feat: add a service to handle user confirmation through GUI

refs #604

src/app/app.module.ts

@@ -127,6 +127,7 @@ import { SelectSectionDetailsComponent } from "./components/select-section-detai
 import { ServiceWorkerModule } from '@angular/service-worker';
 import { environment } from '../environments/environment';
 import { ServiceWorkerUpdateService } from "./services/service-worker-update.service";
+import { UserConfirmationService } from "./services/user-confirmation.service";
 
 const appRoutes: Routes = [
     { path: "list/search", component: CalculatorListComponent },
@@ -282,7 +283,8 @@ const appRoutes: Routes = [
             provide: ErrorStateMatcher,
             useClass: ImmediateErrorStateMatcher
         },
-        ServiceWorkerUpdateService
+        ServiceWorkerUpdateService,
+        UserConfirmationService
     ],
     schemas: [NO_ERRORS_SCHEMA],
     bootstrap: [AppComponent]

src/app/services/user-confirmation.service.ts

+import { Injectable } from "@angular/core";
+
+import { BidirectionalSubject } from "app/util/bidir_subject";
+import { Observer } from "rxjs";
+
+/**
+ * This service enables any class (even another service) to display a confirmation dialog on GUI ans get the user answer
+ */
+@Injectable()
+export class UserConfirmationService {
+
+    // used to communicate with UI component in charge of displaying confirmation dialog
+    // direction 0 : this
+    // direction 1 : UI
+    private _userConfirm: BidirectionalSubject<{}>;
+
+    public constructor() {
+        this._userConfirm = new BidirectionalSubject<{}>();
+
+        // we choose communication canal 0, UI will use 1
+        this._userConfirm.selectPostingChannel(this, 0);
+    }
+
+    /**
+     * add subscription from UI
+     * @param source 
+     */
+    public subscribe(source: any) {
+        this._userConfirm.selectPostingChannel(source, 1);
+    }
+
+    /**
+     * remove UI subscription
+     * @param source 
+     */
+    public unsubscribe(source: any) {
+        this._userConfirm.unselectPostingChannel(source);
+    }
+
+    /**
+     * add a handler (provided bu UI) to confirmation request
+     * @param source normally, UI component
+     * @param obs processing function
+     */
+    public addHandler(source: any, obs: Observer<boolean>) {
+        this._userConfirm.addHandler(source, obs)
+    }
+
+    /**
+     * forward user confirmation from UI to requesting object
+     * @param confirm user confirmation status
+     */
+    public postConfirmation(source: any, confirm: {}) {
+        this._userConfirm.post(source, confirm);
+    }
+
+    /**
+     * forward to UI a request from source to ask a user confirmation with a dialog
+     * @param source object requesting confirmation
+     * @param title confirmation dialog title
+     * @param text confirmation dialog body text
+     * @returns a Promise resolving to a boolean holding user confirmation status
+     */
+    public askUserConfirmation(title: string, text: string): Promise<{}> {
+        const ret = this._userConfirm.getReceivePromise(this);
+        this._userConfirm.post(this, { title: title, body: text }); // false or true, we don't care
+        return ret;
+    }
+}