autocomplete: Add and test MentionAutocompleteQuery

This is a small step toward zulip#49, without changing any UI. Here we
have a simple function `testUser` to test whether a given User
matches a query.

Related: zulip#49

Author: chrisbobbe

lib/model/autocomplete.dart

@@ -0,0 +1,42 @@
+import '../api/model/model.dart';
+
+class MentionAutocompleteQuery {
+  MentionAutocompleteQuery(this.raw)
+    : _lowercaseWords = raw.toLowerCase().split(' ');
+
+  final String raw;
+
+  final List<String> _lowercaseWords;
+
+  bool testUser(User user) {
+    // TODO test email too, not just name
+    // TODO test with diacritics stripped, where appropriate
+
+    // TODO cache, elsewhere
+    final List<String> nameWords = user.fullName.toLowerCase().split(' ');
+
+    int nameWordsIndex = 0;
+    int queryWordsIndex = 0;
+    while (true) {
+      if (queryWordsIndex == _lowercaseWords.length) {
+        return true;
+      }
+      if (nameWordsIndex == nameWords.length) {
+        return false;
+      }
+
+      if (nameWords[nameWordsIndex].startsWith(_lowercaseWords[queryWordsIndex])) {
+        queryWordsIndex++;
+      }
+      nameWordsIndex++;
+    }
+  }
+
+  @override
+  bool operator ==(Object other) {
+    return other is MentionAutocompleteQuery && other.raw == raw;
+  }
+
+  @override
+  int get hashCode => Object.hash('MentionAutocompleteQuery', raw);
+}

test/model/autocomplete_test.dart

@@ -0,0 +1,44 @@
+import 'package:checks/checks.dart';
+import 'package:test/scaffolding.dart';
+import 'package:zulip/api/model/model.dart';
+import 'package:zulip/model/autocomplete.dart';
+
+import '../example_data.dart' as eg;
+
+void main() {
+  test('MentionAutocompleteQuery.testUser', () {
+    doCheck(String rawQuery, User user, bool expected) {
+      final result = MentionAutocompleteQuery(rawQuery).testUser(user);
+      expected ? check(result).isTrue() : check(result).isFalse();
+    }
+
+    doCheck('', eg.user(fullName: 'Full Name'), true);
+    doCheck('', eg.user(fullName: ''), true); // Unlikely case, but should not crash
+    doCheck('Full Name', eg.user(fullName: 'Full Name'), true);
+    doCheck('full name', eg.user(fullName: 'Full Name'), true);
+    doCheck('Full Name', eg.user(fullName: 'full name'), true);
+    doCheck('Full', eg.user(fullName: 'Full Name'), true);
+    doCheck('Name', eg.user(fullName: 'Full Name'), true);
+    doCheck('Full Name', eg.user(fullName: 'Fully Named'), true);
+    doCheck('Full Four', eg.user(fullName: 'Full Name Four Words'), true);
+    doCheck('Name Words', eg.user(fullName: 'Full Name Four Words'), true);
+    doCheck('Full F', eg.user(fullName: 'Full Name Four Words'), true);
+    doCheck('F Four', eg.user(fullName: 'Full Name Four Words'), true);
+    doCheck('full full', eg.user(fullName: 'Full Full Name'), true);
+    doCheck('full full', eg.user(fullName: 'Full Name Full'), true);
+
+    doCheck('F', eg.user(fullName: ''), false); // Unlikely case, but should not crash
+    doCheck('Fully Named', eg.user(fullName: 'Full Name'), false);
+    doCheck('Full Name', eg.user(fullName: 'Full'), false);
+    doCheck('Full Name', eg.user(fullName: 'Name'), false);
+    doCheck('ull ame', eg.user(fullName: 'Full Name'), false);
+    doCheck('ull Name', eg.user(fullName: 'Full Name'), false);
+    doCheck('Full ame', eg.user(fullName: 'Full Name'), false);
+    doCheck('Full Full', eg.user(fullName: 'Full Name'), false);
+    doCheck('Name Name', eg.user(fullName: 'Full Name'), false);
+    doCheck('Name Full', eg.user(fullName: 'Full Name'), false);
+    doCheck('Name Four Full Words', eg.user(fullName: 'Full Name Four Words'), false);
+    doCheck('F Full', eg.user(fullName: 'Full Name Four Words'), false);
+    doCheck('Four F', eg.user(fullName: 'Full Name Four Words'), false);
+  });
+}