Function calculateStablePath

app/utilities/jsonColumnView.ts:148–205

(
  previousPathString: string,
  selectionPathString: string,
  json: unknown
)

//Given the previous path and where the selection is, we calculate the new path
//This allows us to keep the deepest item possible still visible whilst navigating around
export function calculateStablePath(
  previousPathString: string,
  selectionPathString: string,
  json: unknown
): string {
  const previousPath = new JSONHeroPath(previousPathString);
  const selectionPath = new JSONHeroPath(selectionPathString);

  //if we are selecting at the right edge then the selection determines the path
  if (selectionPath.components.length >= previousPath.components.length) {
    return selectionPathString;
  }

  //if the selection is the same as the path from the start up to selection end then we leave the path as is
  const previousPathWithSelectionLength = new JSONHeroPath(
    previousPath.components.slice(0, selectionPath.components.length)
  );
  if (selectionPathString === previousPathWithSelectionLength.toString()) {
    return previousPathString;
  }

  //from the start we add the selection components until they don't match the previous path (this should be until the last one)
  let newComponents: PathComponent[] = [];
  for (let index = 0; index < selectionPath.components.length; index++) {
    const selectionComponent = selectionPath.components[index];
    const previousComponent = previousPath.components[index];

    //if they're different we need to bail and try build an alternative path
    if (selectionComponent.toString() !== previousComponent.toString()) {
      break;
    }

    newComponents.push(selectionComponent);
  }

  //we substitute all the remaining elements from the selection into the previousPath
  const remainingSelectionComponents = selectionPath.components.slice(
    newComponents.length
  );
  const remainingPreviousPathComponents = previousPath.components.slice(
    selectionPath.components.length
  );
  const updatedPathComponents = [
    ...newComponents,
    ...remainingSelectionComponents,
    ...remainingPreviousPathComponents,
  ];
  const updatedPath = new JSONHeroPath(updatedPathComponents);

  const jsonAtUpdatedPath = updatedPath.first(json);

  //not a match then we return the selection path
  if (!jsonAtUpdatedPath) {
    return selectionPathString;
  } else {
    return updatedPath.toString();
  }
}