export type Patch = {
  path: string;
  op: 'add' | 'remove' | 'replace';
  value: any;
};
export const applyPatchWithMinimalMutationChain = <T extends object,>(obj: T, patch: {
  path: string;
  op: 'add' | 'remove' | 'replace';
  value: any;
}, preserveRoot = false): T => {
  if (Object(obj) !== obj) {
    return obj;
  }
  const {
    path,
    op,
    value
  } = patch;
  const pathArr: string[] = path.split(/\//);
  if (pathArr[0] === '') {
    pathArr.shift();
  }
  const newObj = preserveRoot ? obj : {
    ...obj
  };
  let objPart = (newObj as any);
  for (let i = 0; i < pathArr.length; i++) {
    const isLast = i === pathArr.length - 1;
    const property = pathArr[i];
    if (isLast) {
      if (op === 'replace') {
        objPart[property] = value;
      } else if (op === 'add') {
        const index = Number(property);
        if (Array.isArray(objPart)) {
          if (property === '-') {
            objPart.push(value);
          } else {
            objPart.splice(index, 0, value);
          }
        } else {
          objPart[property] = value;
        }
      } else if (op === 'remove') {
        const index = Number(property);
        if (Array.isArray(objPart)) {
          objPart.splice(index, 1);
        } else {
          delete objPart[property];
        }
      }
    } else {
      const nextProperty = pathArr[i + 1];
      const newPart = Object(objPart[property]) === objPart[property] ? objPart[property] : String(Number(nextProperty)) === nextProperty ? [] : {};
      objPart = objPart[property] = Array.isArray(newPart) ? [...newPart] : {
        ...newPart
      };
    }
  }
  return newObj;
}