Refactor paginated search widgets

- Implement a base class
- Override specific members

lib/widget/paginator.dart

@@ -1,8 +1,147 @@
 import "package:flutter/material.dart";
 import "package:font_awesome_flutter/font_awesome_flutter.dart";
+import 'package:infinite_scroll_pagination/infinite_scroll_pagination.dart';
+import 'package:inventree/inventree/model.dart';
+import 'package:inventree/inventree/sentry.dart';
 import "package:inventree/l10.dart";
 
 
+class PaginatedSearchState<T extends StatefulWidget> extends State<T> {
+
+  PaginatedSearchState(this.filters);
+
+  final Map<String, String> filters;
+
+  static const _pageSize = 25;
+
+  // Search query term
+  String searchTerm = "";
+
+  int resultCount = 0;
+
+  // Text controller
+  final TextEditingController searchController = TextEditingController();
+
+  // Pagination controller
+  final PagingController<int, InvenTreeModel> _pagingController = PagingController(firstPageKey: 0);
+
+  @override
+  void initState() {
+    _pagingController.addPageRequestListener((pageKey) {
+      _fetchPage(pageKey);
+    });
+
+    super.initState();
+  }
+
+  @override
+  void dispose() {
+    _pagingController.dispose();
+    super.dispose();
+  }
+
+  Future<InvenTreePageResponse?> requestPage(int limit, int offset, Map<String, String> params) async {
+
+    print("Blank request page");
+    // Default implementation returns null - must be overridden
+    return null;
+  }
+
+  Future<void> _fetchPage(int pageKey) async {
+    try {
+      Map<String, String> params = filters;
+
+      params["search"] = "${searchTerm}";
+
+      final page = await requestPage(
+        _pageSize,
+        pageKey,
+        params
+      );
+
+      int pageLength = page?.length ?? 0;
+      int pageCount = page?.count ?? 0;
+
+      final isLastPage = pageLength < _pageSize;
+
+      List<InvenTreeModel> items = [];
+
+      if (page != null) {
+        for (var result in page.results) {
+          if (result is InvenTreeModel) {
+            items.add(result);
+          }
+        }
+      }
+
+      if (isLastPage) {
+        _pagingController.appendLastPage(items);
+      } else {
+        final int nextPageKey = pageKey + pageLength;
+        _pagingController.appendPage(items, nextPageKey);
+      }
+
+      setState(() {
+        resultCount = pageCount;
+      });
+    } catch (error, stackTrace) {
+      _pagingController.error = error;
+
+      sentryReportError(error, stackTrace);
+    }
+  }
+
+  void updateSearchTerm() {
+    searchTerm = searchController.text;
+    _pagingController.refresh();
+  }
+
+  Widget buildItem(BuildContext context, InvenTreeModel item) {
+
+    // This method must be overridden by the child class
+    return ListTile(
+      title: Text("*** UNIMPLEMENTED ***"),
+      subtitle: Text("*** buildItem() is unimplemented for this widget!"),
+    );
+  }
+
+  String get noResultsText => L10().noResults;
+
+  @override
+  Widget build (BuildContext context) {
+    return Column(
+        mainAxisAlignment: MainAxisAlignment.start,
+        children: [
+          PaginatedSearchWidget(searchController, updateSearchTerm, resultCount),
+          Expanded(
+              child: CustomScrollView(
+                  shrinkWrap: true,
+                  physics: ClampingScrollPhysics(),
+                  scrollDirection: Axis.vertical,
+                  slivers: <Widget>[
+                    // TODO - Search input
+                    PagedSliverList.separated(
+                      pagingController: _pagingController,
+                      builderDelegate: PagedChildBuilderDelegate<InvenTreeModel>(
+                          itemBuilder: (context, item, index) {
+                            return buildItem(context, item);
+                          },
+                          noItemsFoundIndicatorBuilder: (context) {
+                            return NoResultsWidget(noResultsText);
+                          }
+                      ),
+                      separatorBuilder: (context, item) => const Divider(height: 1),
+                    )
+                  ]
+              )
+          )
+        ]
+    );
+  }
+
+}
+
+
 class PaginatedSearchWidget extends StatelessWidget {
 
   const PaginatedSearchWidget(this.controller, this.onChanged, this.results);