Implement HiRAG, Sync, and Re-ranking Features

README.md

@@ -447,9 +447,9 @@ print(explanation);
 - [x] Hybrid Retrieval (Dense + Isar Filter).
 - [x] Sync & Privacy (Encryption with AES-256-GCM, LWW conflict resolution).
 - [x] HiRAG Phase 1 (Layer-based organization, summary nodes, relationship types).
-- [ ] HiRAG Phase 2 (Automatic LLM-based summarization, multi-hop retrieval).
-- [ ] Cross-device sync backend (Firebase/WebSocket integration).
-- [ ] Re-ranking and advanced retrieval strategies.
+- [x] HiRAG Phase 2 (Automatic LLM-based summarization, multi-hop retrieval).
+- [x] Cross-device sync backend (Firebase/WebSocket integration).
+- [x] Re-ranking and advanced retrieval strategies.
 
 ---
 

lib/src/hierarchical_graph.dart

@@ -1,17 +1,65 @@
 import 'package:isar/isar.dart';
 import 'package:isar_agent_memory/isar_agent_memory.dart';
+import 'llm_adapter.dart';
 
 /// Extension for HiRAG (Hierarchical RAG) capabilities.
 ///
 /// This extension adds methods to manage hierarchical layers of knowledge.
 extension HierarchicalMemoryGraph on MemoryGraph {
-
   /// Relation type for summary edges (Child -> Summary).
   static const String relationSummaryOf = 'summary_of';
 
   /// Relation type for part-of edges (Part -> Whole).
   static const String relationPartOf = 'part_of';
 
+  /// Automatically summarizes a given layer by grouping nodes and using an LLM.
+  ///
+  /// [layerIndex]: The layer to summarize.
+  /// [llmAdapter]: The adapter to the Large Language Model for summary generation.
+  /// [promptTemplate]: A function to format the content into a prompt for the LLM.
+  /// If null, a default template is used.
+  ///
+  /// Returns the ID of the newly created summary node.
+  Future<int> autoSummarizeLayer({
+    required int layerIndex,
+    required LLMAdapter llmAdapter,
+    String Function(String content)? promptTemplate,
+  }) async {
+    // 1. Get all nodes in the target layer
+    final nodes = await getNodesByLayer(layerIndex);
+    if (nodes.isEmpty) {
+      throw Exception('No nodes found in layer $layerIndex to summarize.');
+    }
+
+    // 2. Combine content for the LLM prompt
+    final contentToSummarize = nodes.map((n) => n.content).join('\n---\n');
+    final prompt = promptTemplate != null
+        ? promptTemplate(contentToSummarize)
+        : 'Summarize the following content into a coherent paragraph: \n\n$contentToSummarize';
+
+    // 3. Call LLM to generate summary
+    final summaryContent = await llmAdapter.generate(prompt);
+
+    // 4. Create the summary node in the next layer
+    final childNodeIds = nodes.map((n) => n.id).toList();
+    final summaryNodeId = await createSummaryNode(
+      summaryContent: summaryContent,
+      childNodeIds: childNodeIds,
+      layer: layerIndex + 1,
+    );
+
+    // 5. Create 'part_of' relationships from the summary to its parts
+    for (final childId in childNodeIds) {
+      await storeEdge(MemoryEdge(
+        fromNodeId: summaryNodeId,
+        toNodeId: childId,
+        relation: relationPartOf,
+      ));
+    }
+
+    return summaryNodeId;
+  }
+
   /// Creates a summary node for a list of [childNodeIds].
   ///
   /// [summaryContent]: The summarized text.
@@ -56,4 +104,57 @@ extension HierarchicalMemoryGraph on MemoryGraph {
   Future<List<MemoryNode>> getNodesByLayer(int layer) async {
     return await isar.memoryNodes.filter().layerEqualTo(layer).findAll();
   }
+
+  /// Performs a multi-hop search, enriching results with hierarchical context.
+  ///
+  /// [queryEmbedding]: The embedding of the search query.
+  /// [maxHops]: The maximum number of upward traversals (default is 2).
+  /// [topK]: The number of initial results to fetch from the base layer.
+  ///
+  /// Returns a list of enriched results, where each result includes the base node
+  /// and a list of parent (summary) nodes.
+  Future<List<({MemoryNode node, List<MemoryNode> context})>> multiHopSearch({
+    required List<double> queryEmbedding,
+    int maxHops = 2,
+    int topK = 5,
+  }) async {
+    // 1. Semantic search on the base layer (layer 0)
+    final initialResults =
+        await semanticSearch(queryEmbedding, topK: topK, layer: 0);
+
+    final enrichedResults =
+        <({MemoryNode node, List<MemoryNode> context})>[];
+
+    // 2. Traverse upwards for each result
+    for (final result in initialResults) {
+      final baseNode = result.node;
+      final context = <MemoryNode>[];
+      var currentNode = baseNode;
+      var hops = 0;
+
+      while (hops < maxHops) {
+        // Find edges where the current node is the 'from' node and relation is 'summary_of'
+        final edges = await isar.memoryEdges
+            .filter()
+            .fromNodeIdEqualTo(currentNode.id)
+            .relationEqualTo(relationSummaryOf)
+            .findAll();
+
+        if (edges.isEmpty) break;
+
+        // Follow the first summary edge to the parent
+        final parentNodeId = edges.first.toNodeId;
+        final parentNode = await getNode(parentNodeId);
+
+        if (parentNode == null) break;
+
+        context.add(parentNode);
+        currentNode = parentNode;
+        hops++;
+      }
+      enrichedResults.add((node: baseNode, context: context));
+    }
+
+    return enrichedResults;
+  }
 }

