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lib/api/image_provider.dart

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+import 'dart:typed_data';
+
+import 'package:flutter/material.dart';
+import 'package:riverpod_annotation/riverpod_annotation.dart';
+import 'package:shelfsdk/audiobookshelf_api.dart';
+import 'package:whispering_pages/api/api_provider.dart';
+import 'package:whispering_pages/db/cache_manager.dart';
+
+/// provides cover images for the audiobooks
+///
+/// is a stream provider that provides cover images first from the cache then from the server
+/// if the image is not found in the cache, it will be fetched from the server and saved to the cache
+/// if the image is not found in the server it will throw an error
+
+part 'image_provider.g.dart';
+
+@riverpod
+class CoverImage extends _$CoverImage {
+  @override
+  Stream<Uint8List> build(LibraryItem libraryItem) async* {
+    final api = ref.watch(authenticatedApiProvider);
+
+    // try to get the image from the cache
+    final file = await imageCacheManager.getFileFromCache(libraryItem.id);
+
+    if (file != null) {
+      // if the image is in the cache, yield it
+      yield await file.file.readAsBytes();
+      // return if no need to fetch from the server
+      if (libraryItem.updatedAt.isBefore(await file.file.lastModified())) {
+        return;
+      } else {
+        debugPrint(
+          'cover image stale for ${libraryItem.id}, fetching from the server',
+        );
+      }
+    }
+
+    // check if the image is in the cache
+    final coverImage = await api.items.getCover(
+      libraryItemId: libraryItem.id,
+      parameters: const GetImageReqParams(width: 500),
+    );
+    // save the image to the cache
+    final newFile = await imageCacheManager.putFile(
+      libraryItem.id,
+      coverImage ?? Uint8List(0),
+      key: libraryItem.id,
+    );
+    debugPrint(
+      'cover image fetched for for ${libraryItem.id}, file time: ${await newFile.lastModified()}',
+    );
+    yield coverImage ?? Uint8List(0);
+  }
+}