aoc/_utils/index.ts

import { readFile } from "fs";

/**
 *
 * @param filename {string} - name of the filename to read
 * @returns - a Promise containing a list of newline-separated strings
 */
export function readlines(
  filename: string,
  filter?: (value: string) => unknown
): Promise<string[]> {
  return new Promise((resolve, reject) => {
    readFile(filename, "utf8", function (err, data) {
      if (err) {
        reject(err);
      }

      const lines = data.split("\n");

      if (filter) {
        resolve(lines.filter(filter));
      } else {
        resolve(lines);
      }
    });
  });
}

export function group<T>(
  lines: T[],
  cutoffPredicate: (
    previousValue: T[][],
    currentValue: T,
    currentIndex: number,
    array: T[]
  ) => boolean,
  includeCutoffValue: boolean = true
): T[][] {
  return lines.reduce(
    (previousValue, currentValue, currentIndex, array) => {
      const isCutoffPoint = cutoffPredicate(
        previousValue,
        currentValue,
        currentIndex,
        array
      );

      return isCutoffPoint
        ? [...previousValue, includeCutoffValue ? [currentValue] : []]
        : [
            ...previousValue.slice(0, -1),
            [...previousValue[previousValue.length - 1], currentValue],
          ];
    },
    [[]] as T[][]
  );
}

export function sum(a: number, b: number): number {
  return a + b;
}

export function emptyLines(line?: string): boolean {
  return !!line;
}

export function unique<T>(arr: T[]): T[] {
  return arr.reduce<T[]>((res, current) => {
    if (res.includes(current)) {
      return res;
    } else {
      return [...res, current];
    }
  }, []);
}

export function allIndicesOf(s: string, search: string): number[] {
  return unique(
    s
      .split("")
      .reduce((results, _, index) => [...results, s.indexOf(search, index)], [])
  ).filter((x: number) => x >= 0);
}