Add facet search support.

README.md

@@ -96,6 +96,72 @@ To delete a record from the search engine:
 searchEngine.DeleteRecord(1);
 ```
 
+### Pagination
+
+In addition to basic searching, you can easily implement pagination using the `skip` and `limit` parameters in the `Search` method. This is especially useful when dealing with large datasets where you only want to display a subset of the results at a time.
+
+```csharp
+var resultsPage1 = searchEngine.Search(
+    search: "quick fox",
+    respectTokenOrder: true,
+    skip: 0, // Skip 0 records, start from the beginning
+    limit: 10 // Limit to 10 records in this page
+);
+
+var resultsPage2 = searchEngine.Search(
+    search: "quick fox",
+    respectTokenOrder: true,
+    skip: 10, // Skip the first 10 records
+    limit: 10 // Limit to 10 records in this page
+);
+```
+
+### Adding Facets
+
+To associate a facet (e.g., category, author) with a record:
+
+```csharp
+searchEngine.AddFacet(1, "category", "books");
+searchEngine.AddFacet(1, "author", "John Doe");
+```
+
+### Deleting Facets
+
+To remove a specific facet associated with a record:
+
+```csharp
+searchEngine.DeleteFacet(1, "category", "books");
+searchEngine.DeleteFacet(1, "author", "John Doe");
+```
+
+### Faceted Search
+
+If you're also filtering by facets, you can still apply pagination by specifying the `skip` and `limit` parameters:
+
+```csharp
+var facets = new Dictionary<string, string>
+{
+    { "category", "books" },
+    { "author", "John Doe" }
+};
+
+var paginatedFacetedResultsPage1 = searchEngine.Search(
+    search: "quick fox",
+    facets: facets,
+    respectTokenOrder: true,
+    skip: 0, // Start from the first matching record
+    limit: 10 // Retrieve up to 10 records
+);
+
+var paginatedFacetedResultsPage2 = searchEngine.Search(
+    search: "quick fox",
+    facets: facets,
+    respectTokenOrder: true,
+    skip: 10, // Skip the first 10 matching records
+    limit: 10 // Retrieve the next 10 records
+);
+```
+
 ### Cleanup
 
 When you're done using the search engine, ensure proper cleanup:
@@ -259,7 +325,7 @@ Future Search Engines: Additional search engines, such as Phrase Search Engine a
 
 ## License
 
-ZoneTree.FullTextSearch is licensed under the MIT License. See the [LICENSE](LICENSE) file for more details.
+ZoneTree.FullTextSearch is licensed under the MIT License. See the [LICENSE](https://github.com/koculu/ZoneTree.FullTextSearch/blob/main/LICENSE) file for more details.
 
 ---
 

src/ZoneTree.FullTextSaearch/Core/Index/IndexOfTokenRecordPreviousToken.cs

@@ -18,6 +18,12 @@
     where TRecord : unmanaged
     where TToken : unmanaged
 {
+    /// <summary>
+    /// Gets or sets the facet previous token.
+    /// This property represents a token that precedes the current token in the context of facet-based searches.
+    /// </summary>
+    public TToken FacetPreviousToken { get; set; }
+
     /// <summary>
     /// Gets the primary zone tree used to store and retrieve records by token and previous token.
     /// </summary>
@@ -70,7 +76,7 @@
 
     readonly bool useSecondaryIndex;
 
     bool isDropped = false;
 
     readonly SearchOnIndexOfTokenRecordPreviousToken<TRecord, TToken>
         searchAlgorithm;
@@ -197,8 +203,8 @@
         WaitForBackgroundThreads();
         isDropped = true;
         IsReadOnly = true;
-        ZoneTree1.Maintenance.DestroyTree();
-        ZoneTree2?.Maintenance.DestroyTree();
+        ZoneTree1.Maintenance.Drop();
+        ZoneTree2?.Maintenance.Drop();
         ZoneTree1.Dispose();
         ZoneTree2?.Dispose();
     }
@@ -227,6 +233,32 @@
         ZoneTree2.TryAdd(key, new());
     }
 
+    /// <summary>
+    /// Deletes a record from the primary zone tree, and optionally from the secondary zone tree if a secondary index is enabled.
