rider-pro-android-app/app/src/main/java/com/aiosman/riderpro/data/MomentService.kt

package com.aiosman.riderpro.data

import androidx.paging.PagingSource
import androidx.paging.PagingState
import com.aiosman.riderpro.model.MomentItem
import com.aiosman.riderpro.test.TestDatabase
import java.io.IOException
import kotlin.math.min

interface MomentService {
    suspend fun getMomentById(id: Int): MomentItem
    suspend fun likeMoment(id: Int)
    suspend fun getMoments(
        pageNumber: Int,
        author: Int? = null,
        timelineId: Int? = null
    ): ListContainer<MomentItem>
}


class MomentPagingSource(
    private val remoteDataSource: MomentRemoteDataSource,
    private val author: Int? = null,
    private val timelineId: Int? = null
) : PagingSource<Int, MomentItem>() {
    override suspend fun load(params: LoadParams<Int>): LoadResult<Int, MomentItem> {
        return try {
            val currentPage = params.key ?: 1
            val moments = remoteDataSource.getMoments(
                pageNumber = currentPage,
                author = author,
                timelineId = timelineId
            )

            LoadResult.Page(
                data = moments.list,
                prevKey = if (currentPage == 1) null else currentPage - 1,
                nextKey = if (moments.list.isEmpty()) null else moments.page + 1
            )
        } catch (exception: IOException) {
            return LoadResult.Error(exception)
        }
    }

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

}

class MomentRemoteDataSource(
    private val momentService: MomentService,
) {
    suspend fun getMoments(
        pageNumber: Int,
        author: Int?,
        timelineId: Int?
    ): ListContainer<MomentItem> {
        return momentService.getMoments(pageNumber, author, timelineId)
    }
}


class TestMomentServiceImpl() : MomentService {
    val testMomentBackend = TestMomentBackend()

    override suspend fun getMoments(
        pageNumber: Int,
        author: Int?,
        timelineId: Int?
    ): ListContainer<MomentItem> {
        return testMomentBackend.fetchMomentItems(pageNumber, author, timelineId)
    }

    override suspend fun getMomentById(id: Int): MomentItem {
        return testMomentBackend.getMomentById(id)
    }


    override suspend fun likeMoment(id: Int) {
        testMomentBackend.likeMoment(id)
    }

}

class TestMomentBackend(
    private val loadDelay: Long = 500,
) {
    val DataBatchSize = 5
    suspend fun fetchMomentItems(
        pageNumber: Int,
        author: Int? = null,
        timelineId: Int?
    ): ListContainer<MomentItem> {
        var rawList = TestDatabase.momentData
        if (author != null) {
            rawList = rawList.filter { it.authorId == author }
        }
        if (timelineId != null) {
            val followIdList = TestDatabase.followList.filter {
                it.first == timelineId
            }.map { it.second }
            rawList = rawList.filter { it.authorId in followIdList }
        }
        val from = (pageNumber - 1) * DataBatchSize
        val to = (pageNumber) * DataBatchSize
        if (from >= rawList.size) {
            return ListContainer(
                total = rawList.size,
                page = pageNumber,
                pageSize = DataBatchSize,
                list = emptyList()
            )
        }
        val currentSublist = rawList.subList(from, min(to, rawList.size))
        // delay
        kotlinx.coroutines.delay(loadDelay)
        return ListContainer(
            total = rawList.size,
            page = pageNumber,
            pageSize = DataBatchSize,
            list = currentSublist
        )
    }

    suspend fun getMomentById(id: Int): MomentItem {
        return TestDatabase.momentData[id]
    }

    suspend fun likeMoment(id: Int) {
        val oldMoment = TestDatabase.momentData.first {
            it.id == id
        }
        val newMoment = oldMoment.copy(likeCount = oldMoment.likeCount + 1)
        TestDatabase.updateMomentById(id, newMoment)
    }

}