Add BandwidthService and endpoint for retrieving bandwidth statistics

lib/services/bandwidth_service.dart

@@ -0,0 +1,124 @@
+import 'dart:io';
+import 'dart:convert';
+
+class BandwidthService {
+  // In-memory collector state: collector_id -> peer_public_key -> {upload_last_seen, download_last_seen}
+  static final Map<String, Map<String, Map<String, int>>> _collectorStates = {};
+
+  /// Gets bandwidth stats for a collector
+  /// If collector_id is provided, returns incremental usage since last call
+  /// If no collector_id, returns total cumulative usage from WireGuard
+  static Future<Map<String, Map<String, int>>> getBandwidthStats(String? collectorId) async {
+    final currentStats = await _getCurrentWireGuardStats();
+    
+    if (collectorId == null || collectorId.isEmpty) {
+      // No collector ID - return cumulative totals
+      return currentStats;
+    }
+    
+    // Collector ID provided - calculate increments
+    return _calculateIncrementalStats(collectorId, currentStats);
+  }
+
+  /// Gets current WireGuard traffic statistics using 'wg show wg0 dump'
+  static Future<Map<String, Map<String, int>>> _getCurrentWireGuardStats() async {
+    try {
+      final result = await Process.run('wg', ['show', 'wg0', 'dump']);
+      if (result.exitCode != 0) {
+        throw Exception('Failed to get WireGuard stats: ${result.stderr}');
+      }
+      
+      final output = result.stdout.toString().trim();
+      final lines = output.split('\n');
+      
+      final stats = <String, Map<String, int>>{};
+      
+      // Skip first line (server info) and process peer lines
+      for (int i = 1; i < lines.length; i++) {
+        final line = lines[i].trim();
+        if (line.isEmpty) continue;
+        
+        final parts = line.split('\t');
+        if (parts.length >= 7) {
+          final publicKey = parts[0];
+          final uploadBytes = int.tryParse(parts[5]) ?? 0;
+          final downloadBytes = int.tryParse(parts[6]) ?? 0;
+          
+          stats[publicKey] = {
+            'upload_bytes': uploadBytes,
+            'download_bytes': downloadBytes,
+          };
+        }
+      }
+      
+      return stats;
+    } catch (e) {
+      print('Error getting WireGuard stats: $e');
+      return {};
+    }
+  }
+
+  /// Calculates incremental stats for a collector
+  static Map<String, Map<String, int>> _calculateIncrementalStats(
+    String collectorId, 
+    Map<String, Map<String, int>> currentStats
+  ) {
+    // Initialize collector state if it doesn't exist
+    _collectorStates[collectorId] ??= {};
+    
+    final collectorState = _collectorStates[collectorId]!;
+    final incrementalStats = <String, Map<String, int>>{};
+    
+    for (final entry in currentStats.entries) {
+      final publicKey = entry.key;
+      final currentUpload = entry.value['upload_bytes'] ?? 0;
+      final currentDownload = entry.value['download_bytes'] ?? 0;
+      
+      // Get last seen values for this collector and peer
+      final lastSeen = collectorState[publicKey] ?? {'upload_bytes': 0, 'download_bytes': 0};
+      final lastSeenUpload = lastSeen['upload_bytes'] ?? 0;
+      final lastSeenDownload = lastSeen['download_bytes'] ?? 0;
+      
+      // Calculate increments (handle potential WireGuard resets)
+      final uploadIncrement = _calculateSafeIncrement(currentUpload, lastSeenUpload);
+      final downloadIncrement = _calculateSafeIncrement(currentDownload, lastSeenDownload);
+      
+      // Only include peers with non-zero usage (optimization)
+      if (uploadIncrement > 0 || downloadIncrement > 0) {
+        incrementalStats[publicKey] = {
+          'upload_bytes': uploadIncrement,
+          'download_bytes': downloadIncrement,
+        };
+      }
+      
+      // Update collector state with current values
+      collectorState[publicKey] = {
+        'upload_bytes': currentUpload,
+        'download_bytes': currentDownload,
+      };
+    }
+    
+    return incrementalStats;
+  }
+
+  /// Safely calculates increment, handling WireGuard resets
+  static int _calculateSafeIncrement(int current, int lastSeen) {
+    if (current >= lastSeen) {
+      return current - lastSeen;
+    } else {
+      // WireGuard likely reset (server restart) - use current value as increment
+      print('WireGuard reset detected: current=$current < lastSeen=$lastSeen');
+      return current;
+    }
+  }
+
+  /// Clears collector state (for debugging/maintenance)
+  static void clearCollectorState(String collectorId) {
+    _collectorStates.remove(collectorId);
+  }
+
+  /// Gets current collector state (for debugging)
+  static Map<String, Map<String, Map<String, int>>> getCollectorStates() {
+    return Map.from(_collectorStates);
+  }
+}