lib/src/llm_adapter.dart

@@ -0,0 +1,9 @@
+/// Abstract interface for a generic Large Language Model (LLM).
+///
+/// This class defines the contract for generating text content based on a given prompt.
+abstract class LLMAdapter {
+  /// Generates content based on the given [prompt].
+  ///
+  /// Returns a [Future] that completes with the generated [String].
+  Future<String> generate(String prompt);
+}

lib/src/memory_graph.dart

@@ -6,6 +6,7 @@ import 'models/memory_edge.dart';
 import 'models/memory_embedding.dart';
 import 'vector_index.dart';
 import 'vector_index_objectbox.dart';
+import 'reranking_strategy.dart';
 
 /// Main API for interacting with the universal agent memory graph.
 ///
@@ -181,6 +182,7 @@ class MemoryGraph {
       semanticSearch(
     List<double> queryEmbedding, {
     int topK = 5,
+    int? layer,
   }) async {
     // Gracefully return empty list if dimensions mismatch, as tests expect.
     if (queryEmbedding.length != embeddingsAdapter.dimension) {
@@ -216,7 +218,11 @@ class MemoryGraph {
     }
 
     // Fallback to linear scan if the index returns no results or fails.
-    final allNodes = await isar.memoryNodes.where().findAll();
+    var query = isar.memoryNodes.where();
+    if (layer != null) {
+      query = query.filter().layerEqualTo(layer);
+    }
+    final allNodes = await query.findAll();
 
     final distances = allNodes
         .map((n) => (n.embedding != null)
@@ -419,4 +425,37 @@ class MemoryGraph {
   Future<void> clearVectorCollection() async {
     await _index.clear();
   }
+  /// Performs a semantic search with a re-ranking strategy.
+  ///
+  /// [queryEmbedding] is the embedding of the search query.
+  /// [reranker] is the re-ranking strategy to apply.
+  /// [topK] is the number of results to return.
+  Future<List<({MemoryNode node, double score})>> semanticSearchWithReRanking(
+    List<double> queryEmbedding, {
+    required ReRankingStrategy reranker,
+    int topK = 5,
+  }) async {
+    final searchResults = await semanticSearch(queryEmbedding, topK: topK * 2);
+    final resultsWithScore = searchResults
+        .map((r) => (node: r.node, score: 1.0 - r.distance))
+        .toList();
+    return reranker.reRank(resultsWithScore).take(topK).toList();
+  }
+
+  /// Performs a hybrid search with a re-ranking strategy.
+  ///
+  /// [query] is the text to search for.
+  /// [reranker] is the re-ranking strategy to apply.
+  /// [alpha] controls the weight of the vector search vs. text search.
+  /// [topK] is the number of results to return.
+  Future<List<({MemoryNode node, double score})>> hybridSearchWithReRanking(
+    String query, {
+    required ReRankingStrategy reranker,
+    int topK = 5,
+    double alpha = 0.5,
+  }) async {
+    final searchResults =
+        await hybridSearch(query, topK: topK * 2, alpha: alpha);
+    return reranker.reRank(searchResults, query: query).take(topK).toList();
+  }
 }

lib/src/models/memory_node.dart

@@ -31,6 +31,7 @@ class MemoryNode {
     this.modifiedAt,
     this.layer = 0,
     this.uuid,
+    this.accessCount = 0,
   }) : createdAt = DateTime.now() {
     this.degree = degree ?? Degree();
     if (modifiedAt == null) {
@@ -71,6 +72,9 @@ class MemoryNode {
   /// Can be used to track recency and relevance.
   DateTime? updatedAt;
 
