Realm: add PagedList implementation

matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/database/pagedlist/RealmTiledDataSource.kt

@@ -0,0 +1,67 @@
+package org.matrix.android.sdk.internal.database.pagedlist
+
+import androidx.paging.DataSource
+import io.realm.kotlin.Realm
+import io.realm.kotlin.notifications.UpdatedResults
+import io.realm.kotlin.query.RealmQuery
+import io.realm.kotlin.query.RealmResults
+import io.realm.kotlin.types.RealmObject
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.SupervisorJob
+import kotlinx.coroutines.cancelChildren
+import kotlinx.coroutines.flow.launchIn
+import kotlinx.coroutines.flow.onEach
+
+internal class RealmTiledDataSource<T : RealmObject> internal constructor(
+        realm: Realm,
+        queryBuilder: (Realm) -> RealmQuery<T>,
+        coroutineScope: CoroutineScope
+) :
+        TiledDataSource<T>() {
+
+    class Factory<T : RealmObject>(
+            private val realm: Realm,
+            private val queryBuilder: (Realm) -> RealmQuery<T>,
+            private val coroutineScope: CoroutineScope,
+    ) : DataSource.Factory<Int, T>() {
+
+        override fun create(): DataSource<Int, T> {
+            val childScope = CoroutineScope(SupervisorJob() + coroutineScope.coroutineContext)
+            return RealmTiledDataSource(realm, queryBuilder, childScope)
+        }
+    }
+
+    private val results: RealmResults<T>
+
+    init {
+        addInvalidatedCallback {
+            coroutineScope.coroutineContext.cancelChildren()
+        }
+        results = queryBuilder(realm).find()
+        results.asFlow()
+                .onEach { resultsChange ->
+                    when (resultsChange) {
+                        is UpdatedResults -> invalidate()
+                        else -> Unit
+                    }
+                }
+                .launchIn(coroutineScope)
+    }
+
+    override fun countItems(): Int {
+        return results.size
+    }
+
+    override fun loadRange(startPosition: Int, count: Int): List<T> {
+        val size = countItems()
+        if (size == 0) return emptyList()
+        return buildList {
+            val endPosition = minOf(startPosition + count, size)
+            for (position in startPosition until endPosition) {
+                results.getOrNull(position)?.also { item ->
+                    add(item)
+                }
+            }
+        }
+    }
+}

matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/database/pagedlist/TiledDataSource.kt

@@ -0,0 +1,42 @@
+package org.matrix.android.sdk.internal.database.pagedlist
+
+import android.annotation.SuppressLint
+import androidx.paging.PositionalDataSource
+
+@Suppress("DEPRECATION")
+public abstract class TiledDataSource<T : Any> : PositionalDataSource<T>() {
+
+  public abstract fun countItems(): Int
+
+  public abstract fun loadRange(startPosition: Int, count: Int): List<T>?
+
+  @SuppressLint("RestrictedApi") // For computeInitialLoadPosition, computeInitialLoadSize
+  override fun loadInitial(
+    params: LoadInitialParams,
+    callback: LoadInitialCallback<T>
+  ) {
+    val totalCount = countItems()
+    if (totalCount == 0) {
+      callback.onResult(emptyList(), 0, 0)
+      return
+    }
+    val firstLoadPosition = computeInitialLoadPosition(params, totalCount)
+    val firstLoadSize = computeInitialLoadSize(params, firstLoadPosition, totalCount)
+
+    val list = loadRange(firstLoadPosition, firstLoadSize)
+    if (list != null && list.size == firstLoadSize) {
+      callback.onResult(list, firstLoadPosition, totalCount)
+    } else {
+      invalidate()
+    }
+  }
+
+  override fun loadRange(params: LoadRangeParams, callback: LoadRangeCallback<T>) {
+    val list = loadRange(params.startPosition, params.loadSize)
+    if (list != null) {
+      callback.onResult(list)
+    } else {
+      invalidate()
+    }
+  }
+}