeys.delete(event.keyCode)
  }

  private isComboPressed(combo: number[]) {
      let result = true

      combo.forEach(key => {
          if (!this.pressedKeys.has(key)) {
              result = false
          }
      })

      return result
  }

  private registerComboCallback(combo: Array<Key>, callback: Handler) {
      if (!this.mapCombosToHandlers.has(combo)) {
          this.mapCombosToHandlers.set(combo, [])
      }

      const handlers = this.mapCombosToHandlers.get(combo)

      handlers!.push(callback)
  }

  private toCombos(keys: KeyCombo[] | Key[]) {
      if (keys.length === 0) {
          return []
      }

      const isKeys = !Array.isArray(keys[0])
      let combos: KeyCombo[] = []

      if (isKeys) {
          combos = (keys as Key[]).map(key => [key])
      } else {
          combos = keys as KeyCombo[]
          combos = combos.filter(combo => combo.length > 0)
      }

      return combos
  }
}