Budget Tracker

import { readFileSync, writeFileSync, existsSync } from "fs";

const DATA = "budget.json";
const fmt  = amount =>
  new Intl.NumberFormat("en-IN", { style:"currency", currency:"INR" }).format(amount);

export class BudgetTracker {
  #txns;
  constructor(txns = []) { this.#txns = txns; }

  add({ type, amount, category, note = "", date = new Date().toISOString().slice(0,10) }) {
    if (!["income","expense"].includes(type)) throw new Error("type must be income or expense");
    const amt = parseFloat(amount);
    if (isNaN(amt) || amt <= 0) throw new Error("Amount must be a positive number");
    const txn = { id: Date.now(), type, amount: +amt.toFixed(2), category, note, date };
    this.#txns.push(txn);
    return txn;
  }

  balance() {
    return +this.#txns.reduce((sum, t) =>
      t.type === "income" ? sum + t.amount : sum - t.amount, 0).toFixed(2);
  }

  byCategory() {
    return this.#txns.reduce((acc, t) => {
      const key = `${t.type}:${t.category}`;
      acc[key] = +(( acc[key] || 0) + t.amount).toFixed(2);
      return acc;
    }, {});
  }

  byMonth(month) { // "YYYY-MM"
    return this.#txns.filter(t => t.date.startsWith(month));
  }

  summary() {
    const income  = +this.#txns.filter(t=>t.type==="income").reduce((s,t)=>s+t.amount,0).toFixed(2);
    const expense = +this.#txns.filter(t=>t.type==="expense").reduce((s,t)=>s+t.amount,0).toFixed(2);
    return { income, expense, balance: +(income - expense).toFixed(2) };
  }

  all() { return [...this.#txns]; }
  toJSON() { return JSON.stringify(this.#txns, null, 2); }
}

function load() {
  if (!existsSync(DATA)) return new BudgetTracker();
  try { return new BudgetTracker(JSON.parse(readFileSync(DATA,"utf-8"))); } catch { return new BudgetTracker(); }
}
function save(b) { writeFileSync(DATA, b.toJSON()); }

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

switch (cmd) {
  case "income":
  case "expense": {
    const [amount, category="General", ...noteParts] = args;
    if (!amount) { console.error(`Usage: node budget.mjs ${cmd} <amount> [category] [note]`); break; }
    try {
      const t = budget.add({ type: cmd, amount, category, note: noteParts.join(" ") });
      save(budget);
      console.log(`${cmd === "income" ? "+" : "-"}${fmt(t.amount)}  [${t.category}]`);
      console.log(`Balance: ${fmt(budget.balance())}`);
    } catch(e) { console.error(e.message); }
    break;
  }
  case "summary": {
    const { income, expense, balance } = budget.summary();
    console.log(`
Income:   ${fmt(income)}`);
    console.log(`Expenses: ${fmt(expense)}`);
    console.log(`Balance:  ${fmt(balance)}`);
    console.log("
By category:");
    Object.entries(budget.byCategory())
      .sort(([,a],[,b]) => b - a)
      .forEach(([key, val]) => console.log(`  ${key.padEnd(25)} ${fmt(val)}`));
    break;
  }
  case "list":
    if (!budget.all().length) { console.log("No transactions."); break; }
    budget.all().slice(-20).forEach(t => {
      const sign = t.type === "income" ? "+" : "-";
      console.log(`  ${t.date}  ${sign}${fmt(t.amount).padStart(14)}  [${t.category}]  ${t.note}`);
    });
    break;
  default:
    console.log("Commands: income <amount> [category] [note] | expense <amount> [category] [note] | list | summary");
}

import { BudgetTracker } from "./budget.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 b = new BudgetTracker();
b.add({ type:"income",  amount:5000, category:"Salary"  });
b.add({ type:"expense", amount:1200, category:"Rent"    });
b.add({ type:"expense", amount:300,  category:"Food"    });
test("balance is correct",   () => { if(b.balance()!==3500) throw new Error(b.balance()); });
test("summary totals",       () => { const s=b.summary(); if(s.income!==5000||s.expense!==1500) throw new Error(JSON.stringify(s)); });
test("byCategory keys",      () => { const c=b.byCategory(); if(!("income:Salary" in c)) throw new Error(); });
test("income:Salary = 5000", () => { if(b.byCategory()["income:Salary"]!==5000) throw new Error(); });
test("negative amount throws",() => { try{b.add({type:"expense",amount:-100,category:"x"});throw new Error("no");}catch(e){if(e.message==="no")throw e;} });
test("bad type throws",       () => { try{b.add({type:"gift",amount:100,category:"x"});throw new Error("no");}catch(e){if(e.message==="no")throw e;} });
console.log(`
${p} passed, ${f} failed`);

node budget.mjs income 50000 Salary
node budget.mjs expense 8000 Rent
node budget.mjs summary
node budget.test.mjs