//tslint:disable-next-line
const Symbol = require('es6-symbol');

export type Traversable<T> = T | { [key: string]: Traversable<T> };
export type ValueArg = string | number | Symbol;

function traverseGet<T>(ctx: Traversable<T>, ...args: string[]): T {
  return args.reduce((cur: any, key) => cur ? cur[key] : undefined, ctx);
}

function traverseSet<T>(ctx: Traversable<T>, val: any, ...args: string[]) {
  const length = args.length;
  const last = args[length - 1];
  const ancestors = args.slice(0, -1);
  const parent = ancestors.reduce(
    (cur: any, key) => {
      if (!cur[key]) {
        cur[key] = {};
      }

      return cur[key];
    },
    ctx);

  parent[last] = val;
}

const endMarker = Symbol('memoize-end-marker');
export function memoize<T>(memory: Traversable<T>, func: (...args: ValueArg[]) => T): (...args: ValueArg[]) => T {
  const marker = Symbol();

  return (...args: ValueArg[]) => {
    const prev: T = traverseGet.call(null, memory, marker, ...args, endMarker);
    if (prev !== undefined) {
      return prev;
    }
    const result: T = func.call(null, ...args);
    traverseSet.call(null, memory, result, marker, ...args, endMarker);

    return result;
  };
}