Cross-Field Validation and Custom Error Payload Generation

import { AbstractControl, ValidationErrors, ValidatorFn } from '@angular/forms';
 
export function matchFieldsValidator(primaryKey: string, confirmKey: string): ValidatorFn {
  return (group: AbstractControl): ValidationErrors | null => {
    const primary = group.get(primaryKey)?.value;
    const confirm = group.get(confirmKey)?.value;
 
    if (primary && confirm && primary !== confirm) {
      return { mismatch: { fields: [primaryKey, confirmKey], mismatchTime: Date.now() } };
    }
    return null;
  };
}