inversion/examples/InjectionDemo.vala

using Inversion;

/**
 * Injection Demo Example
 * 
 * This example demonstrates the inject<T>() method for property/field injection.
 * The inject method allows dependencies to be resolved during object construction
 * without requiring explicit constructor parameters.
 * 
 * Key concepts:
 * - Using inject<T>() for field initialization
 * - The injection context is automatically set up during container resolution
 * - Multiple dependencies can be injected in the same class
 */
public class InjectionDemoExample : Object {

    // Define service interfaces
    public interface IHandler : Object {
        public abstract void handle(string request);
    }

    public interface IRepository : Object {
        public abstract string get_data();
    }

    // Console handler implementation
    public class ConsoleHandler : Object, IHandler {
        public void handle(string request) {
            stdout.printf("[HANDLER] Processing: %s\n", request);
        }
    }

    // Memory repository implementation
    public class MemoryRepository : Object, IRepository {
        public string get_data() {
            return "Sample data from repository";
        }
    }

    // A service that uses inject<T>() for dependency injection
    // This class demonstrates field injection using the inject method
    public class Controller : Object {
        // Dependencies are injected during object construction
        private IHandler handler = inject<IHandler>();
        private IRepository repository = inject<IRepository>();

        public void process_request(string request) {
            var data = this.repository.get_data();
            stdout.printf("[CONTROLLER] Retrieved data: %s\n", data);
            this.handler.handle(request);
        }
    }

    // Another service demonstrating nested injection
    public class ApiService : Object {
        private Controller controller = inject<Controller>();

        public void execute(string request) {
            stdout.printf("[API] Executing request: %s\n", request);
            this.controller.process_request(request);
        }
    }

    public static int main(string[] args) {
        stdout.printf("=== Inversion IoC Injection Demo ===\n\n");

        // Create the container
        var container = new Container();

        // Register all services with factory delegates
        container.register_singleton<ConsoleHandler>((scope) => new ConsoleHandler())
            .as_type(typeof(IHandler));

        container.register_singleton<MemoryRepository>((scope) => new MemoryRepository())
            .as_type(typeof(IRepository));

        // Register Controller - it will use inject<T>() to resolve its dependencies
        container.register_scoped<Controller>((scope) => new Controller());

        // Register ApiService - demonstrates nested injection
        container.register_transient<ApiService>((scope) => new ApiService());

        stdout.printf("Registered services:\n");
        stdout.printf("  - ConsoleHandler as IHandler (Singleton)\n");
        stdout.printf("  - MemoryRepository as IRepository (Singleton)\n");
        stdout.printf("  - Controller (Scoped) - uses inject<T>()\n");
        stdout.printf("  - ApiService (Transient) - uses inject<T>()\n\n");

        // Create a scope
        var scope = container.create_scope();

        try {
            stdout.printf("--- Resolving ApiService (demonstrates nested injection) ---\n\n");
            
            // Resolve ApiService - this will trigger:
            // 1. ApiService construction -> inject<Controller>()
            // 2. Controller construction -> inject<IHandler>() and inject<IRepository>()
            var api_service = scope.resolve<ApiService>();
            api_service.execute("Test request #1");

            stdout.printf("\n--- Resolving Controller directly ---\n\n");
            
            // Resolve Controller directly
            var controller = scope.resolve<Controller>();
            controller.process_request("Test request #2");

            // Verify scoped behavior - same controller instance within scope
            var controller2 = scope.resolve<Controller>();
            if (controller == controller2) {
                stdout.printf("\n✓ Scoped working: Same Controller instance within scope\n");
            }

            stdout.printf("\n--- Creating another scope ---\n\n");
            
            // Create another scope - should get a new Controller instance
            var scope2 = container.create_scope();
            var controller_in_scope2 = scope2.resolve<Controller>();
            controller_in_scope2.process_request("Test request #3");

            if (controller != controller_in_scope2) {
                stdout.printf("\n✓ Scoped working: Different Controller instance in different scope\n");
            }

        } catch (Error e) {
            stderr.printf("Error: %s\n", e.message);
            return 1;
        }

        stdout.printf("\n=== Example Complete ===\n");
        return 0;
    }
}