package chats.data.local.paging

import androidx.paging.PagingSource
import androidx.paging.PagingState
import chats.data.local.dao.MessageDao
import chats.data.local.database.MessageEntity

/**
 * PagingSource для загрузки сообщений из Room Database
 */
class MessagePagingSource(
    private val chatId: String,
    private val messageDao: MessageDao
) : PagingSource<Int, MessageEntity>() {

    companion object {
        private const val PAGE_SIZE = 30
    }

    override suspend fun load(params: LoadParams<Int>): LoadResult<Int, MessageEntity> {
        return try {
            val position = params.key ?: 0 // Начинаем с 0
            
            val messages = messageDao.getMessagesPaged(
                chatId = chatId,
                offset = position,
                limit = PAGE_SIZE
            )

            LoadResult.Page(
                data = messages,
                prevKey = if (position > 0) position - PAGE_SIZE else null,
                nextKey = if (messages.isEmpty()) null else position + PAGE_SIZE
            )
        } catch (e: Exception) {
            LoadResult.Error(e)
        }
    }

    override fun getRefreshKey(state: PagingState<Int, MessageEntity>): Int? {
        return state.anchorPosition
    }
}