/**
 * An error returned by a GraphQL server.
 */
export interface GraphError {
	message: string;
	path?: string[];
}

/** RawError is an error that can be converted to a string by ErrorMessage */
export type RawError = Error | string | GraphError[];

export class ErrorMessage {
	private _message: string;

	/** converts a RawError to a string and stores it for later access */
	constructor(raw: RawError) {
		this._message = ErrorMessage.rawErrorToString(raw);
	}

	/** returns the stored message */
	get message(): string {
		return this._message;
	}
	/** returns the error as a string */
	toString(): string {
		return this._message;
	}

	/** optionally returns a new ErrorMessage only if the RawError is not empty */
	static from(raw: RawError | null | undefined): ErrorMessage | null {
		if (!raw) return null;
		return new ErrorMessage(raw);
	}

	/** converts a RawError to a string */
	static rawErrorToString(raw: RawError | null | undefined): string {
		if (!raw) return 'No error';

		let errorString: string;
		if (typeof raw === 'string') {
			errorString = raw;
		} else if (raw instanceof Error) {
			errorString = raw.message;
		} else if (Array.isArray(raw)) {
			errorString = raw
				.flatMap((e) => {
					const messageString = e.message || 'Unknown error';
					if (e.path && e.path.length > 0) {
						return `"${messageString}" at ${e.path.join('.')}`;
					}
				})
				.join('<br />');
		} else {
			throw `Bad error value ${raw}`;
		}

		return errorString;
	}
}