import React, { useState } from 'react'
import { DragDropContext, Droppable, Draggable } from '@hello-pangea/dnd'

// fake data generator
const getItems = (count, offset = 0) =>
  Array.from({ length: count }, (v, k) => k).map((k) => ({
    id: `item-${k + offset}-${new Date().getTime()}`,
    content: `item ${k + offset}`,
  }))

const reorder = (list, startIndex, endIndex) => {
  const result = Array.from(list)
  const [removed] = result.splice(startIndex, 1)
  result.splice(endIndex, 0, removed)
  return result
}

// move item from one list to another list.
const move = (source, destination, droppableSource, droppableDestination) => {
  const sourceClone = Array.from(source)
  const destClone = Array.from(destination)
  const [removed] = sourceClone.splice(droppableSource.index, 1)
  destClone.splice(droppableDestination.index, 0, removed)
  const result = {}
  result[droppableSource.droppableId] = sourceClone
  result[droppableDestination.droppableId] = destClone
  return result
}

const getItemStyle = (isDragging, draggableStyle) => ({
  userSelect: 'none',
  padding: '1rem',
  margin: `0 0 1rem 0`,
  background: isDragging ? 'lightgreen' : 'grey',
  ...draggableStyle,
})

const getListStyle = (isDraggingOver) => ({
  background: isDraggingOver ? 'lightblue' : 'lightgrey',
  padding: '1rem',
  width: '16rem',
})

export default function App() {
  const [state, setState] = useState([getItems(4), getItems(4, 4)])

  function onDragEnd(result) {
    const { source, destination } = result
    if (!destination) {
      return
    }
    const sInd = +source.droppableId
    const dInd = +destination.droppableId
    if (sInd === dInd) {
      const items = reorder(state[sInd], source.index, destination.index)
      const newState = [...state]
      newState[sInd] = items
      setState(newState)
    } else {
      const result = move(state[sInd], state[dInd], source, destination)
      const newState = [...state]
      newState[sInd] = result[sInd]
      newState[dInd] = result[dInd]
      setState(newState.filter((group) => group.length))
    }
  }

  return (
    <div>
      <div style={{ display: 'flex' }}>
        <DragDropContext onDragEnd={onDragEnd}>
          {state.map((el, ind) => (
            <Droppable key={ind} droppableId={`${ind}`}>
              {(provided, snapshot) => (
                <div ref={provided.innerRef} style={getListStyle(snapshot.isDraggingOver)} {...provided.droppableProps}>
                  {el.map((item, index) => (
                    <Draggable key={item.id} draggableId={item.id} index={index}>
                      {(provided, snapshot) => (
                        <div
                          ref={provided.innerRef}
                          {...provided.draggableProps}
                          {...provided.dragHandleProps}
                          style={getItemStyle(snapshot.isDragging, provided.draggableProps.style)}>
                          <div
                            style={{
                              display: 'flex',
                              justifyContent: 'space-around',
                            }}>
                            {item.content}
                          </div>
                        </div>
                      )}
                    </Draggable>
                  ))}
                  {provided.placeholder}
                </div>
              )}
            </Droppable>
          ))}
        </DragDropContext>
      </div>
    </div>
  )
}