import { object } from "ts-matches";

export function deepMerge(...args: unknown[]): unknown {
  const lastItem = (args as any)[args.length - 1];
  if (!object.test(lastItem)) return lastItem;
  const objects = args.filter(object.test).filter((x) => !Array.isArray(x));
  if (objects.length === 0) return lastItem as any;
  if (objects.length === 1) objects.unshift({});
  const allKeys = new Set(objects.flatMap((x) => Object.keys(x)));
  for (const key of allKeys) {
    const filteredValues = objects.flatMap((x) =>
      key in x ? [(x as any)[key]] : [],
    );
    (objects as any)[0][key] = deepMerge(...filteredValues);
  }
  return objects[0] as any;
}