Reading and parsing a JSON file using Purify

read-file-purify.ts

import { EitherAsync } from "purify-ts/EitherAsync";
import { identity } from "purify-ts/Function";
import {
  Codec,
  string,
  number,
  date,
  boolean,
  nullType,
  array,
  oneOf,
} from "purify-ts/Codec";
import path from "path";
const fs = require("fs").promises;

const Season = Codec.interface({
  href: string,
  number: number,
});

const ListingEpisode = Codec.interface({
  updated_at: date,
  type: string,
  token: string,
  title: string,
  status: string,
  slug: string,
  season: Season,
  scheduled_for: nullType,
  published_at: date,
  number: number,
  is_hidden: boolean,
  image_url: oneOf([string, nullType]),
  image_path: oneOf([string, nullType]),
  id: string,
  href: string,
  guid: string,
  enclosure_url: string,
  duration: number,
  description: string,
  days_since_release: number,
  audio_status: string,
  analytics: nullType,
});

const ListingEpisodes = Codec.interface({ collection: array(ListingEpisode) });

interface IStringifiable {
  toString: () => string;
}

function getFile(filename: string) {
  return () => {
    const filePath = path.join("./", filename);
    return fs.readFile(filePath);
  };
}

function toString(obj: IStringifiable) {
  return obj.toString();
}

async function loadData(loader: () => Promise<Buffer>) {
  return EitherAsync(loader)
    .map(toString)
    .map(JSON.parse)
    .chain((val) => EitherAsync.liftEither(ListingEpisodes.decode(val)));
}

async function main() {
  const data = await loadData(getFile("episodes.json.tmp"));
  const r = data.caseOf({
    Left: (_) => ({ collection: [] }),
    Right: identity,
  });

  console.log(r);
}

main();