Improve timeline top-merge refresh behavior

shared/src/commonMain/kotlin/dev/dimension/flare/data/datasource/mastodon/HomeTimelineRemoteMediator.kt

@@ -4,6 +4,7 @@ import androidx.paging.ExperimentalPagingApi
 import dev.dimension.flare.data.datasource.microblog.paging.CacheableRemoteLoader
 import dev.dimension.flare.data.datasource.microblog.paging.PagingRequest
 import dev.dimension.flare.data.datasource.microblog.paging.PagingResult
+import dev.dimension.flare.data.datasource.microblog.paging.RefreshBehavior
 import dev.dimension.flare.data.network.mastodon.MastodonService
 import dev.dimension.flare.model.MicroBlogKey
 import dev.dimension.flare.ui.model.UiTimelineV2
@@ -19,6 +20,9 @@ internal class HomeTimelineRemoteMediator(
     override val supportPrepend: Boolean
         get() = true
 
+    override val refreshBehavior: RefreshBehavior
+        get() = RefreshBehavior.MergeTop
+
     override suspend fun load(
         pageSize: Int,
         request: PagingRequest,

shared/src/commonMain/kotlin/dev/dimension/flare/data/datasource/mastodon/ListTimelineRemoteMediator.kt

@@ -4,6 +4,7 @@ import androidx.paging.ExperimentalPagingApi
 import dev.dimension.flare.data.datasource.microblog.paging.CacheableRemoteLoader
 import dev.dimension.flare.data.datasource.microblog.paging.PagingRequest
 import dev.dimension.flare.data.datasource.microblog.paging.PagingResult
+import dev.dimension.flare.data.datasource.microblog.paging.RefreshBehavior
 import dev.dimension.flare.data.network.mastodon.MastodonService
 import dev.dimension.flare.model.MicroBlogKey
 import dev.dimension.flare.ui.model.UiTimelineV2
@@ -20,6 +21,9 @@ internal class ListTimelineRemoteMediator(
     override val supportPrepend: Boolean
         get() = true
 
+    override val refreshBehavior: RefreshBehavior
+        get() = RefreshBehavior.MergeTop
+
     override suspend fun load(
         pageSize: Int,
         request: PagingRequest,

shared/src/commonMain/kotlin/dev/dimension/flare/data/datasource/microblog/MixedRemoteMediator.kt

@@ -6,6 +6,7 @@ import dev.dimension.flare.data.database.cache.connect
 import dev.dimension.flare.data.datasource.microblog.paging.CacheableRemoteLoader
 import dev.dimension.flare.data.datasource.microblog.paging.PagingRequest
 import dev.dimension.flare.data.datasource.microblog.paging.PagingResult
+import dev.dimension.flare.data.datasource.microblog.paging.RefreshBehavior
 import dev.dimension.flare.data.datasource.microblog.paging.ReportableRemoteLoader
 import dev.dimension.flare.ui.model.UiTimelineV2
 import kotlinx.coroutines.async
@@ -52,7 +53,7 @@ internal class MixedRemoteMediator(
                                     reportError?.invoke(it)
                                     PagingResult(endOfPaginationReached = true)
                                 }.let {
-                                    SubResponse(subRequest.mediator, it)
+                                    SubResponse(subRequest.mediator, subRequest.request, it)
                                 }
                             }
                         }.awaitAll()
@@ -72,7 +73,7 @@ internal class MixedRemoteMediator(
 
                 database.connect {
                     response.forEach {
-                        saveSubResponse(request, it)
+                        saveSubResponse(it)
                     }
                 }
 
@@ -114,16 +115,23 @@ internal class MixedRemoteMediator(
                     ?.prevKey
                     ?.let(PagingRequest::Prepend)
 
-            is PagingRequest.Refresh -> PagingRequest.Refresh
+            is PagingRequest.Refresh ->
+                if (mediator.refreshBehavior == RefreshBehavior.MergeTop && mediator.supportPrepend) {
+                    database
+                        .pagingTimelineDao()
+                        .getPagingKey(subKey(mediator))
+                        ?.prevKey
+                        ?.let(PagingRequest::Prepend)
+                        ?: PagingRequest.Refresh
+                } else {
+                    PagingRequest.Refresh
+                }
         }?.let {
             SubRequest(mediator, it)
         }
 
