import { FullGestureState, State, EventTypes } from './state'
import { GestureKey } from './config'
import { DOMHandlers, EventHandler } from './utils'

export type Handler<Key extends GestureKey, EventType = EventTypes[Key]> = (
  state: Omit<FullGestureState<Key>, 'event'> & { event: EventType }
) => any | void

// if no type is provided in the user generic for a given key
// then return the default EventTypes that key
type check<T extends AnyHandlerEventTypes, Key extends GestureKey> = undefined extends T[Key] ? EventTypes[Key] : T[Key]

export type UserHandlers<T extends AnyHandlerEventTypes = EventTypes> = {
  onDrag: Handler<'drag', check<T, 'drag'>>
  onDragStart: Handler<'drag', check<T, 'drag'>>
  onDragEnd: Handler<'drag', check<T, 'drag'>>
  onPinch: Handler<'pinch', check<T, 'pinch'>>
  onPinchStart: Handler<'pinch', check<T, 'pinch'>>
  onPinchEnd: Handler<'pinch', check<T, 'pinch'>>
  onWheel: Handler<'wheel', check<T, 'wheel'>>
  onWheelStart: Handler<'wheel', check<T, 'wheel'>>
  onWheelEnd: Handler<'wheel', check<T, 'wheel'>>
  onMove: Handler<'move', check<T, 'move'>>
  onMoveStart: Handler<'move', check<T, 'move'>>
  onMoveEnd: Handler<'move', check<T, 'move'>>
  onScroll: Handler<'scroll', check<T, 'scroll'>>
  onScrollStart: Handler<'scroll', check<T, 'scroll'>>
  onScrollEnd: Handler<'scroll', check<T, 'scroll'>>
  onHover: Handler<'hover', check<T, 'hover'>>
}

type NativeHandlersKeys = keyof Omit<DOMHandlers, keyof UserHandlers>

type GetEventType<Key extends NativeHandlersKeys> = DOMHandlers[Key] extends EventHandler<infer EventType> | undefined
  ? EventType
  : UIEvent

export type NativeHandlers<T extends AnyHandlerEventTypes = {}> = {
  [key in NativeHandlersKeys]?: (
    state: State['shared'] & { event: undefined extends T[key] ? GetEventType<key> : T[key]; args: any },
    ...args: any
  ) => void
}

// allows overriding the event type from the returned state in handlers
export type AnyHandlerEventTypes = Partial<
  {
    drag: any
    wheel: any
    scroll: any
    move: any
    pinch: any
    hover: any
  } & { [key in NativeHandlersKeys]: any }
>

export type GestureHandlers<HandlerType extends AnyHandlerEventTypes = EventTypes> = Partial<
  NativeHandlers<HandlerType> & UserHandlers<HandlerType>
>

export type InternalHandlers = { [Key in GestureKey]?: Handler<Key, any> }