// React/Redux compatible implementation of RFC 7396
// See https://tools.ietf.org/html/rfc7396
//
// Pseudo algorithm:
//
// define MergePatch(Target, Patch):
//   if Patch is an Object:
//     if Target is not an Object:
//       Target = {} # Ignore the contents and set it to an empty Object
//     for each Name/Value pair in Patch:
//       if Value is null:
//         if Name exists in Target:
//           remove the Name/Value pair from Target
//       else:
//         Target[Name] = MergePatch(Target[Name], Value)
//     return Target
//   else:
//     return Patch

export function applyPatch(target: any, patch: any): Object {
  if (!isObject(patch)) {
    return patch;
  }

  if (!isObject(target)) {
    target = {};
  }

  Object.keys(patch).forEach((key: any) => {
    const value = patch[key];
    target = { ...target };
    if (value === null) {
      delete target[key];
    } else {
      target[key] = applyPatch(target[key], value);
    }
  });

  return target;
}

function isObject(value: any): boolean {
  return value === Object(value);
}