Add swarm mode transport doc

lib/models/contact.dart

@@ -1,10 +1,172 @@
 export 'package:meshcore_client/meshcore_client.dart'
     show Contact, ContactType, ContactTelemetry, AdvertLocation;
 
+import 'dart:math' as math;
+import 'dart:typed_data';
 import 'package:flutter/material.dart';
 import '../l10n/app_localizations.dart';
 import 'package:meshcore_client/meshcore_client.dart';
 
+class ParsedContactRoute {
+  final String canonicalText;
+  final int hashSize;
+  final int hopCount;
+  final int encodedPathLen;
+  final int signedEncodedPathLen;
+  final Uint8List pathBytes;
+  final Uint8List paddedPathBytes;
+
+  const ParsedContactRoute({
+    required this.canonicalText,
+    required this.hashSize,
+    required this.hopCount,
+    required this.encodedPathLen,
+    required this.signedEncodedPathLen,
+    required this.pathBytes,
+    required this.paddedPathBytes,
+  });
+
+  int get byteLength => pathBytes.length;
+  String get summary => hopCount == 0
+      ? 'Direct'
+      : '$hopCount hop${hopCount == 1 ? '' : 's'} via $hashSize-byte hashes';
+}
+
+class ContactRouteFormatException implements Exception {
+  final String message;
+
+  const ContactRouteFormatException(this.message);
+
+  @override
+  String toString() => message;
+}
+
+class ContactRouteCodec {
+  static const int maxHashSize = 3;
+  static const int maxPathBytes = 64;
+  static const int _unknownDescriptor = 0xFF;
+
+  static ParsedContactRoute parse(String input) {
+    final normalized = input.trim().toUpperCase();
+    if (normalized.isEmpty) {
+      throw const ContactRouteFormatException('Route cannot be empty.');
+    }
+
+    final hopTokens = normalized
+        .split(',')
+        .map((token) => token.trim())
+        .toList();
+    if (hopTokens.any((token) => token.isEmpty)) {
+      throw const ContactRouteFormatException('Route contains an empty hop.');
+    }
+
+    final hopBytes = <List<int>>[];
+    int? hashSize;
+    for (final token in hopTokens) {
+      final compact = token.replaceAll(':', '');
+      if (compact.isEmpty || !RegExp(r'^[0-9A-F]+$').hasMatch(compact)) {
+        throw ContactRouteFormatException('Invalid hop "$token".');
+      }
+      if (compact.length.isOdd) {
+        throw ContactRouteFormatException(
+          'Hop "$token" must contain full bytes.',
+        );
+      }
+
+      final currentHashSize = compact.length ~/ 2;
+      if (currentHashSize < 1 || currentHashSize > maxHashSize) {
+        throw ContactRouteFormatException(
+          'Hop "$token" must be 1, 2, or 3 bytes.',
+        );
+      }
+
+      hashSize ??= currentHashSize;
+      if (hashSize != currentHashSize) {
+        throw const ContactRouteFormatException(
+          'All hops in a route must use the same hash size.',
+        );
+      }
+
+      final bytes = <int>[];
+      for (var i = 0; i < compact.length; i += 2) {
+        bytes.add(int.parse(compact.substring(i, i + 2), radix: 16));
+      }
+      hopBytes.add(bytes);
+    }
+
+    final resolvedHashSize = hashSize ?? 1;
+    final flatBytes = Uint8List.fromList(
+      hopBytes.expand((hop) => hop).toList(),
+    );
+    if (flatBytes.length > maxPathBytes) {
+      throw const ContactRouteFormatException(
+        'Route exceeds the 64-byte firmware limit.',
+      );
+    }
+
+    final encodedPathLen =
+        ((resolvedHashSize - 1) << 6) | (hopBytes.length & 0x3F);
+    final padded = Uint8List(maxPathBytes);
+    padded.setRange(0, flatBytes.length, flatBytes);
+
+    return ParsedContactRoute(
+      canonicalText: hopBytes
+          .map(
+            (hop) => hop
+                .map((byte) => byte.toRadixString(16).padLeft(2, '0'))
