/**
 * Utilites for working with multiple pointer events
 */

function findEventIndex(pointers: PointerEvent[], event: PointerEvent) {
  let i = pointers.length
  while (i--) {
    if (pointers[i].pointerId === event.pointerId) {
      return i
    }
  }
  return -1
}

export function addPointer(pointers: PointerEvent[], event: PointerEvent) {
  let i
  // Add touches if applicable
  if ((event as any).touches) {
    i = 0
    for (const touch of (event as any).touches) {
      touch.pointerId = i++
      addPointer(pointers, touch)
    }
    return
  }
  i = findEventIndex(pointers, event)
  // Update if already present
  if (i > -1) {
    pointers.splice(i, 1)
  }
  pointers.push(event)
}

export function removePointer(pointers: PointerEvent[], event: PointerEvent) {
  // Add touches if applicable
  if ((event as any).touches) {
    // Remove all touches
    while (pointers.length) {
      pointers.pop()
    }
    return
  }
  const i = findEventIndex(pointers, event)
  if (i > -1) {
    pointers.splice(i, 1)
  }
}

/**
 * Calculates a center point between
 * the given pointer events, for panning
 * with multiple pointers.
 */
export function getMiddle(pointers: PointerEvent[]) {
  // Copy to avoid changing by reference
  pointers = pointers.slice(0)
  let event1: Pick<PointerEvent, 'clientX' | 'clientY'> = pointers.pop()
  let event2: PointerEvent
  while ((event2 = pointers.pop())) {
    event1 = {
      clientX: (event2.clientX - event1.clientX) / 2 + event1.clientX,
      clientY: (event2.clientY - event1.clientY) / 2 + event1.clientY
    }
  }
  return event1
}

/**
 * Calculates the distance between two points
 * for pinch zooming.
 * Limits to the first 2
 */
export function getDistance(pointers: PointerEvent[]) {
  if (pointers.length < 2) {
    return 0
  }
  const event1 = pointers[0]
  const event2 = pointers[1]
  return Math.sqrt(
    Math.pow(Math.abs(event2.clientX - event1.clientX), 2) +
      Math.pow(Math.abs(event2.clientY - event1.clientY), 2)
  )
}