Add DIContainer with observer registry

Sources/LuminateDI/DIContainer.swift

@@ -0,0 +1,69 @@
+import Foundation
+
+public final class DIContainer {
+
+    public static let shared = DIContainer()
+    public private(set) var values = InjectionValues()
+    private var observers: [AnyKeyPath: [UUID: () -> Void]] = [:]
+    private let lock = NSLock()
+
+    private init() {}
+
+    public func register<T>(
+        _ keyPath: WritableKeyPath<InjectionValues, T?>,
+        value: T
+    ) {
+        lock.withLock {
+            values[keyPath: keyPath] = value
+        }
+        notifyObservers(for: keyPath)
+    }
+
+    public func resolve<T>(
+        _ keyPath: KeyPath<InjectionValues, T?>
+    ) -> T {
+        lock.withLock {
+            guard let value = values[keyPath: keyPath] else {
+                fatalError(
+                    "DIContainer: No value registered for \(keyPath). "
+                        + "Call DIContainer.shared.register(\\.key, value:) during app startup."
+                )
+            }
+            return value
+        }
+    }
+
+    @discardableResult
+    func addObserver<T>(
+        for keyPath: KeyPath<InjectionValues, T?>,
+        handler: @escaping () -> Void
+    ) -> UUID {
+        let id = UUID()
+        lock.withLock {
+            observers[keyPath, default: [:]][id] = handler
+        }
+        return id
+    }
+
+    func removeObserver(_ id: UUID) {
+        lock.withLock {
+            for keyPath in observers.keys {
+                observers[keyPath]?.removeValue(forKey: id)
+            }
+        }
+    }
+
+    private func notifyObservers(for keyPath: AnyKeyPath) {
+        let handlers: [() -> Void] = lock.withLock {
+            Array(observers[keyPath]?.values ?? [])
+        }
+        handlers.forEach { $0() }
+    }
+
+    public func reset() {
+        lock.withLock {
+            values = InjectionValues()
+            observers.removeAll()
+        }
+    }
+}