export interface FieldValidationError {
	field: string;
	code: string;
}

export interface SaveFailure {
	message: string;
	fieldErrors: FieldValidationError[];
}

export function httpErrorMessage(error: unknown, fallback: string): string {
	return typeof error === 'object' &&
		error !== null &&
		'error' in error &&
		typeof error.error === 'object' &&
		error.error !== null &&
		'message' in error.error &&
		typeof error.error.message === 'string'
		? error.error.message
		: fallback;
}

export function saveFailure(error: unknown, fallback: string): SaveFailure {
	const validationErrors = validationErrorsFrom(error);
	if (validationErrors) {
		return {
			message: 'Veuillez corriger les champs signalés.',
			fieldErrors: validationErrors,
		};
	}

	return {
		message: isConflict(error) ? httpErrorMessage(error, fallback) : fallback,
		fieldErrors: [],
	};
}

function validationErrorsFrom(error: unknown): FieldValidationError[] | null {
	if (
		typeof error !== 'object' ||
		error === null ||
		!('error' in error) ||
		typeof error.error !== 'object' ||
		error.error === null ||
		!('code' in error.error) ||
		error.error.code !== 'validation_failed' ||
		!('errors' in error.error) ||
		!Array.isArray(error.error.errors)
	) {
		return null;
	}

	const fieldErrors = error.error.errors.filter(
		(fieldError): fieldError is FieldValidationError =>
			typeof fieldError === 'object' &&
			fieldError !== null &&
			'field' in fieldError &&
			typeof fieldError.field === 'string' &&
			'code' in fieldError &&
			typeof fieldError.code === 'string',
	);
	return fieldErrors.length === error.error.errors.length ? fieldErrors : null;
}

function isConflict(error: unknown): error is { status: number } {
	return typeof error === 'object' && error !== null && 'status' in error && error.status === 409;
}