Create RefdsDictionary.swift

Sources/RefdsShared/Foundation/RefdsDictionary.swift

@@ -0,0 +1,45 @@
+import Foundation
+
+public actor RefdsDictionary<
+    Key: Hashable & Sendable,
+    Value,
+    Transform: Comparable
+> {
+    private var elements: [Key: Value] = [:]
+    private let keyPath: KeyPath<Value, Transform>
+
+    public init(
+        for type: Value.Type,
+        by keyPath: KeyPath<Value, Transform>
+    ) {
+        self.keyPath = keyPath
+    }
+
+    public subscript(key: Key) -> Value? {
+        get { elements[key] }
+        set {
+            guard let newValue else { return remove(for: key) }
+            if elements[key] == nil { insert(for: key) }
+            elements[key] = newValue
+        }
+    }
+
+    public var keys: [Key] = []
+    public var values: [Value] {
+        keys.compactMap { elements[$0] }
+    }
+
+    private func insert(for key: Key) {
+        let index = keys.firstIndex(where: { k in
+            guard let lhs = elements[k].map({ $0[keyPath: keyPath] }),
+                  let rhs = elements[key].map({ $0[keyPath: keyPath] }) else { return false }
+            return lhs >= rhs
+        }) ?? keys.count
+        keys.insert(key, at: index)
+    }
+
+    private func remove(for key: Key) {
+        elements.removeValue(forKey: key)
+        keys.removeAll { $0 == key }
+    }
+}