import { Label } from './types';

export class NeverCaseError extends Error {
  constructor(_value: never) {
    super('should never happen');
  }
}

// based on the openmetrics-documentation, the 3 symbols we have to handle are:
// - \n ... the newline character
// - \  ... the backslash character
// - "  ... the double-quote character
export function escapeLabelValueInExactSelector(labelValue: string): string {
  return labelValue.replace(/\\/g, '\\\\').replace(/\n/g, '\\n').replace(/"/g, '\\"');
}

export function makeSelector(metricName: string, labels?: Label[], labelName?: string): string {
  if (!labels || labels.length === 0) {
    return metricName;
  }

  const allLabels = [...labels].filter((label) => label.name !== labelName && label.value !== '');

  const allLabelTexts = allLabels.map((label) => {
    return `${label.name}${label.op}"${escapeLabelValueInExactSelector(label.value)}"`;
  });

  return `${metricName}{${allLabelTexts.join(',')}}`;
}