+                .join()
+                .toUpperCase(),
+          )
+          .join(','),
+      hashSize: resolvedHashSize,
+      hopCount: hopBytes.length,
+      encodedPathLen: encodedPathLen,
+      signedEncodedPathLen: toSignedDescriptor(encodedPathLen),
+      pathBytes: flatBytes,
+      paddedPathBytes: padded,
+    );
+  }
+
+  static ParsedContactRoute? fromContact(Contact contact) {
+    if (!contact.routeHasPath || contact.routeHopCount == 0) {
+      return null;
+    }
+
+    return ParsedContactRoute(
+      canonicalText: contact.routeCanonicalText,
+      hashSize: contact.routeHashSize,
+      hopCount: contact.routeHopCount,
+      encodedPathLen: contact.routeEncodedPathLen,
+      signedEncodedPathLen: contact.routeSignedPathLen,
+      pathBytes: contact.routePathBytes,
+      paddedPathBytes: _padPath(contact.routePathBytes),
+    );
+  }
+
+  static Uint8List _padPath(Uint8List bytes) {
+    final padded = Uint8List(maxPathBytes);
+    padded.setRange(0, math.min(bytes.length, maxPathBytes), bytes);
+    return padded;
+  }
+
+  static int toSignedDescriptor(int encodedPathLen) =>
+      encodedPathLen > 127 ? encodedPathLen - 256 : encodedPathLen;
+
+  static int toUnsignedDescriptor(int signedPathLen) => signedPathLen & 0xFF;
+
+  static bool isUnknownDescriptor(int signedPathLen) =>
+      toUnsignedDescriptor(signedPathLen) == _unknownDescriptor;
+
+  static bool isValidDescriptor(int signedPathLen) {
+    final raw = toUnsignedDescriptor(signedPathLen);
+    if (raw == _unknownDescriptor) return false;
+    final hashSize = ((raw >> 6) + 1);
+    if (hashSize > maxHashSize) return false;
+    final hopCount = raw & 0x3F;
+    return hopCount * hashSize <= maxPathBytes;
+  }
+}
+
 extension ContactLocalization on Contact {
   /// Returns the localized display name for special contacts (e.g. Public Channel).
   /// For all other contacts, returns [displayName].
@@ -14,4 +176,56 @@ extension ContactLocalization on Contact {
     }
     return displayName;
   }
+
+  int get routeEncodedPathLen =>
+      ContactRouteCodec.toUnsignedDescriptor(outPathLen);
+
+  int get routeSignedPathLen =>
+      ContactRouteCodec.toSignedDescriptor(routeEncodedPathLen);
+
+  bool get routeIsUnknown => ContactRouteCodec.isUnknownDescriptor(outPathLen);
+
+  bool get routeHasPath =>
+      !routeIsUnknown && ContactRouteCodec.isValidDescriptor(outPathLen);
+
+  int get routeHashSize => routeHasPath ? ((routeEncodedPathLen >> 6) + 1) : 1;
+
+  int get routeHopCount => routeHasPath ? (routeEncodedPathLen & 0x3F) : -1;
+
+  int get routeByteLength => routeHasPath
+      ? math.min(routeHopCount * routeHashSize, outPath.length)
+      : 0;
+
+  Uint8List get routePathBytes => routeByteLength <= 0
+      ? Uint8List(0)
+      : Uint8List.fromList(outPath.sublist(0, routeByteLength));
+
+  String get routeCanonicalText {
+    if (!routeHasPath || routeHopCount <= 0) return '';
+    final bytes = routePathBytes;
+    final hops = <String>[];
+    for (var i = 0; i < bytes.length; i += routeHashSize) {
+      hops.add(
+        bytes
+            .sublist(i, i + routeHashSize)
+            .map((byte) => byte.toRadixString(16).padLeft(2, '0'))
+            .join()
+            .toUpperCase(),
+      );
+    }
+    return hops.join(',');
+  }
+
+  String get routeSummary {
+    if (routeIsUnknown || !routeHasPath) {
+      return 'Flood/Unknown';
+    }
+    if (routeHopCount == 0) {
+      return 'Direct';
+    }
+    return '$routeHopCount hop${routeHopCount == 1 ? '' : 's'} via $routeHashSize-byte hashes';
+  }
+
+  bool get routeSupportsLegacyRawTransport =>
+      routeHasPath && routeSignedPathLen >= 0;
 }