import { ValidationPipe } from '@nestjs/common';
import type { ValidationError } from '@nestjs/common';
import { ErrorCode } from '../errors/error-codes';
import { ApiError, type ValidationErrorDetail } from '../errors/api-error';

function flattenValidation(
  errors: ValidationError[],
  parent = '',
): ValidationErrorDetail[] {
  return errors.flatMap((error) => {
    const field = parent ? `${parent}.${error.property}` : error.property;
    const own = error.constraints
      ? [
          {
            field,
            messages: Object.values(error.constraints).map(
              () => 'Ungueltiger Wert.',
            ),
          },
        ]
      : [];
    return [...own, ...flattenValidation(error.children ?? [], field)];
  });
}

export function createValidationPipe(): ValidationPipe {
  return new ValidationPipe({
    whitelist: true,
    forbidNonWhitelisted: true,
    transform: true,
    transformOptions: { enableImplicitConversion: false },
    exceptionFactory: (errors) => {
      const validation = flattenValidation(errors);
      return new ApiError(
        ErrorCode.ValidationFailed,
        'Bitte pruefen Sie die markierten Felder.',
        400,
        validation,
      );
    },
  });
}