Dynamic Element Injection in Angular

This challenge focuses on building a reusable Angular component that can dynamically inject custom HTML elements into a specified location within a parent component. This is a common requirement for building flexible UI libraries, modal systems, or notification services where content needs to be rendered based on external logic.

Problem Description

You need to create an Angular directive that allows a parent component to inject a custom HTML element (defined by a component or a simple HTML string) at a designated spot in its template. This directive should be flexible enough to handle different types of content and provide a clear API for controlling the injection.

Key Requirements:

1. Directive-Based Injection: The core functionality should be implemented as an Angular directive.
2. Content Flexibility: The directive should support injecting:
   • An Angular Component (instantiated dynamically).
   • A simple HTML string.
3. Target Location: The directive should specify the exact location within the host element where the content will be injected.
4. Dynamic Updates: The directive should be able to update or replace the injected content based on input changes.
5. Cleanup: When the host element or the directive is destroyed, any injected content must be properly cleaned up to prevent memory leaks.

Expected Behavior:

When the directive is applied to an element in a parent component's template, and content is provided to it, the directive should render that content inside the host element.

Edge Cases:

• What happens if no content is provided?
• What happens if an invalid component is provided?
• Handling multiple injections (though for this challenge, assume only one injection at a time).

Examples

Example 1: Injecting a Component

Consider a NotificationService that creates a NotificationComponent and injects it into a designated area.

Parent Component Template (app.component.html):

<div class="notification-container" appElementInjector>
  <!-- NotificationComponent will be injected here -->
</div>

Parent Component Logic (Conceptual):

Imagine a service that calls a method like:

this.elementInjectorDirective.injectComponent(NotificationComponent, { message: 'Welcome!' });

Expected Result:

A NotificationComponent instance is rendered within the div.notification-container, displaying "Welcome!".

Example 2: Injecting an HTML String

Injecting a simple HTML snippet, perhaps for a tooltip or a temporary message.

Parent Component Template (my-tooltip.component.html):

<span class="tooltip-trigger" appElementInjector>
  Hover over me
  <!-- HTML string will be injected here on hover -->
</span>

Parent Component Logic (Conceptual):

On mouse enter, the component might call:

this.elementInjectorDirective.injectHtml(`<div>This is a tooltip!</div>`);

Expected Result:

The div with "This is a tooltip!" is rendered inside the span when the user hovers over it.

Constraints

• The directive must be implemented using Angular's Directive decorator.
• Use ViewContainerRef and ComponentFactoryResolver (or createComponent from ViewContainerRef directly if using newer Angular versions) for component injection.
• For HTML string injection, use appropriate DOM manipulation methods.
• The directive should accept inputs for the content to be injected (e.g., a component type, an HTML string, and potentially data for the component).
• The directive should be responsible for its own cleanup.

Notes

• Consider how you will pass data to the dynamically created component.
• Think about the lifecycle of the directive and how it interacts with the host element's lifecycle.
• For component injection, you'll need to use Angular's dynamic component loading mechanisms.
• For HTML string injection, be mindful of security implications if the HTML is not trusted. However, for this challenge, assume safe HTML.
• A good approach for the directive's input would be to have a single input that can accept either a component reference or an HTML string.