import { HashHelper } from './hash.helper';

export class ArrayHelper {
  public static chunks<T>(
    array: Array<T> | null,
    n: number | null
  ): Array<Array<T>> | null {
    if (!array) {
      return null;
    }

    if (!n) {
      return null;
    }

    return array.reduce((array, item, index) => {
      const chunkIndex: number = Math.floor(index / n);

      if (!array[chunkIndex]) {
        array[chunkIndex] = [];
      }

      array[chunkIndex].push(item);

      return array;
    }, [] as Array<Array<T>>);
  }

  public static distinct<T>(
    array: Array<T> | null,
    fn: (x: T) => any
  ): Array<T> | null {
    if (!array) {
      return null;
    }

    return array.filter((x: T, index: number, self: Array<T>) => {
      const item = self.find((y: T) => fn(y) === fn(x));

      if (!item) {
        return false;
      }

      return self.indexOf(item) === index;
    });
  }

  public static fromCsv(content: string | null): Array<any> | null {
    if (!content) {
      return null;
    }

    const lines: Array<string> = content.split('\n');

    const headerLine: string = lines[0];

    const columns: Array<string> = headerLine.split(',');

    return lines.splice(1).reduce((array, x) => {
      const obj = {} as { [key: string]: string };

      for (let index = 0; index < columns.length; index++) {
        obj[columns[index]] = x.split(',')[index];
      }

      array.push(obj);

      return array;
    }, [] as Array<{ [key: string]: string }>);
  }

  public static group<T>(array: Array<T>, fn: (x: T) => any): Array<Array<T>> {
    const dict = {} as { [key: string]: Array<T> };

    for (const x of array) {
      const key: string | null = HashHelper.fromObject(fn(x));

      if (!key) {
        continue;
      }

      if (!dict[key]) {
        dict[key] = [];
      }

      dict[key].push(x);
    }

    return Object.keys(dict).map((key: string) => dict[key]);
  }

  public static repeat<T>(item: T, n: number): Array<T> {
    const array: Array<T> = [];

    for (let i = 0; i < n; i++) {
      array.push(item);
    }

    return array;
  }
}