feat: home grid

2024-09-10 01:14:05 +05:30
parent 80009a77ec
commit 419d3669a2
33 changed files with 808 additions and 429 deletions
@@ -0,0 +1,64 @@
+import 'dart:math' as math;
+
+import 'package:collection/collection.dart';
+import 'package:immich_mobile/domain/interfaces/asset.interface.dart';
+import 'package:immich_mobile/domain/models/asset.model.dart';
+import 'package:immich_mobile/domain/models/render_list_element.model.dart';
+import 'package:immich_mobile/service_locator.dart';
+
+class RenderList {
+  final List<RenderListElement> elements;
+  final int totalCount;
+
+  /// global offset of assets in [_buf]
+  int _bufOffset = 0;
+
+  /// reference to batch of assets loaded from DB with offset [_bufOffset]
+  List<Asset> _buf = [];
+
+  RenderList({required this.elements, required this.totalCount});
+
+  /// Loads the requested assets from the database to an internal buffer if not cached
+  /// and returns a slice of that buffer
+  Future<List<Asset>> loadAssets(int offset, int count) async {
+    assert(offset >= 0);
+    assert(count > 0);
+    assert(offset + count <= totalCount);
+
+    // general case: we have the query to load assets via offset from the DB on demand
+    if (offset < _bufOffset || offset + count > _bufOffset + _buf.length) {
+      // the requested slice (offset:offset+count) is not contained in the cache buffer `_buf`
+      // thus, fill the buffer with a new batch of assets that at least contains the requested
+      // assets and some more
+
+      final bool forward = _bufOffset < offset;
+      // if the requested offset is greater than the cached offset, the user scrolls forward "down"
+      const batchSize = 256;
+      const oppositeSize = 64;
+
+      // make sure to load a meaningful amount of data (and not only the requested slice)
+      // otherwise, each call to [loadAssets] would result in DB call trashing performance
+      // fills small requests to [batchSize], adds some legroom into the opposite scroll direction for large requests
+      final len = math.max(batchSize, count + oppositeSize);
+      // when scrolling forward, start shortly before the requested offset...
+      // when scrolling backward, end shortly after the requested offset...
+      // ... to guard against the user scrolling in the other direction
+      // a tiny bit resulting in a another required load from the DB
+      final start = math.max(
+        0,
+        forward
+            ? offset - oppositeSize
+            : (len > batchSize ? offset : offset + count - len),
+      );
+      // load the calculated batch (start:start+len) from the DB and put it into the buffer
+      _buf =
+          await di<IAssetRepository>().fetchAssets(offset: start, limit: len);
+      _bufOffset = start;
+
+      assert(_bufOffset <= offset);
+      assert(_bufOffset + _buf.length >= offset + count);
+    }
+    // return the requested slice from the buffer (we made sure before that the assets are loaded!)
+    return _buf.slice(offset - _bufOffset, offset - _bufOffset + count);
+  }
+}