-    private suspend fun saveSubResponse(
-        request: PagingRequest,
-        subResponse: SubResponse,
-    ) {
-        val (mediator, result) = subResponse
+    private suspend fun saveSubResponse(subResponse: SubResponse) {
+        val (mediator, request, result) = subResponse
         if (request is PagingRequest.Prepend && result.previousKey != null) {
             database.pagingTimelineDao().updatePagingKeyPrevKey(
                 pagingKey = subKey(mediator),
@@ -157,6 +165,7 @@ internal class MixedRemoteMediator(
 
     private data class SubResponse(
         val mediator: CacheableRemoteLoader<UiTimelineV2>,
+        val request: PagingRequest,
         val result: PagingResult<UiTimelineV2>,
     )
 }

shared/src/commonMain/kotlin/dev/dimension/flare/data/datasource/microblog/paging/BasePagingRemoteMediator.kt

@@ -63,26 +63,7 @@ internal abstract class BasePagingRemoteMediator<T : Any, R : Any>(
                 request = request,
             )
         database.connect {
-            if (loadType == LoadType.REFRESH) {
-                database.pagingTimelineDao().deletePagingKey(pagingKey)
-                database.pagingTimelineDao().insertPagingKey(
-                    DbPagingKey(
-                        pagingKey = pagingKey,
-                        nextKey = result.nextKey,
-                        prevKey = result.previousKey,
-                    ),
-                )
-            } else if (loadType == LoadType.PREPEND && result.previousKey != null) {
-                database.pagingTimelineDao().updatePagingKeyPrevKey(
-                    pagingKey = pagingKey,
-                    prevKey = result.previousKey,
-                )
-            } else if (loadType == LoadType.APPEND && result.nextKey != null) {
-                database.pagingTimelineDao().updatePagingKeyNextKey(
-                    pagingKey = pagingKey,
-                    nextKey = result.nextKey,
-                )
-            }
+            updatePagingKeys(loadType, request, result)
             onSaveCache(request, result.data)
         }
         return MediatorResult.Success(
@@ -100,6 +81,33 @@ internal abstract class BasePagingRemoteMediator<T : Any, R : Any>(
         request: PagingRequest,
     ): PagingResult<R>
 
+    protected open suspend fun updatePagingKeys(
+        loadType: LoadType,
+        request: PagingRequest,
+        result: PagingResult<R>,
+    ) {
+        if (loadType == LoadType.REFRESH) {
+            database.pagingTimelineDao().deletePagingKey(pagingKey)
+            database.pagingTimelineDao().insertPagingKey(
+                DbPagingKey(
+                    pagingKey = pagingKey,
+                    nextKey = result.nextKey,
+                    prevKey = result.previousKey,
+                ),
+            )
+        } else if (loadType == LoadType.PREPEND && result.previousKey != null) {
+            database.pagingTimelineDao().updatePagingKeyPrevKey(
+                pagingKey = pagingKey,
+                prevKey = result.previousKey,
+            )
+        } else if (loadType == LoadType.APPEND && result.nextKey != null) {
+            database.pagingTimelineDao().updatePagingKeyNextKey(
+                pagingKey = pagingKey,
+                nextKey = result.nextKey,
+            )
+        }
+    }
+
     protected abstract suspend fun onSaveCache(
         request: PagingRequest,
         data: List<R>,

shared/src/commonMain/kotlin/dev/dimension/flare/data/datasource/microblog/paging/CacheableRemoteLoader.kt

@@ -1,9 +1,16 @@
 package dev.dimension.flare.data.datasource.microblog.paging
 
+internal enum class RefreshBehavior {
+    Replace,
+    MergeTop,
+}
+
 internal interface CacheableRemoteLoader<T : Any> : RemoteLoader<T> {
     val pagingKey: String
     val supportPrepend: Boolean
         get() = false
+    val refreshBehavior: RefreshBehavior
+        get() = RefreshBehavior.Replace
 }
 
 internal interface ReportableRemoteLoader {