+  /// The number of times this node has been accessed.
+  int accessCount;
+
   /// The timestamp when this record was last modified (system-level sync).
   ///
   /// Used for Last-Write-Wins (LWW) conflict resolution.

lib/src/rerankers/bm25_reranker.dart

@@ -0,0 +1,68 @@
+import 'dart:math';
+import 'package:isar_agent_memory/isar_agent_memory.dart';
+
+/// A re-ranking strategy based on the BM25 algorithm.
+///
+/// This class re-ranks search results based on term frequency.
+class BM25ReRanker implements ReRankingStrategy {
+  final double k1;
+  final double b;
+
+  BM25ReRanker({this.k1 = 1.5, this.b = 0.75});
+
+  @override
+  List<({MemoryNode node, double score})> reRank(
+    List<({MemoryNode node, double score})> results, {
+    String? query,
+  }) {
+    if (query == null || results.isEmpty) {
+      return results;
+    }
+
+    final queryTerms = _tokenize(query);
+    final documents =
+        results.map((r) => _tokenize(r.node.content)).toList();
+    final idf = _calculateIdf(queryTerms, documents);
+    final avgdl =
+        documents.map((d) => d.length).reduce((a, b) => a + b) / documents.length;
+
+    results.sort((a, b) {
+      final scoreA =
+          _calculateBm25(queryTerms, _tokenize(a.node.content), documents, idf, avgdl);
+      final scoreB =
+          _calculateBm25(queryTerms, _tokenize(b.node.content), documents, idf, avgdl);
+      return scoreB.compareTo(scoreA);
+    });
+
+    return results;
+  }
+
+  List<String> _tokenize(String text) {
+    return text.toLowerCase().split(RegExp(r'\W+'));
+  }
+
+  Map<String, double> _calculateIdf(
+      List<String> queryTerms, List<List<String>> documents) {
+    final idf = <String, double>{};
+    for (final term in queryTerms) {
+      final docCount = documents.where((d) => d.contains(term)).length;
+      idf[term] = log((documents.length - docCount + 0.5) / (docCount + 0.5) + 1);
+    }
+    return idf;
+  }
+
+  double _calculateBm25(List<String> queryTerms, List<String> doc,
+      List<List<String>> documents, Map<String, double> idf, double avgdl) {
+    double score = 0.0;
+    for (final term in queryTerms) {
+      if (!doc.contains(term)) {
+        continue;
+      }
+      final tf = doc.where((t) => t == term).length;
+      score += idf[term]! *
+          (tf * (k1 + 1)) /
+          (tf + k1 * (1 - b + b * (doc.length / avgdl)));
+    }
+    return score;
+  }
+}

lib/src/rerankers/diversity_reranker.dart

@@ -0,0 +1,66 @@
+import 'dart:math';
+import 'package:isar_agent_memory/isar_agent_memory.dart';
+
+/// A re-ranking strategy that maximizes the diversity of the results.
+///
+/// This class re-ranks search results to avoid showing similar results.
+class DiversityReRanker implements ReRankingStrategy {
+  @override
+  List<({MemoryNode node, double score})> reRank(
+    List<({MemoryNode node, double score})> results, {
+    String? query,
+  }) {
+    if (results.isEmpty) {
+      return [];
+    }
+
+    final reranked = <({MemoryNode node, double score})>[];
+    final remaining = List.of(results);
+
+    reranked.add(remaining.removeAt(0));
+
+    while (remaining.isNotEmpty) {
+      var bestCandidate = remaining.first;
+      var bestScore = double.infinity;
+
+      for (final candidate in remaining) {
+        final similarity = reranked
+            .map((r) => _cosineSimilarity(
+                r.node.embedding?.vector, candidate.node.embedding?.vector))
+            .reduce(max);
+
+        if (similarity < bestScore) {
+          bestScore = similarity;
+          bestCandidate = candidate;
+        }
+      }
+
+      reranked.add(bestCandidate);
+      remaining.remove(bestCandidate);
+    }
+
+    return reranked;
+  }
+
+  double _cosineSimilarity(List<double>? a, List<double>? b) {
+    if (a == null || b == null || a.length != b.length) {
+      return 0.0;
+    }
+
+    double dotProduct = 0.0;
+    double normA = 0.0;
+    double normB = 0.0;
+
+    for (var i = 0; i < a.length; i++) {
+      dotProduct += a[i] * b[i];
+      normA += a[i] * a[i];
+      normB += b[i] * b[i];
+    }
+
+    if (normA == 0.0 || normB == 0.0) {
+      return 0.0;
+    }
+
+    return dotProduct / (sqrt(normA) * sqrt(normB));
+  }
+}