Flashcard App

import * as readline from "readline/promises";
import { stdin, stdout } from "process";
import { readFileSync, writeFileSync, existsSync } from "fs";

const DATA = "cards.json";

export function shuffle(arr) {
  const a = [...arr];
  for (let i = a.length - 1; i > 0; i--) {
    const j = Math.floor(Math.random() * (i + 1));
    [a[i], a[j]] = [a[j], a[i]];
  }
  return a;
}

export function weightedDeck(cards) {
  // Cards with lower score (harder) appear more times
  const maxScore = Math.max(...cards.map(c => c.score), 1);
  const expanded = cards.flatMap(c => Array(maxScore - c.score + 1).fill(c));
  return shuffle(expanded);
}

function load() {
  if (!existsSync(DATA)) return [];
  try { return JSON.parse(readFileSync(DATA, "utf-8")); } catch { return []; }
}
function save(cards) { writeFileSync(DATA, JSON.stringify(cards, null, 2)); }

const [,, cmd, ...args] = process.argv;
let cards = load();

if (cmd === "add") {
  const [q, ...aParts] = args;
  const a = aParts.join(" ");
  if (!q || !a) { console.error('Usage: node flashcards.mjs add "Question?" "Answer"'); process.exit(1); }
  cards.push({ q: q.trim(), a: a.trim(), score: 1 });
  save(cards);
  console.log(`Card added. Total: ${cards.length}`);

} else if (cmd === "list") {
  if (!cards.length) { console.log("No cards yet."); process.exit(0); }
  cards.forEach((c, i) => console.log(`  ${i+1}. [score:${c.score}] Q: ${c.q}`));

} else if (cmd === "study") {
  if (!cards.length) { console.error("No cards yet. Add some first."); process.exit(1); }
  const rl = readline.createInterface({ input: stdin, output: stdout });
  const deck = weightedDeck(cards);
  let correct = 0;

  console.log(`
Studying ${cards.length} cards (${deck.length} in weighted deck). Press Enter to reveal.
`);

  for (const card of deck) {
    console.log(`Q: ${card.q}`);
    await rl.question("  [Enter to reveal] ");
    console.log(`A: ${card.a}`);
    const rating = await rl.question("  Easy (e) / Hard (h) / Skip (s): ");
    const orig = cards.find(c => c.q === card.q);
    if (rating.toLowerCase() === "e") { orig.score = Math.min(orig.score + 1, 5); correct++; }
    if (rating.toLowerCase() === "h") { orig.score = Math.max(orig.score - 1, 1); }
    console.log();
  }
  rl.close();
  save(cards);
  console.log(`Session complete: ${correct}/${deck.length} marked easy.`);

} else {
  console.log("Commands: add <question> <answer> | list | study");
}

import { shuffle, weightedDeck } from "./flashcards.mjs";
let p=0,f=0;
function test(d,fn){try{fn();console.log("  ✓",d);p++;}catch(e){console.log("  ✗",d,"—",e.message);f++;}}
const cards = [
  { q:"Q1", a:"A1", score:1 },
  { q:"Q2", a:"A2", score:3 },
];
test("shuffle returns same length",   () => { if(shuffle([1,2,3]).length!==3) throw new Error(); });
test("shuffle doesn't mutate orig",   () => { const a=[1,2,3]; shuffle(a); if(a[0]!==1||a[1]!==2||a[2]!==3) throw new Error(); });
test("weighted: score=1 appears more",() => {
  const deck = weightedDeck(cards);
  const q1Count = deck.filter(c=>c.q==="Q1").length;
  const q2Count = deck.filter(c=>c.q==="Q2").length;
  if(q1Count <= q2Count) throw new Error(`Q1:${q1Count} Q2:${q2Count}`);
});
test("weightedDeck returns shuffled array", () => { if(!Array.isArray(weightedDeck(cards))) throw new Error(); });
test("score-1 card expands most",    () => {
  const cs = [{q:"hard",a:"",score:1},{q:"easy",a:"",score:5}];
  const d = weightedDeck(cs);
  if(d.filter(c=>c.q==="hard").length < d.filter(c=>c.q==="easy").length) throw new Error();
});
console.log(`
${p} passed, ${f} failed`);

node flashcards.mjs add "What is hoisting?" "Moving declarations to the top of scope"
node flashcards.mjs study
node flashcards.test.mjs