Add a small IoC framework

src/di.ts

@@ -0,0 +1,74 @@
+
+export type Newable<T> = {
+  new(...args: any): T;
+}
+
+export type Factory<T> = Newable<T>;
+
+export type ServiceID = string | symbol | Factory<any>;
+
+function isFactory(value: any): boolean {
+  return typeof value === 'object'
+      && value !== null
+      && value instanceof Function
+}
+
+export function inject(target: any, key: PropertyKey, index: number) {
+  //return function(target: any) {
+    // This is a no-op because adding the decorator
+    // is enough for TypeScript to emit metadata
+  //}
+}
+
+function describeFactory(factory: Factory<any>): string {
+  return factory.name;
+}
+
+export class Container {
+
+  private factories: Factory<any>[] = [];
+  private singletons = new Map<ServiceID, object>();
+
+  public bindSelf<T extends object>(value: Factory<T> | T): void {
+    if (isFactory(value)) {
+      this.factories.push(value as Factory<T>);
+    } else {
+      this.singletons.set((value as T).constructor as ServiceID, value)
+    }
+  }
+
+  private canResolve(serviceId: ServiceID): boolean {
+    return this.singletons.has(serviceId);
+  }
+
+  private resolve<T>(factory: Factory<T>): T;
+  private resolve(serviceId: ServiceID): any {
+    return this.singletons.get(serviceId);
+  }
+
+  public createInstance<T>(factory: Factory<T>, ...args: any[]): T {
+    const newArgs: any[] = [];
+    const paramTypes = Reflect.getMetadata('design:paramtypes', factory);
+    if (paramTypes === undefined) {
+      return new factory(...args);
+    }
+    let i = 0;
+    for (const paramType of paramTypes) {
+      if (this.canResolve(paramType)) {
+        newArgs.push(this.resolve(paramType));
+      } else {
+        if (i >= args.length) {
+          throw new Error(`Too few arguments provided to constructor of '${describeFactory(factory)}'.`);
+        }
+        newArgs.push(args[i++]);
+      }
+    }
+    if (i < args.length) {
+      throw new Error(`Too many arguments provided to factory function '${describeFactory(factory)}'.`);
+    }
+    return new factory(...newArgs);
+  }
+
+}
+
+