+    /// </summary>
+    /// <param name="token">The token associated with the record to delete.</param>
+    /// <param name="record">The record to be deleted.</param>
+    /// <param name="previousToken">The token that precedes the current token in the record.</param>
+    public void DeleteRecord(TToken token, TRecord record, TToken previousToken)
+    {
+        ThrowIfIndexIsDropped();
+        ZoneTree1.ForceDelete(new CompositeKeyOfTokenRecordPrevious<TRecord, TToken>()
+        {
+            Token = token,
+            Record = record,
+            PreviousToken = previousToken
+        });
+
+        if (!useSecondaryIndex)
+            return;
+
+        ZoneTree2.ForceDelete(new CompositeKeyOfRecordToken<TRecord, TToken>()
+        {
+            Record = record,
+            Token = token,
+        });
+    }
+
     /// <summary>
     /// Deletes a record from the index without using the secondary index.
     /// </summary>
@@ -291,31 +323,61 @@
     }
 
     /// <summary>
-    /// Searches for records that match the provided tokens, with optional parameters for token order,
-    /// skipping records, and limiting the number of results.
+    /// Searches the index for records that match the specified tokens, with optional support for facets, token order respect, and pagination.
     /// </summary>
-    /// <param name="tokens">The tokens to search for.</param>
-    /// <param name="firstLookAt">An optional token to prioritize during the search.</param>
-    /// <param name="respectTokenOrder">Indicates whether the order of tokens should be respected during the search.</param>
-    /// <param name="skip">The number of records to skip in the result set.</param>
-    /// <param name="limit">The maximum number of records to return.</param>
-    /// <returns>An array of records that match the search criteria.</returns>
+    /// <param name="tokens">
+    /// A read-only span of tokens that the records must contain. This parameter is mandatory unless facets are provided.
+    /// The tokens are logically grouped using "AND", meaning all tokens must be present in the matching records.
+    /// If both the tokens span and the facets span are empty, the result will be an empty array, as searching without tokens and facets is not supported.
+    /// Tokens can be empty if facets are provided; in this case, the search will be based solely on the facets.
+    /// To retrieve records without specific search tokens or facets, consider fetching them from the actual record source instead of using the search index.
+    /// </param>
+    /// <param name="firstLookAt">
+    /// An optional token that the search will prioritize when searching. 
+    /// If not specified, the first token in the tokens span is used.
+    /// </param>
+    /// <param name="respectTokenOrder">
+    /// A boolean indicating whether the search should respect the order of tokens in the record.
+    /// If true, the records must contain the tokens in the specified order.
+    /// </param>
+    /// <param name="facets">
+    /// An optional read-only span of tokens that can be used to filter the search results.
+    /// If any facets are provided, records must contain at least one of these facet tokens to be included in the results.
+    /// If the span is empty or not provided, no facet filtering is applied, and all matching records are returned regardless of facet values.
+    /// </param>
+    /// <param name="skip">
+    /// The number of matching records to skip in the result set, useful for pagination.
+    /// Defaults to 0.
+    /// </param>
+    /// <param name="limit">
+    /// The maximum number of records to return, useful for limiting the result set size.
+    /// Defaults to 0, which indicates no limit.
+    /// </param>
+    /// <returns>
+    /// An array of records that match the specified tokens and facets, respecting the token order if specified.
+    /// The array may be empty if no matching records are found.
+    /// </returns>
     public TRecord[] Search(
         ReadOnlySpan<TToken> tokens,
         TToken? firstLookAt = null,
         bool respectTokenOrder = true,
+        ReadOnlySpan<TToken> facets = default,
         int skip = 0,
         int limit = 0)
     {
         return searchAlgorithm
-            .Search(tokens, firstLookAt, respectTokenOrder, skip, limit);
+            .Search(tokens, firstLookAt, respectTokenOrder, facets, skip, limit);
     }
 
+    bool isDisposed = false;
+
     /// <summary>
     /// Disposes the resources used by the index.
     /// </summary>
     public void Dispose()
     {
+        if (isDisposed) return;
+        isDisposed = true;
         Maintainer1.WaitForBackgroundThreads();
         Maintainer1.Dispose();
         ZoneTree1.Dispose();