Shareousel cursor reader

A building block for the payload toggling functinality -- a
bi-directional cursor reaer that starts reading URIs from the cursor
starting at a specified position ignoring all items thad does not match
a given predicate.

Bug: 302691505
Test: IntentResolver-tests-unit
Change-Id: I83d40435f4b73c73f6d8b49080645a008d34727b

2 files changed, 111 insertions, 0 deletions

diff --git a/java/src/com/android/intentresolver/contentpreview/CursorUriReader.kt b/java/src/com/android/intentresolver/contentpreview/CursorUriReader.kt
new file mode 100644
index 00000000..30495b8b
--- /dev/null
+++ b/java/src/com/android/intentresolver/contentpreview/CursorUriReader.kt
@@ -0,0 +1,99 @@
+/*
+ * Copyright 2024 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.intentresolver.contentpreview
+
+import android.database.Cursor
+import android.net.Uri
+import android.util.Log
+import android.util.SparseArray
+
+private const val TAG = ContentPreviewUi.TAG
+
+/**
+ * A bi-directional cursor reader. Reads URI from the [cursor] starting from the given [startPos],
+ * filters items by [predicate].
+ */
+class CursorUriReader(
+    private val cursor: Cursor,
+    startPos: Int,
+    private val pageSize: Int,
+    private val predicate: (Uri) -> Boolean,
+) : PayloadToggleInteractor.CursorReader {
+    override val count = cursor.count
+    // the first position of the next unread page on the right
+    private var rightPos = startPos.coerceIn(0, count)
+    // the first position of the next from the leftmost unread page on the left
+    private var leftPos = rightPos
+
+    override val hasMoreBefore
+        get() = leftPos > 0
+
+    override val hasMoreAfter
+        get() = rightPos < count
+
+    override fun readPageAfter(): SparseArray<Uri> {
+        if (!hasMoreAfter) return SparseArray()
+        if (!cursor.moveToPosition(rightPos)) {
+            rightPos = count
+            Log.w(TAG, "Failed to move the cursor to position $rightPos, stop reading the cursor")
+            return SparseArray()
+        }
+        val result = SparseArray<Uri>(pageSize)
+        do {
+            cursor
+                .getString(0)
+                ?.let(Uri::parse)
+                ?.takeIf { predicate(it) }
+                ?.let { uri -> result.append(rightPos, uri) }
+            rightPos++
+        } while (result.size() < pageSize && cursor.moveToNext())
+        maybeCloseCursor()
+        return result
+    }
+
+    override fun readPageBefore(): SparseArray<Uri> {
+        if (!hasMoreBefore) return SparseArray()
+        val startPos = maxOf(0, leftPos - pageSize)
+        if (!cursor.moveToPosition(startPos)) {
+            leftPos = 0
+            Log.w(TAG, "Failed to move the cursor to position $startPos, stop reading cursor")
+            return SparseArray()
+        }
+        val result = SparseArray<Uri>(leftPos - startPos)
+        for (pos in startPos ..< leftPos) {
+            cursor
+                .getString(0)
+                ?.let(Uri::parse)
+                ?.takeIf { predicate(it) }
+                ?.let { uri -> result.append(pos, uri) }
+            if (!cursor.moveToNext()) break
+        }
+        leftPos = startPos
+        maybeCloseCursor()
+        return result
+    }
+
+    private fun maybeCloseCursor() {
+        if (!hasMoreBefore && !hasMoreAfter) {
+            close()
+        }
+    }
+
+    override fun close() {
+        cursor.close()
+    }
+}
diff --git a/java/src/com/android/intentresolver/contentpreview/PayloadToggleInteractor.kt b/java/src/com/android/intentresolver/contentpreview/PayloadToggleInteractor.kt
index 0e6d3869..87f53e85 100644
--- a/java/src/com/android/intentresolver/contentpreview/PayloadToggleInteractor.kt
+++ b/java/src/com/android/intentresolver/contentpreview/PayloadToggleInteractor.kt
@@ -17,6 +17,8 @@
 package com.android.intentresolver.contentpreview
 
 import android.net.Uri
+import android.util.SparseArray
+import java.io.Closeable
 import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.flowOf
@@ -48,6 +50,16 @@ class PayloadToggleInteractor {
     private data class Item(
         val previewUri: Uri?,
     )
+
+    interface CursorReader : Closeable {
+        val count: Int
+        val hasMoreBefore: Boolean
+        val hasMoreAfter: Boolean
+
+        fun readPageAfter(): SparseArray<Uri>
+
+        fun readPageBefore(): SparseArray<Uri>
+    }
 }
 
 class PayloadTogglePreviewInteractor(