Added base DiskPersistence datastore actor

Author: dimitribouniol

Sources/CodableDatastore/Persistence/Disk Persistence/Datastore/PersistenceDatastore.swift

@@ -0,0 +1,61 @@
+//
+//  PersistenceDatastore.swift
+//  CodableDatastore
+//
+//  Created by Dimitri Bouniol on 2023-06-10.
+//  Copyright © 2023 Mochi Development, Inc. All rights reserved.
+//
+
+import Foundation
+
+typealias DatastoreIdentifier = TypedIdentifier<DiskPersistence<ReadOnly>.Datastore>
+typealias DatastoreRootIdentifier = DatedIdentifier<DiskPersistence<ReadOnly>.Datastore>
+
+extension DiskPersistence {
+    actor Datastore {
+        let id: DatastoreIdentifier
+        
+        unowned let snapshot: Snapshot<AccessMode>
+        
+        var currentRootIdentifier: DatastoreRootIdentifier?
+        var cachedDescriptor: DatastoreDescriptor?
+        
+        var lastUpdateDescriptorTask: Task<Any, Error>?
+        
+        init(
+            id: DatastoreIdentifier,
+            snapshot: Snapshot<AccessMode>
+        ) {
+            self.id = id
+            self.snapshot = snapshot
+        }
+    }
+}
+
+// MARK: - Common URL Accessors
+extension DiskPersistence.Datastore {
+    /// The URL that points to the Snapshot directory.
+    nonisolated var datastoreURL: URL {
+        snapshot
+            .datastoresURL
+            .appendingPathComponent("\(id).datastore", isDirectory: true)
+    }
+    
+    /// The URL that points to the Root directory.
+    nonisolated var rootURL: URL {
+        datastoreURL
+            .appendingPathComponent("Root", isDirectory: true)
+    }
+    
+    /// The URL that points to the DirectIndexes directory.
+    nonisolated var directIndexesURL: URL {
+        datastoreURL
+            .appendingPathComponent("DirectIndexes", isDirectory: true)
+    }
+    
+    /// The URL that points to the SecondaryIndexes directory.
+    nonisolated var secondaryIndexesURL: URL {
+        datastoreURL
+            .appendingPathComponent("SecondaryIndexes", isDirectory: true)
+    }
+}