Added a reference to the preceding snapshot in an iteration

Author: dimitribouniol

Sources/CodableDatastore/Persistence/Disk Persistence/Snapshot/SnapshotIteration.swift

@@ -30,6 +30,11 @@ struct SnapshotIteration: Codable, Equatable, Identifiable {
     /// The iteration this one replaces.
     var precedingIteration: SnapshotIterationIdentifier?
 
+    /// The snapshot the preceding iteration belongs to.
+    ///
+    /// When set, the specified snapshot should be referenced to load the ``precedingIteration`` from. When `nil`, the current snapshot should be used.
+    var precedingSnapshot: SnapshotIdentifier?
+    
     /// The iterations that replace this one.
     ///
     /// If changes branched at this point in time, there may be more than one iteration to choose from. In this case, the first entry will be the oldest successor, while the last entry will be the most recent.

Tests/CodableDatastoreTests/SnapshotIterationTests.swift

@@ -89,4 +89,48 @@ final class SnapshotIterationTests: XCTestCase, @unchecked Sendable {
         decoder.dateDecodingStrategy = .iso8601WithMilliseconds
         _ = try decoder.decode(SnapshotIteration.self, from: data)
     }
+    
+    func testDecodingOptionalPrecedingSnapshotIdentifiers() throws {
+        let data = Data("""
+        {
+          "addedDatastoreRoots" : [
+            {
+              "datastoreID" : "Store-FD9BA6F1BD3667C8",
+              "datastoreRootID" : "2025-02-12 00-00-00-046 44BBE608B9CBF788"
+            }
+          ],
+          "addedDatastores" : [
+
+          ],
+          "creationDate" : "2025-02-12T00:00:00.057Z",
+          "dataStores" : {
+            "Store" : {
+              "id" : "Store-FD9BA6F1BD3667C8",
+              "key" : "Store",
+              "root" : "2024-08-24 09-39-57-775 66004A6BA331B89C"
+            }
+          },
+          "id" : "2025-02-12 00-00-00-057 0130730F8F6A1ACC",
+          "precedingIteration" : "2025-02-11 23-59-54-727 447A1A1E1CF82177",
+          "precedingSnapshot" : "2024-04-14 13-09-27-739 A1EEB1A3AF102F15",
+          "removedDatastoreRoots" : [
+            {
+              "datastoreID" : "Store-FD9BA6F1BD3667C8",
+              "datastoreRootID" : "2025-02-11 23-59-54-721 2AAEA12A38303055"
+            }
+          ],
+          "removedDatastores" : [
+
+          ],
+          "successiveIterations" : [
+
+          ],
+          "version" : "alpha"
+        }
+        """.utf8)
+        
+        let decoder = JSONDecoder()
+        decoder.dateDecodingStrategy = .iso8601WithMilliseconds
+        _ = try decoder.decode(SnapshotIteration.self, from: data)
+    }
 }