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app/src/main/java/com/aiosman/riderpro/SimpleUtils.kt

@@ -0,0 +1,50 @@
+package com.aiosman.riderpro
+
+import androidx.paging.PagingSource
+import androidx.paging.PagingState
+import kotlin.math.ceil
+import kotlinx.coroutines.delay
+
+internal class TestBackend(
+    private val backendDataList: List<MomentItem>,
+    private val loadDelay: Long = 500,
+) {
+    val DataBatchSize = 5
+    class DesiredLoadResultPageResponse(val data: List<MomentItem>)
+    /** Returns [DataBatchSize] items for a key */
+    fun searchItemsByKey(key: Int): DesiredLoadResultPageResponse {
+        val maxKey = ceil(backendDataList.size.toFloat() / DataBatchSize).toInt()
+        if (key >= maxKey) {
+            return DesiredLoadResultPageResponse(emptyList())
+        }
+        val from = key * DataBatchSize
+        val to = minOf((key + 1) * DataBatchSize, backendDataList.size)
+        val currentSublist = backendDataList.subList(from, to)
+        return DesiredLoadResultPageResponse(currentSublist)
+    }
+    fun getAllData() = TestPagingSource(this, loadDelay)
+}
+internal class TestPagingSource(
+    private val backend: TestBackend,
+    private val loadDelay: Long,
+) : PagingSource<Int, MomentItem>() {
+    override suspend fun load(params: LoadParams<Int>): LoadResult<Int, MomentItem> {
+        // Simulate latency
+        delay(loadDelay)
+        val pageNumber = params.key ?: 0
+        val response = backend.searchItemsByKey(pageNumber)
+        // Since 0 is the lowest page number, return null to signify no more pages should
+        // be loaded before it.
+        val prevKey = if (pageNumber > 0) pageNumber - 1 else null
+        // This API defines that it's out of data when a page returns empty. When out of
+        // data, we return `null` to signify no more pages should be loaded
+        val nextKey = if (response.data.isNotEmpty()) pageNumber + 1 else null
+        return LoadResult.Page(data = response.data, prevKey = prevKey, nextKey = nextKey)
+    }
+    override fun getRefreshKey(state: PagingState<Int, MomentItem>): Int? {
+        return state.anchorPosition?.let {
+            state.closestPageToPosition(it)?.prevKey?.plus(1)
+                ?: state.closestPageToPosition(it)?.nextKey?.minus(1)
+        }
+    }
+}