import { registerHelper } from '@ember/test';

const invariant = (truthy, error) => {
  if (!truthy) throw new Error(error);
};

export function getCodeMirrorInstance(container) {
  return function(selector) {
    const cmService = container.lookup('service:code-mirror');

    const element = document.querySelector(selector);
    invariant(element, `Selector ${selector} matched no elements`);

    const cm = cmService.instanceFor(element.id);
    invariant(cm, `No registered CodeMirror instance for ${selector}`);

    return cm;
  };
}

export default function registerCodeMirrorHelpers() {
  registerHelper('getCodeMirrorInstance', function(app, selector) {
    const helper = getCodeMirrorInstance(app.__container__);
    return helper(selector);
  });
}