@ExperimentalPagingApi
class RoomRemoteMediator(private val database: RoomTestDatabase)
    : RemoteMediator<Int, RoomEntity>(){
    private val userDao = database.roomDao()

    override suspend fun load(
        loadType: LoadType,
        state: PagingState<Int, RoomEntity>
    ): MediatorResult {
        return try {
            val loadKey = when (loadType) {
                //表示 刷新.
                LoadType.REFRESH -> null    //loadKey 是页码标志, null代表第一页;
                LoadType.PREPEND ->
                    return MediatorResult.Success(endOfPaginationReached = true)
                LoadType.APPEND -> {
                    val lastItem = state.lastItemOrNull()
                    val first = state.firstItemOrNull()

                    Log.d("pppppppppppppppppp", "last index=${lastItem?.index}  id=${lastItem?.id}")
                    Log.d("pppppppppppppppppp", "first index=${first?.index}  id=${first?.id}")

                    //这里用 NoMoreException 方式显示没有更多;
                    if(index>=15){
                        return MediatorResult.Error(NoMoreException())
                    }

                    if (lastItem == null) {
                        return MediatorResult.Success(
                            endOfPaginationReached = true
                        )
                    }

                    lastItem.index
                }
            }

            //页码标志, 官方文档用的 lastItem.index 方式,  但这方式似乎有问题,第一页last.index 应当是9. 但博主这里总是0 ,
            //也可以数据库存储.  SharePrefences等;
            //如果数据库数据仅用作 没有网络时显示.  不设置有效状态或有效时长时,  则可以直接在 RemoteMediator 页码计数;
//            val response = ApiManager.INSTANCE.mApi.getDynamicList()
            val data = createListData(loadKey)

            database.withTransaction {
                if (loadType == LoadType.REFRESH) {
                    userDao.clearAll()
                }
                userDao.insertAll(data)
            }

            //endOfPaginationReached 表示 是否最后一页;  如果用 NoMoreException(没有更多) 方式, 则必定false
            MediatorResult.Success(
                endOfPaginationReached = false
            )
        } catch (e: IOException) {
            MediatorResult.Error(e)
        } catch (e: HttpException) {
            MediatorResult.Error(e)
        }
    }

    private var index = 0
    private fun createListData(min: Int?) : MutableList<RoomEntity>{
        val result = mutableListOf<RoomEntity>()
        Log.d("pppppppppppppppppp", "啦数据了当前index=$index")
        repeat(10){
//            val p = min ?: 0 + it
            index++
            val p = index
            result.add(RoomEntity().apply {
                id = "test$p"
                name = "小明$p"
                title = "干哈呢$p"
                index = p
            })
        }
        return result
    }
}