import { isArray, isFunction, isNil, isObject } from 'lodash';

interface NonPrimitive extends Object {
  [key: string]: any;
  [index: number]: any;
}

export interface MapFn {
  (key: string, value: any): string;
}

export interface Opts {
  thisArg?: any;
}

export class DeepMapKeys {
  private cache = new WeakMap<NonPrimitive, any>();

  constructor(private mapFn: MapFn, private opts: Opts) {}

  public map(value: any): any {
    return isArray(value)
      ? this.mapArray(value)
      : isObject(value)
      ? this.mapObject(value)
      : value;
  }

  private mapArray(arr: any[]): any[] {
    if (this.cache.has(arr)) {
      return this.cache.get(arr);
    }

    let length = arr.length;
    let result: any[] = [];
    this.cache.set(arr, result);

    for (let i = 0; i < length; i++) {
      result.push(this.map(arr[i]));
    }

    return result;
  }

  private mapObject(obj: NonPrimitive): NonPrimitive {
    if (this.cache.has(obj)) {
      return this.cache.get(obj);
    }

    let {
      mapFn,
      opts: { thisArg },
    } = this;
    let result: NonPrimitive = {};
    this.cache.set(obj, result);

    for (let key in obj) {
      if (obj.hasOwnProperty(key)) {
        result[mapFn.call(thisArg, key, obj[key])] = this.map(obj[key]);
      }
    }

    return result;
  }
}

export function deepMapKeys<T>(object: any, mapFn: MapFn, options?: Opts): T {
  options = isNil(options) ? {} : options;

  if (!mapFn) {
    throw new Error('mapFn is required');
  } else if (!isFunction(mapFn)) {
    throw new TypeError('mapFn must be a function');
  } else if (!isObject(options)) {
    throw new TypeError('options must be an object');
  }

  return new DeepMapKeys(mapFn, options).map(object);
}