import { FormGroup, FormControl, ValidatorFn, AsyncValidatorFn, AbstractControlOptions } from '@angular/forms';

type TSupported = string | number | boolean;

class TypedControl<T extends TSupported> extends FormControl {
    constructor(
        formState?: any, // TODO any -> T?
        validatorOrOpts?: ValidatorFn | ValidatorFn[] | AbstractControlOptions | null | undefined,
        asyncValidator?: AsyncValidatorFn | AsyncValidatorFn[] | null | undefined
    ) {
        super(formState, validatorOrOpts, asyncValidator);
    }

    public static fromFormGroup<G extends TSupported>(fg: FormGroup, controlName: string): TypedControl<G> {
        const control = fg.get(controlName);

        if (control) {
            return <TypedControl<G>>control;
        } else {
            throw new Error('Control not found.');
        }
    }

    public getValue(): T {
        return <T>this.value;
    }

    public setValue(value: T): void {
        super.setValue(value);
    }
}

const form = new FormGroup({
    foo: new FormControl('bar'),
});

const fooControl = TypedControl.fromFormGroup<string>(form, 'foo');

const value = fooControl.getValue();

fooControl.setValue('bar'); // fine
// fooControl.setValue(42); // error