Dynamic Form Builder with Custom Components in Angular

Imagine you need to create a flexible form generation system for a web application. Users should be able to dynamically assemble forms by selecting from a predefined set of input types, and crucially, have the ability to extend this set with their own custom-built input components. This challenge focuses on building such a dynamic form builder in Angular, emphasizing reusability and extensibility.

Problem Description

Your task is to develop a dynamic form builder component in Angular. This builder will allow users to define a form structure by specifying various input fields. The system should be capable of rendering standard form elements (like text inputs, checkboxes) and also accommodate custom components that developers can register and use within the form.

Key Requirements:

1. Dynamic Form Rendering: Create a component that can render a form based on a configuration object.
2. Field Configuration: The configuration object should define each form field, including its type, label, name, and any specific properties (e.g., placeholder for text input, options for a select).
3. Component Mapping: Implement a mechanism to map field types to corresponding Angular components. This should include built-in support for common HTML input types.
4. Custom Component Registration: Allow developers to register their own custom Angular components as form field types. These custom components should be able to receive and emit data related to the form field.
5. Data Binding: Ensure proper two-way data binding between the form fields and the underlying form data.
6. Form Submission: Provide a way to submit the form data.

Expected Behavior:

When the DynamicFormBuilderComponent is provided with a configuration, it should render the form accordingly. When a user interacts with a field, the data should be updated. If a custom component is registered for a specific type, that custom component should be rendered. Submitting the form should yield the current state of all form data.

Edge Cases:

• Handling of missing or invalid field types.
• Ensuring custom components correctly handle input and output events.
• What happens if a registered custom component fails to render?

Examples

Example 1: Simple Text Input and Checkbox

Input Configuration:

{
  "fields": [
    {
      "type": "text",
      "label": "Full Name",
      "name": "fullName",
      "placeholder": "Enter your full name"
    },
    {
      "type": "checkbox",
      "label": "Agree to Terms",
      "name": "agreeTerms"
    }
  ]
}

Expected Form Rendering (visual representation, not literal output):

[Label: Full Name] [Input: placeholder="Enter your full name"]
[Label: Agree to Terms] [Checkbox]

Explanation: The builder renders a text input for "fullName" and a checkbox for "agreeTerms" based on their type property.

Example 2: Select Dropdown with Options

Input Configuration:

{
  "fields": [
    {
      "type": "select",
      "label": "Country",
      "name": "country",
      "options": [
        {"value": "us", "label": "United States"},
        {"value": "ca", "label": "Canada"},
        {"value": "mx", "label": "Mexico"}
      ]
    }
  ]
}

Expected Form Rendering:

[Label: Country] [Select Dropdown: Options="United States", "Canada", "Mexico"]

Explanation: The builder renders a select dropdown, populating its options from the options array in the configuration.

Example 3: Custom Component Integration

Let's assume a custom component RatingInputComponent has been registered for the type "rating".

Input Configuration:

{
  "fields": [
    {
      "type": "rating",
      "label": "Your Rating",
      "name": "userRating",
      "maxStars": 5
    }
  ]
}

Expected Form Rendering:

[Label: Your Rating] [Custom Rating Component: displaying 5 stars, user can interact]

Explanation: The builder identifies "rating" as a custom type and renders the registered RatingInputComponent, passing maxStars and binding to userRating.

Constraints

• The form configuration will be provided as a JSON object.
• The DynamicFormBuilderComponent must be reusable and accept the configuration as an @Input() property.
• Custom components must adhere to a defined interface for interaction with the form builder (e.g., implement ControlValueAccessor or use @Output() events and @Input() properties for data exchange).
• The solution should be written in TypeScript.
• Consider that the number of fields in a form could range from 1 to 100.
• The number of custom component types could range from 0 to 20.

Notes

• You'll likely need to dynamically create Angular components. The ComponentFactoryResolver and ViewContainerRef are key services for this.
• Consider how to manage the mapping between string types (e.g., "text", "rating") and their corresponding Angular component classes. A simple object map could work.
• For custom components, think about how they will communicate their value changes back to the main form builder. Implementing ControlValueAccessor is a standard Angular way to integrate custom form controls.
• Error handling for unknown field types should be graceful, perhaps by displaying a placeholder or an error message.
• This challenge is about building the builder itself. You are not expected to implement the actual RatingInputComponent or other custom components, but rather the mechanism to register and use them. Assume they exist and follow a standard interface for integration.