feat: introduce dioc into hoppscotch-common

packages/dioc/lib/container.ts

@@ -0,0 +1,147 @@
+import { Service } from "./service"
+import { Observable, Subject } from 'rxjs'
+
+/**
+ * Stores the current container instance in the current operating context.
+ *
+ * NOTE: This should not be used outside of dioc library code
+ */
+export let currentContainer: Container | null = null
+
+/**
+ * The events emitted by the container
+ *
+ * `SERVICE_BIND` - emitted when a service is bound to the container directly or as a dependency to another service
+ * `SERVICE_INIT` - emitted when a service is initialized
+ */
+export type ContainerEvent =
+  | {
+    type: 'SERVICE_BIND';
+
+    /** The Service ID of the service being bounded (the dependency) */
+    boundeeID: string;
+
+    /**
+     * The Service ID of the bounder that is binding the boundee (the dependent)
+     *
+     * NOTE: This will be undefined if the service is bound directly to the container
+     */
+    bounderID: string | undefined
+  }
+  | {
+    type: 'SERVICE_INIT';
+
+    /** The Service ID of the service being initialized */
+    serviceID: string
+  }
+
+/**
+ * The dependency injection container, allows for services to be initialized and maintains the dependency trees.
+ */
+export class Container {
+  /** Used during the `bind` operation to detect circular dependencies */
+  private bindStack: string[] = []
+
+  /** The map of bound services to their IDs */
+  protected boundMap = new Map<string, Service<unknown>>()
+
+  /** The RxJS observable representing the event stream */
+  protected event$ = new Subject<ContainerEvent>()
+
+  /**
+   * Returns whether a container has the given service bound
+   * @param service The service to check for
+   */
+  public hasBound<
+    T extends typeof Service<any> & { ID: string }
+  >(service: T): boolean {
+    return this.boundMap.has(service.ID)
+  }
+
+  /**
+   * Returns the service bound to the container with the given ID or if not found, undefined.
+   *
+   * NOTE: This is an advanced method and should not be used as much as possible.
+   *
+   * @param serviceID The ID of the service to get
+   */
+  public getBoundServiceWithID(serviceID: string): Service<unknown> | undefined {
+    return this.boundMap.get(serviceID)
+  }
+
+  /**
+   * Binds a service to the container. This is equivalent to marking a service as a dependency.
+   * @param service The class reference of a service to bind
+   * @param bounder The class reference of the service that is binding the service (if bound directly to the container, this should be undefined)
+   */
+  public bind<T extends typeof Service<any> & { ID: string }>(
+    service: T,
+    bounder: ((typeof Service<T>) & { ID: string }) | undefined = undefined
+  ): InstanceType<T> {
+    // We need to store the current container in a variable so that we can restore it after the bind operation
+    const oldCurrentContainer = currentContainer;
+    currentContainer = this;
+
+    // If the service is already bound, return the existing instance
+    if (this.hasBound(service)) {
+      this.event$.next({
+        type: 'SERVICE_BIND',
+        boundeeID: service.ID,
+        bounderID: bounder?.ID // Return the bounder ID if it is defined, else assume its the container
+      })
+
+      return this.boundMap.get(service.ID) as InstanceType<T> // Casted as InstanceType<T> because service IDs and types are expected to match
+    }
+
+    // Detect circular dependency and throw error
+    if (this.bindStack.findIndex((serviceID) => serviceID === service.ID) !== -1) {
+      const circularServices = `${this.bindStack.join(' -> ')} -> ${service.ID}`
+
+      throw new Error(`Circular dependency detected.\nChain: ${circularServices}`)
+    }
+
+    // Push the service ID onto the bind stack to detect circular dependencies
+    this.bindStack.push(service.ID)
+
+    // Initialize the service and emit events
+
+    // NOTE: We need to cast the service to any as TypeScript thinks that the service is abstract
+    const instance: Service<any> = new (service as any)()
+
+    this.boundMap.set(service.ID, instance)
+
+    this.bindStack.pop()
+
+    this.event$.next({
+      type: 'SERVICE_INIT',
+      serviceID: service.ID,
+    })
+
+    this.event$.next({
+      type: 'SERVICE_BIND',
+      boundeeID: service.ID,
+      bounderID: bounder?.ID
+    })
+
+
+    // Restore the current container
+    currentContainer = oldCurrentContainer;
+
+    // We expect the return type to match the service definition
+    return instance as InstanceType<T>
+  }
+
+  /**
+   * Returns an iterator of the currently bound service IDs and their instances
+   */
+  public getBoundServices(): IterableIterator<[string, Service<any>]> {
+    return this.boundMap.entries()
+  }
+
+  /**
+   * Returns the public container event stream
+   */
+  public getEventStream(): Observable<ContainerEvent> {
+    return this.event$.asObservable()
+  }
+}