add changeset comment tracking and message notification bubble on startup

lib/services/changeset_comments_service.dart

@@ -0,0 +1,182 @@
+import 'dart:convert';
+import 'package:shared_preferences/shared_preferences.dart';
+import '../state/settings_state.dart';
+import 'http_client.dart';
+
+/// Tracks unread comments on the user's own changesets.
+///
+/// The OSM API has no "read" concept for changeset comments, so we track it
+/// ourselves: we remember the `comments_count` we last saw for each of the
+/// user's recent changesets, and flag a changeset as having unread comments
+/// if it now has a higher count than what we last recorded.
+///
+/// This only looks at the user's most recent 100 changesets (the OSM API's
+/// max page size, and it doesn't support simple offset paging). If a
+/// changeset receives a new comment and then ages out of that window
+/// entirely before the next check, we will miss it - an accepted limitation
+/// of polling a bounded recent-activity window rather than a real
+/// notification feed.
+class ChangesetCommentsService {
+  static const _cacheDuration = Duration(minutes: 5);
+  final _client = UserAgentClient();
+
+  DateTime? _lastCheck;
+  int? _lastResult; // ID of changeset with unread comments, or null if none
+  bool _lastResultIsSet = false; // whether _lastResult holds a valid cached value
+  UploadMode? _lastMode;
+
+  /// Returns the ID of a changeset with more comments now than the last
+  /// time [markRead] was called for this upload mode, or null if there are
+  /// none (or if not logged in, in simulate mode, or on error). When
+  /// multiple changesets have new comments, returns the most recent one
+  /// (the API returns changesets newest-first).
+  Future<int?> getUnreadChangesetId({
+    required String? username,
+    required UploadMode uploadMode,
+    bool forceRefresh = false,
+  }) async {
+    if (uploadMode == UploadMode.simulate) return null;
+    if (username == null || username.isEmpty) return null;
+
+    if (!forceRefresh &&
+        _lastResultIsSet &&
+        _lastMode == uploadMode &&
+        _lastCheck != null &&
+        DateTime.now().difference(_lastCheck!) < _cacheDuration) {
+      return _lastResult;
+    }
+
+    try {
+      final current = await _fetchCommentCounts(username, uploadMode);
+      if (current == null) return null;
+
+      final seen = await _loadSeenCounts(uploadMode);
+      // current is built from the API response, which is ordered
+      // newest-first, so the first match found is the most recent one.
+      int? unreadId;
+      for (final entry in current.entries) {
+        if (entry.value > (seen[entry.key] ?? 0)) {
+          unreadId = entry.key;
+          break;
+        }
+      }
+
+      _lastCheck = DateTime.now();
+      _lastResult = unreadId;
+      _lastResultIsSet = true;
+      _lastMode = uploadMode;
+
+      return unreadId;
+    } catch (e) {
+      return null;
+    }
+  }
+
+  /// Mark all currently-visible changeset comments as read by saving the
+  /// current comment counts as the new baseline.
+  Future<void> markRead({
+    required String? username,
+    required UploadMode uploadMode,
+  }) async {
+    if (uploadMode == UploadMode.simulate) return;
+    if (username == null || username.isEmpty) return;
+
+    try {
+      final current = await _fetchCommentCounts(username, uploadMode);
+      if (current == null) return;
+
+      await _saveSeenCounts(uploadMode, current);
+
+      // Update in-memory cache so getUnreadChangesetId() doesn't need to
+      // re-fetch immediately after marking read.
+      _lastCheck = DateTime.now();
+      _lastResult = null;
+      _lastResultIsSet = true;
+      _lastMode = uploadMode;
+    } catch (e) {
+      // Best-effort - if this fails the badge will just persist until the
+      // next successful mark-read attempt.
+    }
+  }
+
+  /// Clear cached state (useful on logout or upload mode change).
+  void clearCache() {
+    _lastCheck = null;
+    _lastResult = null;
+    _lastResultIsSet = false;
+    _lastMode = null;
+  }
+
+  /// Build the URL to the given changeset on the OSM website for the given
+  /// upload mode.
+  String getChangesetUrl(int changesetId, UploadMode uploadMode) {
+    switch (uploadMode) {
+      case UploadMode.production:
+        return 'https://www.openstreetmap.org/changeset/$changesetId';
+      case UploadMode.sandbox:
+        return 'https://master.apis.dev.openstreetmap.org/changeset/$changesetId';
+      case UploadMode.simulate:
+        return 'https://www.openstreetmap.org/changeset/$changesetId';
+    }
+  }
+
+  /// Fetches the user's most recent changesets and returns a map of
+  /// changeset ID -> comments_count. Returns null on any error.
+  Future<Map<int, int>?> _fetchCommentCounts(
+    String username,
+    UploadMode uploadMode,
+  ) async {
+    final apiHost = _getApiHost(uploadMode);
+    final response = await _client.get(
+      Uri.parse('$apiHost/api/0.6/changesets.json?display_name=${Uri.encodeQueryComponent(username)}'),
+    );
+
+    if (response.statusCode != 200) return null;
+
+    final data = jsonDecode(response.body);
+    final changesets = data['changesets'];
+    if (changesets is! List) return null;
+
+    final result = <int, int>{};
+    for (final cs in changesets) {
+      final id = cs['id'];
+      final count = cs['comments_count'];
+      if (id is int && count is int) {
+        result[id] = count;
+      }
+    }
+    return result;
+  }
+
+  Future<Map<int, int>> _loadSeenCounts(UploadMode uploadMode) async {
+    final prefs = await SharedPreferences.getInstance();
+    final json = prefs.getString(_prefsKey(uploadMode));
+    if (json == null) return {};
+    try {
+      final decoded = jsonDecode(json) as Map<String, dynamic>;
+      return decoded.map((k, v) => MapEntry(int.parse(k), v as int));
+    } catch (e) {
+      return {};
+    }
+  }
+
+  Future<void> _saveSeenCounts(UploadMode uploadMode, Map<int, int> counts) async {
+    final prefs = await SharedPreferences.getInstance();
+    final encoded = jsonEncode(counts.map((k, v) => MapEntry(k.toString(), v)));
+    await prefs.setString(_prefsKey(uploadMode), encoded);
+  }
+
+  String _prefsKey(UploadMode uploadMode) =>
+      'changeset_comments_seen_${uploadMode.name}';
+
+  String _getApiHost(UploadMode uploadMode) {
+    switch (uploadMode) {
+      case UploadMode.production:
+        return 'https://api.openstreetmap.org';
+      case UploadMode.sandbox:
+        return 'https://api06.dev.openstreetmap.org';
+      case UploadMode.simulate:
+        return 'https://api.openstreetmap.org';
+    }
+  }
+}